- Email: [email protected]
Fluorescent and colorimetric dual detection of mercury (II) by H2O2 oxidation of o-phenylenediamine using Pt nanoparticles as the catalyst
Sensors and Actuators B 249 (2017) 53–58
Contents lists available at ScienceDirect
Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
Fluorescent and colorimetric dual detection of mercury (II) by H2 O2 oxidation of o-phenylenediamine using Pt nanoparticles as the catalyst Yuan Zhou, Zhanfang Ma ∗ Department of Chemistry, Capital Normal University, Beijing 100048, China
a r t i c l e
i n f o
Article history: Received 17 December 2016 Received in revised form 12 April 2017 Accepted 12 April 2017 Available online 13 April 2017 Keywords: Mercury ions Colorimetric detection Fluorescent detection o-Phenylenediamine Catalytic activity
a b s t r a c t Pt nanoparticles (Pt NPs) can catalyze the oxidative reaction of o-phenylenediamine (OPD) with hydrogen peroxide (H2 O2 ). In this study, o-phenylenediamine was oxidized to 2, 3-phenazinediamin, and the color changed to bright yellow and produced yellow fluorescence. However, the catalytic activity of the Pt NPs was inhibited by the citrate reduction of Hg2+ at the Pt NPs surface. When the concentrations of Pt NPs, H2 O2 , and OPD were constant, the color changed from colorless to bright yellow, which totally depended on the concentration of Hg2+ . Inspired by these principles, we developed a colorimetric and fluorescent dual-readout method for the sensitive determination of Hg2+ , thus effectively improving the accuracy of the detection. The fluorescence and colorimetric linear responses of the proposed method exhibited a wide linear range from 10 nM–2 M with ultralow detection limits of 0.14 nM and 0.8 nM, respectively, values that are much lower than the maximum permitted level of Hg2+ in drinking water by the United States Environmental Protection Agency (EPA). The relative errors of real samples were from −2.54% to 2.36%, indicating the high accuracy of the proposed approach. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Hg, which is mainly released from the combustion of coal and solid wastes and widely remains in air and water, is recognized as the most toxic metal pollutant. Residual Hg2+ is the steadiest form in our daily life, resulting in serious environmental pollution and health problems by contaminating rivers and drinking water [1–4]. Therefore, it is very urgent to monitor the level of Hg2+ . Traditional techniques for Hg2+ detection are inductively coupled plasma mass spectrometry (ICP-MS) [5], inductively coupled plasma atomic emission spectroscopy (ICP-AES) [6], and spectroscopic techniques [7]. However, high sensitivity and selectivity are accompanied by time-consuming and tedious sample preparation. Therefore, a facile, time-saving, and cost-effective method to detect Hg2+ is highly desired. Colorimetric or fluorescent methods are very promising among numerous methods because of their simplicity and sensitivity, respectively [8–15]. Recently, dual-readout detection, which possesses advantages such as high selectivity, high noise-to-signal ratios, and low environmental interference, has attracted a lot of
∗ Corresponding author. E-mail address: [email protected] (Z. Ma). http://dx.doi.org/10.1016/j.snb.2017.04.076 0925-4005/© 2017 Elsevier B.V. All rights reserved.
attention [16–20]. Two types of dual-readout detection by fluorescent and colorimetric methods is the most widely used among all the available methods. One is to use the fluorescence resonance energy transfer between gold nanoparticles (AuNPs) and quantum dots to achieve the dual-readout detection [21,22]. The drawback of this method is that dialysis of the quantum dots takes a long time, and the order of the addition of the reagent is very limited because the quantum dots and target ions are in a competitive relationship with the AuNPs. The other is to synthesize an organic fluorescent molecule whose color and fluorescence change after reacting with the target metal ion. However, the fabrication of these molecules requires a complex process of organic synthesis [23–25]. Accordingly, a facile and universally applicable method for determining Hg2+ levels is necessary. Platinum nanoparticles (Pt NPs) can be used to catalyze the oxidation of o-phenylenediamine (OPD) by hydrogen peroxide (H2 O2 ). 2, 3-phenazinediamine, the oxidized product of OPD, exhibits a bright yellow color and yellow fluorescence [26,27]. When Hg2+ is added to a Pt NP suspension, the catalytic activity of Pt NPs is significantly inhibited because Hg2+ is reduced by citrate on the Pt NPs surface to form a Pt–Hg amalgam. With these insights, we propose a one-step method that simultaneously applies fluorescent and colorimetric dual-readout for Hg2+ detection. With this method, the sensitive detection of Hg2+ can be achieved just by changing the
54
Y. Zhou, Z. Ma / Sensors and Actuators B 249 (2017) 53–58
Scheme 1. Schematic illustration of fluorescence and colorimetric detection of Hg2 .
catalytic activity of the Pt NPs. Moreover, not only is this reaction time-saving and easy, it also exhibits outstanding selectivity and less interference from the environment. 2. Experimental 2.1. Materials and reagents Chloroplatinic acid (H2 PtCl6 ·6H2 O) and sodium borohydride (NaBH4 ) were purchased from Alfa Aesar. Trisodium citrate (Na3 C6 H5 O7 ·2H2 O) and HgCl2 were purchased from Beijing Chemical Reagents Company (Beijing, China). o-Phenylenediamine, BaCl2 ·2H2 O, Pb(NO3 )2 , FeCl3 ·6H2 O, Zn(NO3 )2 ·6H2 O, KCl, MgCl2 ·6H2 O, CdCl2 ·5/2H2 O, Al(NO3 )3 ·9H2 O, FeCl2 ·4H2 O, and CrCl3 ·6H2 O were obtained from Tianjin Guangfu Science and Technology Development Limited company. A nylon syringe filter (0.45 m) was purchased from Membrane Solutions Company. Ultrapure water purified through an Olst Ultrapure K8 apparatus (Ost, Ltd., resistivity >18 M cm) was used throughout the experiments. All the reagents were of analytical grade and used as received without further purification. 2.2. Apparatus and characterization The absorption spectra were measured with a 2550 ultravioletvisible-near infrared (UV-vis-NIR) spectrometer (Shimadzu, Japan). All the fluorescence spectra were measured using an F-7000 fluorescence spectrophotometer (AXimA-CFR, Hitachi, Japan). Highresolution transmission electron microscope (HRTEM) images were acquired on a JEOL-2011 electron microscope. X-ray photoelectron spectroscopy (XPS) was carried on an Escalab 250 X-ray photoelectron spectroscope (Thermo Fisher, American) employing Al (mono) K␣ radiation. 2.3. Synthesis of Pt NPs The Pt NPs were prepared according to a previously described method in which the applied H2 PtCl6 ·6H2 O was reduced by trisodium citrate [28]. Briefly, 1 mL of aqueous H2 PtCl6 ·6H2 O solution (16 mM) and 1 mL of trisodium citrate solution (40 mM) were added to 38 mL of water and stirred at room temperature for 30 min. Then, 200 L of NaBH4 solution (50 mM) was added to the mixture. After 1 h, a brownish Pt NPs suspension was obtained. The Pt NPs suspension was kept at 4 ◦ C before use. 2.4. Detection of Hg2+ in the deionized water In a typical experiment, 100 L of Pt NPs (as prepared) was mixed with 500 L of different concentrations of Hg2+ solutions to obtain final concentrations between 10 nM and 10 M. Then, 200 L of o-phenylenediamine solution (10 mM) and 200 L of H2 O2 solution (10 mM) were added into the mixture. Finally, the color and fluorescent changes were determined using 2550 UV–visNIR spectroscopy and F-7000 Fluorescence spectrophotometer. All experiments were performed three times.
2.5. Detection of Hg2+ in real water samples River water samples were used to evaluate the practical performance of the sensing system. River water was collected from the Linglong River in Beijing. Water samples were centrifuged for 15 min at 12,000 rpm and then filtered through a 0.45 m membrane to remove the large particles. The water samples were then spiked with different concentrations of Hg2+ to prepare them for detection.
3. Results and discussion 3.1. Design and fabrication of Hg2+ colorimetric detection sensing system Scheme 1 illustrates the sensing mechanism of Hg2+ . It is well known that 2,3-phenazinediamine, which provides a bright yellow color and yellow fluorescence, is the main oxidized product of OPD. Initially, the color of the solution changed from colorless to bright yellow and displayed yellow fluorescence when the Pt NPs suspension was added to the H2 O2 and o-phenylenediamine. In this reaction, the as-prepared Pt NPs possessed peroxidase-like activity, which can catalyze the oxidative reaction of OPD with H2 O2 to produce 2,3-phenazinediamine. However, the citrate reduction of Hg2+ on the PtNP surface, thus forming a Pt–Hg amalgam, effectively inhibited the catalytic activity of the Pt NPs. Consequently, the color of the solution changed to pale yellow and produced a weak fluorescence when H2 O2 and o-phenylenediamine were added into the solution. The color changed from bright yellow to pale yellow and the fluorescence intensity changed from strong to weak, behavior that depended on the growth inhibition by the Pt–Hg amalgam; however, the growth inhibition of the Pt–Hg amalgam increased as the concentration of Hg2+ increased. Therefore, the sensitive determination of Hg2+ was achieved.
3.2. Characterization of Pt NPs and Pt-Hg amalgam The Pt NPs were prepared according to a previously reported method [28]. A typical high-resolution TEM image of the Pt NPs is displayed in Fig. 1(A). The Pt NPs are spherical with an average diameter of ca. 2.8 nm. The lattice spacing of the Pt NPs is 0.223 nm, which conformed to the (111) facet [29]. The detailed components of the Pt–Hg amalgam were analyzed and compared to those of the Pt NPs by XPS [Fig. 1(B)]. For the Pt NPs, no peaks of reduced Hg 4f (99.82 eV) were observed. However, a peak of Hg 4f (98.74 eV) for the mercury-treated Pt NPs have appeared. This indicated the reduction of Hg2+ on the surfaces of the Pt NPs. Fig. 1 The peroxide-like activity of the Pt NPs was also investigated [Fig. 2(A) and 2(B)]. After H2 O2 and OPD were added to the Pt NPs suspension, an obvious fluorescence peak at 555 nm and an absorption peak at approximately 420 nm was observed, values that are similar to those of 2,3-phenazinediamine reported in the literature. However, the aqueous solution of H2 O2 and OPD showed negligible fluorescence and a pale yellow color.
Y. Zhou, Z. Ma / Sensors and Actuators B 249 (2017) 53–58
55
Fig. 1. (A) HRTEM image of PtNPs, (B) survey XPS spectra of PtNPs and Pt-Hg amalgam.
Fig. 2. (A) Fluorescence emission and (B) UV-vis spectra of PtNPs, PtNPs + OPD + H2 O2 , and PtNPs + OPD + H2 O2 + Hg2+ .
Fig. 3. The effect of the concentration of H2 O2 and reaction time on this sensing system.
3.3. Fluorescent and colorimetric dual-readout assays for Hg2+ The reaction time and amount of Pt NPs added for the proposed method were optimized because these parameters play an important role in the formation of 2,3-phenazinediamine. As shown in Fig. 3, 100 L of Pt NPs and 20 min of reaction time were optimal. Under the optimized conditions, Hg2+ solutions with several differ-
ent concentrations between 10 nM and 10 M were added into the Pt NPs suspension. The fluorescence intensity of the solution gradually decreased with increasing Hg2+ concentration, suggesting that the peroxide-like activity of the Pt NPs depends on the concentration of Hg2+ . The fluorescence correlation coefficient of linear regression was 0.9976 at Hg2+ concentrations ranging from 10 nM to 2 M. The color gradually changed from bright yellow to pale yellow with increasing Hg2+ concentration. A linear relationship between the absorbance at 420 nm and the concentration of Hg2+ was achieved ranging from 10 nM to 2 M (R2 = 0.9902) (Fig. 4). The fluorescent and optical limits of detection (LOD) of Hg2+ (S/N = 3, where S represents sensitivity and N represents noise) using this method were calculated to be 0.14 nM and 0.8 nM, respectively. These values are much lower than the Hg2+ maximum permitted level (2.0 ppb = 10 nM) in drinking water by the EPA. To determine the selectivity of the sensing system, other heavy metal ions, including Cr3+ , Al3+ , Ba2+ , Cd2+ , Fe2+ , Pb2+ , Fe3+ , Mg2+ , and K+ , were tested using the proposed method under the same conditions. No obvious decrease of fluorescence intensity was observed upon the addition of these metal ions (10 M), whereas the fluorescence intensity decreased significantly after the addition of Hg2+ (Fig. 5). Similarly, the color of the solution changed to bright yellow when these metal ions were added. However, it remained pale yellow after the addition of Hg2+ . Therefore, the results of the fluorescence and colorimetric dual-readout indicate good selectivity of the sensing system for Hg2+ ions. The reason for the selectivity of Hg2+ is attributed to the specificity of the interaction of the Pt–Hg amalgam, which remarkably inhibited the catalytic activity [28].
56
Y. Zhou, Z. Ma / Sensors and Actuators B 249 (2017) 53–58
Fig. 4. (A) Fluorescence emission and (C) UV-vis spectra of H2 O2 + OPD + PtNPs in the presence of different concentrations of Hg2+ . (B) The plot of the fluorescence intensity at 555 nm versus the concentration of Hg2+ . Inset: Linear curve of Hg2+ . (D) The plot of the absorbance at 420 nm versus the concentration of Hg2+ . Inset: Linear curve of Hg2+ .
Fig. 5. (A) The fluorescence intensity at 555 nm and (B) the absorbance intensity at 420 nm of PtNPs + OPD + H2 O2 system in the presence of other metal ions with concentrations of 10 M.
3.4. Detection of Hg2+ in river water samples To evaluate the practicality of the fluorescence and colorimetric method to real water samples, river water samples spiked with Hg2+ were tested. First, the river water samples were filtered with a 0.45 m membrane to remove large suspended particles. As shown in Table 1, it indicated that there was no significant difference between the added value and the measured one, whereas the average standard deviation of the measurement was 2.45%. The low standard deviation confirmed that present method possessed high
Table 1 Result of Hg2+ recovery experiment in river water samples. Sample
Added (nM)
Found (nM)
Recovery (%)
River water River water
50 100
48.73 102.36
97.46 102.36
accuracy for the detection of Hg2+ in river water and it can therefore be applied to real samples. A comparison between the present method and other methods is presented in Table 2. The analytical performance of our method is superior to that of other methods.
Y. Zhou, Z. Ma / Sensors and Actuators B 249 (2017) 53–58
57
Table 2 Comparison between the proposed method and other methods for the detection of Hg2+. Methods
Probe type
LOD (nM)
Liner range
Real samples
Ref.
Colorimetric Colorimetric Colorimetric Fluorescent Fluorescent and colorimetric
AuHg nanoparticles AuNCs Pt nanozyme Carbon nanoparticles & Rhodamine B O-(N-butyl-1,8-naphthalimide)-4-ylO-phenyl carbonothioate AuNPs and OliGreen A peptidyl chemosensor AuNPs PtNPs
2 30 7.2 45 1.9
5 nM–100 nM 0.2–60 M 0–120 nM 0–6 M 0.1–10 M
Lake water River water Tap and purified water
[30] [31] [32] [33] [3]
25 25.6 50 0.14 and 0.8
50–2.5 M 0.2–60 M 50–250 nM 0.01–2 M
Pond water River, tap and sea water
Fluorescent Fluorescent and colorimetric Colorimetric Fluorescent and colorimetric
4. Conclusions In summary, we have demonstrated a fluorescent and colorimetric dual-readout sensing system for simple and fast recognition of Hg2+ . Pt nanoparticles, whose peroxidase-like catalytic ability can be inhibited by Hg2+ , can catalyze the oxidation of OPD to form 2, 3-phenazinediamine by H2 O2 . 2, 3-phenazinediamine, which exhibits a bright yellow color and yellow fluorescence, can provide dual-readout via colorimetry and fluorescence. The current method not only exhibited high sensitivity and selectivity, it also achieved acceptable recoveries in real samples. Owing to the fact that the catalytic properties of noble metal nanoparticles can be changed by simple modification, the sensing system proved to have potential for the detection of other ions. Acknowledgments This research was financed by Grants from the Natural Science Foundation of Beijing Municipality (2132008), the Research Base Construction Projects of Beijing Municipal Education Commission. References [1] P. Bian, L. Xing, Z. Liu, Z. Ma, Functionalized-tryptophan stabilized fluorescent Ag nanoclusters: synthesis and its application as Hg2+ ions sensor, Sens. Actuators B 203 (2014) 252–257. [2] G.K. Darbha, A. Ray, P.C. Ray, Gold Nanoparticle-based miniaturized nanomaterial surface energy transfer probe for rapid and ultrasensitive detection of mercury in soil, water, and fish, ACS Nano 1 (2007) 208–214. [3] W. Shu, Y. Wang, L. Wu, Z. Wang, Q. Duan, Y. Gao, et al., Novel carbonothioate-based colorimetric and fluorescent probe for selective detection of mercury ions, Ind. Eng. Chem. Res. 55 (2016) 8713–8718. [4] L. Zhang, H. Chang, A. Hirata, H. Wu, Q.-K. Xue, M. Chen, Nanoporous gold based optical sensor for sub-ppt detection of mercury ions, ACS Nano 7 (2013) 4595–4600. [5] H. Hintelmann, N. Ogrinc, Determination of Stable Mercury Isotopes by ICP/MS and Their Application in Environmental Studies, Biogeochemistry of Environmentally Important Trace Elements, American Chemical Society, 2002, pp. 321–338. [6] N. Amiri, M.K. Rofouei, J.B. Ghasemi, Multivariate optimization, preconcentration and determination of mercury ions with (1-(p-acetyl phenyl)-3-(o-methyl benzoate)) triazene in aqueous samples using ICP-AES, Anal. Methods 8 (2016) 1111–1119. [7] H. Erxleben, J. Ruzicka, Atomic absorption spectroscopy for mercury, automated by sequential injection and miniaturized in lab-on-valve system, Anal. Chem. 77 (2005) 5124–5128. [8] Z. Liu, X. Jia, P. Bian, Z. Ma, A simple and novel system for colorimetric detection of cobalt ions, Analyst 139 (2014) 585–588. [9] G. Sener, L. Uzun, A. Denizli, Lysine-promoted colorimetric response of gold nanoparticles: a simple assay for ultrasensitive mercury(II) detection, Anal. Chem. 86 (2014) 514–520. [10] Y. Zhou, Z. Ma, A novel fluorescence enhanced route to detect copper(II) by click chemistry-catalyzed connection of Au@SiO2 and carbon dots, Sens. Actuators B 233 (2016) 426–430. [11] B. Yang, J. Wang, D. Bin, M. Zhu, P. Yang, Y. Du, A three dimensional Pt nanodendrite/graphene/MnO2 nanoflower modified electrode for the sensitive and selective detection of dopamine, J. Mater. Chem. B 3 (2015) 7440–7448.
Tap and river water
River water
[34] [35] [36] This work
[12] J. Hu, Z. Wang, J. Li, Gold nanoparticles with special shapes: controlled synthesis, surface-enhanced raman scattering, and the application in biodetection, Sensors 7 (2007). [13] J. Yan, L. Wang, L. Tang, L. Lin, Y. Liu, J. Li, Enzyme-guided plasmonic biosensor based on dual-functional nanohybrid for sensitive detection of thrombin, Biosens. Bioelectron. 70 (2015) 404–410. [14] Y. Zhou, Z. Ma, Colorimetric detection of Hg2+ by Au nanoparticles formed by H2 O2 reduction of HAuCl4 using Au nanoclusters as the catalyst, Sens. Actuators B 241 (2017) 1063–1068. [15] S.R. Patil, A.S. Choudhary, N. Sekar, A Lawsone–DAMN based colorimetric chemosensor for rapid naked-eye detection of mercury(II), New J. Chem. 40 (2016) 6803–6811. [16] S. Lee, B.A. Rao, Y.-A. Son, Colorimetric and turn-on fluorescent determination of Hg2+ ions based on a rhodamine–pyridine derivative, Sens. Actuators B 196 (2014) 388–397. [17] D. Huang, C. Niu, M. Ruan, X. Wang, G. Zeng, C. Deng, Highly sensitive strategy for Hg2+ detection in environmental water samples using long lifetime fluorescence quantum dots and gold nanoparticles, Environ. Sci. Technol. 47 (2013) 4392–4398. [18] Y. Zhang, H. Chen, D. Chen, D. Wu, Z. Chen, J. Zhang, et al., A colorimetric and ratiometric fluorescent probe for mercury (II) in lysosome, Sens. Actuators B 224 (2016) 907–914. [19] J.W. Jeong, B.A. Rao, Y.-A. Son, Rhodamine-chloronicotinaldehyde-based off–on chemosensor for the colorimetric and fluorescent determination of Al3+ ions, Sens. Actuators B 208 (2015) 75–84. [20] H.Y. Lee, K.M.K. Swamy, J.Y. Jung, G. Kim, J. Yoon, Rhodamine hydrazone derivatives based selective fluorescent and colorimetric chemodosimeters for Hg2+ and selective colorimetric chemosensor for Cu2+ , Sens. Actuators B 182 (2013) 530–537. [21] Y. Shi, Y. Pan, H. Zhang, Z. Zhang, M.-J. Li, C. Yi, et al., A dual-mode nanosensor based on carbon quantum dots and gold nanoparticles for discriminative detection of glutathione in human plasma, Biosens. Bioelectron. 56 (2014) 39–45. [22] C.H. Lei, X.E. Zhao, S.L. Jiao, L. He, Y. Li, S.Y. Zhu, et al., A turn-on fluorescent sensor for the detection of melamine based on the anti-quenching ability of Hg2+ to carbon nanodots, Anal. Methods 8 (2016) 4438–4444. [23] Y.-K. Yang, K.-J. Yook, J. Tae, A rhodamine-based fluorescent and colorimetric chemodosimeter for the rapid detection of Hg2+ ions in aqueous media, J. Am. Chem. Soc. 127 (2005) 16760–16761. [24] X. Chen, S.-W. Nam, M.J. Jou, Y. Kim, S.-J. Kim, S. Park, et al., Hg2+ selective fluorescent and colorimetric sensor: its crystal structure and application to bioimaging, Org. Lett. 10 (2008) 5235–5238. [25] V.K. Gupta, S.K. Shoora, L.K. Kumawat, A.K. Jain, A highly selective colorimetric and turn-on fluorescent chemosensor based on 1-(2-pyridylazo)-2-naphthol for the detection of aluminium(III) ions, Sens. Actuators B 209 (2015) 15–24. [26] X. Yang, E. Wang, A nanoparticle autocatalytic sensor for Ag+ and Cu2+ ions in aqueous solution with high sensitivity and selectivity and its application in test paper, Anal. Chem. 83 (2011) 5005–5011. [27] J. Sun, B. Wang, X. Zhao, Z.-J. Li, X. Yang, Fluorescent and colorimetric dual-readout assay for inorganic pyrophosphatase with Cu2+ -triggered oxidation of o-phenylenediamine, Anal. Chem. 88 (2016) 1355–1361. [28] G.-W. Wu, S.-B. He, H.-P. Peng, H.-H. Deng, A.-L. Liu, X.-H. Lin, et al., Citrate-capped platinum nanoparticle as a smart probe for ultrasensitive mercury sensing, Anal. Chem. 86 (2014) 10955–10960. [29] Y. Borodko, P. Ercius, V. Pushkarev, C. Thompson, G. Somorjai, From single Pt atoms to Pt nanocrystals: photoreduction of Pt2+ inside of a PAMAM dendrimer, J. Phys. Chem. Lett. 3 (2012) 236–241. [30] S. Li, J. Lai, L. Qi, M. Saqib, S. Majeed, Y. Tong, et al., Sensitive and selective colorimetric detection of Hg2+ by a Hg2+ induced dual signal amplification strategy based on cascade-type catalytic reactions, Analyst 141 (2016) 2362–2366. [31] Y.-W. Wang, S. Tang, H.-H. Yang, H. Song, A novel colorimetric assay for rapid detection of cysteine and Hg2+ based on gold clusters, Talanta 146 (2016) 71–74. [32] W. Li, B. Chen, H. Zhang, Y. Sun, J. Wang, J. Zhang, et al., BSA-stabilized Pt nanozyme for peroxidase mimetics and its application on colorimetric detection of mercury(II) ions, Biosens. Bioelectron. 66 (2015) 251–258.
58
Y. Zhou, Z. Ma / Sensors and Actuators B 249 (2017) 53–58
[33] M. Lan, J. Zhang, Y.-S. Chui, P. Wang, X. Chen, C.-S. Lee, et al., Carbon nanoparticle-based ratiometric fluorescent sensor for detecting mercury ions in aqueous media and living cells, ACS Appl. Mater. Interfaces 6 (2014) 21270–21278. [34] C.-W. Liu, C.-C. Huang, H.-T. Chang, Control over surface DNA density on gold nanoparticles allows selective and sensitive detection of mercury(II), Langmuir 24 (2008) 8346–8350. [35] J. Park, B. In, K.-H. Lee, Highly selective colorimetric and fluorescent detection for Hg2+ in aqueous solutions using a dipeptide-based chemosensor, RSC Adv. 5 (2015) 56356–56361. [36] J. Du, S. Yin, L. Jiang, B. Ma, X. Chen, A colorimetric logic gate based on free gold nanoparticles and the coordination strategy between melamine and mercury ions, Chem. Commun. 49 (2013) 4196–4198.
Biographies Yuan Zhou received B.S. degree from Beijing Institute of Fashion Technology in 2014. Now she is a graduate student at Capital Normal University. Her research focused on the heavy metal ion detection. Zhanfang Ma received a B.S. degree from Northeast Normal University and a Ph.D. in colloid and interface science in Key Laboratory of Colloid and Interface Chemistry, Institute of Photographic Chemistry, Chinese Academy of Sciences. He is currently a full professor of physical chemistry in Department of Chemistry of Capital Normal University. His current research interests include nanobiosensor, nanofabrication, and electrochemical biosensors.
Contents lists available at ScienceDirect
Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
Fluorescent and colorimetric dual detection of mercury (II) by H2 O2 oxidation of o-phenylenediamine using Pt nanoparticles as the catalyst Yuan Zhou, Zhanfang Ma ∗ Department of Chemistry, Capital Normal University, Beijing 100048, China
a r t i c l e
i n f o
Article history: Received 17 December 2016 Received in revised form 12 April 2017 Accepted 12 April 2017 Available online 13 April 2017 Keywords: Mercury ions Colorimetric detection Fluorescent detection o-Phenylenediamine Catalytic activity
a b s t r a c t Pt nanoparticles (Pt NPs) can catalyze the oxidative reaction of o-phenylenediamine (OPD) with hydrogen peroxide (H2 O2 ). In this study, o-phenylenediamine was oxidized to 2, 3-phenazinediamin, and the color changed to bright yellow and produced yellow fluorescence. However, the catalytic activity of the Pt NPs was inhibited by the citrate reduction of Hg2+ at the Pt NPs surface. When the concentrations of Pt NPs, H2 O2 , and OPD were constant, the color changed from colorless to bright yellow, which totally depended on the concentration of Hg2+ . Inspired by these principles, we developed a colorimetric and fluorescent dual-readout method for the sensitive determination of Hg2+ , thus effectively improving the accuracy of the detection. The fluorescence and colorimetric linear responses of the proposed method exhibited a wide linear range from 10 nM–2 M with ultralow detection limits of 0.14 nM and 0.8 nM, respectively, values that are much lower than the maximum permitted level of Hg2+ in drinking water by the United States Environmental Protection Agency (EPA). The relative errors of real samples were from −2.54% to 2.36%, indicating the high accuracy of the proposed approach. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Hg, which is mainly released from the combustion of coal and solid wastes and widely remains in air and water, is recognized as the most toxic metal pollutant. Residual Hg2+ is the steadiest form in our daily life, resulting in serious environmental pollution and health problems by contaminating rivers and drinking water [1–4]. Therefore, it is very urgent to monitor the level of Hg2+ . Traditional techniques for Hg2+ detection are inductively coupled plasma mass spectrometry (ICP-MS) [5], inductively coupled plasma atomic emission spectroscopy (ICP-AES) [6], and spectroscopic techniques [7]. However, high sensitivity and selectivity are accompanied by time-consuming and tedious sample preparation. Therefore, a facile, time-saving, and cost-effective method to detect Hg2+ is highly desired. Colorimetric or fluorescent methods are very promising among numerous methods because of their simplicity and sensitivity, respectively [8–15]. Recently, dual-readout detection, which possesses advantages such as high selectivity, high noise-to-signal ratios, and low environmental interference, has attracted a lot of
∗ Corresponding author. E-mail address: [email protected] (Z. Ma). http://dx.doi.org/10.1016/j.snb.2017.04.076 0925-4005/© 2017 Elsevier B.V. All rights reserved.
attention [16–20]. Two types of dual-readout detection by fluorescent and colorimetric methods is the most widely used among all the available methods. One is to use the fluorescence resonance energy transfer between gold nanoparticles (AuNPs) and quantum dots to achieve the dual-readout detection [21,22]. The drawback of this method is that dialysis of the quantum dots takes a long time, and the order of the addition of the reagent is very limited because the quantum dots and target ions are in a competitive relationship with the AuNPs. The other is to synthesize an organic fluorescent molecule whose color and fluorescence change after reacting with the target metal ion. However, the fabrication of these molecules requires a complex process of organic synthesis [23–25]. Accordingly, a facile and universally applicable method for determining Hg2+ levels is necessary. Platinum nanoparticles (Pt NPs) can be used to catalyze the oxidation of o-phenylenediamine (OPD) by hydrogen peroxide (H2 O2 ). 2, 3-phenazinediamine, the oxidized product of OPD, exhibits a bright yellow color and yellow fluorescence [26,27]. When Hg2+ is added to a Pt NP suspension, the catalytic activity of Pt NPs is significantly inhibited because Hg2+ is reduced by citrate on the Pt NPs surface to form a Pt–Hg amalgam. With these insights, we propose a one-step method that simultaneously applies fluorescent and colorimetric dual-readout for Hg2+ detection. With this method, the sensitive detection of Hg2+ can be achieved just by changing the
54
Y. Zhou, Z. Ma / Sensors and Actuators B 249 (2017) 53–58
Scheme 1. Schematic illustration of fluorescence and colorimetric detection of Hg2 .
catalytic activity of the Pt NPs. Moreover, not only is this reaction time-saving and easy, it also exhibits outstanding selectivity and less interference from the environment. 2. Experimental 2.1. Materials and reagents Chloroplatinic acid (H2 PtCl6 ·6H2 O) and sodium borohydride (NaBH4 ) were purchased from Alfa Aesar. Trisodium citrate (Na3 C6 H5 O7 ·2H2 O) and HgCl2 were purchased from Beijing Chemical Reagents Company (Beijing, China). o-Phenylenediamine, BaCl2 ·2H2 O, Pb(NO3 )2 , FeCl3 ·6H2 O, Zn(NO3 )2 ·6H2 O, KCl, MgCl2 ·6H2 O, CdCl2 ·5/2H2 O, Al(NO3 )3 ·9H2 O, FeCl2 ·4H2 O, and CrCl3 ·6H2 O were obtained from Tianjin Guangfu Science and Technology Development Limited company. A nylon syringe filter (0.45 m) was purchased from Membrane Solutions Company. Ultrapure water purified through an Olst Ultrapure K8 apparatus (Ost, Ltd., resistivity >18 M cm) was used throughout the experiments. All the reagents were of analytical grade and used as received without further purification. 2.2. Apparatus and characterization The absorption spectra were measured with a 2550 ultravioletvisible-near infrared (UV-vis-NIR) spectrometer (Shimadzu, Japan). All the fluorescence spectra were measured using an F-7000 fluorescence spectrophotometer (AXimA-CFR, Hitachi, Japan). Highresolution transmission electron microscope (HRTEM) images were acquired on a JEOL-2011 electron microscope. X-ray photoelectron spectroscopy (XPS) was carried on an Escalab 250 X-ray photoelectron spectroscope (Thermo Fisher, American) employing Al (mono) K␣ radiation. 2.3. Synthesis of Pt NPs The Pt NPs were prepared according to a previously described method in which the applied H2 PtCl6 ·6H2 O was reduced by trisodium citrate [28]. Briefly, 1 mL of aqueous H2 PtCl6 ·6H2 O solution (16 mM) and 1 mL of trisodium citrate solution (40 mM) were added to 38 mL of water and stirred at room temperature for 30 min. Then, 200 L of NaBH4 solution (50 mM) was added to the mixture. After 1 h, a brownish Pt NPs suspension was obtained. The Pt NPs suspension was kept at 4 ◦ C before use. 2.4. Detection of Hg2+ in the deionized water In a typical experiment, 100 L of Pt NPs (as prepared) was mixed with 500 L of different concentrations of Hg2+ solutions to obtain final concentrations between 10 nM and 10 M. Then, 200 L of o-phenylenediamine solution (10 mM) and 200 L of H2 O2 solution (10 mM) were added into the mixture. Finally, the color and fluorescent changes were determined using 2550 UV–visNIR spectroscopy and F-7000 Fluorescence spectrophotometer. All experiments were performed three times.
2.5. Detection of Hg2+ in real water samples River water samples were used to evaluate the practical performance of the sensing system. River water was collected from the Linglong River in Beijing. Water samples were centrifuged for 15 min at 12,000 rpm and then filtered through a 0.45 m membrane to remove the large particles. The water samples were then spiked with different concentrations of Hg2+ to prepare them for detection.
3. Results and discussion 3.1. Design and fabrication of Hg2+ colorimetric detection sensing system Scheme 1 illustrates the sensing mechanism of Hg2+ . It is well known that 2,3-phenazinediamine, which provides a bright yellow color and yellow fluorescence, is the main oxidized product of OPD. Initially, the color of the solution changed from colorless to bright yellow and displayed yellow fluorescence when the Pt NPs suspension was added to the H2 O2 and o-phenylenediamine. In this reaction, the as-prepared Pt NPs possessed peroxidase-like activity, which can catalyze the oxidative reaction of OPD with H2 O2 to produce 2,3-phenazinediamine. However, the citrate reduction of Hg2+ on the PtNP surface, thus forming a Pt–Hg amalgam, effectively inhibited the catalytic activity of the Pt NPs. Consequently, the color of the solution changed to pale yellow and produced a weak fluorescence when H2 O2 and o-phenylenediamine were added into the solution. The color changed from bright yellow to pale yellow and the fluorescence intensity changed from strong to weak, behavior that depended on the growth inhibition by the Pt–Hg amalgam; however, the growth inhibition of the Pt–Hg amalgam increased as the concentration of Hg2+ increased. Therefore, the sensitive determination of Hg2+ was achieved.
3.2. Characterization of Pt NPs and Pt-Hg amalgam The Pt NPs were prepared according to a previously reported method [28]. A typical high-resolution TEM image of the Pt NPs is displayed in Fig. 1(A). The Pt NPs are spherical with an average diameter of ca. 2.8 nm. The lattice spacing of the Pt NPs is 0.223 nm, which conformed to the (111) facet [29]. The detailed components of the Pt–Hg amalgam were analyzed and compared to those of the Pt NPs by XPS [Fig. 1(B)]. For the Pt NPs, no peaks of reduced Hg 4f (99.82 eV) were observed. However, a peak of Hg 4f (98.74 eV) for the mercury-treated Pt NPs have appeared. This indicated the reduction of Hg2+ on the surfaces of the Pt NPs. Fig. 1 The peroxide-like activity of the Pt NPs was also investigated [Fig. 2(A) and 2(B)]. After H2 O2 and OPD were added to the Pt NPs suspension, an obvious fluorescence peak at 555 nm and an absorption peak at approximately 420 nm was observed, values that are similar to those of 2,3-phenazinediamine reported in the literature. However, the aqueous solution of H2 O2 and OPD showed negligible fluorescence and a pale yellow color.
Y. Zhou, Z. Ma / Sensors and Actuators B 249 (2017) 53–58
55
Fig. 1. (A) HRTEM image of PtNPs, (B) survey XPS spectra of PtNPs and Pt-Hg amalgam.
Fig. 2. (A) Fluorescence emission and (B) UV-vis spectra of PtNPs, PtNPs + OPD + H2 O2 , and PtNPs + OPD + H2 O2 + Hg2+ .
Fig. 3. The effect of the concentration of H2 O2 and reaction time on this sensing system.
3.3. Fluorescent and colorimetric dual-readout assays for Hg2+ The reaction time and amount of Pt NPs added for the proposed method were optimized because these parameters play an important role in the formation of 2,3-phenazinediamine. As shown in Fig. 3, 100 L of Pt NPs and 20 min of reaction time were optimal. Under the optimized conditions, Hg2+ solutions with several differ-
ent concentrations between 10 nM and 10 M were added into the Pt NPs suspension. The fluorescence intensity of the solution gradually decreased with increasing Hg2+ concentration, suggesting that the peroxide-like activity of the Pt NPs depends on the concentration of Hg2+ . The fluorescence correlation coefficient of linear regression was 0.9976 at Hg2+ concentrations ranging from 10 nM to 2 M. The color gradually changed from bright yellow to pale yellow with increasing Hg2+ concentration. A linear relationship between the absorbance at 420 nm and the concentration of Hg2+ was achieved ranging from 10 nM to 2 M (R2 = 0.9902) (Fig. 4). The fluorescent and optical limits of detection (LOD) of Hg2+ (S/N = 3, where S represents sensitivity and N represents noise) using this method were calculated to be 0.14 nM and 0.8 nM, respectively. These values are much lower than the Hg2+ maximum permitted level (2.0 ppb = 10 nM) in drinking water by the EPA. To determine the selectivity of the sensing system, other heavy metal ions, including Cr3+ , Al3+ , Ba2+ , Cd2+ , Fe2+ , Pb2+ , Fe3+ , Mg2+ , and K+ , were tested using the proposed method under the same conditions. No obvious decrease of fluorescence intensity was observed upon the addition of these metal ions (10 M), whereas the fluorescence intensity decreased significantly after the addition of Hg2+ (Fig. 5). Similarly, the color of the solution changed to bright yellow when these metal ions were added. However, it remained pale yellow after the addition of Hg2+ . Therefore, the results of the fluorescence and colorimetric dual-readout indicate good selectivity of the sensing system for Hg2+ ions. The reason for the selectivity of Hg2+ is attributed to the specificity of the interaction of the Pt–Hg amalgam, which remarkably inhibited the catalytic activity [28].
56
Y. Zhou, Z. Ma / Sensors and Actuators B 249 (2017) 53–58
Fig. 4. (A) Fluorescence emission and (C) UV-vis spectra of H2 O2 + OPD + PtNPs in the presence of different concentrations of Hg2+ . (B) The plot of the fluorescence intensity at 555 nm versus the concentration of Hg2+ . Inset: Linear curve of Hg2+ . (D) The plot of the absorbance at 420 nm versus the concentration of Hg2+ . Inset: Linear curve of Hg2+ .
Fig. 5. (A) The fluorescence intensity at 555 nm and (B) the absorbance intensity at 420 nm of PtNPs + OPD + H2 O2 system in the presence of other metal ions with concentrations of 10 M.
3.4. Detection of Hg2+ in river water samples To evaluate the practicality of the fluorescence and colorimetric method to real water samples, river water samples spiked with Hg2+ were tested. First, the river water samples were filtered with a 0.45 m membrane to remove large suspended particles. As shown in Table 1, it indicated that there was no significant difference between the added value and the measured one, whereas the average standard deviation of the measurement was 2.45%. The low standard deviation confirmed that present method possessed high
Table 1 Result of Hg2+ recovery experiment in river water samples. Sample
Added (nM)
Found (nM)
Recovery (%)
River water River water
50 100
48.73 102.36
97.46 102.36
accuracy for the detection of Hg2+ in river water and it can therefore be applied to real samples. A comparison between the present method and other methods is presented in Table 2. The analytical performance of our method is superior to that of other methods.
Y. Zhou, Z. Ma / Sensors and Actuators B 249 (2017) 53–58
57
Table 2 Comparison between the proposed method and other methods for the detection of Hg2+. Methods
Probe type
LOD (nM)
Liner range
Real samples
Ref.
Colorimetric Colorimetric Colorimetric Fluorescent Fluorescent and colorimetric
AuHg nanoparticles AuNCs Pt nanozyme Carbon nanoparticles & Rhodamine B O-(N-butyl-1,8-naphthalimide)-4-ylO-phenyl carbonothioate AuNPs and OliGreen A peptidyl chemosensor AuNPs PtNPs
2 30 7.2 45 1.9
5 nM–100 nM 0.2–60 M 0–120 nM 0–6 M 0.1–10 M
Lake water River water Tap and purified water
[30] [31] [32] [33] [3]
25 25.6 50 0.14 and 0.8
50–2.5 M 0.2–60 M 50–250 nM 0.01–2 M
Pond water River, tap and sea water
Fluorescent Fluorescent and colorimetric Colorimetric Fluorescent and colorimetric
4. Conclusions In summary, we have demonstrated a fluorescent and colorimetric dual-readout sensing system for simple and fast recognition of Hg2+ . Pt nanoparticles, whose peroxidase-like catalytic ability can be inhibited by Hg2+ , can catalyze the oxidation of OPD to form 2, 3-phenazinediamine by H2 O2 . 2, 3-phenazinediamine, which exhibits a bright yellow color and yellow fluorescence, can provide dual-readout via colorimetry and fluorescence. The current method not only exhibited high sensitivity and selectivity, it also achieved acceptable recoveries in real samples. Owing to the fact that the catalytic properties of noble metal nanoparticles can be changed by simple modification, the sensing system proved to have potential for the detection of other ions. Acknowledgments This research was financed by Grants from the Natural Science Foundation of Beijing Municipality (2132008), the Research Base Construction Projects of Beijing Municipal Education Commission. References [1] P. Bian, L. Xing, Z. Liu, Z. Ma, Functionalized-tryptophan stabilized fluorescent Ag nanoclusters: synthesis and its application as Hg2+ ions sensor, Sens. Actuators B 203 (2014) 252–257. [2] G.K. Darbha, A. Ray, P.C. Ray, Gold Nanoparticle-based miniaturized nanomaterial surface energy transfer probe for rapid and ultrasensitive detection of mercury in soil, water, and fish, ACS Nano 1 (2007) 208–214. [3] W. Shu, Y. Wang, L. Wu, Z. Wang, Q. Duan, Y. Gao, et al., Novel carbonothioate-based colorimetric and fluorescent probe for selective detection of mercury ions, Ind. Eng. Chem. Res. 55 (2016) 8713–8718. [4] L. Zhang, H. Chang, A. Hirata, H. Wu, Q.-K. Xue, M. Chen, Nanoporous gold based optical sensor for sub-ppt detection of mercury ions, ACS Nano 7 (2013) 4595–4600. [5] H. Hintelmann, N. Ogrinc, Determination of Stable Mercury Isotopes by ICP/MS and Their Application in Environmental Studies, Biogeochemistry of Environmentally Important Trace Elements, American Chemical Society, 2002, pp. 321–338. [6] N. Amiri, M.K. Rofouei, J.B. Ghasemi, Multivariate optimization, preconcentration and determination of mercury ions with (1-(p-acetyl phenyl)-3-(o-methyl benzoate)) triazene in aqueous samples using ICP-AES, Anal. Methods 8 (2016) 1111–1119. [7] H. Erxleben, J. Ruzicka, Atomic absorption spectroscopy for mercury, automated by sequential injection and miniaturized in lab-on-valve system, Anal. Chem. 77 (2005) 5124–5128. [8] Z. Liu, X. Jia, P. Bian, Z. Ma, A simple and novel system for colorimetric detection of cobalt ions, Analyst 139 (2014) 585–588. [9] G. Sener, L. Uzun, A. Denizli, Lysine-promoted colorimetric response of gold nanoparticles: a simple assay for ultrasensitive mercury(II) detection, Anal. Chem. 86 (2014) 514–520. [10] Y. Zhou, Z. Ma, A novel fluorescence enhanced route to detect copper(II) by click chemistry-catalyzed connection of Au@SiO2 and carbon dots, Sens. Actuators B 233 (2016) 426–430. [11] B. Yang, J. Wang, D. Bin, M. Zhu, P. Yang, Y. Du, A three dimensional Pt nanodendrite/graphene/MnO2 nanoflower modified electrode for the sensitive and selective detection of dopamine, J. Mater. Chem. B 3 (2015) 7440–7448.
Tap and river water
River water
[34] [35] [36] This work
[12] J. Hu, Z. Wang, J. Li, Gold nanoparticles with special shapes: controlled synthesis, surface-enhanced raman scattering, and the application in biodetection, Sensors 7 (2007). [13] J. Yan, L. Wang, L. Tang, L. Lin, Y. Liu, J. Li, Enzyme-guided plasmonic biosensor based on dual-functional nanohybrid for sensitive detection of thrombin, Biosens. Bioelectron. 70 (2015) 404–410. [14] Y. Zhou, Z. Ma, Colorimetric detection of Hg2+ by Au nanoparticles formed by H2 O2 reduction of HAuCl4 using Au nanoclusters as the catalyst, Sens. Actuators B 241 (2017) 1063–1068. [15] S.R. Patil, A.S. Choudhary, N. Sekar, A Lawsone–DAMN based colorimetric chemosensor for rapid naked-eye detection of mercury(II), New J. Chem. 40 (2016) 6803–6811. [16] S. Lee, B.A. Rao, Y.-A. Son, Colorimetric and turn-on fluorescent determination of Hg2+ ions based on a rhodamine–pyridine derivative, Sens. Actuators B 196 (2014) 388–397. [17] D. Huang, C. Niu, M. Ruan, X. Wang, G. Zeng, C. Deng, Highly sensitive strategy for Hg2+ detection in environmental water samples using long lifetime fluorescence quantum dots and gold nanoparticles, Environ. Sci. Technol. 47 (2013) 4392–4398. [18] Y. Zhang, H. Chen, D. Chen, D. Wu, Z. Chen, J. Zhang, et al., A colorimetric and ratiometric fluorescent probe for mercury (II) in lysosome, Sens. Actuators B 224 (2016) 907–914. [19] J.W. Jeong, B.A. Rao, Y.-A. Son, Rhodamine-chloronicotinaldehyde-based off–on chemosensor for the colorimetric and fluorescent determination of Al3+ ions, Sens. Actuators B 208 (2015) 75–84. [20] H.Y. Lee, K.M.K. Swamy, J.Y. Jung, G. Kim, J. Yoon, Rhodamine hydrazone derivatives based selective fluorescent and colorimetric chemodosimeters for Hg2+ and selective colorimetric chemosensor for Cu2+ , Sens. Actuators B 182 (2013) 530–537. [21] Y. Shi, Y. Pan, H. Zhang, Z. Zhang, M.-J. Li, C. Yi, et al., A dual-mode nanosensor based on carbon quantum dots and gold nanoparticles for discriminative detection of glutathione in human plasma, Biosens. Bioelectron. 56 (2014) 39–45. [22] C.H. Lei, X.E. Zhao, S.L. Jiao, L. He, Y. Li, S.Y. Zhu, et al., A turn-on fluorescent sensor for the detection of melamine based on the anti-quenching ability of Hg2+ to carbon nanodots, Anal. Methods 8 (2016) 4438–4444. [23] Y.-K. Yang, K.-J. Yook, J. Tae, A rhodamine-based fluorescent and colorimetric chemodosimeter for the rapid detection of Hg2+ ions in aqueous media, J. Am. Chem. Soc. 127 (2005) 16760–16761. [24] X. Chen, S.-W. Nam, M.J. Jou, Y. Kim, S.-J. Kim, S. Park, et al., Hg2+ selective fluorescent and colorimetric sensor: its crystal structure and application to bioimaging, Org. Lett. 10 (2008) 5235–5238. [25] V.K. Gupta, S.K. Shoora, L.K. Kumawat, A.K. Jain, A highly selective colorimetric and turn-on fluorescent chemosensor based on 1-(2-pyridylazo)-2-naphthol for the detection of aluminium(III) ions, Sens. Actuators B 209 (2015) 15–24. [26] X. Yang, E. Wang, A nanoparticle autocatalytic sensor for Ag+ and Cu2+ ions in aqueous solution with high sensitivity and selectivity and its application in test paper, Anal. Chem. 83 (2011) 5005–5011. [27] J. Sun, B. Wang, X. Zhao, Z.-J. Li, X. Yang, Fluorescent and colorimetric dual-readout assay for inorganic pyrophosphatase with Cu2+ -triggered oxidation of o-phenylenediamine, Anal. Chem. 88 (2016) 1355–1361. [28] G.-W. Wu, S.-B. He, H.-P. Peng, H.-H. Deng, A.-L. Liu, X.-H. Lin, et al., Citrate-capped platinum nanoparticle as a smart probe for ultrasensitive mercury sensing, Anal. Chem. 86 (2014) 10955–10960. [29] Y. Borodko, P. Ercius, V. Pushkarev, C. Thompson, G. Somorjai, From single Pt atoms to Pt nanocrystals: photoreduction of Pt2+ inside of a PAMAM dendrimer, J. Phys. Chem. Lett. 3 (2012) 236–241. [30] S. Li, J. Lai, L. Qi, M. Saqib, S. Majeed, Y. Tong, et al., Sensitive and selective colorimetric detection of Hg2+ by a Hg2+ induced dual signal amplification strategy based on cascade-type catalytic reactions, Analyst 141 (2016) 2362–2366. [31] Y.-W. Wang, S. Tang, H.-H. Yang, H. Song, A novel colorimetric assay for rapid detection of cysteine and Hg2+ based on gold clusters, Talanta 146 (2016) 71–74. [32] W. Li, B. Chen, H. Zhang, Y. Sun, J. Wang, J. Zhang, et al., BSA-stabilized Pt nanozyme for peroxidase mimetics and its application on colorimetric detection of mercury(II) ions, Biosens. Bioelectron. 66 (2015) 251–258.
58
Y. Zhou, Z. Ma / Sensors and Actuators B 249 (2017) 53–58
[33] M. Lan, J. Zhang, Y.-S. Chui, P. Wang, X. Chen, C.-S. Lee, et al., Carbon nanoparticle-based ratiometric fluorescent sensor for detecting mercury ions in aqueous media and living cells, ACS Appl. Mater. Interfaces 6 (2014) 21270–21278. [34] C.-W. Liu, C.-C. Huang, H.-T. Chang, Control over surface DNA density on gold nanoparticles allows selective and sensitive detection of mercury(II), Langmuir 24 (2008) 8346–8350. [35] J. Park, B. In, K.-H. Lee, Highly selective colorimetric and fluorescent detection for Hg2+ in aqueous solutions using a dipeptide-based chemosensor, RSC Adv. 5 (2015) 56356–56361. [36] J. Du, S. Yin, L. Jiang, B. Ma, X. Chen, A colorimetric logic gate based on free gold nanoparticles and the coordination strategy between melamine and mercury ions, Chem. Commun. 49 (2013) 4196–4198.
Biographies Yuan Zhou received B.S. degree from Beijing Institute of Fashion Technology in 2014. Now she is a graduate student at Capital Normal University. Her research focused on the heavy metal ion detection. Zhanfang Ma received a B.S. degree from Northeast Normal University and a Ph.D. in colloid and interface science in Key Laboratory of Colloid and Interface Chemistry, Institute of Photographic Chemistry, Chinese Academy of Sciences. He is currently a full professor of physical chemistry in Department of Chemistry of Capital Normal University. His current research interests include nanobiosensor, nanofabrication, and electrochemical biosensors.