- Email: [email protected]
silver nanoclusters
Author’s Accepted Manuscript A novel fluorometric and colorimetric sensor for iodide determination using DNA-templated gold/silver nanoclusters Zihao Li, Ruiyi Liu, Guofeng Xing, Tong Wang, Siyu Liu www.elsevier.com/locate/bios
PII: DOI: Reference:
S0956-5663(17)30005-2 http://dx.doi.org/10.1016/j.bios.2017.01.005 BIOS9470
To appear in: Biosensors and Bioelectronic Received date: 3 December 2016 Accepted date: 4 January 2017 Cite this article as: Zihao Li, Ruiyi Liu, Guofeng Xing, Tong Wang and Siyu Liu, A novel fluorometric and colorimetric sensor for iodide determination using DNA-templated gold/silver nanoclusters, Biosensors and Bioelectronic, http://dx.doi.org/10.1016/j.bios.2017.01.005 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. 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.
A
novel
fluorometric
and
colorimetric
sensor
for
iodide
determination using DNA-templated gold/silver nanoclusters Zihao Li1 , Ruiyi Liu, Guofeng Xing, Tong Wang, Siyu Liu1*
College of Life and Health Sciences, Northeastern University, Shenyang 110000, China.
*
Corresponding author. Email address: [email protected] (S.Y. Liu)
ABSTRACT: Recognition and sensing of iodide ions specially have been of considerable interest in the light of the significance and urgency. Herein, we have developed a simple, selective and cost-effective method for quantification of iodide ions based on the DNA-templated gold/silver nanoclusters (DNA-Au/Ag NCs). In the presence of iodide ions concentration, the DNA-Au/Ag NCs solution showed an obvious fluorescence quenching. Simultaneously, it is accompanied by an obvious surface plasmon resonance band change around 540 nm, and naked-eye visible color change from colorless transparent to purple red. Therefore, a new colorimetric and fluorometric strategy for the detection of iodide ions was developed.
Keywords: DNA; gold/silver nanoclusters; Fluorescence quenching; Colorimetry; Iodide ions
1
These authors contributed equally to this work. 1
1. Introduction Iodine, as a kind of essential trace elements for human being, has a key role in several biological activities such as neurological activity and thyroid function (Zimmermann et al., 2015). Deficiency of iodine in body that could result in serious diseases, such as cretinism and endemic goiter, is a widespread public health problem in many developing countries (Hetzel, 2002). Thus most countries have resorted to iodine supplementation and monitoring programs. The most appropriate way to reduce this problem is by means of the universal salt iodization due to its widespread consumption as well as for economic considerations (Lima et al., 2012). Not only that， both iodide deficiency and excessive intake can lead to thyroid diseases. Therefore, it is necessary to develop a simple and convenient method to assay I- ions content. Until now, various kinds of analytical techniques have been applied to determine the iodide content, such as gas chromatography with mass spectrometry detection (Bichsel and Gunten, 1999), capillary electrophoresis (Ito et al., 2003), electrochemical analysis (Pereira et al., 2006), ions chromatography(Rebary et al., 2010) and indirect atomic absorption spectrometry(Bermejo-Barrera et al., 2001). However, these methods have some limitations, such as long examination time, complicated operation and sophisticated instrumentation (Lee et al., 2014). Recently, efforts towards the development of colorimetric and fluorescence assays for ions have been greatly made due to their simple and convenient measurement and low cost (Zhang et al., 2017; Wang et al., 2016; Yang et al., 2016; Bai et al., 2016). Au nanoparticles (Au NPs), consisted of dozens to hundreds of gold
atoms, with strong surface plasmon
resonance(SPR) absorption are particularly sensitive to their size, shape, and interparticle distance (Sankoh et al., 2016; Kang et al., 2016; Kumar et al.,2015). Therefore, many colorimetric sensors were designed utilizing the changes of the SPR absorption of Au NPs for ions detection. And these methods usually require some special ligands to modify Au NPs. For instance, Lee et al have prepared a triazole acetamide modified Au NPs by a reductive single chemical step using a Cu(I)-catalyzed click reaction for the sensitive and selective colorimetric 2
determination of iodide (Lee et al 2014). Thus to develop a simple and convenient technology for iodides detection in aqueous media still remains a worthwhile challenging task up to date. In recent years, fluorescent gold nanoclusters (Au NCs) and silver nanoclusters (Ag NCs)，usually attracted
great
consisted
of
several
to
dozens
of
atoms, have
attention due to their ultra small size，discreted energy levels with
molecular-like properties and unique physical and chemical properties. With the rapid development of noble metal nanoclusters, various kinds of environmentally friendly templates such as peptides, proteins and DNA have been adopted to synthesize fluorescent Au NCs and Ag NCs (Sun et al., 2014; Li et al., 2014; Su et al., 2010). These fluorescent noble metal nanoclusters have been extensively applied in bioimaging, catalysis, and analytes sensing (Yoon et al., 2005; Liu et al., 2011). For example,
Yang’
team
prepared
positively
charged
and
red-emitting
lysozyme-stabilized Ag nanoclusters using NaBH4 as a reducing agent, and applied it in the highly selective detection of Hg2+(Zhou et al., 2012). Mu et al. employed L-proline as the stabilizer to synthesize water-soluble Au NCs as sensing probes for serum iron detection (Mu et al., 2013). The applications of fluorescent metal nanoclusters in analysis are usually based on the fluorescence quenching effect of metal nanoclusters through the interaction between metal atoms and the analytes (Xie et al., 2010). Until now, several research groups have been trying to prepare highly fluorescent bimetallic Au/AgNCs by the introduction of silver (Zhou et al., 2013; Sun et al., 2014; Pal et al., 2014; Dou et al., 2014). Compared to Ag NCs, bimetallic Au/Ag NCs offers more excellent stability under lighting high ionic concentration conditions and tunable optical properties by adjusting the proportion of gold and silver atom (Dou et al., 2013). For example, Zhang and coworkers prepared bimetallic alloying Au/Ag NCs using bovine serum albumin (BSA) as the protein stabilization by a facile one-pot biomineralization route, and employed the bimetallic alloyed Au/AgNCs as probes to detect Hg2+ and Cu2+ ions levels (Zhang et al., 2014). In the present work, the fluorescent alloyed Au/Ag NCs were prepared with 3
DNA sequence 5′-CCCTTAATCCCC-3′ as a template (DNA-Au/Ag NCs), and were further employed as a selective probe for detection of iodide (I- ions). It was demonstrated that the DNA-Au/Ag NCs solution not only exhibited an obvious fluorescence quenching phenomenon with the addition of I- ions, but a naked eye visible color changes. Therefore, a dual signal sensing strategy for iodide-specific detection was developed based on the DNA-Au/Ag NCs probe. 2. Materials and methods 2.1．Apparatus The fluorescence and ultraviolet-visible (UV-Vis) spectra were obtained by using a Biotek SynergyTM H1 microplate reader. Fourier Transform Infrared Spectroscopy (FT-IR) were recorded with a Bruker IFS66V FT-IR spectrometer equipped with a DGTS detector (32 scans). The dynamic light scattering (DLS) analysis was finished on Malvern Nano ZS90. Transmission electron microscopy (TEM) experiments and Energy Dispersive (EDS) analysis were performed on a JEM-ARM200F TEM operating at 200KV acceleration voltage. TEM samples were prepared by dropping the aqueous DNA-Au/Ag NCs or DNA-Au/Ag NCs and I- mixed solution onto carbon-coated copper grids and allowing the excess solvent to evaporate. 2.2．Reagents The chloroauric acid (HAuCl4)，silver nitrate (AgNO3), sodium borohydride (NaBH4), DNA sequence (5′-CCCTTAATCCCC-3′),
potatossium iodide (KI) and
other inorganic salt were obtained from Bejing Dingguo Genetech Co., Ltd. Citrate-citric acid buffer solution (0.1 mol/L pH 3.4) was used to keep the pH environment of the system. All other reagents were of analytical reagent grade and 4
were used without further purification. The deionized water used in all experiments had a resistivity higher than 18 MΩ cm-1. 2.3．Preparation of DNA-templated gold/silver nanoclusters The DNA-Au/Ag NCs were prepared according to some previous reports (Dou et al., 2013). AgNO3 (1 mmol/L, 30 μL) and HAuCl4 (1 mmol/L, 30 μL) solution were added to aliquots of DNA (200 μmol/L, 25 μL) solution containing 40 mmol/L citrate-citric acid buffer solution (pH 5.0) to provide a Ag+-to-Au3+-to-DNA molar ratio of 6:6:1 incubated in an ice bath for 15 minutes, and reduced by the addition of NaBH4 solution (1 mmol/L, 15 μL). This mixture was kept in the dark for 4 hours. The DNA-Au/Ag NCs solution obtained was dialyzed in membrane tubing with a
molecular
weight
cut-off
of
3 KDa
against
ultrapure
water
to
remove small molecules and ions. 2.4．Establishment of the fluorescence sensing system for iodide ions 20 μL of citrate-citric acid buffer solution (pH 3.4, 0.1 mol/L), varying amounts of potassium iodide solution and 20 μL synthesized DNA-Au/Ag NCs solution were successively added into 200 μL calibrated test tube. Then the solution was diluted to 200 µL with deionized water followed by the thoroughly shaking and equilibrated for 20 minutes. The fluorescence emission and UV-Vis absorption spectra were recorded and used for quantitative analysis. The fluorescence spectra were recorded with the excitation wavelength of 260 nm. The slit widths of excitation and emission were both 10 nm. The fluorescence intensity of the maximum emission peak at 660 nm was used for the quantitative analysis of iodide ions concentration. 5
2.5．The Fluorescence recovery induced by Ag+ ions based on the sensing system 20 μL of citrate-citric acid buffer solution (pH 3.4, 0.1 mol/L), varying amounts of silver nitrate solution and a certain amount of potassium iodide solution were successively added into 200 μL calibrated test tube followed by the thoroughly shaking and equilibrated for 15 minutes. Then 20 μL synthesized DNA-Au/Ag NCs solution was added into the test tube, and the mixture solution was diluted to 200 µL with deionized water followed by the thoroughly shaking and equilibrated for 20 minutes. The fluorescence emission and UV-Vis absorption spectra were recorded and used for quantitative analysis. The fluorescence spectra were recorded with the excitation wavelength of 260 nm. The slit widths of excitation and emission were both 10 nm.
3. Results and Discussion 3.1．Synthesis and characterization of the DNA-Au/Ag NCs Herein, we employed one-pot approach to prepare highly fluorescent DNA-Au/Ag NCs in aqueous solution. The synthetic process of DNA-Au/Ag NCs was shown in Scheme 1. DNA-Au/Ag NCs were prepared by first mixing Au3+ and Ag+ with DNA sequence and then utilizing NaBH4 as reducing reagents. Fig.1 offered the fluorescence spectra and photo images of the DNA-Au/Ag NCs. It could be found that the DNA-Au/Ag NCs have two distinct excitation bands respectively at 260 nm and 420 nm, and a strong fluorescence emission peak around 660 nm upon excitation at 260 nm. The appearance of obtained DNA-Au/Ag NCs solution was light yellow transparent liquid under visible light, whereas it emitted bright red fluorescence under 6
ultraviolet light, due to the size and the quantum effect of the metal nanoclusters, and
Scheme 1 The synthetic process of DNA-Au/Ag NCs and the detection of iodide ions.
Fig.1 Fluorescence excitation and emission spectra of DNA-Au/Ag NCs solution. The excitation wavelength was set to 260 nm. Inset: the photo images of DNA-Au/Ag NCs solution under visible light (a) and ultraviolet light (b).
the interaction between the metal core and surface ligands (Dou et al., 2013; Wen et al., 2013). As shown in Scheme 1, the DNA sequence (5′-CCCTTAATCCCC-3′) was employed to prepare fluorescent alloyed DNA-Au/Ag NCs, which effectively 7
passivated the surface of alloyed Au/Ag NCs rendering them water-soluble and stable against aggregation. Herein, FT-IR was measured to further confirm the coordination of the DNA on the surface of Au/Ag NCs. As shown in Fig.S1, the majority of DNA functional groups were found through the stretching vibrations of C=O(1560 cm-1) and –OH (3390cm-1) the -NH2 feature (1660 cm-1), the asymmetric stretching vibrations of the PO2-(1260 cm-1), the out of phase symmetrical stretches (1070 cm-1), and the P–O stretches of the main chain (930 cm-1), which indicated the successful capping of DNA on the surface of the Au/Ag NCs. 3.2．Fluorescence quenching of DNA-Au/Ag NCs by I- ions
Fig.2 The fluorescence emission intensity of DNA-Au/Ag NCs incubated respectively with individual anions for 20 minutes (100 μ mol/L F-, Cl-, Br-, SO42-, S2O82-, CO32-, NO3- , PO43- and P2O74- ions, 25 μ mol/L I- or 50 μ mol/L S2-). F and F0 is respectively the fluorescence intensity of DNA-Au/Ag NCs solution with or without additional anions.
In order to explore the potential application of DNA-Au/Ag NCs in biosensing, we respectively tested their stability under various ionic and pH environments. As shown 8
in Fig.2, we systematically investigated the effect of various kinds of anions including F-, Cl-, Br-, I-, S2-, SO42-, S2O82-, CO32-, NO3- , PO43- and P2O74- ions on the fluorescence of DNA-Au/Ag NCs. And it was found that the fluorescence of DNA-Au/Ag NCs could be only quenched by 20-fold with the incubation of 25 μ mol/L I- ions for 20 minutes, and remain about the same incubated with other kinds of anions. Herein, we further investigated the influence of pH environment on the prepared DNA-Au/Ag NCs. The results indicated the fluorescence intensity of the DNA-Au/Ag NCs solution was almost the same in the range from 3.4 to 7.4 (see Fig.S2).And I- ions showed a better ability of quenching to the fluorescence of DNA-Au/Ag NCs in the acid conditions. Therefore, we intend to systematically investigate the quenching ability of I- ions to DNA-Au/Ag NCs at pH 3.4 conditions. Fig.S3 showed the temporal evolution of fluorescence of DNA-Au/Ag NCs incubated with different concentration of I- ions. And it could be seen that the fluorescence gradually decreased and remained nearly constant after 20 minute. Such fluorescence quenching process indicated the interaction between DNA-Au/Ag NCs and I- ions. The effect of various concentration of I- ions on the fluorescence emission of DNA-Au/Ag NCs was provided in Fig.3.
The fluorescence of DNA-Au/Ag NCs
was obviously quenched with the increase of I- ions concentration in the range from 0 to 25 μmol/L. The fluorescence quenching effect was related to the concentration of Iions. And the Fig.3B demonstrated there was a good linear relationship between the fluorescence intensity ratio F0/F (F0 is the original fluorescence intensity of DNA-Au/Ag NCs solution, and F is the fluorescence intensity of DNA-Au/Ag NCs 9
with the addition of various concentration of I- ions) and I- ions concentration in the
Fig.3 Fluorescence spectra of DNA-Au/Ag NCs solution upon the addition of different concentration of I- ions (respectively 0、0.5、1.25、2.5、3.75、5、7.5、10、11.25、12.5、15、 17.5、20、25 μmol/L). Inset: The linear plots of F0/ F versus the I- ions concentration in the range of 0-10 μmol/L. Measurement in citrate-citric acid buffer solution (pH 3.4, 10 mmol/L)
range from 0 to 10 μmol/L. The linear relationship could be described by a Stern-Volmer regression equation： F0/F=0.9894+0.0985[I-], μmol/L
(1)
The corresponding regression coefficient (R2) is 0.995 with 0.3 μmol/L detection limit for I- calculated by the 3σ IUPAC criteria. Therefore, the prepared DNA-Au/Ag NCs has been successfully demonstrated as a fluorescent probe for I- ions assay.
10
Fig.4 The UV-Vis absorption spectra and photo images (Inset) of DNA-Au/Ag NCs solution respectively incubated with of (a) 0 μmol/L (b) 5 μmol/L (c) 12.5 μmol/L (d) 25μmol/L I- ions.
Not only the fluorescence changes, the addition of I- ions could also induce the significant absorption changes of DNA-Au/Ag NCs solutions (Fig.4). It could be found that there was no prominent absorption feature around 540 nm attributed to larger gold nanoparticles in the absorption spectra of original DNA-Au/Ag NCs solution. And with the increase of I- ions concentration, a new broad surface plasmon band was observed at 540 nm that could be attributed to the growth of larger gold nanoparticles as shown in Fig. 4. The appearance of the new absorption peak around 540 nm further indicated that the fluorescence quenching of DNA-Au/Ag NCs induced by I- ions could be attributed to static quenching. And not only that, there was also a color gradient from colorless transparent to purple red incubated with the increase of I- ions concentration in the assay systems accompanied by the enhancement of the absorption peak around 540 nm. Therefore, the DNA-Au/Ag NCs could be also used as a colorimetric sensor for I- ions besides fluorescence measurement. 11
Correlated with the spectroscopic phenomenon and the visible morphology observation of DNA-Au/Ag NCs were performed. And the TEM images and particle size distribution images of the prepared DNA-Au/Ag NCs were offered in Fig.S4. It could be seen that DNA-Au/Ag NCs alone was near spherical with well-dispersion and had an average diameter of 2.37 nm with no formation of larger gold nanoparticles or aggregates observed by TEM measurements. Fig.S4Inset indicated that the majority of DNA-Au/Ag NCs in the absence of I- ions are with the size range of 1.8-3.0 nm. As shown in Fig.4, a new absorption peak around 540 nm appeared after incubation with I- ions, and it was speculated that the larger gold nanoparticles induced by I- ions were generated. In order to confirm this conclusion, further TEM measurements and the dynamic light scattering (DLS) analysis was performed. Fig.S5 demonstrated some larger-size particles were generated and tend to agglomerate in the solution after the incubation with 12.5 and 25 μmol/L I- ion. Meanwhile the DLS analysis also indicated that the hydrodynamic size of DNA-Au/Ag NCs also displayed the obvious increase after the incubation with I- ions, which was consistent with the TEM observations (Fig.S6). Furthermore, we respectively investigated the effect of various metal ions including K+, Na+, Ca2+, Mg2+, Zn2+, Cd2+, Fe3+, Ni2+, Cu2+, Ag+ , Pb2+ on the fluorescence of DNA-Au/Ag NCs (Fig.S7). It was found that these metal ions even Cu2+, Hg2+ and Ag+ ions had no obvious influence on the fluorescence of DNA-Au/Ag NCs, and only high concentration of Fe3+ ions had some interfere with DNA-Au/Ag NCs. It is generally known that some metal ions sensors are based on 12
the displacement approach, in which sensors bond to anions and then release them again in the presence of metal cations (Choi et al., 2016; Sarkar et al., 2016). Fig.3 and Fig.4 indicated that the addition of I- ions could induce obvious fluorescence quenching and naked-eye color changes of DNA-Au/Ag NCs solution. Therefore, we could utilize the DNA-Au/Ag NCs and I- ions mixture system as a novel platform to detect metal cations. In order to investigate the fluorescence response of the DNA-Au/Ag NCs and I- ions mixture system against to some metal cations, K+, Na+, Ca2+, Mg2+, Zn2+, Cd2+, Fe3+, Ni2+, Cu2+, Ag+, Pb2+ was respectively added into the mixed system. As shown in Fig.S8, only Ag+ ions can induce an obvious fluorescence recovery among of these metal ions, which suggests that the proposed DNA-Au/Ag NCs and I- ions mixture system may offer a potential platform for Ag+ ions detection. The fluorescence recovery phenomenon induced by Ag+ ions was based on the strong and specific interaction between I- with Ag+ due to the low solubility product value (Ksp) of AgI. I- ions preferentially reacted with Ag+ ions to form insoluble silver iodide (AgI) to exit the DNA-Au/Ag NCs detection systems, and the fluorescence quenching induced by I- ions of DNA-Au/Ag NCs could be inhibited (Xu et al., 2015; Li et al., 2014). Herein, we systematically investigated the influence of Ag+ concentration on the fluorescence of DNA-Au/Ag NCs and I- ions mixed system. Fig.5 offered that the
13
Fig.5 The fluorescence emission spectra and fluorescence intensity ratio (Inset) of DNA-Au/Ag NCs solution in the presence of 20 μmol/L I- ions and different concentration of Ag+ ions (0, 2.5, 5, 7.5, 10, 12.5, 15, 17.5, 20, 25 μmol/L ). (10 mmol/L pH 3.4 citrate-citric acid buffer solution)
quenched fluorescence of mixed system could be recovered accordingly with the increase of Ag+ ions concentration in the range from 0 to 25 μmol/L (F is the fluorescence intensity of the DNA-Au/Ag NCs in the presence of 20 μmol/L I- ions and various concentrations of Ag+ ion, and F0 is the fluorescence intensity of the original DNA-Au/Ag NCs). UV-Vis spectra were also used to monitor the reaction process between Ag+ and I- ions. It is seen that, DNA-Au/Ag NCs and I- ions mixed solution in the absence of Ag+ ions exhibits strong absorption peak at 540 nm, that is attributed to the surface plasmon resonance of generated lager gold nanoparticle (Fig.S8). With the increase of Ag+ ion concentration, the characteristic surface plasmon resonance band of gold nanoparticles disappeared gradually in the UV-Vis 14
spectra. Meanwhile, the DNA-Au/Ag NCs and I- ions mixed solution changes from purple red to colorless transparent, which indicated the generation of gold nanoparticles were inhibited with the addition of I- ions. In order to evaluate the feasibility of the proposed method in real water samples detection, the developed DNA-Au/Ag NCs probe was applied to the determination of I- ions in spring water and tap water samples. And the obtained water samples were diluted by 5 times with deionized water. Different amount of I- ions were added to diluted water samples prepare the spiked samples. The results obtained by standard addition method were shown in Table S1, and the accuracy of the proposed method was evaluated by determining the recoveries of I- ions in water samples. It can be seen that the recoveries in the water samples was between 98-104% and the relative standard deviation (RSD) was no more than 2.5%. The above results demonstrated the potential applicability of the method for the detection of I- ions in water samples. 4. Conclusion In summary, we have presented that the DNA-Au/Ag NCs could be used as a simple, convenient and selective probe for detection of I- ions. The determination of Iions was performed based on the fluorescence quenching and naked eye visible color changes of DNA-Au/Ag NCs solution. We further illustrated that the addition of Ag+ ions could effectively reverse the I- ions-induced fluorescence quenching and color changes of DNA-AuAg NCs solution.
Acknowledgements This work was supported by the Fundamental Research Funds for Central 15
Universities of China (N152004002), the Doctoral Scientific Research Foundation of LiaoNing Province (L201501145) and College Students’ Innovation entrepreneurship training program of Northeastern University (161119). Reference Bai, L., Tou, L.J., Gao, Q., Bose, P., Zhao, Y., 2016. Chem. Commun. (Camb). 52, 13691-13694. Choi, S., Lee, G., Park, I., Son, M. K. W., Lee, H., Lee, S.Y., Na. S., Yoon D.S., Bashir, R., Park. J., Lee, S.W., 2016. Anal. Chem. 88, 10867-10875. Dou, X., Yuan, X., Yu, Y., Luo, Z.T., Yao, Q.F., Leong, D. T., Xie, J.P., 2014. Nanoscale. 6, 157-161. Dou, Yao., Yang, X.M., 2013. Anal. Chim. Acta. 784, 53-58. Hetzel, B. S., 2002. Bull. World. Health. Organ. 80, 410-417. Hu, W. Z., Yang, P.J., Hasebe, K., Haddad, P. R., Tanaka, K., 2002, J.Chromatogr. A. 956, 103-107. Ito, K., Ichihara, T., Zhuo, H., Kumamoto, K., Timerbaev, A., R., Hirokawa, T., 2003. Anal. Chim. Acta. 497, 67-74. Kang, J., Zhang, Y., Li, X., Miao, L., Wu, A., 2016. ACS Appl. Mater. Interfaces. 8, 1-5. Kumar, A., Hens, A., Arun, R.K., Chatterjee, M., Mahato, K., Layek, K., Chanda, N., 2015. Analyst. 140, 1817-1821. Lee, I. L., Sung, Y.M., Wu, C.H., Wu, S.P., 2014. Microchim. Acta.181, 573-579. Li, D.D., Chen, X.L., Li, Yang., Cheng, T.Y., Zhu, W.P., Xu, Y.F., Qian, X.H., 2014. 16
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18
Highlights：
Highly fluorescent alloyed DNA-Au/Ag NCs were simple
prepared
via
a
approach.
The decrease in fluorescence intensity of DNA-Au/Ag NCs showed the linear relationship with iodide ions concentration.
Iodide ions could induce a naked eye visible color change of DNA-Au/Ag NCs solution.
19
PII: DOI: Reference:
S0956-5663(17)30005-2 http://dx.doi.org/10.1016/j.bios.2017.01.005 BIOS9470
To appear in: Biosensors and Bioelectronic Received date: 3 December 2016 Accepted date: 4 January 2017 Cite this article as: Zihao Li, Ruiyi Liu, Guofeng Xing, Tong Wang and Siyu Liu, A novel fluorometric and colorimetric sensor for iodide determination using DNA-templated gold/silver nanoclusters, Biosensors and Bioelectronic, http://dx.doi.org/10.1016/j.bios.2017.01.005 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. 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.
A
novel
fluorometric
and
colorimetric
sensor
for
iodide
determination using DNA-templated gold/silver nanoclusters Zihao Li1 , Ruiyi Liu, Guofeng Xing, Tong Wang, Siyu Liu1*
College of Life and Health Sciences, Northeastern University, Shenyang 110000, China.
*
Corresponding author. Email address: [email protected] (S.Y. Liu)
ABSTRACT: Recognition and sensing of iodide ions specially have been of considerable interest in the light of the significance and urgency. Herein, we have developed a simple, selective and cost-effective method for quantification of iodide ions based on the DNA-templated gold/silver nanoclusters (DNA-Au/Ag NCs). In the presence of iodide ions concentration, the DNA-Au/Ag NCs solution showed an obvious fluorescence quenching. Simultaneously, it is accompanied by an obvious surface plasmon resonance band change around 540 nm, and naked-eye visible color change from colorless transparent to purple red. Therefore, a new colorimetric and fluorometric strategy for the detection of iodide ions was developed.
Keywords: DNA; gold/silver nanoclusters; Fluorescence quenching; Colorimetry; Iodide ions
1
These authors contributed equally to this work. 1
1. Introduction Iodine, as a kind of essential trace elements for human being, has a key role in several biological activities such as neurological activity and thyroid function (Zimmermann et al., 2015). Deficiency of iodine in body that could result in serious diseases, such as cretinism and endemic goiter, is a widespread public health problem in many developing countries (Hetzel, 2002). Thus most countries have resorted to iodine supplementation and monitoring programs. The most appropriate way to reduce this problem is by means of the universal salt iodization due to its widespread consumption as well as for economic considerations (Lima et al., 2012). Not only that， both iodide deficiency and excessive intake can lead to thyroid diseases. Therefore, it is necessary to develop a simple and convenient method to assay I- ions content. Until now, various kinds of analytical techniques have been applied to determine the iodide content, such as gas chromatography with mass spectrometry detection (Bichsel and Gunten, 1999), capillary electrophoresis (Ito et al., 2003), electrochemical analysis (Pereira et al., 2006), ions chromatography(Rebary et al., 2010) and indirect atomic absorption spectrometry(Bermejo-Barrera et al., 2001). However, these methods have some limitations, such as long examination time, complicated operation and sophisticated instrumentation (Lee et al., 2014). Recently, efforts towards the development of colorimetric and fluorescence assays for ions have been greatly made due to their simple and convenient measurement and low cost (Zhang et al., 2017; Wang et al., 2016; Yang et al., 2016; Bai et al., 2016). Au nanoparticles (Au NPs), consisted of dozens to hundreds of gold
atoms, with strong surface plasmon
resonance(SPR) absorption are particularly sensitive to their size, shape, and interparticle distance (Sankoh et al., 2016; Kang et al., 2016; Kumar et al.,2015). Therefore, many colorimetric sensors were designed utilizing the changes of the SPR absorption of Au NPs for ions detection. And these methods usually require some special ligands to modify Au NPs. For instance, Lee et al have prepared a triazole acetamide modified Au NPs by a reductive single chemical step using a Cu(I)-catalyzed click reaction for the sensitive and selective colorimetric 2
determination of iodide (Lee et al 2014). Thus to develop a simple and convenient technology for iodides detection in aqueous media still remains a worthwhile challenging task up to date. In recent years, fluorescent gold nanoclusters (Au NCs) and silver nanoclusters (Ag NCs)，usually attracted
great
consisted
of
several
to
dozens
of
atoms, have
attention due to their ultra small size，discreted energy levels with
molecular-like properties and unique physical and chemical properties. With the rapid development of noble metal nanoclusters, various kinds of environmentally friendly templates such as peptides, proteins and DNA have been adopted to synthesize fluorescent Au NCs and Ag NCs (Sun et al., 2014; Li et al., 2014; Su et al., 2010). These fluorescent noble metal nanoclusters have been extensively applied in bioimaging, catalysis, and analytes sensing (Yoon et al., 2005; Liu et al., 2011). For example,
Yang’
team
prepared
positively
charged
and
red-emitting
lysozyme-stabilized Ag nanoclusters using NaBH4 as a reducing agent, and applied it in the highly selective detection of Hg2+(Zhou et al., 2012). Mu et al. employed L-proline as the stabilizer to synthesize water-soluble Au NCs as sensing probes for serum iron detection (Mu et al., 2013). The applications of fluorescent metal nanoclusters in analysis are usually based on the fluorescence quenching effect of metal nanoclusters through the interaction between metal atoms and the analytes (Xie et al., 2010). Until now, several research groups have been trying to prepare highly fluorescent bimetallic Au/AgNCs by the introduction of silver (Zhou et al., 2013; Sun et al., 2014; Pal et al., 2014; Dou et al., 2014). Compared to Ag NCs, bimetallic Au/Ag NCs offers more excellent stability under lighting high ionic concentration conditions and tunable optical properties by adjusting the proportion of gold and silver atom (Dou et al., 2013). For example, Zhang and coworkers prepared bimetallic alloying Au/Ag NCs using bovine serum albumin (BSA) as the protein stabilization by a facile one-pot biomineralization route, and employed the bimetallic alloyed Au/AgNCs as probes to detect Hg2+ and Cu2+ ions levels (Zhang et al., 2014). In the present work, the fluorescent alloyed Au/Ag NCs were prepared with 3
DNA sequence 5′-CCCTTAATCCCC-3′ as a template (DNA-Au/Ag NCs), and were further employed as a selective probe for detection of iodide (I- ions). It was demonstrated that the DNA-Au/Ag NCs solution not only exhibited an obvious fluorescence quenching phenomenon with the addition of I- ions, but a naked eye visible color changes. Therefore, a dual signal sensing strategy for iodide-specific detection was developed based on the DNA-Au/Ag NCs probe. 2. Materials and methods 2.1．Apparatus The fluorescence and ultraviolet-visible (UV-Vis) spectra were obtained by using a Biotek SynergyTM H1 microplate reader. Fourier Transform Infrared Spectroscopy (FT-IR) were recorded with a Bruker IFS66V FT-IR spectrometer equipped with a DGTS detector (32 scans). The dynamic light scattering (DLS) analysis was finished on Malvern Nano ZS90. Transmission electron microscopy (TEM) experiments and Energy Dispersive (EDS) analysis were performed on a JEM-ARM200F TEM operating at 200KV acceleration voltage. TEM samples were prepared by dropping the aqueous DNA-Au/Ag NCs or DNA-Au/Ag NCs and I- mixed solution onto carbon-coated copper grids and allowing the excess solvent to evaporate. 2.2．Reagents The chloroauric acid (HAuCl4)，silver nitrate (AgNO3), sodium borohydride (NaBH4), DNA sequence (5′-CCCTTAATCCCC-3′),
potatossium iodide (KI) and
other inorganic salt were obtained from Bejing Dingguo Genetech Co., Ltd. Citrate-citric acid buffer solution (0.1 mol/L pH 3.4) was used to keep the pH environment of the system. All other reagents were of analytical reagent grade and 4
were used without further purification. The deionized water used in all experiments had a resistivity higher than 18 MΩ cm-1. 2.3．Preparation of DNA-templated gold/silver nanoclusters The DNA-Au/Ag NCs were prepared according to some previous reports (Dou et al., 2013). AgNO3 (1 mmol/L, 30 μL) and HAuCl4 (1 mmol/L, 30 μL) solution were added to aliquots of DNA (200 μmol/L, 25 μL) solution containing 40 mmol/L citrate-citric acid buffer solution (pH 5.0) to provide a Ag+-to-Au3+-to-DNA molar ratio of 6:6:1 incubated in an ice bath for 15 minutes, and reduced by the addition of NaBH4 solution (1 mmol/L, 15 μL). This mixture was kept in the dark for 4 hours. The DNA-Au/Ag NCs solution obtained was dialyzed in membrane tubing with a
molecular
weight
cut-off
of
3 KDa
against
ultrapure
water
to
remove small molecules and ions. 2.4．Establishment of the fluorescence sensing system for iodide ions 20 μL of citrate-citric acid buffer solution (pH 3.4, 0.1 mol/L), varying amounts of potassium iodide solution and 20 μL synthesized DNA-Au/Ag NCs solution were successively added into 200 μL calibrated test tube. Then the solution was diluted to 200 µL with deionized water followed by the thoroughly shaking and equilibrated for 20 minutes. The fluorescence emission and UV-Vis absorption spectra were recorded and used for quantitative analysis. The fluorescence spectra were recorded with the excitation wavelength of 260 nm. The slit widths of excitation and emission were both 10 nm. The fluorescence intensity of the maximum emission peak at 660 nm was used for the quantitative analysis of iodide ions concentration. 5
2.5．The Fluorescence recovery induced by Ag+ ions based on the sensing system 20 μL of citrate-citric acid buffer solution (pH 3.4, 0.1 mol/L), varying amounts of silver nitrate solution and a certain amount of potassium iodide solution were successively added into 200 μL calibrated test tube followed by the thoroughly shaking and equilibrated for 15 minutes. Then 20 μL synthesized DNA-Au/Ag NCs solution was added into the test tube, and the mixture solution was diluted to 200 µL with deionized water followed by the thoroughly shaking and equilibrated for 20 minutes. The fluorescence emission and UV-Vis absorption spectra were recorded and used for quantitative analysis. The fluorescence spectra were recorded with the excitation wavelength of 260 nm. The slit widths of excitation and emission were both 10 nm.
3. Results and Discussion 3.1．Synthesis and characterization of the DNA-Au/Ag NCs Herein, we employed one-pot approach to prepare highly fluorescent DNA-Au/Ag NCs in aqueous solution. The synthetic process of DNA-Au/Ag NCs was shown in Scheme 1. DNA-Au/Ag NCs were prepared by first mixing Au3+ and Ag+ with DNA sequence and then utilizing NaBH4 as reducing reagents. Fig.1 offered the fluorescence spectra and photo images of the DNA-Au/Ag NCs. It could be found that the DNA-Au/Ag NCs have two distinct excitation bands respectively at 260 nm and 420 nm, and a strong fluorescence emission peak around 660 nm upon excitation at 260 nm. The appearance of obtained DNA-Au/Ag NCs solution was light yellow transparent liquid under visible light, whereas it emitted bright red fluorescence under 6
ultraviolet light, due to the size and the quantum effect of the metal nanoclusters, and
Scheme 1 The synthetic process of DNA-Au/Ag NCs and the detection of iodide ions.
Fig.1 Fluorescence excitation and emission spectra of DNA-Au/Ag NCs solution. The excitation wavelength was set to 260 nm. Inset: the photo images of DNA-Au/Ag NCs solution under visible light (a) and ultraviolet light (b).
the interaction between the metal core and surface ligands (Dou et al., 2013; Wen et al., 2013). As shown in Scheme 1, the DNA sequence (5′-CCCTTAATCCCC-3′) was employed to prepare fluorescent alloyed DNA-Au/Ag NCs, which effectively 7
passivated the surface of alloyed Au/Ag NCs rendering them water-soluble and stable against aggregation. Herein, FT-IR was measured to further confirm the coordination of the DNA on the surface of Au/Ag NCs. As shown in Fig.S1, the majority of DNA functional groups were found through the stretching vibrations of C=O(1560 cm-1) and –OH (3390cm-1) the -NH2 feature (1660 cm-1), the asymmetric stretching vibrations of the PO2-(1260 cm-1), the out of phase symmetrical stretches (1070 cm-1), and the P–O stretches of the main chain (930 cm-1), which indicated the successful capping of DNA on the surface of the Au/Ag NCs. 3.2．Fluorescence quenching of DNA-Au/Ag NCs by I- ions
Fig.2 The fluorescence emission intensity of DNA-Au/Ag NCs incubated respectively with individual anions for 20 minutes (100 μ mol/L F-, Cl-, Br-, SO42-, S2O82-, CO32-, NO3- , PO43- and P2O74- ions, 25 μ mol/L I- or 50 μ mol/L S2-). F and F0 is respectively the fluorescence intensity of DNA-Au/Ag NCs solution with or without additional anions.
In order to explore the potential application of DNA-Au/Ag NCs in biosensing, we respectively tested their stability under various ionic and pH environments. As shown 8
in Fig.2, we systematically investigated the effect of various kinds of anions including F-, Cl-, Br-, I-, S2-, SO42-, S2O82-, CO32-, NO3- , PO43- and P2O74- ions on the fluorescence of DNA-Au/Ag NCs. And it was found that the fluorescence of DNA-Au/Ag NCs could be only quenched by 20-fold with the incubation of 25 μ mol/L I- ions for 20 minutes, and remain about the same incubated with other kinds of anions. Herein, we further investigated the influence of pH environment on the prepared DNA-Au/Ag NCs. The results indicated the fluorescence intensity of the DNA-Au/Ag NCs solution was almost the same in the range from 3.4 to 7.4 (see Fig.S2).And I- ions showed a better ability of quenching to the fluorescence of DNA-Au/Ag NCs in the acid conditions. Therefore, we intend to systematically investigate the quenching ability of I- ions to DNA-Au/Ag NCs at pH 3.4 conditions. Fig.S3 showed the temporal evolution of fluorescence of DNA-Au/Ag NCs incubated with different concentration of I- ions. And it could be seen that the fluorescence gradually decreased and remained nearly constant after 20 minute. Such fluorescence quenching process indicated the interaction between DNA-Au/Ag NCs and I- ions. The effect of various concentration of I- ions on the fluorescence emission of DNA-Au/Ag NCs was provided in Fig.3.
The fluorescence of DNA-Au/Ag NCs
was obviously quenched with the increase of I- ions concentration in the range from 0 to 25 μmol/L. The fluorescence quenching effect was related to the concentration of Iions. And the Fig.3B demonstrated there was a good linear relationship between the fluorescence intensity ratio F0/F (F0 is the original fluorescence intensity of DNA-Au/Ag NCs solution, and F is the fluorescence intensity of DNA-Au/Ag NCs 9
with the addition of various concentration of I- ions) and I- ions concentration in the
Fig.3 Fluorescence spectra of DNA-Au/Ag NCs solution upon the addition of different concentration of I- ions (respectively 0、0.5、1.25、2.5、3.75、5、7.5、10、11.25、12.5、15、 17.5、20、25 μmol/L). Inset: The linear plots of F0/ F versus the I- ions concentration in the range of 0-10 μmol/L. Measurement in citrate-citric acid buffer solution (pH 3.4, 10 mmol/L)
range from 0 to 10 μmol/L. The linear relationship could be described by a Stern-Volmer regression equation： F0/F=0.9894+0.0985[I-], μmol/L
(1)
The corresponding regression coefficient (R2) is 0.995 with 0.3 μmol/L detection limit for I- calculated by the 3σ IUPAC criteria. Therefore, the prepared DNA-Au/Ag NCs has been successfully demonstrated as a fluorescent probe for I- ions assay.
10
Fig.4 The UV-Vis absorption spectra and photo images (Inset) of DNA-Au/Ag NCs solution respectively incubated with of (a) 0 μmol/L (b) 5 μmol/L (c) 12.5 μmol/L (d) 25μmol/L I- ions.
Not only the fluorescence changes, the addition of I- ions could also induce the significant absorption changes of DNA-Au/Ag NCs solutions (Fig.4). It could be found that there was no prominent absorption feature around 540 nm attributed to larger gold nanoparticles in the absorption spectra of original DNA-Au/Ag NCs solution. And with the increase of I- ions concentration, a new broad surface plasmon band was observed at 540 nm that could be attributed to the growth of larger gold nanoparticles as shown in Fig. 4. The appearance of the new absorption peak around 540 nm further indicated that the fluorescence quenching of DNA-Au/Ag NCs induced by I- ions could be attributed to static quenching. And not only that, there was also a color gradient from colorless transparent to purple red incubated with the increase of I- ions concentration in the assay systems accompanied by the enhancement of the absorption peak around 540 nm. Therefore, the DNA-Au/Ag NCs could be also used as a colorimetric sensor for I- ions besides fluorescence measurement. 11
Correlated with the spectroscopic phenomenon and the visible morphology observation of DNA-Au/Ag NCs were performed. And the TEM images and particle size distribution images of the prepared DNA-Au/Ag NCs were offered in Fig.S4. It could be seen that DNA-Au/Ag NCs alone was near spherical with well-dispersion and had an average diameter of 2.37 nm with no formation of larger gold nanoparticles or aggregates observed by TEM measurements. Fig.S4Inset indicated that the majority of DNA-Au/Ag NCs in the absence of I- ions are with the size range of 1.8-3.0 nm. As shown in Fig.4, a new absorption peak around 540 nm appeared after incubation with I- ions, and it was speculated that the larger gold nanoparticles induced by I- ions were generated. In order to confirm this conclusion, further TEM measurements and the dynamic light scattering (DLS) analysis was performed. Fig.S5 demonstrated some larger-size particles were generated and tend to agglomerate in the solution after the incubation with 12.5 and 25 μmol/L I- ion. Meanwhile the DLS analysis also indicated that the hydrodynamic size of DNA-Au/Ag NCs also displayed the obvious increase after the incubation with I- ions, which was consistent with the TEM observations (Fig.S6). Furthermore, we respectively investigated the effect of various metal ions including K+, Na+, Ca2+, Mg2+, Zn2+, Cd2+, Fe3+, Ni2+, Cu2+, Ag+ , Pb2+ on the fluorescence of DNA-Au/Ag NCs (Fig.S7). It was found that these metal ions even Cu2+, Hg2+ and Ag+ ions had no obvious influence on the fluorescence of DNA-Au/Ag NCs, and only high concentration of Fe3+ ions had some interfere with DNA-Au/Ag NCs. It is generally known that some metal ions sensors are based on 12
the displacement approach, in which sensors bond to anions and then release them again in the presence of metal cations (Choi et al., 2016; Sarkar et al., 2016). Fig.3 and Fig.4 indicated that the addition of I- ions could induce obvious fluorescence quenching and naked-eye color changes of DNA-Au/Ag NCs solution. Therefore, we could utilize the DNA-Au/Ag NCs and I- ions mixture system as a novel platform to detect metal cations. In order to investigate the fluorescence response of the DNA-Au/Ag NCs and I- ions mixture system against to some metal cations, K+, Na+, Ca2+, Mg2+, Zn2+, Cd2+, Fe3+, Ni2+, Cu2+, Ag+, Pb2+ was respectively added into the mixed system. As shown in Fig.S8, only Ag+ ions can induce an obvious fluorescence recovery among of these metal ions, which suggests that the proposed DNA-Au/Ag NCs and I- ions mixture system may offer a potential platform for Ag+ ions detection. The fluorescence recovery phenomenon induced by Ag+ ions was based on the strong and specific interaction between I- with Ag+ due to the low solubility product value (Ksp) of AgI. I- ions preferentially reacted with Ag+ ions to form insoluble silver iodide (AgI) to exit the DNA-Au/Ag NCs detection systems, and the fluorescence quenching induced by I- ions of DNA-Au/Ag NCs could be inhibited (Xu et al., 2015; Li et al., 2014). Herein, we systematically investigated the influence of Ag+ concentration on the fluorescence of DNA-Au/Ag NCs and I- ions mixed system. Fig.5 offered that the
13
Fig.5 The fluorescence emission spectra and fluorescence intensity ratio (Inset) of DNA-Au/Ag NCs solution in the presence of 20 μmol/L I- ions and different concentration of Ag+ ions (0, 2.5, 5, 7.5, 10, 12.5, 15, 17.5, 20, 25 μmol/L ). (10 mmol/L pH 3.4 citrate-citric acid buffer solution)
quenched fluorescence of mixed system could be recovered accordingly with the increase of Ag+ ions concentration in the range from 0 to 25 μmol/L (F is the fluorescence intensity of the DNA-Au/Ag NCs in the presence of 20 μmol/L I- ions and various concentrations of Ag+ ion, and F0 is the fluorescence intensity of the original DNA-Au/Ag NCs). UV-Vis spectra were also used to monitor the reaction process between Ag+ and I- ions. It is seen that, DNA-Au/Ag NCs and I- ions mixed solution in the absence of Ag+ ions exhibits strong absorption peak at 540 nm, that is attributed to the surface plasmon resonance of generated lager gold nanoparticle (Fig.S8). With the increase of Ag+ ion concentration, the characteristic surface plasmon resonance band of gold nanoparticles disappeared gradually in the UV-Vis 14
spectra. Meanwhile, the DNA-Au/Ag NCs and I- ions mixed solution changes from purple red to colorless transparent, which indicated the generation of gold nanoparticles were inhibited with the addition of I- ions. In order to evaluate the feasibility of the proposed method in real water samples detection, the developed DNA-Au/Ag NCs probe was applied to the determination of I- ions in spring water and tap water samples. And the obtained water samples were diluted by 5 times with deionized water. Different amount of I- ions were added to diluted water samples prepare the spiked samples. The results obtained by standard addition method were shown in Table S1, and the accuracy of the proposed method was evaluated by determining the recoveries of I- ions in water samples. It can be seen that the recoveries in the water samples was between 98-104% and the relative standard deviation (RSD) was no more than 2.5%. The above results demonstrated the potential applicability of the method for the detection of I- ions in water samples. 4. Conclusion In summary, we have presented that the DNA-Au/Ag NCs could be used as a simple, convenient and selective probe for detection of I- ions. The determination of Iions was performed based on the fluorescence quenching and naked eye visible color changes of DNA-Au/Ag NCs solution. We further illustrated that the addition of Ag+ ions could effectively reverse the I- ions-induced fluorescence quenching and color changes of DNA-AuAg NCs solution.
Acknowledgements This work was supported by the Fundamental Research Funds for Central 15
Universities of China (N152004002), the Doctoral Scientific Research Foundation of LiaoNing Province (L201501145) and College Students’ Innovation entrepreneurship training program of Northeastern University (161119). Reference Bai, L., Tou, L.J., Gao, Q., Bose, P., Zhao, Y., 2016. Chem. Commun. (Camb). 52, 13691-13694. Choi, S., Lee, G., Park, I., Son, M. K. W., Lee, H., Lee, S.Y., Na. S., Yoon D.S., Bashir, R., Park. J., Lee, S.W., 2016. Anal. Chem. 88, 10867-10875. Dou, X., Yuan, X., Yu, Y., Luo, Z.T., Yao, Q.F., Leong, D. T., Xie, J.P., 2014. Nanoscale. 6, 157-161. Dou, Yao., Yang, X.M., 2013. Anal. Chim. Acta. 784, 53-58. Hetzel, B. S., 2002. Bull. World. Health. Organ. 80, 410-417. Hu, W. Z., Yang, P.J., Hasebe, K., Haddad, P. R., Tanaka, K., 2002, J.Chromatogr. A. 956, 103-107. Ito, K., Ichihara, T., Zhuo, H., Kumamoto, K., Timerbaev, A., R., Hirokawa, T., 2003. Anal. Chim. Acta. 497, 67-74. Kang, J., Zhang, Y., Li, X., Miao, L., Wu, A., 2016. ACS Appl. Mater. Interfaces. 8, 1-5. Kumar, A., Hens, A., Arun, R.K., Chatterjee, M., Mahato, K., Layek, K., Chanda, N., 2015. Analyst. 140, 1817-1821. Lee, I. L., Sung, Y.M., Wu, C.H., Wu, S.P., 2014. Microchim. Acta.181, 573-579. Li, D.D., Chen, X.L., Li, Yang., Cheng, T.Y., Zhu, W.P., Xu, Y.F., Qian, X.H., 2014. 16
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Highlights：
Highly fluorescent alloyed DNA-Au/Ag NCs were simple
prepared
via
a
approach.
The decrease in fluorescence intensity of DNA-Au/Ag NCs showed the linear relationship with iodide ions concentration.
Iodide ions could induce a naked eye visible color change of DNA-Au/Ag NCs solution.
19