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Gram-Scale Synthesis of Hydrophilic PEI-Coated AgInS2 Quantum Dots and Its Application in Hydrogen Peroxide/Glucose Detection and Cell Imaging Lan Wang,†,‡ Xiaojiao Kang,*,† and Daocheng Pan*,† †

State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin Road, Changchun, Jilin 130022, P. R. China ‡ University of the Chinese Academy of Sciences, Beijing 10049, P. R. China S Supporting Information *

ABSTRACT: Assisted with polyethylenimine, 4.0 L of water-soluble AgInS2 quantum dots (AIS QDs) were successfully synthesized in an electric pressure cooker. As-prepared QDs exhibit yellow emission with a photoluminescence (PL) quantum yield up to 32%. The QDs also show excellent water/buffer stability. The highly luminescent AIS QDs are used to explore their dualfunctional behavior: detection of hydrogen peroxide (H2O2)/glucose and cell imaging. The amino-functionalized AIS QDs show high sensitivity and specificity for H2O2 and glucose with detection limits of 0.42 and 0.90 μM, respectively. A linear correlation was established between PL intensity and concentration of H2O2 in the ranges of 0.5−10 μM and 10−300 μM, while the linear ranges were 1−10 μM and 10−1000 μM for detection of glucose. The AIS QDs reveal negligible cytotoxicity on HeLa cells. Furthermore, the luminescence of AIS QDs gives the function of optical imaging.

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INTRODUCTION Ternary I−III−VI quantum dots (QDs) have experienced rapid development owing to their low toxicity compared with highly toxic cadmium- and lead-based QDs1−5 in recent years. Luminescent I−III−VI QDs (AgInS2 and CuInS2) have been shown to have promising applications in biomedical imaging, optical sensing, light emitting diodes (LEDs), and photovoltaic devices, because they possess unique optoelectronic properties including high photoluminescence quantum yields (PLQYs), composition/size-dependent emission, long photoluminescence (PL) lifetime, and good photostability.6−13 These ternary QDs have been prepared in organic media or in aqueous phase.14−20 The organic solvents are often expensive and hazardous to the environment. Moreover, the hydrophobicity of QDs could hamper their utility in biological applications.16 Hence, the aqueous phase process is relatively straightforward, and many attempts have been made to prepare water-soluble AgInS2 (AIS) and CuInS2 QDs.17−25 The most widely used hydrophilic capping ligands are thiol-based species, such as 3-mercaptopropionic acid (MPA), mercaptoacetic acid (MAA), L-cysteine, and glutathione.21−25 Sulfhydryl compounds such as MAA and MPA are smelly and corrosive to skin and eyes. Thus, the synthesis of MPA-capped QDs must be handled in a fume hood. We should avoid the use of these smelly chemicals during QD preparation to reduce environmental hazards. Thus, there is an urgent need for developing a green and large-scale approach to synthesize water-soluble I−III−VI QDs using lowtoxicity or nontoxic ligands. © 2017 American Chemical Society

Glucose is not only an important energy source for living cells but also a metabolic intermediate in the synthesis of complex molecules.26,27 Moreover, the glucose in blood is an important signaling substance for identifying many diseases such as hypoglycemia and diabetes. The rapid detection and quantification of glucose is necessary for diagnosis and bioengineering.28 In addition, the accurate determination of H2O2 is also of high interest, because it is extensively used in biomedicine, environmental protection, and food industry.29 Various analytic methods have been developed to detect glucose and H2O2.30−34 Fluorophotometry is a widely used method because of its easy operation and high sensitivity.35−40 QDs have become one of the most popular fluorescent sensors.41−49 In this paper, we utilized polyethylenimine (PEI) as ligands to synthesize water-soluble AIS QDs in an electric pressure cooker. As shown in Scheme 1, PEI is a hydrophilic polymer containing primary, secondary, and tertiary amino groups, which has an overall positive charge.27,38,50−55 PEI can be used as the stabilizing agent to balance the reactivity of both Ag+ and In3+ ions and impede phase separation. Highly reactive Na2S was chosen as the sulfur source. The mixed precursor solution was reacted in an electric pressure cooker for 1.0 h, and 4.0 L of luminescent AIS QDs with a PLQY of 32% was obtained in a batch. The AIS QDs dispersion possesses good colloidal Received: January 12, 2017 Published: May 5, 2017 6122

DOI: 10.1021/acs.inorgchem.7b00053 Inorg. Chem. 2017, 56, 6122−6130

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Inorganic Chemistry

Scheme 1. Schematic for the Gram-Scale Preparation Process of AIS QDs and Their Detection of Hydrogen Peroxide/Glucose and Cell-Imaging Applications

For the glucose detection, 0.05 mL of glucose solutions with various concentrations were mixed with 0.05 mL of GOx, and the mixture solutions were incubated at 37 °C for 15 min, and then 3.0 mL of AIS phosphate buffer solution was added into the mixture solution for 20 min. The PL intensity was measured in the wavelength range of 410− 730 nm. In Vitro Cytotoxicity of AgInS2 QDs. The in vitro cytotoxicity of AIS QDs was recorded by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. First, the HeLa cells were cultured in 96-well plates at a density of 5000 per well with 5% CO2 at 37 °C for 12 h. Next, AIS QDs were added to the wells, and the cells were further cultured for 24 h. The concentrations of QDs were 15.625, 31.25, 62.5, 125, 250, and 500 μg/mL, respectively. Afterward, the media containing AIS QDs was removed, and cell samples were treated with MTT for another 4 h. Finally, 150 μL of dimethyl sulfoxide (DMSO) was added into the cell samples before the plate was examined using a microplate reader (Therom Multkiskan MK 3) at the wavelength of 490 nm. To exclude the QDs interference, the cell viability was calculated using the following equation: cell viability (%) = [A]test − [A]background/[A]control × 100, where [A]test is absorbance value of test group, [A]background is absorbance value of pure QDs with the same concentration of MTT, and [A]control is absorbance value of control group. Averages and standard deviations were based on four samples, and all tests were performed in triplicate. In Vitro Cell Microscopy Imaging. Microscopy images of the cells were taken by Olympus BX-51 optical system microscopy. Before imaging, the HeLa cells with a density of 2 × 104 were plated in a 12well plate for 12 h to allow the cells to attach. After that, the cells were washed two times with PBS, and AIS QD solution with a concentration of 50 μg/mL was added to the cell culture medium. After they were incubated for 4 h, the cells were washed again with PBS several times to remove the remaining QDs. Characterizations. UV−vis absorption spectra were recorded by Metash 5200 spectrophotometer. PL spectra were recorded by using Shimadzu RF 5301PC spectrofluorimeter (wavelength of emission filters is 390 nm; the excitation and emission slit width are both 3 nm). All the samples were measured in air. Absolute PLQYs were obtained by Hamamatsu C9920−02 equipped with an integrating sphere. The luminescence decay curve was recorded by a Lecroy Wave Runner 6100 digital oscilloscope (1 GHz) using a tunable laser (pulse width = 4 ns, gate = 50 ns) as the excitation source (Continuum Sunlite OPO).

stability due to large amounts of the positively charged amino groups of PEI. The AIS QDs-based H2O2 sensors were studied by using electron-transfer quenching. In addition, glucose can be converted into gluconic acid and H2O2 under the catalyzation of glucose oxidase (GOx). Thus, the determination and quantification of glucose is also realized based on the change of QD fluorescence. Finally, in vitro imaging of HeLa cells was realized by using AIS QD probes.

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EXPERIMENTAL SECTION

Chemicals. Silver nitrate (AgNO3, A.R.), indium chloride (InCl3, 99.9%), PEI (MW 1800, 99%), PEI (MW 10 000, 99%), hydrogen peroxide solution (A.R., 30 wt % in H2O), glucose, lactose, surcose, and fructose were purchased from Aladdin Inc. PEI (MW 25 000) and glucose oxidase were supplied by Sigma-Aldrich. Sodium sulfide (Na2S·9H2O, 98%) was supplied by Beijing Chemical plant. All chemicals were used as received. Synthesis of Amine-Functionalized Water-Soluble AgInS2 QDs. In our experiments, a typical synthesis of AgInS2 QDs with a Ag/In ratio of 1/16 is as follows: 5.00 g of PEI was added into a 1.0 L beaker containing 0.9 L of deionized water (DI water) under magnetic stirring. Then, 0.10 g of AgNO3 (0.58 mmol) and 2.08 g of InCl3 (9.42 mmol) were added into the above water solution. Afterward, the mixed solution was put into a 5 L electric pressure cooker and was diluted to 3.0 L with DI water. Next, 2.40 g of Na2S·9H2O (10.0 mmol) dissolved in 1.0 L of DI water was injected into the above cooker under vigorous magnetic stirring. Finally, the reaction mixture was sealed and heated to ∼120 °C (∼180 kPa) for 1.0 h. For the purification of AIS QDs, 4.0 mL of acetone and 2.0 mL of ethyl acetate were added to 4.0 mL of QD crude solution, and the QDs were collected by centrifugation. The precipitate was then redissolved in 4.0 mL of DI water for various types of measurements. Fluorescence Measurements. The detection procedure of H2O2 was conducted as follows: 1 mL of AIS solution (∼0.4 mg) was added into 2 mL of phosphate buffer solution (PBS, pH 9). Subsequently, various concentrations of 0.05 mL of H2O2 solution were added, and the mixture solution was incubated for 20 min. The PL emission spectra were recorded, and the PL intensity of the AIS QDs before (F0) and after (F) addition of H2O2 was obtained at the maximum emission wavelength, respectively. 6123

DOI: 10.1021/acs.inorgchem.7b00053 Inorg. Chem. 2017, 56, 6122−6130

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Figure 1. XRD pattern (a), TEM image (b), size distribution histogram (c), and HRTEM image (d) of AIS QDs. The X-ray diffraction (XRD) measurements were performed on a D8 Focus diffractometer (Bruker) with Cu Kα radiation (λ = 0.154 05 nm). High-resolution transmission electron microscopy (HRTEM) was performed using FEI Tecnai G2 S-Twin with a field emission gun operating at 200 kV. The Fourier transform infrared (FTIR) spectra were recorded on a Nicolet 6700 spectrophotometer (USA) in the range of 4000−400 cm−1. Dynamic light scattering (DLS) experiments and surface zeta potential measurements were performed on a Malvern Instruments Zetasizer Nano at 25 °C. The DLS setup was equipped with a He−Ne laser (λ = 663 nm) at a scattering angle of 90°. The Xray photoelectron spectra (XPS) were recorded on an ECSALAB 250. The chemical compositions of the samples were measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES; Thermo Elemental IRIS 1000). Energy-disperse spectroscopy (EDS) spectra were recorded by using a scanning electron microscope (Hitachi S-4800) equipped with a Bruker AXS XFlash detector 4010.

branched PEI can effectively prevent the aggregation of QDs. The histogram of size distribution and HR-TEM image are given in Figure 1c,d. HR-TEM image showed clear lattice fringes, indicating the high crystallinity of these QDs. Because of the amino groups, PEI can be used as the stabilizing agent to prevent the aggregation of AIS QDs. FTIR spectrum was recorded and shown in Figure 2a. The strong peaks located at 3428 and 1635 cm−1 are ascribed to the stretching vibration and N−H bending of amino groups, respectively. Zeta potential measurement of the AIS QDs further confirmed the presence of PEI on the QD surface, since QD solution has a positive potential of +15.6 mV. In addition, the size distribution of QD dispersion in solution was measured by DLS (Figure 2b). The average particle diameter was ∼18.2 nm. The valence state of the AIS QDs was investigated by the XPS. Figure S1 shows a survey XPS spectrum of QDs and highresolution narrow-scan spectra of each element. The strong C and N signals are asigned to the PEI polymer. The N 1s region can be fitted to three peaks at 398.5, 399.3, and 400.4 eV, corresponding to tertiary, secondary, and primary N of PEI, respectively. According to the reported values for primary amines of pristine PEI (399.8 eV), this increased binding energy indicates that AIS QDs are capped by PEI via its primary amine groups.51 The peaks at 373.4 and 367.3 eV are attributed to Ag 3d3/2 and Ag 3d5/2, confirming that the valence state of Ag ions is +1. Moreover, three peaks corresponding to In 3d3/2, In 3d5/2, and S 2p3/2 were located at 452.1, 444.3, and 161.3 eV, respectively, revealing that indium and sulfur ions of the QDs are in their expected valence states (+3 and −2).

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RESULTS AND DISCUSSION Direct aqueous synthesis of AIS QDs was utilized in our paper. PEI, not thiol-based ligand, was used as the sole capping agent. Amino group of PEI has a strong chelating ability with both Ag+ and In3+ ions without the need of second ligand. Figure 1a displays the XRD pattern of AIS QD sample. Three diffraction peaks were observed, which can be indexed as the diffraction from (112), (204), and (312) planes of tetragonal AgInS2 (JCPDS No. 75−0117). According to the standard XRD patterns of Ag2S and In2S3 (JCPDS No. 14−0072 and No. 05− 0731), these impurities are not found in the product (see Figure 1a), revealing that PEI can effectively avoid phase separation. The corresponding TEM image of the AIS QDs was presented in Figure 1b, showing that the nanocrystals were well-dispersed and that their average size was 3.1 nm. The 6124

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32%, so the QDs emit bright yellow fluorescence under UV light excitation, as shown in the inset of Figure 3a. Besides UV−vis and PL characterizations, we also conducted PL lifetime measurement of the QDs. Figure 3b shows the normalized decay curve for the AIS dispersion. The PL decay curve of these AIS QDs can be well-described by a biexponential fit, with a fast lifetime τ1 = 55 ns and a slow lifetime τ2 = 312 ns. The shorter and the longer lifetimes can be assigned to surface trap states and donor−acceptor transition of trap states, respectively. The average PL lifetime value is calculated to be 171.3 ns, which is longer than that of the most organic dyes and carbon dots. Our prepared QDs are thus good candidates for long-term fluorescent imaging. The reaction parameters have significant influence on the optical properties of I−III−VI QDs. Herein we focused on the dependence of PL intensity on the molecular weight (MW) of PEI, concentration of PEI, starting Ag/In ratios, and reaction time (see Figure 4). First, the effect of PEI molecular weight on the PL intensity of AIS QDs was investigated. As shown in Figure 4a,b, we can see that the higher MW of PEI results in the stronger PL intensity of AIS QDs. The branched PEI contains plenty of amino groups, which are capable of coordinating with metal ions. PEI with a longer chain (high MW) shows better chelating ability, because they possess more coordination sites. Figure 4c shows the PL intensities of AIS QDs with different concentration of PEI ranging from 0.25 to 5.00 mg/mL. The PL intensity of sample reached a maximum when the concentration of PEI was 1.25 mg/mL. An appropriate amount of PEI can effectively passivate surface defects, which will result in a significant enhancement of the PL intensity. Figure 4d shows the PL spectra of AIS QDs, while the starting ratios of Ag/In was varied from 1/2 to 1/18. We found that the PL peaks of AIS QDs were limited around 550−560 nm, which are independent of the Ag/In ratio. The actual Ag/In ratios of our as-prepared AIS QDs were determined by EDS and ICP, respectively (see Figure S2 and Table S1). We can observe that the final Ag/In ratios in QD nanocrystals are very close to the target ratios. It has been confirmed that luminescence from AIS QDs has two different radiative decay processes, which can be assigned to the radiative recombination at surface trap states (τ1 = 55 ns) and donor−acceptor transition of trap states (τ2 = 312 ns), respectively. According to the literature reports, the donor−acceptor pair recombination is from Vs to VAg, where VS (S vacancy) acts as a donor state, and VAg (Ag vacancy) serves as an acceptor state, respectively.56−59 It should be mentioned that the band-to-band emission is not observed for our AIS QDs, which is different from those of organic thiols-capped AIS QDs in the literature.56−59 For organic thiols-capped CuInS2 and AgInS2 QDs, the band-to-band emission was widely observed, so their emission colors are strongly related on the Cu/In and Ag/In ratios.56−59 In our case, sulfur-free PEI was used as the capping agents instead of organic thiols, which will lead to much more S vacancies compared with thiols-capped AgInS2 QDs. Therefore, there is no clear correlation between the emission of PEI-capped AIS QDs and Ag/In ratio of AIS QDs owing to the absence of band-to-band emission. However, the PL intensity of AIS QDs is strongly affected by Ag/In ratio, and the optimal Ag/In ratio was found to be 1/16. In addition, the influence of reaction time on the PL intensity was studied. As seen from Figure 4e, PL intensities of samples increased with the reaction time due to the improvement of the crystallinity of AIS QDs. When the reaction time is beyond 2 h, the PL emission slightly decreased. To further improve the

Figure 2. (a) FTIR spectrum of AIS QDs. (b) Particle size distributions of AIS QDs in water, determined by DLS.

The optical behaviors of the obtained AIS QDs were then characterized. Figure 3a shows the UV−vis, PLE, and PL spectra of the sample. The UV−vis absorption edge of AIS QDs was 460 nm. The PLE spectrum consists of a strong broad band ranging from 300 to 550 nm with a maximum at 420 nm. The PL emission was observed around 560 nm with a full width at half-maximum (fwhm) of 70 nm under 420 nm excitation. The QDs aqueous solution exhibited an absolute PLQY of

Figure 3. UV−vis absorption, PLE, and PL spectra (a) and PL decay curve (b) of AIS QDs. 6125

DOI: 10.1021/acs.inorgchem.7b00053 Inorg. Chem. 2017, 56, 6122−6130

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Figure 4. Influence of PEI MW (a, b), concentration of PEI (c), starting Ag/In ratios (d), reaction time (e), and ZnS shell coating (f) on PL intensity of AIS QDs under 420 nm excitation.

QD luminescence, we tried to deposit ZnS shell on the surface of AIS QDs, as shown in Figure 4f. However, the PL intensity of AIS QDs has no obvious increase after depositing ZnS shell. This may be due to a very strong chelating coordination of PEI and Zn2+ ions, which will impede the formation of ZnS shell. Finally, the synthesis of AIS QDs was conducted in a 5 L electric pressure cooker for 1.0 h, and ∼4 L of yellow-emitting AIS QDs (Ag:In = 1/16) were obtained. Approximately 1.6 g of AIS QDs was synthesized in a batch. The calculated cost of AIS QDs is ∼$4/g (Table S2). The photostability of QDs is very important for their practical application. We had repeated the experiment for the synthesis of AIS QDs in triplicate, and their PL intensities and peak positions of AIS QDs are almost the same, as shown in Figure S3. In addition, the PL intensities and peak positions of AIS QDs are kept unchanged after being stored for 14 d in air, as shown in Figure 5a. The high density of primary amino groups of PEI renders the AIS QDs with good colloidal stability. Moreover, we measured PL emission of AIS QDs dispersed in PBS with pH value ranging from 3 to 11 to evaluate the optical stability of AIS QDs (see Figure 5b). The PL intensity of QDs is stable especially in pH range of 6−11. The decline in PL intensities of the samples dispersed in acidic

PBS is relatively obvious. The emission of sample stored in PBS with pH = 9 exhibited a maximum value. The pKa value of PEI is 9.0. The strongest PL emission may be also attributed to strongest bonding strength between PEI and QDs at pH 9.0. The AIS QDs-based H2O2 sensors can be fabricated by using electron-transfer quenching. As shown in Figure S4, the H2O2induced PL quenching would be completed within 20 min. In addition, the optimum PL quenching effect was observed at pH 9. Hence, incubation time of 20 min and pH value of 9 were used in sensing system, respectively. It was found that the amount of H2O2 greatly influences the degree of PL quenching, as shown in Figure 6a. The PL intensity linearly decreased with H2O2 concentration from 0.5 to 10 μM with a calibration function of F0 − F = 13.959 + 6.1331C (R1 = 0.9978) and from 10 to 300 μM with a calibration function of F0 − F = 59.447 + 1.7497C (R2 = 0.9969), where F0 and F are the PL intensity of AIS QDs before and after addition of H2O2, and C presents the concentration of H2O2. The AIS QDs-based H2O2 sensor is highly sensitive, and the limit of detection (LOD) is 420 nM (signal-to-noise (S/N) ratio = 3), which is comparative to other fluorescence methods for H2O2 detection.36,37 The relative standard deviation (RSD) was estimated to be 2.9% based on three successive detections of 100 μM H2O2 in AIS QDs (see 6126

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based on the enzyme-catalyzed oxidation mechanism. The controlled experimental results show that the PL intensity has no change when glucose or GOx exists solely (see the inset of Figure 7a). Statistical analysis of PL intensity versus glucose

Figure 5. (a) PL intensity and peak position of AIS QDs recorded daily for 14 d. (b) PL intensity of AIS QDs dispersed in PBS with different pH values.

Figure 7. (a) PL spectra representing the quenching effect of the glucose−GOx system with different glucose concentrations on the PL intensity of AIS QDs under 420 nm excitation. (inset) PL spectra of AIS QDs (1), AIS QDs with glucose (2), AIS QDs with glucose oxidase (3), and AIS QDs with glucose and glucose oxidase (4). (b) The relationship between relative PL intensity of AIS QDs and the concentration of glucose (1−1000 μM).

concentration showed two linear ranges for glucose detection (Figure 7b). The limit of detection of the AIS QDs sensor for glucose was 9.0 × 10−7 M (S/N = 3). In addition, compared with some other methods in literature, our method has a lower detection limit than those in literature (see Table S3 in Supporting Information).31−37 To assess the selectivity of the AIS probe for glucose, several glucose analogues (lactose, sucrose, and fructose) and metal ions (Na+, K+, Ca2+, Mg2+, and Zn2+) were added into the AIS QDs solution, respectively. We studied their effects on the PL responses of the AIS QDs. As depicted in Figure S6, the addition of glucose significantly changed the value of (F0 − F)/ F0, whereas no obvious change was observed for other glucose analogues and metal ions under the same conditions. These results indicated that AIS QDs can be used as highly selective and sensitive fluorescence probes for glucose. The biocompatibility of AIS QDs was also investigated via MTT assay. Figure 8 shows the viability of cells incubated with QDs over a range of concentrations for 24 h. The averages and standard deviations were obtained based on four samples, and all of the tests were conducted in triplicate. When the concentration of QDs was 15.625−500 μg/mL, the cell viability values were all greater than 88%, and the IC50 value was 57 523.27 μg/mL. These results indicated that these QDs exhibit negligible cytotoxicity and would be suitable for biomedical applications. Furthermore, the utilization of AIS

Figure 6. (a) PL response of AIS QDs after the addition of H2O2 with different concentrations under 420 nm excitation. (b) The plot of relative PL intensity of AIS QDs vs the concentration of H2O2 (0.5− 300 μM).

Figure S5), which indicated that our method has a good reproducibility. At the existence of GOx and O2, glucose is oxidized to gluconic acid and H2O2. The quantification of glucose can be realized via accurate determination of the generated H2O2. Thus, glucose also exhibited quenching ability to the AIS QDs 6127

DOI: 10.1021/acs.inorgchem.7b00053 Inorg. Chem. 2017, 56, 6122−6130

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μM glucose and other carbohydrates, metal ions (1000 μM); the atom ratios (Ag/In) of as-synthesized AIS QDs measured by EDS and ICP; calculated cost of AIS QDs with an initial Ag/In ratio of 1/16; analysis of glucose by different methods (PDF)

AUTHOR INFORMATION

Corresponding Authors

*Phone: +86-431-85262941. E-mail: [email protected]. (D.P.) *E-mail: [email protected]. (X.K.) ORCID

Lan Wang: 0000-0001-9576-9290 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grant Nos. 51402285 and 51672267).

Figure 8. MTT assay for cell toxicity of AIS QDs in HeLa cells treated with different concentrations of these QDs at 37 °C for 24 h under 5% CO2. Error bars were based on triplicate samples.

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QDs for cell imaging applications was explored. Figure 9 shows the fluorescent microscopy images of AIS QDs. The bright

(1) Bruchez, M.; Moronne, M.; Gin, P.; Weiss, S.; Alivisatos, A. P. Semiconductor Nanocrystals as Fluorescent Biological Labels. Science 1998, 281, 2013−2016. (2) Akkerman, Q. A.; Genovese, A.; George, C.; Prato, M.; Moreels, I.; Casu, A.; Marras, S.; Curcio, A.; Scarpellini, A.; Pellegrino, T.; Manna, L.; Lesnyak, V. From Binary Cu2S to Ternary Cu-In-S and Quaternary Cu-In-Zn-S Nanocrystals with Tunable Composition via Partial Cation Exchange. ACS Nano 2015, 9, 521−531. (3) Chen, Y. F.; Vela, J.; Htoon, H.; Casson, J. L.; Werder, D. J.; Bussian, D. A.; Klimov, V. I.; Hollingsworth, J. A. Giant” Multishell CdSe Nanocrystal Quantum Dots with Suppressed Blinking. J. Am. Chem. Soc. 2008, 130, 5026−5027. (4) Kim, S.; Fisher, B.; Eisler, H. J.; Bawendi, M. Type-II Quantum Dots: CdTe/CdSe (Core/Shell) and CdSe/ZnTe (Core/Shell) Heterostructures. J. Am. Chem. Soc. 2003, 125, 11466−11467. (5) Huang, G. G.; Wang, C. L.; Xu, S. H.; Qi, Z. Q.; Lu, C. G.; Cui, Y. P. Ag- and Mn-doped ZnInS/ZnS dual-emission quantum dots with zone tunability in the color coordinate. Nanotechnology 2016, 27, 185602. (6) Liu, L. W.; Hu, R.; Roy, I.; Lin, G. M.; Ye, L.; Reynolds, J. L.; Liu, J. W.; Liu, J.; Schwartz, S. A.; Zhang, X. H.; Yong, K.-T. Synthesis of Luminescent Near-Infrared AgInS2 Nanocrystals as Optical Probes for In Vivo Applications. Theranostics 2013, 3, 109−115. (7) Wang, Y. C.; Hu, R.; Lin, G. M.; Roy, I.; Yong, K.-T. Functionalized Quantum Dots for Biosensing and Bioimaging and Concerns on Toxicity. ACS Appl. Mater. Interfaces 2013, 5, 2786− 2799. (8) Costas-Mora, I.; Romero, V.; Lavilla, I.; Bendicho, C. An Overview of Recent Advances in the Application of Quantum Dots as Luminescent Probes to Inorganic-Trace Analysis. TrAC, Trends Anal. Chem. 2014, 57, 64−72. (9) Liu, Z. P.; Ma, Q.; Wang, X. Y.; Lin, Z. H.; Zhang, H.; Liu, L. L.; Su, X. G. A Novel Fluorescent Nanosensor for Detection of Heparin and Heparinase Based on CuInS2 Quantum Dots. Biosens. Bioelectron. 2014, 54, 617−622. (10) Yoon, H. C.; Oh, J. H.; Ko, M.; Yoo, H.; Do, Y. R. Synthesis and Characterization of Green Zn-Ag-In-S and Red Zn-Cu-In-S Quantum Dots for Ultrahigh Color Quality of Down-Converted White LEDs. ACS Appl. Mater. Interfaces 2015, 7, 7342−7350. (11) Torimoto, T.; Kameyama, T.; Kuwabata, S. Photofunctional Materials Fabricated with Chalcopyrite-Type Semiconductor Nanoparticles Composed of AgInS2 and Its Solid Solutions. J. Phys. Chem. Lett. 2014, 5, 336−347. (12) Bai, Z. L.; Ji, W. Y.; Han, D. B.; Chen, L. L.; Chen, B. K.; Shen, H. B.; Zou, B. S.; Zhong, H. Z. Hydroxyl-Terminated CuInS2 Based

Figure 9. Fluorescent microscopic images of HeLa cells incubated with AIS QDs for 4 h.

fluorescence image confirmed the successful cellular uptake of AIS QDs when they were incubated for 4 h with HeLa cells, and the concentration of AIS QDs is ∼50 μg/mL.

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CONCLUSIONS Highly luminescent AIS QD aqueous solution (4 L) was synthesized in an electric pressure cooker. This method is simple, green, cost-effective, and highly reproducible. The detection and quantification of H2O2 and glucose were realized through the change in the PL intensity of the AIS QDs. The detection limit of H2O2 and glucose was 0.42 and 0.90 μM, respectively. Cytotoxicity studies indicated the AIS QDs possess good biocompatibility and low toxicity to HeLa cells. The AIS QDs can be directly used in labeling HeLa cells.

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REFERENCES

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b00053. XPS analysis of the AIS QDs; EDS spectra of AIS QDs with different Ag/In ratios; PL spectra of three batches of AIS QDs; PL spectra of H2O2-sensing system with different incubation time; PL spectra of three replicate detections of 100 μM H2O2 in the AIS QDs; the relative fluorescence intensities of AIS QDs after addition of 300 6128

DOI: 10.1021/acs.inorgchem.7b00053 Inorg. Chem. 2017, 56, 6122−6130

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DOI: 10.1021/acs.inorgchem.7b00053 Inorg. Chem. 2017, 56, 6122−6130

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DOI: 10.1021/acs.inorgchem.7b00053 Inorg. Chem. 2017, 56, 6122−6130