Chemiluminescence studies between aqueous phase synthesized mercaptosuccinic acid capped cadmium telluride quantum dots and luminol-H2O2

    Chemiluminescence studies between aqueous phase synthesized mercaptosuccinic acid capped cadmium telluride quantum dots and luminol-H 2O2 Kulandaivelu Kaviyarasan, Sambandam Anandan, Ramalinga Viswanathan Mangalaraja, Abdullah M. Asiri, Jerry J. Wu PII: DOI: Reference:

S1386-1425(16)30210-4 doi: 10.1016/j.saa.2016.04.038 SAA 14401

To appear in: Received date: Revised date: Accepted date:

12 January 2016 14 April 2016 17 April 2016

Please cite this article as: Kulandaivelu Kaviyarasan, Sambandam Anandan, Ramalinga Viswanathan Mangalaraja, Abdullah M. Asiri, Jerry J. Wu, Chemiluminescence studies between aqueous phase synthesized mercaptosuccinic acid capped cadmium telluride quantum dots and luminol-H2 O2 , (2016), doi: 10.1016/j.saa.2016.04.038

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ACCEPTED MANUSCRIPT Chemiluminescence Studies between Aqueous Phase Synthesized Mercaptosuccinic Acid Capped Cadmium Telluride Quantum Dots and Luminol-H2O2

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Kulandaivelu Kaviyarasan†, Sambandam Anandan†,‡,*, Ramalinga Viswanathan Mangalaraja#,

Nanomaterials & Solar Energy Conversion Lab, Department of Chemistry, National Institute of

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Abdullah M. Asiri$, Jerry J. Wu‡,**

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Technology, Trichy 620 015, India. Advanced Ceramics and Nanotechnology Laboratory, Department of Materials Engineering,

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Faculty of Engineering, University of Concepcion, Concepcion 407-0409, Chile. The Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah

Department of Environmental Engineering and Science, Feng Chia University, Taichung 407,

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Taiwan

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21413, P.O. Box 80203, Saudi Arabia

To whom correspondence should be addressed: E-mail: [email protected], [email protected],

Tel.: +91 431 2503639, +886-4-24517250 Ext. 5206, Fax: +91 431 2500133, +886-4-24517686

ABSTRACT

Mercaptosuccinic acid capped Cadmium telluride quantum dots have been successfully synthesized via aqueous phase method. The products were well characterized by a number of analytical techniques, including FT-IR, XRD, HRTEM, and a corrected particle size analysis by the statistical treatment of several AFM measurements. Chemiluminescence experiments were performed to explore the resonance energy transfer between chemiluminescence donor (luminolH2O2 system) and acceptor CdTe QDs. The combination of such donor and acceptor dramatically

ACCEPTED MANUSCRIPT reduce the fluorescence while compared to pristine CdTe QDs without any exciting light source, which is due to the occurrence of chemiluminescence resonance energy transfer (CRET)

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processes.

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KEYWORDS: CdTe quantum dots, chemiluminescence, luminol, resonance energy transfer

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1. INTRODUCTION

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Quantum dots (QDs), also called semiconductor nanocrystals, have attracted tremenduous

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attention due to their unique size-dependent optical properties, including wide excitation, narrow and tunable emission, high quantum yield, excellent photostability, high efficient multiple

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exciton generating capacity, and high efficient multi-photon absorption ability. These QDs can

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be smaller than the exciton diameter and possess dimensions ranging from 2 to 10 nm.[1-16] After the pioneering work of Alivisatos [2], the synthesis and application of semiconductor

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quantum dots (QDs) with high photoluminescence and especially water dispersed nanocrystals (NCs) have generated great interest in the fields of industrial and biomedical applications

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because they have shown higher sensitivity and better photostability and chemical stability. Furthermore, advantages of QDs over other fluorescent dyes include their excellent optical

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properties, such as high brightness. [17-19] The most studied and applied QDs were made of elements from the II and VI group (e.g. CdSe, PbSe, CdS, and CdTe) of the periodic table. [20,21] For example, CdTe nanocrystals of different sizes have tunable emission from green to red due to quantum confinement and have been substantially studied as light-emitting devices (LEDs), [22] the fluorescence reporter for sensing events, gene-based fluorescent probes [23], optical biosensor [24], FRET (Forster resonance energy transfer) microscopy [25], and proteolytic activity monitoring [26].

In addition to the above, it was used in bioluminescence resonance energy transfer (BRET) [26,27] and the chemiluminescence resonance energy transfer (CRET) processes [28,29], where quantum dot acts as an acceptor. CRET, which occurs by oxidation of a luminescent substrate

ACCEPTED MANUSCRIPT without an excitation source, could dramatically reduce the background auto fluorescence and fluorescence bleaching. Therefore, it is a promising technique in biochemical application. In this

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regard, many researchers [30-37] studied chemiluminescence (CL) reaction in the presence of

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luminol–H2O2 system as energy donor by using CdTe QDs as acceptor and achieved higher CRET efficiency. Hence the aim of our investigation was to synthesize water-soluble

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mercaptosuccinic acid capped CdTe QDs via a simple aqueous phase method in the presence of

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3-mercaptosuccinic acid (MSA) as a stabilizing and sodium borohydride NaBH4 as reducing reagent to explore chemiluminescent energy transfer reactions without any exciting light source.

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Chemiluminescence experiments were performed between prepared CdTe QDs as acceptor and

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chemiluminescence donor (luminol-H2O2 system) to prove the CRET processes.

2. EXPERIMENTAL DETAILS

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Cadmium chloride [CdCl2.2H2O], sodium tellurite [Na2TeO3], tri-sodium citrate dihydrate [C6H5Na3O7.2H2O], 3-mercaptosuccinic acid (MSA) [C4H6O4S], sodium borohydride [NaBH4], luminol [C8H7N3O2], and Hydrogen peroxide [H2O2] were purchased from SigmaAldrich and were used as received. Unless otherwise specified, all the reagents used were of analytical grade and the solutions were prepared using millipore DDI water (18.2 MΩ). 2.1. Synthesis of mercaptosuccinic acid capped CdTe QDs Mercaptosuccinic acid capped CdTe QDs were synthesized in aqueous phase [38]. In concise, about 4 mL of cadmium chloride CdCl2.2H2O (0.04 M) was withdrawn in a single-neck round bottomed flask containing 50 mL of double distilled water. Subsequently, tri sodium citrate dihydrate (100 mg), Sodium tellurite (1 ml of 0.01 M), then 3-mercaptosuccinic acid (50 mg) and finally sodium borohydride (100 mg) were added successively under vigorous stirring at

ACCEPTED MANUSCRIPT room temperature until the color of the solution changed to green. Then, the flask was attached to a condenser and refluxed at 100oC under open-air conditions for 10 hours. The resulting solution

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was washed with ethanol twice and separated by centrifugation to form red color MSA capped CdTe QDs, which is dispersed in the Tris-HCl buffer (0.01 M, pH 7.0) solution. This solution is

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stored at 40C in the dark for later use. The role of citrate here was to avoid the deposition of

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Cadmium tellurite (CdTeO3).

2.2. Characterization techniques

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The ATR spectra of the prepared MSA capped CdTe QDs were measured at room temperature by a Thermo Nicolet iS5 FT-IR spectrophotometer. The X-ray diffraction (XRD)

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patterns were recorded using Rigaku Ultima III diffractometer (Japan) with Cu-Kα radiation in

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the scan angle 2θ ranged from 10° to 80°. High Resolution Transmission electron microscopic

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(HR-TEM) images were recorded using JEOL JEM-2010 model. Energy dispersive X-ray (EDX) analysis was used to determine the elements present in the mixture. Particle size and size distribution of the MSA capped CdTe QDs were analyzed using particle size analyzer (Nanotrac Wave instrument, USA). Atomic Force Microscope (AFM) analyses (non-contact mode) were performed on a XE-100 scanning probe microscope, Park systems, South Korea. Ultravioletvisible absorption and chemiluminescence emission spectral techniques were recorded on a Specord S 600 diode-array spectrophotometer and Shimadzu RF5301PC spectrophotometer.

3. RESULTS AND DISCUSSION Figure 1A shows the FT-IR spectra of prepared MSA capped CdTe QDs. The observed characteristic broad band around 3300-3500 cm-1 belongs to hydroxyl (υOH) stretching

ACCEPTED MANUSCRIPT vibration, which can be attributed to water molecules in the QDs. While the other noticed peaks around 3000 cm-1, 1600 cm-1, and 1390 cm-1 belong to the -υCH2, -sυCOO−, and -mυCOO−

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stretching vibrations of MSA. The observed peak around 970 cm-1 belongs to δOH stretching.

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Disappearance of –SH group found at 2600 cm-1 infers thiol group of MSA coordinated CdTe QD formation. Thus, FT-IR results illustrate the presence of free carboxylic functional moiety

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and CdTe coordination from thiol moiety of MSA, indicating the formation of MSA capped

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CdTe QDs [39].

To confirm the crystallite structure and phase purity of the prepared MSA capped CdTe

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QDs, X-ray diffraction patterns were recorded for thin films. MSA capped CdTe QDs show intense peaks positioned at 2values of 26.36, 43.16, and 51.64, which match well with the

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(111), (200), and (311) diffraction planes of cubic (zinc blende) structure (JCPDS file no. 651046) (Figure 1B). [40-42] Furthermore, the absence of additional peaks indicates that the

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samples are in cubic phase without any impurity, such as cadmium oxide or tellurium, and in addition it belongs to F-43m space group.

The crystallite size can be calculated according to the modified Scherer equation [43],

𝑙𝑛𝛽 = 𝑙𝑛

𝐾𝜆 1 + ln 𝐷 𝑐𝑜𝑠𝜃

where D is the crystallite size, λ is the X-ray wavelength, θ is the Bragg diffraction angle, and β is the full width at half maximum (FWHM) intensity. By plotting lnβ against ln(1/cos) by considering the FWHM of the peaks (111), (200), and (311) diffraction planes (Figure S1), the crystallite size calculated using the obtained intercept is found to be 3.47 nm. The separation of

ACCEPTED MANUSCRIPT size and strain broadening analysis depending on the different θ positions is done using

𝑘𝜆 ) + 4𝜀 sin 𝜃 𝐷

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𝛽ℎ𝑘𝑙 . 𝑐𝑜𝑠𝜃 = (

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where ε is the strain. By rearranging the above equation,

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𝑘𝜆 𝛽ℎ𝑘𝑙 = ( ) + 4𝜀 tan 𝜃 𝐷𝑐𝑜𝑠 𝜃

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Williamson and Hall method [44], which can be denoted as

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The above equation stands for uniform deformation model (UDM), in which it is assumed that stain is uniform in all crystallographic directions. The crystallite size is calculated by considering

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the full width at half maximum (FWHM) of the peaks (111), (200), and (311) diffraction planes.

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By plotting βcosθ against 4sinθ for the peaks of CdTe QDs (Figure S2), the particle size

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calculated from the y-intercept of the fitted line is 4.12 nm. The particle size distribution of freshly prepared MSA capped CdTe QDs were analyzed and the particle size of about 3.72 nm (Figure 1C) matches well with the observed XRD results.

The size distribution of the MSA capped CdTe QDs crystallites was investigated by High Resolution Transmission Electron Microscopy (HR-TEM) (Figure 2A-B). The images were acquired by observing many different areas of the samples in order to assess its average characteristics. The size of the MSA capped CdTe QDs were acquired and allowed the determination of the quantum size distribution. Figure 2B shows MSA capped CdTe QDs imaged in HR-TEM with their atomic planes resolved in the image. The geometrical forms marked in white color (Figure 2B) define the frontiers of individual crystallites which were unequivocally seen. The Selected Area Electron Diffraction (SAED) pattern was shown in

ACCEPTED MANUSCRIPT Figure 2C and it reveals that the synthesized CdTe QDs possess excellent monodispersity. The rings clearly show that the particles are crystalline and the rings can be assigned to (111), (220),

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and (311) planes of cubic MSA capped CdTe QDs. In addition, the calculated the distance

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between the rings are 0.211 and 0.347 A, matching well with that of (111) and (220) planes. Energy dispersive X-ray (EDX) analysis of MSA capped CdTe QDs are shown in Figure 2D.

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The percentage of Cd and Te values obtained are 93.38% and 6.62%, which clearly indicate that

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they did not deviate from their initial stoichiometry. Based on this, it is interesting to note that the aqueous phase synthesis completely favors the formation of MSA capped CdTe QDs. Further

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AFM is an important technique used to understand about the surface morphology of the QDs. The AFM picture (Figure 2E, F) was provided here to indicate that the CdTe QDs are small

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round structures i.e., the shape of the colloidal quantum dots should be close to spherical morphology. Furthermore, the calculated particle sizes from AFM analysis are in the range 3-4

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nm.

Figure 3A shows the absorption spectra of MSA capped CdTe QDs in aqueous solution. The characteristic absorption peak of MSA capped CdTe QDs is located around 599 nm (Fig 3A). This red shift in the absorption peak of the previously reported MSA capped CdTe QDs [45] can be attributed to the refluxing time of 10 hours in the synthesis procedure [46]. The concentration and the particle size of the CdTe QDs can be calculated from the first absorption maximum (λabs) by using the method cited by Shang et al., [37]. The particle size D is 𝐷 = (9. 8127 × 10−7 )𝜆3𝑎𝑏𝑠 − (1.7147 × 10−3 )𝜆2𝑎𝑏𝑠 + (1.0064)𝜆𝑎𝑏𝑠 − 194.84 The concentration C can be calculated using the particle size D as follows: 𝐶=

𝐴 10043 × (𝐷2.12 ) × 𝑙

ACCEPTED MANUSCRIPT where A is the absorbance and l is the path length. Using the above equations, the particle size and the concentrations are found to be 3.64 nm and 4.299 μM. Inset of Figure 3A shows photo

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image of as-synthesized red color MSA capped CdTe QDs.

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Photoluminescence maximum was observed at 625 nm upon excitation of CdTe QDs at 380 nm (Figure 3B). To better understand the influence of CdTe QD as acceptor,

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chemiluminescence experiments were performed in the presence of luminol-H2O2 system as the

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donor. Luminol (1x10-4 M) in NaOH media shows two absorption peaks, one at 302 nm and the other at 349 nm (Fig. S3). Upon the addition of H2O2 (0.15 M), hyperchromic shift was noticed

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(the absorption maximum gets increased slightly), which implies that some changes may take place between the species after the reaction probably because hydrogen peroxide could directly

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oxidize the luminol molecule (Figure S1). However after the addition of CdTe QDs into luminol and luminol-H2O2 system, the observed absorbance maximum of pristine CdTe QDs (395 nm)

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gets hypsochromic (blue shifted to 358 nm and 354 nm) and as well as hypochromic effect (decrease in absorbance maximum) (Figure 3C). Reason may be that luminol is linked to MSA capped CdTe QDs through free -COOH group on the surface of QDs and the added H2O2 involves in the formation of excited state luminol QDs conjugate through chemiluminescent energy transfer processes [29,32] or emergence of aggregation of CdTe nanocrystals leads to quenching effect [46]. To confirm this chemiluminscence, experiments were performed as follows. Luminol in NaOH media shows weak emission maximum at about 428 nm upon excitation at 290 nm (Fig. S2) whereas upon the addition of H2O2 emission maximum gets enhanced five-fold, which is probably that hydrogen peroxide could directly oxidize the luminol molecule (Figure S4). However addition of MSA capped CdTe QDs to luminol and luminol-H2O2 system, a dramatic

ACCEPTED MANUSCRIPT reduction in the fluorescence intensity is noticed (Figure 3D) while compared to pristine CdTe QDs and such processes occurs without any exciting light source, which may be due to

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chemiluminescence resonance energy transfer (CRET) processes. Reason for such processes may

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be due to the formation of excited state luminol QDs conjugate between luminol and free COOH group of MSA capped CdTe QDs. [26] In general, the mechanism of luminol oxidation

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using metal catalysts generates new luminophor (excited 3-aminophthalate anion), which

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enhances the chemiluminescence. In addition, such reduction in the fluorescence intensity may be either due to added H2O2 which destroies the CdTe nanocrystal lattice structure. [47]

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However in our system, no such things happened and hence dramatic decrease was substantially observed in emission maximum, which may be due to the aggregation of CdTe caused by

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4. CONCLUSION

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chemiluminescence quenching effect. [48]

MSA capped CdTe QDs were synthesized via aqueous phase method and characterized well by FT-IR, XRD, TEM, AFM and particle size analyzer. The interaction between MSA capped CdTe QDs as acceptor and luminol-H2O2 as donor were investigated using chemiluminescence studies. Dramatic reduction in emission maximum was noticed for the combined system (MSA capped CdTe QDs with luminol-H2O2), which may be due to the formation of excited state luminol QDs conjugate between luminol and free -COOH group of MSA capped CdTe QDs.

ACKNOWLEDGMENT

ACCEPTED MANUSCRIPT The authors wish to express their appreciation to the financial support by the Department of Science and Technology, India (GITA/DST/TWN/P-50/2013) and Ministry of Science and

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Technology (MOST), Taiwan (NSC-102-2923-035-001-MY3), under the India–Taiwan

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collaborative research grant.

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[46] Bao H, Wang E, Dong S, One-pot synthesis of CdTe nanocrystals and shape control of luminescent CdTe-cystine nanocomposites. Small 2 (2006) 476-480. [47] B. Ling, J. Bi, Z. Pi, H. Dong, L. Dong, Chemiluminescence behavior of CdTe-hydrogen peroxide enhanced by sodium hypochlorite and sensitized sensing of estrogens, Nanoscale Res Lett. 9 (2014) 201-

[48] L. Zhang, N. He, C. Lu, Aggregation-induced Emission: A simple strategy to improve Chemiluminescence Resonance Energy Transfer, Anal. Chem. 87 (2015) 1351-1357.

ACCEPTED MANUSCRIPT FIGURE CAPTIONS FTIR (A), XRD (B), Particle size analysis (C) spectra of MSA capped CdTe QDs

Figure 2

HRTEM image (A,B), SAED (C), EDX (D), AFM (E,F) images of MSA capped

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Figure 1

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Absorbance (A) and Photoluminescence (B) spectra of MSA capped CdTe QDs.

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Absorbance (C) and Chemiluminescence (D) spectra of MSA capped CdTe QDs

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(a) in the presence of Luminol (b) and Luminol-H2O2 (c). Inset shows

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photographic image MSA capped CdTe QDs.

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Figure 3.

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CdTe QDs

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Figure 1

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200

-

3000

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-1

1000

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Wavenumber (cm )

50

40

20

10

100

C

90 80 70 60 50 40 30

10

20 10

0

0 0

4

8

Size (nm)

12

20

30

40

50

2 Theta (degree)

16

% Passing

30

50

D

3500

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96 4000

100

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-COO

(200)

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Intensity (a.u)

-

-COO

% Channel

Tranmittance (%)

150

-OH

98

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-CH2

-OH

B

(311)

A

(111)

100

60

70

80

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A

C Å

Å

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0.211

0.347

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D

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B

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Figure 2

[111]

[220]

2

1 / n m

D

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E

F

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Figure 3

2.0

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1.0

0.0 400

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Wavelength (nm)

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0.5

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Absorbance (a.u.)

1.5

800

B

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Graphical Abstract

ACCEPTED MANUSCRIPT Highlights

Mercaptosuccinic acid capped Cadmium telluride quantum dots were synthesized via aqueous phase method

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To explore the resonance energy transfer, chemiluminescence experiments were performed between luminol-H2O2 and CdTe QDs

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A dramatic reduction in the fluorescence quantum yield is noticed while compared to pristine CdTe QDs

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