- Email: [email protected]
ZnS quantum dot structures originated by precursors
Journal Pre-proof Structural, luminescent and antimicrobial properties of ZnS and CdSe/ZnS quantum dot structures originated by precursors
Asha Kumari, Nutan Thakur, Jitendraa Vashishtt, Ragini Raj Singh PII:
S1386-1425(19)31353-8
DOI:
https://doi.org/10.1016/j.saa.2019.117962
Reference:
SAA 117962
To appear in:
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Received date:
20 August 2019
Revised date:
3 December 2019
Accepted date:
13 December 2019
Please cite this article as: A. Kumari, N. Thakur, J. Vashishtt, et al., Structural, luminescent and antimicrobial properties of ZnS and CdSe/ZnS quantum dot structures originated by precursors, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy(2018), https://doi.org/10.1016/j.saa.2019.117962
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2018 Published by Elsevier.
Journal Pre-proof
Structural, luminescent and antimicrobial properties of ZnS and CdSe/ZnS quantum dot structures originated by precursors Asha Kumari1, Nutan Thakur2, Jitendraa Vashishtt2, Ragini Raj Singh*,1 1
Department of Physics and Materials Science (Nanotechnology Laboratory), Jaypee University of Information Technology, Waknaghat, Solan-173234, India
2
Department of Biotechnology and Bioinformatics, Jaypee University of Information Technology, Waknaghat, Solan-173234, India
of
Abstract
ro
ZnS quantum dots (QDs) and their core/shell (CdSe/ZnS) structures were studied for Zn based
-p
precursor reactivities. ZnS and CdSe/ZnS QDs were prepared selecting aqueous route and then characterized via XRD, TEM, EDX, PL, RAMAN and FTIR practices. Core/shell nanostructures
re
were synthesized by taking dissimilar precursors for the shell formation. Photoluminescence
lP
spectra of prepared QDs corroborate the effectual luminescence. Prepared QDs have large
na
surface area that make them useful alternative as organic antimicrobial agent which are highly irritant and unstable. Study of antimicrobial behavior of QD structures was carried out by disc
ur
diffusion method. Antimicrobial study of QDs and their core/shell structures was performed
Jo
against gram negative and gram positive bacteria, E. coli, A. baumanni and Bacillus subtilis respectively. It is found that elemental composition and size of QDs plays important role in antimicrobial behavior. Prepared QDs are fluorescent and have a key role in complex microbial population studies and identification of bacteria. Keywords: Quantum dots; core/shell structures; precursor reactivity; luminescent properties; antimicrobial activity *Corresponding Author: [email protected]
1
Journal Pre-proof
1. Introduction Semiconducting nanoparticles and their core/shell structures have turn out as the material of immense attention due to their applications like optical fibres amplifier[1], color displaying LED [2,3] as well as in biomedical field[4]. CdSe/ZnS quantum dots (QDs) are the most common type of QDs those have been developed for biological applications [5]. These QDs hold a special place due to their easy preparation and tunable luminescence in visible region. Novel properties
of
of these core/shell type QDs make them interesting. Covering of CdSe QDs with higher band gap
ro
semiconducting materials helps in improving photoluminescence quantum yields. This
-p
improvement takes place as nonradiative recombination sites on the surface of cre/shell QDs got
re
passivated through shell formation [6-8]. Rate of conversion and reactivity of precursors play an
lP
essential role in growth of the QDs. Slower precursor reactivity and its conversion results in production of few nuclei during nucleation process. This process results in extended growth
na
period and generates the larger particle size [9-14]. Size dependent unique optical properties of QDs makes them exceptional participant for biological activities [15-17]. These nanomaterials
ur
posses small size and large surface area, due to this unique property of nanomaterials they are
Jo
being considered as superior candidates to substitute conventional antimicrobial agents those are organic and are tremendously toxic and irritant [18,19]. Metal based nanoparticles have been reported to corroborate superior antimicrobial activity against both Gram (+ve) and Gram (-ve) bacteria [15]. But QDs in addition to antimicrobial activity possess narrow emission, excellent photostability, broad absorption spectra and bright photoluminescence [20, 15]. Due to these unique characteristics these QDs could be used in many other biological applications like in biosensors, cell imaging [21] etc. QDs posses good fluorescence characteristic and this fluorescent recognition plays considerable role to study complex microbial populations along
2
Journal Pre-proof with detection of bacteria. Imaging of bacteria by probe-conjugated QDs is most feasible research areas in bio based applications of QDs [22, 20]. On account of their wide probable applications, QDs have been planned for antimicrobial activities. These QDs mainly contains heavy metals, Pb, Te, Cd Se etc. and liberation of such heavy metals could be toxic to bacteria [23]. Different reasons for QDs antimicrobial behavior were explained by different research groups in previous reports. Previous studies have credited the photo-generation and free radicals
of
formation to play major role in antibacterial activity [24-26]. The photo-toxicity produced by
ro
sunlight and other high intensity light sources results in liberation of metal ions (Cd2+) which are
-p
toxic to the bacteria [27,28].
re
Current research is focused towards the synthesis of QDs and their core/shell nanostructures in aqueous media. In this work we have studied effect of diverse experimental
lP
parameters on optical characteristics. This work also involves precursor’s effect on
na
photoluminescence of ZnS and CdSe/ZnS QDs on the basis of precursor’s reactivity. X-ray diffraction (XRD), Photoluminescence spectroscopy (PL) and Transmission electron microscopy
ur
(TEM), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy, were
Jo
employed to study structural, morphological, optical and size distribution properties along with surface functional group chemistry. Importantly this study is also an attempt to study antimicrobial effects of prepared QDs towards different bacteria.
2.0 Experimental Details Chemicals: Cadmium chloride (CdCl2), sodiumselenosulphate (Na2SeSO3), triethanolamine and zinc sulphate heptahydrate (ZnSO4.7H2O), zinc chloride (ZnCl2), thiourea and hydrazine hydrate were supplied from Merck (India). All the analytical grade chemical products were used as attained form the manufacturer.
3
Journal Pre-proof 2.1 Method for CdSe QDs synthesis: Synthesis of CdSe QDs was done by same procedure as we have opted in our previous paper [29]. 2.2 Method for ZnS QDs synthesis: ZnS QDs were prepared by using two different precursors of zinc source. ZnS1 QDs were synthesized by using ZnSO4.7H20 as Zn source and ZnS2 were synthesized by using dry ZnCl2 as Zn source. Precursors ZnSO4.7H20, ZnCl2 and thiourea were used in 0.025:0.035 molar ratios. ZnS QDs were synthesized using wet chemical method where o
of
distilled water was used as solvent and temperature was maintained at 70 C. In typical synthesis
ro
ZnSO4.7H20 for ZnS1 and ZnCl2 for ZnS2 and hydrazine hydrate were added in 70 ml of o
-p
distilled water. Reaction mixture was followed by thiourea at 70 C temperature and continuously
re
stirred for 3 hours. Finally samples were washed, filtered and dehydrated at room temperature.
lP
2.3 Synthesis of CdSe/ZnS QDs: We have utilized a two-step synthesis process to produce core/shell CdSe/ZnS QDs. CdSe/ZnS core/shell structures were prepared by seed growth method
na
using aqueous solvent. First step was synthesis of CdSe QDs. These prepared CdSe dots are
ur
named as “bare “dots even though their surface is stabilized with 2-ME capping groups. For synthesis of CdSe/ZnS core/shell QDs, Zn precursors were followed by addition of 10 ml
Jo
Hydrazine hydrate. At 50°C 0.8 gm of CdSe solution was added to solution subsequent to adjusted pH 10. Sulphur source thiourea was then added to 80 ml of ready solution and continuously stirred for1 hour. CdSe/ZnS1 was synthesized by using ZnSO4.7H20 as precursor and CdSe/ZnS2 was synthesized by using ZnCl2 as precursor. After 1 hour samples were washed with distilled water. 2.4 Growth of Bacterial cultures and their treatment with QDs 2.4.1 Material and methods
4
Journal Pre-proof Culture media like Mueller Hinton agar, MacConkey agar, Mueller Hinton broth and luria broth used in microbiology experiments were purchased from Hi-Media Pvt. Ltd. (India). Antibiotic cotrimoxazole (1.25/23.75 mcg) and meropenem was purchased from Hi-Media Pvt. Ltd. (India). Escherichia coli (ATCC 25922) and Acinetobacter baumannii (ATCC 19606) used in antimicrobial susceptibility testing were obtained as a gift from respected Dr. Arti Kapil, Head of Bacteriology Division, Department of Microbiology, All India Institute of Medical Sciences
of
(AIIMS), New Delhi, India.
ro
2.4.2 Investigation of antimicrobial activity
-p
Antimicrobial activity of six compounds of QDs and their core/shell structures was investigated
re
by Kirby Bauer’s disk diffusion technique for gram negative strains; Escherichia coli (ATCC
lP
25922), Acinetobacter baumannii (ATCC 19606) and, gram positive strain Bacillus Subtilis (MTCC 441) [30]. All the protocols followed were adopted from the CLSI (Clinical laboratory
na
standard institute) and ICMR (Indian Council of Medical Research) guidelines [31]. Briefly, single pure colony of bacterial cultures was inoculated in Luria broth and then incubated
ur
overnight at 37°C. The bacterial culture of 0.5 optical density McFarland standards was mop up
Jo
onto Muller Hinton agar plate and allowed to dry for 15 minutes. Antibiotic disk of control antibiotics along with compounds were placed on agar plates. Then plates were incubated at 37°C for 16-18 hours and circular zones of lysis around disk were interpreted according to CLSI and ICMR guidelines [32].
3.0 Characterization techniques XRD spectra were traced by x-ray diffractometer (Shimadzu, japan), which use Cu Kα1 radiation for confirmation of the particle size and crystal structure of prepared samples. TEM analysis was performed as the supreme evidence of morphology and particle size distribution of synthesized 5
Journal Pre-proof samples on TEM HITACHI (H-7500). For confirmation of elemental composition of samples EDX analysis for samples were carry out in HRTEM instrument make TECNAI G2 20S-TWIN (FEI Neitherlands). Luminescent properties of QDs were recorded by photoluminescence spectroscopy (Perkin Elmer LS55 spectrophotometer). Photoluminescence excitation (PLE) spectra were recorded to know about excitation of QDs. FTIR spectra were recorded using model Cary 630 spectrophotometer from Agilent technology within the range 4000 – 400 cm-1. Raman
of
photospectrometer (Lab RAM HR Evolution Horiba) was used to record raman spectra of
ro
samples.
-p
3.1 Structural characterization
re
XRD patterns were recorded for structural determination of different samples and, obtained
lP
spectra for all QDs are shown in figure 1(a-e). XRD spectra shown in figure1 (a) for CdSe QDs demonstrate that four prominent peaks are present at 2 = 25.43, 42.12, 30.63 and 50°. These 2
na
values correspond to hkl planes (111), (200), (220) and (311) and represent cubic phase of CdSe. In XRD spectra of ZnS1 (figure1 (b)), four peaks are present and these peaks represent pure
ur
cubic phase of ZnS1. Similarly in XRD spectra of ZnS2 (figure 1(c)) occurrence of three well-
Jo
known peaks at 2 positions 28°, 47° and 56° corresponds to (111), (220) and (311) indicates the cubic structure for ZnS2 QDs. Along with these peaks in ZnS2 there is presence of more peaks at 2 positions 31°, 34°, 36°, 62°and 67°. Miller indices related to these peaks are (l00), (002), (101), (013) and (112) respectively [33, 34] and present the hexagonal phase of ZnO. Therefore, it is clear from these XRD results that in case of ZnS2 where ZnCl2 was used as precursor, there was biased oxidation of ZnS nanocrystal because of highly hygroscopic character of zinc chloride. Obtained XRD spectra for core/shell structures CdSe/ZnS1 and CdSe/ZnS2 are shown in (figure1 (d) & (e)) respectively. Other structural parameters like 2 positions, hkl planes, and 6
Journal Pre-proof phase for all these samples are presented in table1. It can be concluded from the table 1 and from figure ((d) & (e)) that the XRD spectra of core/shell QDs shows major reflections located at the middle of the positions evaluated for CdSe and ZnS. 2 positions shifting toward red side are clear evidence of core/shell structure. Crystallite size of CdSe, ZnS1 and ZnS2 QDs were acquired using the Scherrer’s formula (Eq. (1)). (1)
of
D = Kλ/βCosθ
ro
3.2 Morphological studies
-p
TEM micrographs of CdSe, ZnS1, ZnS2, CdSe/ZnS1 and CdSe/ZnS2 are shown in figure 2 (a-e).
re
These images corroborate uniform particle size distribution without agglomeration. Image-J software was used to calculate average diameter of QDs. Histograms for each QD type has been
lP
inserted in the corresponding TEM image. It is clearly visualized from figure 2 (a) that CdSe
na
QDs are consistently distributed having particle size 1.90.1 nm. Similarly TEM for ZnS1 (figure 2(b)) and ZnS2 (figure 2(c)) clearly reveal that these particles do not agglomerate
ur
instantaneously and are spherical in shape. Particle size of ZnS1 (3.00.5 nm) is bigger as
Jo
contrast of ZnS2 (2.30.2 nm) as outcome of the difference in the reactivity of precursors selected for synthesis of ZnS1 and ZnS2. In Case of core/shell structures CdSe/ZnS1 (3.70.2 nm) and CdSe/ZnS2 (3.5 30.2 nm) figure 2(d) and (e) there is clear depiction of shell formation on CdSe core QDs. This leads to confirmation of shell formation on CdSe QDs. Obtained average particle size have been tabulated in Table 1 together with the XRD results.
3.3 Energy-dispersive X-ray spectra Prepared samples were characterized by EDX to confirm elemental composition. Table 2 presents the ratio of peak intensities for all the prepared samples. An EDX spectrum for CdSe
7
Journal Pre-proof confirms the pure CdSe QD formation. Spectra contain intense peaks of cadmium and selenium. It was concluded from Table 2 that ratio of Cd: Se was 1:0.82 and this was due to high concentration of their precursors. Peak of sulfur is due to presence of 2-Mercaptoethanol. The peaks of carbon and copper in all EDX spectra present due to the carbon coated copper grid used as sample holder while characterizing the samples. In EDX spectra of ZnS1, ratio of peaks intensity was found 1:0.75 revealed that there are peaks of Zn and S due to high concentration of
of
its precursors. Similarly an EDX spectrum for ZnS2 contains intense peaks of Zn and S. EDX
ro
spectra of CdSe/ZnS1 and CdSe/ZnS2, where there is presence of Cd and Se peaks from core
-p
CdSe and peaks of Zn and S come from ZnS shell. The ratio presented in Table 2 concludes that
re
there was formation of CdSe/ZnS core/shell nanostructures. Figures showing EDX spectra are being provided in supplementary information figures SI-1 to SI- 5.
lP
3.4 Photoluminescence Studies
na
PL spectra and PLE spectra of all synthesized ZnS and their CdSe/ZnS QDs were recorded at room temperature and are shown in Figures 3(a-g). PL spectra were attained by excitation of
ur
samples at dissimilar excitation wavelengths. All the samples show emission at fixed
Jo
wavelength. While PLE spectra for all QDs recorded by setting up PL emission on blue end of PL peak. Figure 3(a) presents the PL and PLE spectra for CdSe QDs and it is concluded from figure 3(a) that in PLE spectra; we have observed band edge transition that is 1se and 1sh around 2.6 eV or 476 nm, while the emission wavelength is observed at 2.5 eV or 481 nm. Emission spectra of CdSe QDs possess band edge luminescence along with significant trap emission. Explanation of defect emission in case of CdSe QDs has already been conversed in our previous report [29]. In case of ZnS1 (Figure 3(b)) where ZnSO4.7H2O was used as precursor, emission spectra corresponds to emission at 337, 427, 486 nm have been recorded,
8
Journal Pre-proof which shows weak absorption at 333 nm. In PL spectra of ZnS1 band emission was near about 337 nm with only some defects at 427 & 486 nm. Graphical representation of emission transitions in ZnS1 QDs are given in figure 3(b1). Similarly emission spectrum of ZnS2 (figure 3(c)) shows peak at 380 nm. Emission peaks correspond to different emission centers at 422, 445, 486 and 529 along with band edge emission at 384. Schematic representation of emission transitions in ZnS2 QDs are presented in figure 3 (c1).
of
Table 3(a) consists of all the emission peak positions along with PLE. To determine the
ro
peak positions in samples CdSe, ZnS1, and ZnS2 deconvulation has been performed on the PL
-p
spectra. Deconvulated PL spectra was in shape for different peaks which can be seen from figure
re
(3(a, b & c)). The peak E1 will match with the emission due to band edge in all samples and other peaks present defects. All the peaks along with intensity and respective FWHM values are
lP
tabulated in table 3(b). The emission band centered between 400-450 nm in case of ZnS1 and
na
ZnS2 (figure 3b and 3c) are attributed to interstitial zinc and sulfur vacancies. Emission near about 485-490 nm was attributed to Zn-vacancies [35]. Peaks centered near about 525 nm are
ur
attributed to vacancy associated with recombination of electron from sulfur vacancy energy level
Jo
to hole on the Zn vacancy energy level [36]. In case of ZnS1 this has not been observed. PLE spectra of CdSe/ZnS1 (Figure 3(d)) core/shell show excitation peak at 474 nm and it corresponds to emission from band edge at 487 nm along with defect generated luminescence at 531 nm respectively. Likewise, in CdSe/ZnS2 (Figure 3(e)) PLE spectra show absorption peaks at 472 nm and corresponds to emission due to band edge at 484 nm with defect generated emission at 532 nm in PL. In case of core/shell structure the peak remained at 532 nm is due to sulfur vacancies. We compared the PL spectra of CdSe QDs with core/shell structure CdSe/ZnS1 (Figure 3 (f)) and CdSe/ZnS2 (Figure3 (g)) and observed that the intensity of emission peak gets
9
Journal Pre-proof improved on shell formation with decrease in defect emission states. This defect luminescence mainly originate due to dangling or unsatisfactory bonds available on QDs surface which escort generation of trap states and these traps have very strong hole acceptor trait. In CdSe QDs luminescence intensity at the band edge is more or less equivalent to defect luminescence. However, in core/shell CdSe-QDs structures emission at band edge is outstanding in contrast to luminescence caused by defects and this happens because of passivation of
of
deprived bonds on shell formation. From these PL studies it is concluded that all these QDs
-p
ro
posses fluorescence and this property of QDs get improved on formation of shell on core surface.
re
3.5 FTIR analysis
FTIR analysis of CdSe QDs, ZnS QDs and core/shell nanostructures was performed for
lP
confirmation of surface functionalities. Peaks observed at 1462 cm-1 corresponds to CH2 bending
na
and 1630 cm-1 corresponds to -NH bending in spectra of CdSe-QD (figure (4a)). Intense peak in spectra at 3346 cm-1 corresponds to -OH group. The peak around 1100 cm-1 is assigned to CH2
assigned to C-O stretching. Band stretching was observed at 706-899 cm-1 due to C-S bond.
Jo
1
ur
rocking. Band at 2200 cm-1 appears weaker and due to thiol group. Peak at 1067 cm-1 - 1041 cm-
Some extra peaks in CdSe are present because of some impurities. In the spectrum of ZnS1 (figure (4b)) peak with high intensity at 3249 cm-1 is due to presence of -OH group. Peak at 2100 cm-1 and 1640 cm-1 corresponds to -NH bands characteristic vibrations. Spectrum of ZnS2 (figure (4c)) showed the peaks at 3290 and 1640 this matched up to -OH group and -NH bending respectively. Weak peak around the 1402 cm-1 and 1503 cm-1 corresponds to C-N vibrations. FTIR spectrum of CdSe/ ZnS1 (figure (4d)) indicates intense peaks at 3387 cm-1, 1503 cm-1 and 1395 cm-1 corresponds to OH group and C-N vibrations respectively. Peak around 1197 cm-1
10
Journal Pre-proof corresponds to CH2 rocking. Band around 709 - 899 cm-1 is due to C-S stretching. Likewise in case of CdSe/ZnS2 (figure (4e)) band at 3387 cm-1 for -OH, 2117 cm-1 for alkynes and at 1547 cm-1 due to C-N vibrations. Peak around 1119 cm-1 corresponds to CH2 rocking. FTIR spectra of these QDs contain functional groups such as -NH and -OH which makes them hydrophilic and biocompatible. Some extra peaks are present in CdSe other than -NH and -OH group because of some remaining impurities and these extra peaks somewhere affect the biocompatibility of bare
of
CdSe QDs.
ro
3.6 Raman Spectroscopy
-p
Raman spectroscopy is a spectroscopic technique which was used to find out vibrational modes
re
of prepared quantum dots. In Raman spectroscopy monochromatic light source is used, typically
lP
from a laser in visible or near ultraviolet range. The laser light interacts with molecular vibrations, phonons or other excitations in the system, resulting in the energy of the laser photons
na
being shifted up or down. The shift in energy gives information about the vibrational modes in the system. Figure 5 shows raman spectra of all synthesized CdSe, ZnS and its core shell
ur
structure, we have not recorded the Raman spectra of ZnS2 and CdSe/ZnS2 as it has been
Jo
already discussed that the structural, fluorescence and EDX results confirms the defects present in ZnS2 as used precursor was different in ZnS2 with respect to ZnS1. The Raman peak in ZnS-1 (figure 5(b)) of wide multimodal feature are in region of 160.06 cm-1, 246.35 cm-1 and wide structure lies in region of 345 cm-1. In case of core CdSe quantum dots (figure 5(a)) Raman peaks are at position 30.06 cm-1, 191.77 cm-1, 278.86 cm-1 [37]. Peak near about 278.86 cm-1 was assigned to Cd-S vibrations. Raman spectra of core shell structures i.e., CdSe/ZnS1 (figure 5(c)) revealed Raman shift in peak position as compared to core CdSe QDs. In CdSe/ZnS1 peak position are shifted to 38.06 cm-1, 201.27 cm-1, 278.86 cm-1 with a shift of 7.9 cm-1, 9.5 cm-1 and
11
Journal Pre-proof 3.5 cm-1 respectively with respect to CdSe QDs. Similarly shifts in CdSe/ZnS1 peak position are shifted to 169.56 cm-1, 256.78 cm-1, with a shift of 9 cm-1 and 10.43 cm-1 respectively with respect to ZnS1 QDs. This shift in Raman peaks in core shell structures as compared to core CdSe and shell ZnS was attributed to the shell formation over the core surface. These observations were also supported by our PL and FTIR studies. The presence of these broad peaks
3.7 Antimicrobial activity of compounds
ro
optical properties can be utilized in bio based application.
of
in Raman spectra confirms quantum confinement in these small particles. These QDs on basis of
-p
Complex microbial populations and recognition of bacteria can be done by fluorescent detection.
re
We can use these fluorescent QDs for single bacterial imaging by generating probe-conjugated
lP
QDs. In this regard we studied antimicrobial activity and results showed that A and F compounds having potent antibacterial behavior towards gram negative pathogens and gram positive strain
na
Bacillus subtilis (Table 4). Different synthesized QDs have been named as compound (A)CdSe, Compound (B)ZnS1, Compound (C) ZnS2, Compound (D) CdSe/ZnS1, compound (E)-
ur
CdSe/ZnS2 and compound (F) -poly CdSe correspondingly. Several strains of E. coli are
Jo
responsible for intestinal and extra-intestinal infections [38]. Acinetobacter baumannii is considered as leading cause of nosocomial disease causing pathogen; originate several blood, skin, soft tissue and respiratory infections. Recently, A. baumannii has already been premeditated as the topmost multidrug opposing bacteria with hospital setting by (WHO). Several species of Bacillus are sometimes allied with infections of the ears, wounds, eyes, urinary tract and gastrointestinal tract. Figure 6 (a) shows clear spherical lysis zones produced by compound (A) with control (tested) antibiotics against E. coli (Gram –ve). Figure 6(b) shows compound A against
12
Journal Pre-proof Acinetobacter baumannii (Gram –ve). It is clear from the figures that compound (A) shows antimicrobial action against E.coli but there was no antimicrobial effect noticed against Acinetobacter baumannii. Likewise figure 6 (c) and 6(d) present the lysis zone for compound (F) against E. coli and Acinetobacter baumannii respectively. Observed zones for all samples are in mm and given in Table 4, it was concluded from the Table 4 that compound (A) and (F) possesses fine antimicrobial activity. However, there were no presence of zone lysis values
of
found for compound (B), (C), (D) & (E) validate that prepared compounds did not inhibit either
ro
E.coli or Acinetobacter baumannii growth [Supplementary information Figures SI(6-11)].
-p
Similar trend was seen in case of antimicrobial activity of Compound (A) to Compound (F)
re
towards gram positive strain Bacillus subtilis (Table 4). This was concluded from Table 4 that compound (A) and (F) possesses fine antimicrobial activity against gram +ve bacterial strain
lP
with difference in size of zone of inhibition as shown in Figure 6 (e) and 6 (f) respectively.
na
Supplementary figures from SI-6 to SI-11 further provide visual proof to elucidate that there were no zone of lysis found in compound (B) to compound (E) for either Acinetobacter
ur
baumannii , E.coli and Bacillus subtilis respectively. Here these different sizes of inhibition
Jo
zones between QDs could be correlated to surface modification, particles size, elemental composition, and diffusion propensity of particles with cell wall. This behavior can also be accounted to different size of QDs and binding tendency of QDs to bacterial wall. CdSe QDs contain very toxic heavy metals this have been inveterate from EDX. Due to such toxic composition of CdSe QDs they demonstrate antimicrobial behavior. In comparison with CdSe QDs, ZnS1 and ZnS2 QDs are not showing any antimicrobial behavior concludes no zone of inhibition is formed in case of ZnS1 and ZnS2 (Table 4). Bactericidal behavior of these CdSe QDs has also been attributed to their smaller size as compared to ZnS1 and ZnS2. It has
13
Journal Pre-proof been already incorrigible from XRD and TEM analysis of these QDs that CdSe QDs are smaller in size as compare to ZnS1 and ZnS2. Similarly CdSe/ZnS1 and CdSe/ZnS2 do not show any antimicrobial property. This is due to increase in size on shell formation. Formation of shell also avoids leakage of heavy toxic metal from core material CdSe and prevents core material from photo oxidation. Along with all these factors antimicrobial behavior and dissimilarity in zone lysis size between QDs could be correlated to diffusion affinity of nanoparticles with cell wall.
of
This behavior can also be accounted to different size of QDs and binding tendency of QDs to
ro
bacterial wall. Luminescent QDs ZnS1, ZnS2, CdSe/ZnS1, CdSe/ZnS2 which are not showing
-p
antimicrobial activity are biocompatible and can be used to study microbial inhabitants and
re
identification of bacteria by conjugation with probe. Imaging of bacterial inhabitants by means of probe-conjugated QDs regarded as one of the mainly practicable areas in bio based applications.
lP
4. Conclusions
na
In this paper we went through the effect of ZnS precursor reactivity on size and optical properties of ZnS QDs. Structural analysis confirms that particle size of ZnS1 was larger as compared to
ur
ZnS2. It was found from optical studies that precursor used for synthesis of ZnS1 and ZnS2
Jo
affect the emission at band edge and emission due to defect position in these QDs. In ZnS1 the emission for band edge was at 337 nm along with defect emission at 427 nm, 486 nm and in ZnS2 emission for band edge was found at 384 nm along with defects at 422 nm, 445 nm, 486 nm and 529 nm. The wide peaks in the Raman spectra can be accredited to quantum effects of the prepared QDs and their core/shell structures. Because of unique optical properties these quantum dots can be useful in many applications such as biolabeling. A correlation was found between reactivity of precursors’ to optical properties and size of QDs. Antimicrobial behavior of all synthesized QDs was studied by Kirby Bauer’s disk diffusion
14
Journal Pre-proof method (against potential gram negative pathogens; Escherichia coli (ATCC 25922), Acinetobacter baumannii (ATCC 19606) and gram positive strain Bacillus Subtilis. Poly CdSe and CdSe QDs were found to show good antimicrobial activity because of their toxic composition toward gram +ve and gram -ve strain. As A. baumannii has been found listed as the topmost multidrug resistant bacteria the antimicrobial properties of compound F can be a breach. In contrast with CdSe QDs, ZnS1 and ZnS2 QDs do not show any antimicrobial tendency.
of
Bactericidal behavior of these CdSe QDs has also been attributed to their small size as compared
ro
to ZnS1 and ZnS2. In case of CdSe/ZnS1 and CdSe/ZnS2 no antimicrobial property was found
-p
and this was due to shell formation which prevents leakage of heavy toxic metal from core
re
material CdSe and prevents core material from photo oxidation. PL spectra clearly reveal that the fluorescent properties of these QDs improved on shell formation. Luminescent QDs which are
lP
not showing antimicrobial tendency are biocompatible as depicted from FTIR and can be used
Acknowledgements
na
for imaging of bacterial population by probe-conjugated QDs.
Jo
032/2013].
ur
This research work was support by SERB (DST), India, grant [grant number SR/FTP/PS-
“Data Availability: The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.”
References [1] Tierno A, Ackemann T, Leburn CG, Brown CT. Saturation of absorption and gain in a quantum dot diode with continuous-wave driving. Applied Physics Letters. 2010 Dec 6; 97 (23):231104.
15
Journal Pre-proof [2] Mora-Seró I, Giménez S, Moehl T, Fabregat-Santiago F, Lana-Villareal T, Gómez R, Bisquert J. Factors determining the photovoltaic performance of a CdSe quantum dot sensitized solar cell: the role of the linker molecule and of the counter electrode. Nanotechnology. 2008 Sep 25; 19(42):424007. [3] Wang T, Pang F, Wang K, Zhang R, Liu G. Evanescent wave coupled semiconductor
of
quantum dots fiber amplifier based on reverse Micelle method. In Nanotechnology, 2007. IEEE-
ro
NANO 2007. 7th IEEE Conference on 2007 Aug 2 (pp. 819-822).
-p
[4] Kim L, Anikeeva PO, Coe-Sullivan SA, Steckel JS, Bawendi MG, Bulovic V. Contact
re
printing of quantum dot light-emitting devices. Nano letters. 2008 Nov 18; 8(12):4513-7. [5] Delehanty JB, Medintz IL, Pons T, Brunel FM, Dawson PE, Mattoussi H. Self-assembled
lP
quantum dot− peptide bioconjugates for selective intracellular delivery. Bioconjugate chemistry.
na
2006 Jul 19; 17(4):920-7.
ur
[6] Kim J, Lee J, Kyhm K. Surface-plasmon-assisted modal gain enhancement in Au-hybrid
Jo
CdSe/ZnS nanocrystal quantum dots. Applied Physics Letters. 2011 Nov 21; 99(21):213112. [7] Nirmal M, Brus L. Luminescence photophysics in semiconductor nanocrystals. Accounts of chemical research. 1999 May 18;32(5):407-14. [8] Mattoussi H, Mauro JM, Goldman ER, Anderson GP, Sundar VC, Mikulec FV, Bawendi MG. Self-assembly of CdSe− ZnS quantum dot bioconjugates using an engineered recombinant protein. Journal of the American Chemical Society. 2000 Dec 13; 122(49):12142-50. [9] Viswanatha R, Sarma DD. Growth of nanocrystals in solution. Nanomaterials chemistry: recent developments and new directions. 2007:139-70. 16
Journal Pre-proof [10] Rempel JY, Bawendi MG, Jensen KF. Insights into the kinetics of semiconductor nanocrystal nucleation and growth. Journal of the American Chemical Society. 2009 Mar 10; 131(12):4479-89. [11] Clark MD, Kumar SK, Owen JS, Chan EM. Focusing nanocrystal size distributions via production control. Nano letters. 2011 Apr 8; 11(5):1976-80.
of
[12] Hens Z, Čapek RK. Size tuning at full yield in the synthesis of colloidal semiconductor
ro
nanocrystals, reaction simulations and experimental verification. Coordination Chemistry
-p
Reviews. 2014 Mar 15; 263:217-28.
re
[13] Abé S, Capek R, De Geyter B, Hens Z. Using the acid concentration and chain length as a tuning strategy in the hot injection synthesis, an experimental and theoretical analysis. In5th
lP
Conference on Nanoscience with Nanocrystals (NaNax 5) 2012.
na
[14] Sugimoto T, Shiba F, Sekiguchi T, Itoh H. Spontaneous nucleation of monodisperse silver
ur
halide particles from homogeneous gelatin solution I: silver chloride. Colloids and Surfaces A:
Jo
Physicochemical and Engineering Aspects. 2000 May 15;164(2):183-203. [15] Adams LK, Lyon DY, Alvarez PJ. Comparative eco-toxicity of nanoscale TiO 2, SiO 2, and ZnO water suspensions. Water research. 2006 Nov 30; 40(19):3527-32. [16] Panáček A, Kvítek L, Prucek R, Kolář M, Večeřová R, Pizúrová N, Sharma VK, Nevěčná TJ, Zbořil R. Silver colloid nanoparticles: synthesis, characterization, and their antibacterial activity. J. Phys. Chem. B. 2006 Aug 1; 110(33):16248-53. [17] Li P, Li J, Wu C, Wu Q, Li J. Synergistic antibacterial effects of β-lactam antibiotic combined with silver nanoparticles. Nanotechnology. 2005 Jul 28; 16(9):1912. 17
Journal Pre-proof [18] Klaine SJ, Alvarez PJ, Batley GE, Fernandes TF, Handy RD, Lyon DY, Mahendra S, McLaughlin MJ, Lead JR. Nanomaterials in the environment: behavior, fate, bioavailability, and effects. Environmental toxicology and chemistry. 2008 Sep 1; 27(9):1825-51. [19] Lee D, Cohen RE, Rubner MF. Antibacterial properties of Ag nanoparticle loaded multilayers and formation of magnetically directed antibacterial microparticles. Langmuir. 2005
of
Oct 11; 21(21):9651-9.
ro
[20] Constantine CA, Gattás-Asfura KM, Mello SV, Crespo G, Rastogi V, Cheng TC, DeFrank
-p
JJ, Leblanc RM. Layer-by-layer biosensor assembly incorporating functionalized quantum dots.
re
Langmuir. 2003 Nov 11; 19(23):9863-7.
[21] Biju V, Muraleedharan D, Nakayama KI, Shinohara Y, Itoh T, Baba Y, Ishikawa M.
lP
Quantum dot-insect neuropeptide conjugates for fluorescence imaging, transfection, and nucleus
na
targeting of living cells. Langmuir. 2007 Sep 25; 23(20):10254-61.
ur
[22] Voura EB, Jaiswal JK, Mattoussi H, Simon SM. Tracking metastatic tumor cell extravasation with quantum dot nanocrystals and fluorescence emission-scanning microscopy.
Jo
Nature medicine. 2004 Sep 1; 10(9):993-8. [23] Park S, Chibli H, Wong J, Nadeau JL. Antimicrobial activity and cellular toxicity of nanoparticle–polymyxin B conjugates. Nanotechnology. 2011 [24] Wei C, Lin WY, Zainal Z, Williams NE, Zhu K, Kruzic AP, Smith RL, Rajeshwar K. Bactericidal activity of TiO2 photocatalyst in aqueous media: toward a solar-assisted water disinfection system. Environmental science & technology. 1994 May; 28(5):934-8.
18
Journal Pre-proof [25] Hajkova P, Patenka PS, Horsky J, Horska I, Kolouch A. Antiviral and antibacterial effect of photocatalytic TiO2 films. In Tissue Engineering 2007 Apr 1 (Vol. 13, No. 4, pp. 908-908). 140 HUGUENOT STREET, 3RD FL, NEW ROCHELLE, NY 10801 USA: MARY ANN LIEBERT INC. [26] Ipe BI, Lehnig M, Niemeyer CM. On the generation of free radical species from quantum
of
dots. Small. 2005 Jul 1; 1(7):706-9.
ro
[27] Dumas EM, Ozenne V, Mielke RE, Nadeau JL. Toxicity of CdTe quantum dots in bacterial
-p
strains. IEEE transactions on nanobioscience. 2009 Mar; 8(1):58-64.
re
[28] Dumas E, Gao C, Suffern D, Bradforth SE, Dimitrijevic NM, Nadeau JL. Interfacial charge transfer between CdTe quantum dots and gram negative vs gram positive bacteria. Environ. Sci.
lP
Technol. 2010 Jan 19; 44(4):1464-70.
na
[29] Kumari A, Singh RR. Encapsulation of highly confined CdSe quantum dots for defect free
Jo
2017 May 31; 89:77-85.
ur
luminescence and improved stability. Physica E: Low-dimensional Systems and Nanostructures.
[30] Bauer AW, PERRY DM, KIRBY WM. Single-disk antibiotic-sensitivity testing of staphylococci: An analysis of technique and results. AMA archives of internal medicine. 1959 Aug 1; 104(2):208-16. [31] Patel JB, Cockerill FR, Alder J, Bradford PA, Eliopoulos GM, Hardy D, Hindler JA, Jenkins SG, Lewis JS, Miller LA, Powell M. Performance standards for antimicrobial susceptibility testing; twenty-fourth informational supplement. CLSI standards for antimicrobial susceptibility testing. 2014 Jan; 34(1):1-226.
19
Journal Pre-proof [32] www.icmr.nic.in/Publications/SOP/SOP_Bacteriology.pdf [33] Murugadoss G, Ramasamy V, Kumar MR. Photoluminescence enhancement of hexagonalphase ZnS: Mn nanostructures using 1-thioglycolic acid. Applied Nanoscience. 2014 Apr 1;4(4):449-54. [34]Rathore KS, Patidar D, Janu Y, Saxena NS, Sharma K, Sharma TP. Structural and optical characterization of chemically synthesized ZnS nanoparticles. Chalcogenide Letters. 2008 Jun 1;
of
5(6):105-10.
ro
[35] Hu PA, Liu Y, Fu L, Cao L, Zhu D. Self-assembled growth of ZnS nanobelt networks. The
-p
Journal of Physical Chemistry B. 2004 Jan 22; 108(3):936-8.
re
[36] Hou L, Gao F. Phase and morphology controlled synthesis of high-quality ZnS nanocrystals. Materials letters. 2011 Feb 15; 65(3):500-3.
lP
[37] Trajić J, Kostić R, Romčević N, Romčević M, Mitrić M, Lazović V, Balaž P, Stojanović D.
na
Raman spectroscopy of ZnS quantum dots. Journal of Alloys and Compounds. 2015 Jul 15;637:401-6.
Jo
Jan 1; 11(1):142-201.
ur
[38] Nataro JP, Kaper JB. Diarrheagenic escherichia coli. Clinical microbiology reviews. 1998
20
Journal Pre-proof
Figure Captions: Figure 1: XRD patterns for (a) CdSe-QDs; (b) ZnS1 QDs; (c) ZnS2 QDs; (d) CdSe/ZnS1QDs and (e) CdSe/ZnS2QDs.
Figure 2: TEM images for (a) CdSe-QDs; (b) ZnS1 QDs; (c) ZnS2 QDs; (d) CdSe/ZnS1QDs and (e) CdSe/ZnS2QDs.
Figure 3: Photoluminescence spectra (a) CdSe QDs (b) ZnS1 (b1) Graphical demonstration of
of
emission transitions in ZnS1 QDs (c) ZnS2 (c1) Graphical demonstration of emission transitions
-p
and (g) Relative PL spectra for CdSe and CdSe/ZnS2.
ro
in ZnS-2 QDs (d) CdSe/ZnS1 (e) CdSe/ZnS2; (f) Relative PL spectra for CdSe and CdSe/ZnS1
re
Figure 4: FTIR spectrum for (a) CdSe-QDs; (b) ZnS1 QDs; (c) ZnS2 QDs; (d) CdSe/ZnS1QDs and (e) CdSe/ZnS2 QDs.
lP
Figure 5: Raman spectra for (a) CdSe-QDs; (b) ZnS1 QDs; (c) CdSe/ZnS1 QDs.
na
Figure 6: Antimicrobial findings for compound (A) against (a) E. coli; (b) A.baumannii.; (c) (F) against E. coli; (d) (F) against A.baumannii; (e) (A) against gram +ve Bacillus subtilis (f)
Jo
ur
((F)against gram +ve Bacillus subtilis. 1= Meropenem (10 mcg) and 2= Cotrimoxazole (25 mcg).
21
Journal Pre-proof
Table Captions: Table 1: XRD evaluations of CdSe, ZnS1, ZnS2, CdSe/ZnS1 and CdSe/ZnS2 QDs. Table 2: Intensity ratio for CdSe, ZnS1, ZnS2, CdSe/ZnS1 and CdSe/ZnS2 QDs from EDX analysis. Table 3(a): PLE and emission wavelengths for CdSe, ZnS1, ZnS2, CdSe/ZnS1 and CdSe/ZnS2.
of
Table 3(b): Deconvoluted PL peak positions, relative intensities and corresponding FWHM values for CdSe, ZnS1 and ZnS2.
ro
Table 4: Zone of inhibition for compounds obtained for gram negative and gram positive
Jo
ur
na
lP
re
-p
pathogens where E. coli (-ve)[E.C.], A. baumannii (-ve)[A.B.], Bacillus subtilis (+ve)[B.S.].
22
Journal Pre-proof
Table 1:
re
-p
ro
of
hkl Size : XRD (nm) Size: TEM(nm) 111 1.8 1.9 200 220 311 111 2.8 3.1 200 220 311 111 2.5 2.5 100 002 101 220 311 013 112 111 3.7 200 200 220 311 311 111 3.5 100 002 101 220 220 311 013 112
Jo
ur
na
lP
Sample Name 2 (in degrees) 25.47 CdSe 30.39 42.58 49.11 29.18 ZnS1 33.08 48.73 58.13 28.74 ZnS2 31.65 34.19 36.05 47.48 56.55 62.82 67.83 25.53 CdSe/ZnS1 31.69 34.40 42.78 49.19 58.15 25.49 CdSe/ZnS2 31.69 34.57 36.19 42.61 47.74 56.69 62.76 67.89
Table 2:
Sample Name CdSe ZnS1 ZnS2 CdSe/ZnS1 CdSe/ZnS2
Cd: Se 1:0.82 1:0.85 1:0.85
S 0.65 -
23
Zn:S 1:0.75 1:0.70 1:1 1:1
Journal Pre-proof
Table 3(a):
Sample Name PLE: Wavelength (nm) Emission: Wavelength (nm) CdSe 476 481 333
337, 427, 486
ZnS-2 CdSe/ZnS1 CdSe/ZnS2
380 474 472
385, 422, 445, 486, 529 487, 531 484, 532
ro
of
ZnS-1
re
-p
Table 3(b):
E1 481 335 384
E2 529 357 405
Jo
Concentration of compounds in μg/ml
E4
E5
491 487
529
E1 30 29 21
E2 56 45 39
E3 139 63 56
Intensity
E4
E5
29 14
38
E1 192 276 312
E2 72 250 228
E3 198 185 217
E4
E5
91 149
135
ur
Table 4:
E3 586 417 442
FWHM (nm)
lP
CdSe ZnS1 ZnS2
PL emission: Spectral position
na
Sample Name
(A)
Zone of inhibition in mm (C) (D)
(B)
(E)
(F)
1024
E. C. 29
A. B. -
B. S. 15
E. C. -
A. B. -
B. S. -
E. C. -
A. B. -
B. S. -
E. C. -
A. B. -
B. S. -
E. C. -
A. B. -
B. S. -
E. C. 20
A. B. 25
B. S. 13
512
16
-
14
-
-
-
-
-
-
-
-
-
-
-
-
17
23
12
256
13
-
13
-
-
-
-
-
-
-
-
-
-
-
-
15
21
11
128
12
-
12
-
-
-
-
-
-
-
-
-
-
-
-
12
19
10
64
10
-
11
-
-
-
-
-
-
-
-
-
-
-
-
-
17
08
32
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
16
-
24
Journal Pre-proof
Contribution of the authors 1. Dr. Asha Kumari- First Author- All the work has been done: Sample preparation, characterization, interpretation and manuscript writing. 2. Dr. Nutan Thakur-Second Author-Carried out antimicrobial studies of
of
samples, also wrote part of the discussions on this study.
ro
3. Dr. Jitendraa Vashistt-Third Author- Helped in antimicrobial studies of
-p
samples.
4. Dr. Ragini Raj Singh-Corresponding and senior author- All work has
re
been planned and guided, interpretation of the results and manuscript
Jo
ur
na
lP
writing.
25
Jo
ur
na
lP
re
-p
ro
of
Journal Pre-proof
26
Journal Pre-proof
Highlights 1. Development of CdSe, ZnS QDs and CdSe/ZnS core/shell QDs using aqueous route. 2. Evaluated precursor reactivity link with the size of QDs and optical properties. 3. Effect of shell formation on antimicrobial behavior was studied. 4. Non antibacterial core/shell QDs can be used to study the microbial population.
Jo
ur
na
lP
re
-p
ro
of
5. QDs are antibacterial against multidrug resistant bacteria A. baumannii.
27
Figure 1
Figure 2
Figure 3ac
Figure 3dg
Figure 4
Figure 5
Figure 6
Asha Kumari, Nutan Thakur, Jitendraa Vashishtt, Ragini Raj Singh PII:
S1386-1425(19)31353-8
DOI:
https://doi.org/10.1016/j.saa.2019.117962
Reference:
SAA 117962
To appear in:
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Received date:
20 August 2019
Revised date:
3 December 2019
Accepted date:
13 December 2019
Please cite this article as: A. Kumari, N. Thakur, J. Vashishtt, et al., Structural, luminescent and antimicrobial properties of ZnS and CdSe/ZnS quantum dot structures originated by precursors, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy(2018), https://doi.org/10.1016/j.saa.2019.117962
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2018 Published by Elsevier.
Journal Pre-proof
Structural, luminescent and antimicrobial properties of ZnS and CdSe/ZnS quantum dot structures originated by precursors Asha Kumari1, Nutan Thakur2, Jitendraa Vashishtt2, Ragini Raj Singh*,1 1
Department of Physics and Materials Science (Nanotechnology Laboratory), Jaypee University of Information Technology, Waknaghat, Solan-173234, India
2
Department of Biotechnology and Bioinformatics, Jaypee University of Information Technology, Waknaghat, Solan-173234, India
of
Abstract
ro
ZnS quantum dots (QDs) and their core/shell (CdSe/ZnS) structures were studied for Zn based
-p
precursor reactivities. ZnS and CdSe/ZnS QDs were prepared selecting aqueous route and then characterized via XRD, TEM, EDX, PL, RAMAN and FTIR practices. Core/shell nanostructures
re
were synthesized by taking dissimilar precursors for the shell formation. Photoluminescence
lP
spectra of prepared QDs corroborate the effectual luminescence. Prepared QDs have large
na
surface area that make them useful alternative as organic antimicrobial agent which are highly irritant and unstable. Study of antimicrobial behavior of QD structures was carried out by disc
ur
diffusion method. Antimicrobial study of QDs and their core/shell structures was performed
Jo
against gram negative and gram positive bacteria, E. coli, A. baumanni and Bacillus subtilis respectively. It is found that elemental composition and size of QDs plays important role in antimicrobial behavior. Prepared QDs are fluorescent and have a key role in complex microbial population studies and identification of bacteria. Keywords: Quantum dots; core/shell structures; precursor reactivity; luminescent properties; antimicrobial activity *Corresponding Author: [email protected]
1
Journal Pre-proof
1. Introduction Semiconducting nanoparticles and their core/shell structures have turn out as the material of immense attention due to their applications like optical fibres amplifier[1], color displaying LED [2,3] as well as in biomedical field[4]. CdSe/ZnS quantum dots (QDs) are the most common type of QDs those have been developed for biological applications [5]. These QDs hold a special place due to their easy preparation and tunable luminescence in visible region. Novel properties
of
of these core/shell type QDs make them interesting. Covering of CdSe QDs with higher band gap
ro
semiconducting materials helps in improving photoluminescence quantum yields. This
-p
improvement takes place as nonradiative recombination sites on the surface of cre/shell QDs got
re
passivated through shell formation [6-8]. Rate of conversion and reactivity of precursors play an
lP
essential role in growth of the QDs. Slower precursor reactivity and its conversion results in production of few nuclei during nucleation process. This process results in extended growth
na
period and generates the larger particle size [9-14]. Size dependent unique optical properties of QDs makes them exceptional participant for biological activities [15-17]. These nanomaterials
ur
posses small size and large surface area, due to this unique property of nanomaterials they are
Jo
being considered as superior candidates to substitute conventional antimicrobial agents those are organic and are tremendously toxic and irritant [18,19]. Metal based nanoparticles have been reported to corroborate superior antimicrobial activity against both Gram (+ve) and Gram (-ve) bacteria [15]. But QDs in addition to antimicrobial activity possess narrow emission, excellent photostability, broad absorption spectra and bright photoluminescence [20, 15]. Due to these unique characteristics these QDs could be used in many other biological applications like in biosensors, cell imaging [21] etc. QDs posses good fluorescence characteristic and this fluorescent recognition plays considerable role to study complex microbial populations along
2
Journal Pre-proof with detection of bacteria. Imaging of bacteria by probe-conjugated QDs is most feasible research areas in bio based applications of QDs [22, 20]. On account of their wide probable applications, QDs have been planned for antimicrobial activities. These QDs mainly contains heavy metals, Pb, Te, Cd Se etc. and liberation of such heavy metals could be toxic to bacteria [23]. Different reasons for QDs antimicrobial behavior were explained by different research groups in previous reports. Previous studies have credited the photo-generation and free radicals
of
formation to play major role in antibacterial activity [24-26]. The photo-toxicity produced by
ro
sunlight and other high intensity light sources results in liberation of metal ions (Cd2+) which are
-p
toxic to the bacteria [27,28].
re
Current research is focused towards the synthesis of QDs and their core/shell nanostructures in aqueous media. In this work we have studied effect of diverse experimental
lP
parameters on optical characteristics. This work also involves precursor’s effect on
na
photoluminescence of ZnS and CdSe/ZnS QDs on the basis of precursor’s reactivity. X-ray diffraction (XRD), Photoluminescence spectroscopy (PL) and Transmission electron microscopy
ur
(TEM), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy, were
Jo
employed to study structural, morphological, optical and size distribution properties along with surface functional group chemistry. Importantly this study is also an attempt to study antimicrobial effects of prepared QDs towards different bacteria.
2.0 Experimental Details Chemicals: Cadmium chloride (CdCl2), sodiumselenosulphate (Na2SeSO3), triethanolamine and zinc sulphate heptahydrate (ZnSO4.7H2O), zinc chloride (ZnCl2), thiourea and hydrazine hydrate were supplied from Merck (India). All the analytical grade chemical products were used as attained form the manufacturer.
3
Journal Pre-proof 2.1 Method for CdSe QDs synthesis: Synthesis of CdSe QDs was done by same procedure as we have opted in our previous paper [29]. 2.2 Method for ZnS QDs synthesis: ZnS QDs were prepared by using two different precursors of zinc source. ZnS1 QDs were synthesized by using ZnSO4.7H20 as Zn source and ZnS2 were synthesized by using dry ZnCl2 as Zn source. Precursors ZnSO4.7H20, ZnCl2 and thiourea were used in 0.025:0.035 molar ratios. ZnS QDs were synthesized using wet chemical method where o
of
distilled water was used as solvent and temperature was maintained at 70 C. In typical synthesis
ro
ZnSO4.7H20 for ZnS1 and ZnCl2 for ZnS2 and hydrazine hydrate were added in 70 ml of o
-p
distilled water. Reaction mixture was followed by thiourea at 70 C temperature and continuously
re
stirred for 3 hours. Finally samples were washed, filtered and dehydrated at room temperature.
lP
2.3 Synthesis of CdSe/ZnS QDs: We have utilized a two-step synthesis process to produce core/shell CdSe/ZnS QDs. CdSe/ZnS core/shell structures were prepared by seed growth method
na
using aqueous solvent. First step was synthesis of CdSe QDs. These prepared CdSe dots are
ur
named as “bare “dots even though their surface is stabilized with 2-ME capping groups. For synthesis of CdSe/ZnS core/shell QDs, Zn precursors were followed by addition of 10 ml
Jo
Hydrazine hydrate. At 50°C 0.8 gm of CdSe solution was added to solution subsequent to adjusted pH 10. Sulphur source thiourea was then added to 80 ml of ready solution and continuously stirred for1 hour. CdSe/ZnS1 was synthesized by using ZnSO4.7H20 as precursor and CdSe/ZnS2 was synthesized by using ZnCl2 as precursor. After 1 hour samples were washed with distilled water. 2.4 Growth of Bacterial cultures and their treatment with QDs 2.4.1 Material and methods
4
Journal Pre-proof Culture media like Mueller Hinton agar, MacConkey agar, Mueller Hinton broth and luria broth used in microbiology experiments were purchased from Hi-Media Pvt. Ltd. (India). Antibiotic cotrimoxazole (1.25/23.75 mcg) and meropenem was purchased from Hi-Media Pvt. Ltd. (India). Escherichia coli (ATCC 25922) and Acinetobacter baumannii (ATCC 19606) used in antimicrobial susceptibility testing were obtained as a gift from respected Dr. Arti Kapil, Head of Bacteriology Division, Department of Microbiology, All India Institute of Medical Sciences
of
(AIIMS), New Delhi, India.
ro
2.4.2 Investigation of antimicrobial activity
-p
Antimicrobial activity of six compounds of QDs and their core/shell structures was investigated
re
by Kirby Bauer’s disk diffusion technique for gram negative strains; Escherichia coli (ATCC
lP
25922), Acinetobacter baumannii (ATCC 19606) and, gram positive strain Bacillus Subtilis (MTCC 441) [30]. All the protocols followed were adopted from the CLSI (Clinical laboratory
na
standard institute) and ICMR (Indian Council of Medical Research) guidelines [31]. Briefly, single pure colony of bacterial cultures was inoculated in Luria broth and then incubated
ur
overnight at 37°C. The bacterial culture of 0.5 optical density McFarland standards was mop up
Jo
onto Muller Hinton agar plate and allowed to dry for 15 minutes. Antibiotic disk of control antibiotics along with compounds were placed on agar plates. Then plates were incubated at 37°C for 16-18 hours and circular zones of lysis around disk were interpreted according to CLSI and ICMR guidelines [32].
3.0 Characterization techniques XRD spectra were traced by x-ray diffractometer (Shimadzu, japan), which use Cu Kα1 radiation for confirmation of the particle size and crystal structure of prepared samples. TEM analysis was performed as the supreme evidence of morphology and particle size distribution of synthesized 5
Journal Pre-proof samples on TEM HITACHI (H-7500). For confirmation of elemental composition of samples EDX analysis for samples were carry out in HRTEM instrument make TECNAI G2 20S-TWIN (FEI Neitherlands). Luminescent properties of QDs were recorded by photoluminescence spectroscopy (Perkin Elmer LS55 spectrophotometer). Photoluminescence excitation (PLE) spectra were recorded to know about excitation of QDs. FTIR spectra were recorded using model Cary 630 spectrophotometer from Agilent technology within the range 4000 – 400 cm-1. Raman
of
photospectrometer (Lab RAM HR Evolution Horiba) was used to record raman spectra of
ro
samples.
-p
3.1 Structural characterization
re
XRD patterns were recorded for structural determination of different samples and, obtained
lP
spectra for all QDs are shown in figure 1(a-e). XRD spectra shown in figure1 (a) for CdSe QDs demonstrate that four prominent peaks are present at 2 = 25.43, 42.12, 30.63 and 50°. These 2
na
values correspond to hkl planes (111), (200), (220) and (311) and represent cubic phase of CdSe. In XRD spectra of ZnS1 (figure1 (b)), four peaks are present and these peaks represent pure
ur
cubic phase of ZnS1. Similarly in XRD spectra of ZnS2 (figure 1(c)) occurrence of three well-
Jo
known peaks at 2 positions 28°, 47° and 56° corresponds to (111), (220) and (311) indicates the cubic structure for ZnS2 QDs. Along with these peaks in ZnS2 there is presence of more peaks at 2 positions 31°, 34°, 36°, 62°and 67°. Miller indices related to these peaks are (l00), (002), (101), (013) and (112) respectively [33, 34] and present the hexagonal phase of ZnO. Therefore, it is clear from these XRD results that in case of ZnS2 where ZnCl2 was used as precursor, there was biased oxidation of ZnS nanocrystal because of highly hygroscopic character of zinc chloride. Obtained XRD spectra for core/shell structures CdSe/ZnS1 and CdSe/ZnS2 are shown in (figure1 (d) & (e)) respectively. Other structural parameters like 2 positions, hkl planes, and 6
Journal Pre-proof phase for all these samples are presented in table1. It can be concluded from the table 1 and from figure ((d) & (e)) that the XRD spectra of core/shell QDs shows major reflections located at the middle of the positions evaluated for CdSe and ZnS. 2 positions shifting toward red side are clear evidence of core/shell structure. Crystallite size of CdSe, ZnS1 and ZnS2 QDs were acquired using the Scherrer’s formula (Eq. (1)). (1)
of
D = Kλ/βCosθ
ro
3.2 Morphological studies
-p
TEM micrographs of CdSe, ZnS1, ZnS2, CdSe/ZnS1 and CdSe/ZnS2 are shown in figure 2 (a-e).
re
These images corroborate uniform particle size distribution without agglomeration. Image-J software was used to calculate average diameter of QDs. Histograms for each QD type has been
lP
inserted in the corresponding TEM image. It is clearly visualized from figure 2 (a) that CdSe
na
QDs are consistently distributed having particle size 1.90.1 nm. Similarly TEM for ZnS1 (figure 2(b)) and ZnS2 (figure 2(c)) clearly reveal that these particles do not agglomerate
ur
instantaneously and are spherical in shape. Particle size of ZnS1 (3.00.5 nm) is bigger as
Jo
contrast of ZnS2 (2.30.2 nm) as outcome of the difference in the reactivity of precursors selected for synthesis of ZnS1 and ZnS2. In Case of core/shell structures CdSe/ZnS1 (3.70.2 nm) and CdSe/ZnS2 (3.5 30.2 nm) figure 2(d) and (e) there is clear depiction of shell formation on CdSe core QDs. This leads to confirmation of shell formation on CdSe QDs. Obtained average particle size have been tabulated in Table 1 together with the XRD results.
3.3 Energy-dispersive X-ray spectra Prepared samples were characterized by EDX to confirm elemental composition. Table 2 presents the ratio of peak intensities for all the prepared samples. An EDX spectrum for CdSe
7
Journal Pre-proof confirms the pure CdSe QD formation. Spectra contain intense peaks of cadmium and selenium. It was concluded from Table 2 that ratio of Cd: Se was 1:0.82 and this was due to high concentration of their precursors. Peak of sulfur is due to presence of 2-Mercaptoethanol. The peaks of carbon and copper in all EDX spectra present due to the carbon coated copper grid used as sample holder while characterizing the samples. In EDX spectra of ZnS1, ratio of peaks intensity was found 1:0.75 revealed that there are peaks of Zn and S due to high concentration of
of
its precursors. Similarly an EDX spectrum for ZnS2 contains intense peaks of Zn and S. EDX
ro
spectra of CdSe/ZnS1 and CdSe/ZnS2, where there is presence of Cd and Se peaks from core
-p
CdSe and peaks of Zn and S come from ZnS shell. The ratio presented in Table 2 concludes that
re
there was formation of CdSe/ZnS core/shell nanostructures. Figures showing EDX spectra are being provided in supplementary information figures SI-1 to SI- 5.
lP
3.4 Photoluminescence Studies
na
PL spectra and PLE spectra of all synthesized ZnS and their CdSe/ZnS QDs were recorded at room temperature and are shown in Figures 3(a-g). PL spectra were attained by excitation of
ur
samples at dissimilar excitation wavelengths. All the samples show emission at fixed
Jo
wavelength. While PLE spectra for all QDs recorded by setting up PL emission on blue end of PL peak. Figure 3(a) presents the PL and PLE spectra for CdSe QDs and it is concluded from figure 3(a) that in PLE spectra; we have observed band edge transition that is 1se and 1sh around 2.6 eV or 476 nm, while the emission wavelength is observed at 2.5 eV or 481 nm. Emission spectra of CdSe QDs possess band edge luminescence along with significant trap emission. Explanation of defect emission in case of CdSe QDs has already been conversed in our previous report [29]. In case of ZnS1 (Figure 3(b)) where ZnSO4.7H2O was used as precursor, emission spectra corresponds to emission at 337, 427, 486 nm have been recorded,
8
Journal Pre-proof which shows weak absorption at 333 nm. In PL spectra of ZnS1 band emission was near about 337 nm with only some defects at 427 & 486 nm. Graphical representation of emission transitions in ZnS1 QDs are given in figure 3(b1). Similarly emission spectrum of ZnS2 (figure 3(c)) shows peak at 380 nm. Emission peaks correspond to different emission centers at 422, 445, 486 and 529 along with band edge emission at 384. Schematic representation of emission transitions in ZnS2 QDs are presented in figure 3 (c1).
of
Table 3(a) consists of all the emission peak positions along with PLE. To determine the
ro
peak positions in samples CdSe, ZnS1, and ZnS2 deconvulation has been performed on the PL
-p
spectra. Deconvulated PL spectra was in shape for different peaks which can be seen from figure
re
(3(a, b & c)). The peak E1 will match with the emission due to band edge in all samples and other peaks present defects. All the peaks along with intensity and respective FWHM values are
lP
tabulated in table 3(b). The emission band centered between 400-450 nm in case of ZnS1 and
na
ZnS2 (figure 3b and 3c) are attributed to interstitial zinc and sulfur vacancies. Emission near about 485-490 nm was attributed to Zn-vacancies [35]. Peaks centered near about 525 nm are
ur
attributed to vacancy associated with recombination of electron from sulfur vacancy energy level
Jo
to hole on the Zn vacancy energy level [36]. In case of ZnS1 this has not been observed. PLE spectra of CdSe/ZnS1 (Figure 3(d)) core/shell show excitation peak at 474 nm and it corresponds to emission from band edge at 487 nm along with defect generated luminescence at 531 nm respectively. Likewise, in CdSe/ZnS2 (Figure 3(e)) PLE spectra show absorption peaks at 472 nm and corresponds to emission due to band edge at 484 nm with defect generated emission at 532 nm in PL. In case of core/shell structure the peak remained at 532 nm is due to sulfur vacancies. We compared the PL spectra of CdSe QDs with core/shell structure CdSe/ZnS1 (Figure 3 (f)) and CdSe/ZnS2 (Figure3 (g)) and observed that the intensity of emission peak gets
9
Journal Pre-proof improved on shell formation with decrease in defect emission states. This defect luminescence mainly originate due to dangling or unsatisfactory bonds available on QDs surface which escort generation of trap states and these traps have very strong hole acceptor trait. In CdSe QDs luminescence intensity at the band edge is more or less equivalent to defect luminescence. However, in core/shell CdSe-QDs structures emission at band edge is outstanding in contrast to luminescence caused by defects and this happens because of passivation of
of
deprived bonds on shell formation. From these PL studies it is concluded that all these QDs
-p
ro
posses fluorescence and this property of QDs get improved on formation of shell on core surface.
re
3.5 FTIR analysis
FTIR analysis of CdSe QDs, ZnS QDs and core/shell nanostructures was performed for
lP
confirmation of surface functionalities. Peaks observed at 1462 cm-1 corresponds to CH2 bending
na
and 1630 cm-1 corresponds to -NH bending in spectra of CdSe-QD (figure (4a)). Intense peak in spectra at 3346 cm-1 corresponds to -OH group. The peak around 1100 cm-1 is assigned to CH2
assigned to C-O stretching. Band stretching was observed at 706-899 cm-1 due to C-S bond.
Jo
1
ur
rocking. Band at 2200 cm-1 appears weaker and due to thiol group. Peak at 1067 cm-1 - 1041 cm-
Some extra peaks in CdSe are present because of some impurities. In the spectrum of ZnS1 (figure (4b)) peak with high intensity at 3249 cm-1 is due to presence of -OH group. Peak at 2100 cm-1 and 1640 cm-1 corresponds to -NH bands characteristic vibrations. Spectrum of ZnS2 (figure (4c)) showed the peaks at 3290 and 1640 this matched up to -OH group and -NH bending respectively. Weak peak around the 1402 cm-1 and 1503 cm-1 corresponds to C-N vibrations. FTIR spectrum of CdSe/ ZnS1 (figure (4d)) indicates intense peaks at 3387 cm-1, 1503 cm-1 and 1395 cm-1 corresponds to OH group and C-N vibrations respectively. Peak around 1197 cm-1
10
Journal Pre-proof corresponds to CH2 rocking. Band around 709 - 899 cm-1 is due to C-S stretching. Likewise in case of CdSe/ZnS2 (figure (4e)) band at 3387 cm-1 for -OH, 2117 cm-1 for alkynes and at 1547 cm-1 due to C-N vibrations. Peak around 1119 cm-1 corresponds to CH2 rocking. FTIR spectra of these QDs contain functional groups such as -NH and -OH which makes them hydrophilic and biocompatible. Some extra peaks are present in CdSe other than -NH and -OH group because of some remaining impurities and these extra peaks somewhere affect the biocompatibility of bare
of
CdSe QDs.
ro
3.6 Raman Spectroscopy
-p
Raman spectroscopy is a spectroscopic technique which was used to find out vibrational modes
re
of prepared quantum dots. In Raman spectroscopy monochromatic light source is used, typically
lP
from a laser in visible or near ultraviolet range. The laser light interacts with molecular vibrations, phonons or other excitations in the system, resulting in the energy of the laser photons
na
being shifted up or down. The shift in energy gives information about the vibrational modes in the system. Figure 5 shows raman spectra of all synthesized CdSe, ZnS and its core shell
ur
structure, we have not recorded the Raman spectra of ZnS2 and CdSe/ZnS2 as it has been
Jo
already discussed that the structural, fluorescence and EDX results confirms the defects present in ZnS2 as used precursor was different in ZnS2 with respect to ZnS1. The Raman peak in ZnS-1 (figure 5(b)) of wide multimodal feature are in region of 160.06 cm-1, 246.35 cm-1 and wide structure lies in region of 345 cm-1. In case of core CdSe quantum dots (figure 5(a)) Raman peaks are at position 30.06 cm-1, 191.77 cm-1, 278.86 cm-1 [37]. Peak near about 278.86 cm-1 was assigned to Cd-S vibrations. Raman spectra of core shell structures i.e., CdSe/ZnS1 (figure 5(c)) revealed Raman shift in peak position as compared to core CdSe QDs. In CdSe/ZnS1 peak position are shifted to 38.06 cm-1, 201.27 cm-1, 278.86 cm-1 with a shift of 7.9 cm-1, 9.5 cm-1 and
11
Journal Pre-proof 3.5 cm-1 respectively with respect to CdSe QDs. Similarly shifts in CdSe/ZnS1 peak position are shifted to 169.56 cm-1, 256.78 cm-1, with a shift of 9 cm-1 and 10.43 cm-1 respectively with respect to ZnS1 QDs. This shift in Raman peaks in core shell structures as compared to core CdSe and shell ZnS was attributed to the shell formation over the core surface. These observations were also supported by our PL and FTIR studies. The presence of these broad peaks
3.7 Antimicrobial activity of compounds
ro
optical properties can be utilized in bio based application.
of
in Raman spectra confirms quantum confinement in these small particles. These QDs on basis of
-p
Complex microbial populations and recognition of bacteria can be done by fluorescent detection.
re
We can use these fluorescent QDs for single bacterial imaging by generating probe-conjugated
lP
QDs. In this regard we studied antimicrobial activity and results showed that A and F compounds having potent antibacterial behavior towards gram negative pathogens and gram positive strain
na
Bacillus subtilis (Table 4). Different synthesized QDs have been named as compound (A)CdSe, Compound (B)ZnS1, Compound (C) ZnS2, Compound (D) CdSe/ZnS1, compound (E)-
ur
CdSe/ZnS2 and compound (F) -poly CdSe correspondingly. Several strains of E. coli are
Jo
responsible for intestinal and extra-intestinal infections [38]. Acinetobacter baumannii is considered as leading cause of nosocomial disease causing pathogen; originate several blood, skin, soft tissue and respiratory infections. Recently, A. baumannii has already been premeditated as the topmost multidrug opposing bacteria with hospital setting by (WHO). Several species of Bacillus are sometimes allied with infections of the ears, wounds, eyes, urinary tract and gastrointestinal tract. Figure 6 (a) shows clear spherical lysis zones produced by compound (A) with control (tested) antibiotics against E. coli (Gram –ve). Figure 6(b) shows compound A against
12
Journal Pre-proof Acinetobacter baumannii (Gram –ve). It is clear from the figures that compound (A) shows antimicrobial action against E.coli but there was no antimicrobial effect noticed against Acinetobacter baumannii. Likewise figure 6 (c) and 6(d) present the lysis zone for compound (F) against E. coli and Acinetobacter baumannii respectively. Observed zones for all samples are in mm and given in Table 4, it was concluded from the Table 4 that compound (A) and (F) possesses fine antimicrobial activity. However, there were no presence of zone lysis values
of
found for compound (B), (C), (D) & (E) validate that prepared compounds did not inhibit either
ro
E.coli or Acinetobacter baumannii growth [Supplementary information Figures SI(6-11)].
-p
Similar trend was seen in case of antimicrobial activity of Compound (A) to Compound (F)
re
towards gram positive strain Bacillus subtilis (Table 4). This was concluded from Table 4 that compound (A) and (F) possesses fine antimicrobial activity against gram +ve bacterial strain
lP
with difference in size of zone of inhibition as shown in Figure 6 (e) and 6 (f) respectively.
na
Supplementary figures from SI-6 to SI-11 further provide visual proof to elucidate that there were no zone of lysis found in compound (B) to compound (E) for either Acinetobacter
ur
baumannii , E.coli and Bacillus subtilis respectively. Here these different sizes of inhibition
Jo
zones between QDs could be correlated to surface modification, particles size, elemental composition, and diffusion propensity of particles with cell wall. This behavior can also be accounted to different size of QDs and binding tendency of QDs to bacterial wall. CdSe QDs contain very toxic heavy metals this have been inveterate from EDX. Due to such toxic composition of CdSe QDs they demonstrate antimicrobial behavior. In comparison with CdSe QDs, ZnS1 and ZnS2 QDs are not showing any antimicrobial behavior concludes no zone of inhibition is formed in case of ZnS1 and ZnS2 (Table 4). Bactericidal behavior of these CdSe QDs has also been attributed to their smaller size as compared to ZnS1 and ZnS2. It has
13
Journal Pre-proof been already incorrigible from XRD and TEM analysis of these QDs that CdSe QDs are smaller in size as compare to ZnS1 and ZnS2. Similarly CdSe/ZnS1 and CdSe/ZnS2 do not show any antimicrobial property. This is due to increase in size on shell formation. Formation of shell also avoids leakage of heavy toxic metal from core material CdSe and prevents core material from photo oxidation. Along with all these factors antimicrobial behavior and dissimilarity in zone lysis size between QDs could be correlated to diffusion affinity of nanoparticles with cell wall.
of
This behavior can also be accounted to different size of QDs and binding tendency of QDs to
ro
bacterial wall. Luminescent QDs ZnS1, ZnS2, CdSe/ZnS1, CdSe/ZnS2 which are not showing
-p
antimicrobial activity are biocompatible and can be used to study microbial inhabitants and
re
identification of bacteria by conjugation with probe. Imaging of bacterial inhabitants by means of probe-conjugated QDs regarded as one of the mainly practicable areas in bio based applications.
lP
4. Conclusions
na
In this paper we went through the effect of ZnS precursor reactivity on size and optical properties of ZnS QDs. Structural analysis confirms that particle size of ZnS1 was larger as compared to
ur
ZnS2. It was found from optical studies that precursor used for synthesis of ZnS1 and ZnS2
Jo
affect the emission at band edge and emission due to defect position in these QDs. In ZnS1 the emission for band edge was at 337 nm along with defect emission at 427 nm, 486 nm and in ZnS2 emission for band edge was found at 384 nm along with defects at 422 nm, 445 nm, 486 nm and 529 nm. The wide peaks in the Raman spectra can be accredited to quantum effects of the prepared QDs and their core/shell structures. Because of unique optical properties these quantum dots can be useful in many applications such as biolabeling. A correlation was found between reactivity of precursors’ to optical properties and size of QDs. Antimicrobial behavior of all synthesized QDs was studied by Kirby Bauer’s disk diffusion
14
Journal Pre-proof method (against potential gram negative pathogens; Escherichia coli (ATCC 25922), Acinetobacter baumannii (ATCC 19606) and gram positive strain Bacillus Subtilis. Poly CdSe and CdSe QDs were found to show good antimicrobial activity because of their toxic composition toward gram +ve and gram -ve strain. As A. baumannii has been found listed as the topmost multidrug resistant bacteria the antimicrobial properties of compound F can be a breach. In contrast with CdSe QDs, ZnS1 and ZnS2 QDs do not show any antimicrobial tendency.
of
Bactericidal behavior of these CdSe QDs has also been attributed to their small size as compared
ro
to ZnS1 and ZnS2. In case of CdSe/ZnS1 and CdSe/ZnS2 no antimicrobial property was found
-p
and this was due to shell formation which prevents leakage of heavy toxic metal from core
re
material CdSe and prevents core material from photo oxidation. PL spectra clearly reveal that the fluorescent properties of these QDs improved on shell formation. Luminescent QDs which are
lP
not showing antimicrobial tendency are biocompatible as depicted from FTIR and can be used
Acknowledgements
na
for imaging of bacterial population by probe-conjugated QDs.
Jo
032/2013].
ur
This research work was support by SERB (DST), India, grant [grant number SR/FTP/PS-
“Data Availability: The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.”
References [1] Tierno A, Ackemann T, Leburn CG, Brown CT. Saturation of absorption and gain in a quantum dot diode with continuous-wave driving. Applied Physics Letters. 2010 Dec 6; 97 (23):231104.
15
Journal Pre-proof [2] Mora-Seró I, Giménez S, Moehl T, Fabregat-Santiago F, Lana-Villareal T, Gómez R, Bisquert J. Factors determining the photovoltaic performance of a CdSe quantum dot sensitized solar cell: the role of the linker molecule and of the counter electrode. Nanotechnology. 2008 Sep 25; 19(42):424007. [3] Wang T, Pang F, Wang K, Zhang R, Liu G. Evanescent wave coupled semiconductor
of
quantum dots fiber amplifier based on reverse Micelle method. In Nanotechnology, 2007. IEEE-
ro
NANO 2007. 7th IEEE Conference on 2007 Aug 2 (pp. 819-822).
-p
[4] Kim L, Anikeeva PO, Coe-Sullivan SA, Steckel JS, Bawendi MG, Bulovic V. Contact
re
printing of quantum dot light-emitting devices. Nano letters. 2008 Nov 18; 8(12):4513-7. [5] Delehanty JB, Medintz IL, Pons T, Brunel FM, Dawson PE, Mattoussi H. Self-assembled
lP
quantum dot− peptide bioconjugates for selective intracellular delivery. Bioconjugate chemistry.
na
2006 Jul 19; 17(4):920-7.
ur
[6] Kim J, Lee J, Kyhm K. Surface-plasmon-assisted modal gain enhancement in Au-hybrid
Jo
CdSe/ZnS nanocrystal quantum dots. Applied Physics Letters. 2011 Nov 21; 99(21):213112. [7] Nirmal M, Brus L. Luminescence photophysics in semiconductor nanocrystals. Accounts of chemical research. 1999 May 18;32(5):407-14. [8] Mattoussi H, Mauro JM, Goldman ER, Anderson GP, Sundar VC, Mikulec FV, Bawendi MG. Self-assembly of CdSe− ZnS quantum dot bioconjugates using an engineered recombinant protein. Journal of the American Chemical Society. 2000 Dec 13; 122(49):12142-50. [9] Viswanatha R, Sarma DD. Growth of nanocrystals in solution. Nanomaterials chemistry: recent developments and new directions. 2007:139-70. 16
Journal Pre-proof [10] Rempel JY, Bawendi MG, Jensen KF. Insights into the kinetics of semiconductor nanocrystal nucleation and growth. Journal of the American Chemical Society. 2009 Mar 10; 131(12):4479-89. [11] Clark MD, Kumar SK, Owen JS, Chan EM. Focusing nanocrystal size distributions via production control. Nano letters. 2011 Apr 8; 11(5):1976-80.
of
[12] Hens Z, Čapek RK. Size tuning at full yield in the synthesis of colloidal semiconductor
ro
nanocrystals, reaction simulations and experimental verification. Coordination Chemistry
-p
Reviews. 2014 Mar 15; 263:217-28.
re
[13] Abé S, Capek R, De Geyter B, Hens Z. Using the acid concentration and chain length as a tuning strategy in the hot injection synthesis, an experimental and theoretical analysis. In5th
lP
Conference on Nanoscience with Nanocrystals (NaNax 5) 2012.
na
[14] Sugimoto T, Shiba F, Sekiguchi T, Itoh H. Spontaneous nucleation of monodisperse silver
ur
halide particles from homogeneous gelatin solution I: silver chloride. Colloids and Surfaces A:
Jo
Physicochemical and Engineering Aspects. 2000 May 15;164(2):183-203. [15] Adams LK, Lyon DY, Alvarez PJ. Comparative eco-toxicity of nanoscale TiO 2, SiO 2, and ZnO water suspensions. Water research. 2006 Nov 30; 40(19):3527-32. [16] Panáček A, Kvítek L, Prucek R, Kolář M, Večeřová R, Pizúrová N, Sharma VK, Nevěčná TJ, Zbořil R. Silver colloid nanoparticles: synthesis, characterization, and their antibacterial activity. J. Phys. Chem. B. 2006 Aug 1; 110(33):16248-53. [17] Li P, Li J, Wu C, Wu Q, Li J. Synergistic antibacterial effects of β-lactam antibiotic combined with silver nanoparticles. Nanotechnology. 2005 Jul 28; 16(9):1912. 17
Journal Pre-proof [18] Klaine SJ, Alvarez PJ, Batley GE, Fernandes TF, Handy RD, Lyon DY, Mahendra S, McLaughlin MJ, Lead JR. Nanomaterials in the environment: behavior, fate, bioavailability, and effects. Environmental toxicology and chemistry. 2008 Sep 1; 27(9):1825-51. [19] Lee D, Cohen RE, Rubner MF. Antibacterial properties of Ag nanoparticle loaded multilayers and formation of magnetically directed antibacterial microparticles. Langmuir. 2005
of
Oct 11; 21(21):9651-9.
ro
[20] Constantine CA, Gattás-Asfura KM, Mello SV, Crespo G, Rastogi V, Cheng TC, DeFrank
-p
JJ, Leblanc RM. Layer-by-layer biosensor assembly incorporating functionalized quantum dots.
re
Langmuir. 2003 Nov 11; 19(23):9863-7.
[21] Biju V, Muraleedharan D, Nakayama KI, Shinohara Y, Itoh T, Baba Y, Ishikawa M.
lP
Quantum dot-insect neuropeptide conjugates for fluorescence imaging, transfection, and nucleus
na
targeting of living cells. Langmuir. 2007 Sep 25; 23(20):10254-61.
ur
[22] Voura EB, Jaiswal JK, Mattoussi H, Simon SM. Tracking metastatic tumor cell extravasation with quantum dot nanocrystals and fluorescence emission-scanning microscopy.
Jo
Nature medicine. 2004 Sep 1; 10(9):993-8. [23] Park S, Chibli H, Wong J, Nadeau JL. Antimicrobial activity and cellular toxicity of nanoparticle–polymyxin B conjugates. Nanotechnology. 2011 [24] Wei C, Lin WY, Zainal Z, Williams NE, Zhu K, Kruzic AP, Smith RL, Rajeshwar K. Bactericidal activity of TiO2 photocatalyst in aqueous media: toward a solar-assisted water disinfection system. Environmental science & technology. 1994 May; 28(5):934-8.
18
Journal Pre-proof [25] Hajkova P, Patenka PS, Horsky J, Horska I, Kolouch A. Antiviral and antibacterial effect of photocatalytic TiO2 films. In Tissue Engineering 2007 Apr 1 (Vol. 13, No. 4, pp. 908-908). 140 HUGUENOT STREET, 3RD FL, NEW ROCHELLE, NY 10801 USA: MARY ANN LIEBERT INC. [26] Ipe BI, Lehnig M, Niemeyer CM. On the generation of free radical species from quantum
of
dots. Small. 2005 Jul 1; 1(7):706-9.
ro
[27] Dumas EM, Ozenne V, Mielke RE, Nadeau JL. Toxicity of CdTe quantum dots in bacterial
-p
strains. IEEE transactions on nanobioscience. 2009 Mar; 8(1):58-64.
re
[28] Dumas E, Gao C, Suffern D, Bradforth SE, Dimitrijevic NM, Nadeau JL. Interfacial charge transfer between CdTe quantum dots and gram negative vs gram positive bacteria. Environ. Sci.
lP
Technol. 2010 Jan 19; 44(4):1464-70.
na
[29] Kumari A, Singh RR. Encapsulation of highly confined CdSe quantum dots for defect free
Jo
2017 May 31; 89:77-85.
ur
luminescence and improved stability. Physica E: Low-dimensional Systems and Nanostructures.
[30] Bauer AW, PERRY DM, KIRBY WM. Single-disk antibiotic-sensitivity testing of staphylococci: An analysis of technique and results. AMA archives of internal medicine. 1959 Aug 1; 104(2):208-16. [31] Patel JB, Cockerill FR, Alder J, Bradford PA, Eliopoulos GM, Hardy D, Hindler JA, Jenkins SG, Lewis JS, Miller LA, Powell M. Performance standards for antimicrobial susceptibility testing; twenty-fourth informational supplement. CLSI standards for antimicrobial susceptibility testing. 2014 Jan; 34(1):1-226.
19
Journal Pre-proof [32] www.icmr.nic.in/Publications/SOP/SOP_Bacteriology.pdf [33] Murugadoss G, Ramasamy V, Kumar MR. Photoluminescence enhancement of hexagonalphase ZnS: Mn nanostructures using 1-thioglycolic acid. Applied Nanoscience. 2014 Apr 1;4(4):449-54. [34]Rathore KS, Patidar D, Janu Y, Saxena NS, Sharma K, Sharma TP. Structural and optical characterization of chemically synthesized ZnS nanoparticles. Chalcogenide Letters. 2008 Jun 1;
of
5(6):105-10.
ro
[35] Hu PA, Liu Y, Fu L, Cao L, Zhu D. Self-assembled growth of ZnS nanobelt networks. The
-p
Journal of Physical Chemistry B. 2004 Jan 22; 108(3):936-8.
re
[36] Hou L, Gao F. Phase and morphology controlled synthesis of high-quality ZnS nanocrystals. Materials letters. 2011 Feb 15; 65(3):500-3.
lP
[37] Trajić J, Kostić R, Romčević N, Romčević M, Mitrić M, Lazović V, Balaž P, Stojanović D.
na
Raman spectroscopy of ZnS quantum dots. Journal of Alloys and Compounds. 2015 Jul 15;637:401-6.
Jo
Jan 1; 11(1):142-201.
ur
[38] Nataro JP, Kaper JB. Diarrheagenic escherichia coli. Clinical microbiology reviews. 1998
20
Journal Pre-proof
Figure Captions: Figure 1: XRD patterns for (a) CdSe-QDs; (b) ZnS1 QDs; (c) ZnS2 QDs; (d) CdSe/ZnS1QDs and (e) CdSe/ZnS2QDs.
Figure 2: TEM images for (a) CdSe-QDs; (b) ZnS1 QDs; (c) ZnS2 QDs; (d) CdSe/ZnS1QDs and (e) CdSe/ZnS2QDs.
Figure 3: Photoluminescence spectra (a) CdSe QDs (b) ZnS1 (b1) Graphical demonstration of
of
emission transitions in ZnS1 QDs (c) ZnS2 (c1) Graphical demonstration of emission transitions
-p
and (g) Relative PL spectra for CdSe and CdSe/ZnS2.
ro
in ZnS-2 QDs (d) CdSe/ZnS1 (e) CdSe/ZnS2; (f) Relative PL spectra for CdSe and CdSe/ZnS1
re
Figure 4: FTIR spectrum for (a) CdSe-QDs; (b) ZnS1 QDs; (c) ZnS2 QDs; (d) CdSe/ZnS1QDs and (e) CdSe/ZnS2 QDs.
lP
Figure 5: Raman spectra for (a) CdSe-QDs; (b) ZnS1 QDs; (c) CdSe/ZnS1 QDs.
na
Figure 6: Antimicrobial findings for compound (A) against (a) E. coli; (b) A.baumannii.; (c) (F) against E. coli; (d) (F) against A.baumannii; (e) (A) against gram +ve Bacillus subtilis (f)
Jo
ur
((F)against gram +ve Bacillus subtilis. 1= Meropenem (10 mcg) and 2= Cotrimoxazole (25 mcg).
21
Journal Pre-proof
Table Captions: Table 1: XRD evaluations of CdSe, ZnS1, ZnS2, CdSe/ZnS1 and CdSe/ZnS2 QDs. Table 2: Intensity ratio for CdSe, ZnS1, ZnS2, CdSe/ZnS1 and CdSe/ZnS2 QDs from EDX analysis. Table 3(a): PLE and emission wavelengths for CdSe, ZnS1, ZnS2, CdSe/ZnS1 and CdSe/ZnS2.
of
Table 3(b): Deconvoluted PL peak positions, relative intensities and corresponding FWHM values for CdSe, ZnS1 and ZnS2.
ro
Table 4: Zone of inhibition for compounds obtained for gram negative and gram positive
Jo
ur
na
lP
re
-p
pathogens where E. coli (-ve)[E.C.], A. baumannii (-ve)[A.B.], Bacillus subtilis (+ve)[B.S.].
22
Journal Pre-proof
Table 1:
re
-p
ro
of
hkl Size : XRD (nm) Size: TEM(nm) 111 1.8 1.9 200 220 311 111 2.8 3.1 200 220 311 111 2.5 2.5 100 002 101 220 311 013 112 111 3.7 200 200 220 311 311 111 3.5 100 002 101 220 220 311 013 112
Jo
ur
na
lP
Sample Name 2 (in degrees) 25.47 CdSe 30.39 42.58 49.11 29.18 ZnS1 33.08 48.73 58.13 28.74 ZnS2 31.65 34.19 36.05 47.48 56.55 62.82 67.83 25.53 CdSe/ZnS1 31.69 34.40 42.78 49.19 58.15 25.49 CdSe/ZnS2 31.69 34.57 36.19 42.61 47.74 56.69 62.76 67.89
Table 2:
Sample Name CdSe ZnS1 ZnS2 CdSe/ZnS1 CdSe/ZnS2
Cd: Se 1:0.82 1:0.85 1:0.85
S 0.65 -
23
Zn:S 1:0.75 1:0.70 1:1 1:1
Journal Pre-proof
Table 3(a):
Sample Name PLE: Wavelength (nm) Emission: Wavelength (nm) CdSe 476 481 333
337, 427, 486
ZnS-2 CdSe/ZnS1 CdSe/ZnS2
380 474 472
385, 422, 445, 486, 529 487, 531 484, 532
ro
of
ZnS-1
re
-p
Table 3(b):
E1 481 335 384
E2 529 357 405
Jo
Concentration of compounds in μg/ml
E4
E5
491 487
529
E1 30 29 21
E2 56 45 39
E3 139 63 56
Intensity
E4
E5
29 14
38
E1 192 276 312
E2 72 250 228
E3 198 185 217
E4
E5
91 149
135
ur
Table 4:
E3 586 417 442
FWHM (nm)
lP
CdSe ZnS1 ZnS2
PL emission: Spectral position
na
Sample Name
(A)
Zone of inhibition in mm (C) (D)
(B)
(E)
(F)
1024
E. C. 29
A. B. -
B. S. 15
E. C. -
A. B. -
B. S. -
E. C. -
A. B. -
B. S. -
E. C. -
A. B. -
B. S. -
E. C. -
A. B. -
B. S. -
E. C. 20
A. B. 25
B. S. 13
512
16
-
14
-
-
-
-
-
-
-
-
-
-
-
-
17
23
12
256
13
-
13
-
-
-
-
-
-
-
-
-
-
-
-
15
21
11
128
12
-
12
-
-
-
-
-
-
-
-
-
-
-
-
12
19
10
64
10
-
11
-
-
-
-
-
-
-
-
-
-
-
-
-
17
08
32
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
16
-
24
Journal Pre-proof
Contribution of the authors 1. Dr. Asha Kumari- First Author- All the work has been done: Sample preparation, characterization, interpretation and manuscript writing. 2. Dr. Nutan Thakur-Second Author-Carried out antimicrobial studies of
of
samples, also wrote part of the discussions on this study.
ro
3. Dr. Jitendraa Vashistt-Third Author- Helped in antimicrobial studies of
-p
samples.
4. Dr. Ragini Raj Singh-Corresponding and senior author- All work has
re
been planned and guided, interpretation of the results and manuscript
Jo
ur
na
lP
writing.
25
Jo
ur
na
lP
re
-p
ro
of
Journal Pre-proof
26
Journal Pre-proof
Highlights 1. Development of CdSe, ZnS QDs and CdSe/ZnS core/shell QDs using aqueous route. 2. Evaluated precursor reactivity link with the size of QDs and optical properties. 3. Effect of shell formation on antimicrobial behavior was studied. 4. Non antibacterial core/shell QDs can be used to study the microbial population.
Jo
ur
na
lP
re
-p
ro
of
5. QDs are antibacterial against multidrug resistant bacteria A. baumannii.
27
Figure 1
Figure 2
Figure 3ac
Figure 3dg
Figure 4
Figure 5
Figure 6