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Electrochemical Sensing of Neurotoxic Agents Based on Their Electron Transfer Promotion Effect on an Au Electrode Hiroshi Shimada, Shiori Noguchi, Masahiro Yamamoto, Katsuhiko Nishiyama, Yusuke Kitamura, and Toshihiro Ihara Anal. Chem., Just Accepted Manuscript • Publication Date (Web): 09 May 2017 Downloaded from http://pubs.acs.org on May 11, 2017

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Analytical Chemistry

Electrochemical Sensing of Neurotoxic Agents Based on Their Electron Transfer Promotion Effect on an Au Electrode Hiroshi Shimada,†,§ Shiori Noguchi,† Masahiro Yamamoto,‡ Katsuhiko Nishiyama,† Yusuke Kitamura,† Toshihiro Ihara*† † Division of Materials Science, Faculty of Advanced Science and Technology, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto 860-8555, Japan ‡ Department of Chemistry, Konan University, 8-9-1 Okamoto, Higashi-Nada, Kobe, Hyogo 658-8501, Japan § Forensic Science Laboratory, Nagasaki Prefectural Police H.Q., 4-8 Manzai-machi, Nagasaki 850-8548, Japan * Tel. & Fax: +81 96 342 3873, E-mail: [email protected]

ABSTRACT: An electrochemical molecular sensor based on a new principle is reported. Nereistoxin (NRT, 4-N,Ndimethylamino-1,2-dithiolane), a naturally occurring neurotoxin (nicotinic acetylcholine receptor agonist), was adsorbed on an Au electrode via Au-S covalent bonding and accelerated the electron transfer between the electrode and the marker, ferricyanide anion. The contrast between the electrochemical responses obtained with the bare and NRT-modified Au electrodes was more pronounced at a low ionic strength of the supporting electrolyte, KCl. In the presence of 1 mM KCl, almost a 0/1 contrast between the signals was obtained through electrostatic interaction between the protonated tertiary amino group of NRT and the anionic ferricyanide ion. No current was observed with an electrode modified with mercaptopropionic acid. An unusually low ionic strength thickened the electric double layer to the degree where current was not observed with the bare electrode. The effect of the electrostatic concentration of the marker ion becomes obvious under such conditions. Commercially available NRT-related pesticides such as Cartap and Bensultap were also detected using the same format after pretreatments by hydrolysis/reduction. The present sensing method was successfully applied to human serum with satisfactory sensitivity.

INTRODUCTION Pesticides are essential for the stable supply of food in modern life. Negative impacts of pesticides, however, should be considered as well. Contamination of foods and drinks, and pollution of the environment from misapplication or misuse of pesticides occur every year. Poisoning events such as those involved in suicides and crimes are serious issues that should be prevented by every possible means. In such cases, it is important for analysts to identify the causative agents as soon as possible by detecting toxic agents in biological samples such as blood and urine. Effective assay techniques for various types of pesticides are essential for both clinical care and criminal investigation. Lipophilic compounds such as organophosphorus are a major class of insecticides, and are also used as warfare agents. They can be extracted with organic solvents and simple analytical methods for them have been established.1 However, it remains difficult to extract and detect polar ionic (watersoluble) pesticides. For example, analysis of phosphoruscontaining amino acid herbicides (PAAHs) requires complex pretreatments because of their zwitterionic nature. Watanabe et al. used a ZrO2 column for solid phase extraction, in which the retention mechanism is based on the specific interaction between ZrO2 and the phosphonate or phosphinate group of PAAHs.2 Although efficient extraction was achieved with this

method, the analysis still requires a derivatization step and a LC/MS2 system. Nereistoxin (NRT, 4-N,N-dimethylamino-1,2-dithiolane; Figure 1a) is a naturally occurring neurotoxin that was isolated from the marine annelid worm, Lumbriconereis heteropoda.3,4 NRT blocks the nicotinic acetylcholine receptor of insects and mammals, to induce a nervous system disorder.5 It is available to consumers as the oxalate salt. NRT-related pesticides shown in Figure 1b-d are metabolically hydrolyzed to regenerate NRT in an insect’s body and exert the insecticidal activity.6 Cartap and Thiocyclam are polar, water-soluble pesticides that are commercially available as hydrochloride and oxalate salts, respectively, and are widely used for protection of crops and vegetables. For analysis of NRT and NRT derivatives, high performance liquid chromatography-electrochemical detector (HPLC-ECD),7 gas chromatography/mass spectrometry (GC/MS)8,9 and liquid chromatography/mass spectrometry (LC/MS)10-12 have been used in combination with several extraction and purification techniques. Namera et al. extracted NRT and its metabolites from human serum by solid-phase microextraction (SPME) and analyzed samples using GC/MS.8 Park et al. used mixed-mode cationic exchange solid phase extraction prior to GC/MS analysis.9 The QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) method is often used for analysis of residual pesticides in food and thiocyclam was successfully detected in various food samples.10-12 Alt-

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hough these techniques are sensitive, they are not as simple and rapid as expected. Recently, colorimetric13,14 and fluorometric15 detection techniques for NRT and Cartap have been reported. In those methods, Au nanoparticles (AuNPs) and NaYF4:Yb,Ho nanocrystals are used as probes and the signals are based on the interactions between AuNPs and the sulfur atoms in NRT or the nitrogen atoms in Cartap. The methods make it possible to detect pesticides with the naked eye but preparing such nanomaterials is not easy.

Figure 1. Chemical structures of (a) Nereistoxin (NRT) and three examples of NRT-related pesticides: (b) Cartap, (c) Thiocyclam and (d) Bensultap.

It is well known that thiol and disulfide compounds form self-assembled monolayers (SAMs) on an Au surface.16,17 AuS covalent bond forms spontaneously simply by exposing the Au electrode to a solution of the desired thiol and disulfide compounds. SAM is regarded as a promising tool for preparing “functional electrodes”, especially in electrochemistry.18 Taniguchi et al. modified the surface of an Au electrode with 4-pyridine thiol and succeeded in observing the redox signal of cytochrome c,19 which is barely observable using bare Au electrodes. This kind of modification reagent for electrodes is called a “promoter”. A variety of thiolated, thioated and disulfide compounds have been used to fabricate analytical devices for metal ions,20-22 nanoparticles,23 proteins,24,25 nucleic acids2628 and other species. One of the characteristic substructures in NRT is disulfide. Therefore, NRT adsorbs on the Au surface by Au-S bond formation. In our previous study, NRTs were adsorbed on a single-crystal Au surface and showed a unique reductive desorption behavior in 0.1 M KOH.29 The reductive desorption wave was so characteristic that we could distinguish NRT from other thiolated aliphatic amines. The detection limit was as low as 1 nM using an Au(100) single-crystal. However, the preparation of a single-crystal is not easy and requires elaborate techniques and a skilled operator. Another substructure in NRT is the tertiary amino group. If NRT molecules modified onto Au electrodes promoted electron transfer by anionic marker ions, this phenomenon could be used as a principle for electrochemical NRT sensing. Here, we report a simple, rapid and costeffective method for detection of NRT and its commercially available derivatives. The technique requires minimum electrochemistry equipment. EXPERIMENTAL SECTION General. Milli-Q water (Millipore Corp., Bedford, MA) was used to prepare all aqueous solutions. NRT oxalate, Cartap hydrochloride, Bensultap, mercaptopropionic acid (MPA), potassium hydroxide, potassium chloride, and potas-

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sium ferricyanide were purchased from Wako Pure Chemicals (Osaka, Japan). Tris(2-carboxyethyl)phosphine (TCEP) hydrochloride was purchased from Tokyo Chemical Industry (Tokyo, Japan). All the reagents were more than analytical grade and used without further purification. Normal human serum was purchased from Chemicon International (Temecula, CA). Because NRT and their derivatives are neurotoxic, it is necessary to avoid the inhalation of their dust and the direct contact by skin and eyes. The procedure for NRT sensing proposed in this report consists of two steps: 1) NRT sampling by exposing the polished bare Au electrode to the NRT solution and 2) Electrochemical measurements in an electrolysis solution containing potassium ferricyanide at low ionic strength. To optimize the procedure, the effects of pH and exposure time for the sampling step and ionic strength and pH for the electrochemical measurements were examined. Conversion of NRT derivatives to NRT. To 5 mL of 6.7 µM Cartap hydrochloride or Bensultap solution, 50 µL of TCEP hydrochloride aqueous solution (50 mM) was added. After standing for 10 min, potassium hydroxide (100 mM) was added to adjust the pH of the solution to 9. Bensultap was first dissolved in acetone, and the solution was then diluted with milli-Q water to adjust the concentration to 6.7 µM. Electrode Preparation and Sampling. The pH of the NRT aqueous solution was adjusted with KOH and HCl. A polycrystalline Au disk electrode (1.6 mm φ) was polished with diamond (particle size 6 µm, 1 µm) and alumina (0.05 µm) slurries, consecutively, and rinsed with milli-Q water followed by 1 minute sonication. After removing the water remaining on the electrode surface, a 5-µL drop of the sample solution containing NRT was placed onto the electrode and allowed to stand for certain specified times at room temperature. After rinsing with milli-Q water, the electrode was subjected to electrochemical measurements. For NRT sensing in human serum, the exposure (sampling) time was fixed at 30 seconds. The electrode was then washed with 1 M NaOH aqueous solution for 20 seconds to remove nonspecific binding and subjected to electrochemical measurements. Electrochemical Measurements. Electrochemical measurements were performed using an Electrochemical Analyzer (ALS 842 B; BAS, Tokyo, Japan) with a conventional threeelectrode system at room temperature. A bare or NRT (or NRT derivative)-treated Au disk, platinum wire, and Ag/AgCl (with 3.0 M NaCl) were used as the working, auxiliary, and reference electrodes, respectively. Cyclic voltammetry (CV) was carried out with 0.5 mM potassium ferricyanide as a marker ion in the presence of various concentrations of supporting electrolyte, KCl, in a potential window from -0.1 to 0.5 V with a scan rate of 50 mV/sec. Differential pulse voltammetry (DPV) was performed over a scanning potential from -0.2 to 0.5 V with a 200 ms pulse period, 25 mV pulse amplitude and 50 ms pulse width. The pH of the electrolysis solutions was adjusted with KOH or HCl aqueous solution in a draft chamber, in case hazardous HCN gas might be generated accidentally as decomposition product from [Fe(CN)6]3– in acidic solution The rate constants for the electron transfer were estimated using the simulation program DigiSim (BAS) by fitting the obtained cyclic voltammograms to the simulated ones.30 This

program is based on the Butler-Volmer equation and Fick’s law of diffusion. Such as the number of electrons to be transferred, concentrations of the reactant, scanning poten-


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tial range, scan rate, half wave potential, electrode geometry and its area are used as parameters for the optimizing the simulation. High electrical resistance attributed to the low concentration of supporting electrolyte was also taken into account when performing the simulation. RESULTS AND DISCUSSION Figure 2a and b show the cyclic voltammograms for [Fe(CN)6]3– in the presence of various concentrations of KCl (1, 10 and 100 mM) obtained with bare and NRT-treated Au electrodes, respectively. The adsorption of NRT onto the Au surface was confirmed by Raman spectroscopy (see Supporting Information). The negative shift of the redox peak potentials of [Fe(CN)6]3-/4- should be attributes to the increase of the reorganization energy with lower ionic strength. The redox current observed with the bare electrode declined with decreasing KCl concentration to almost disappear at 1 mM. On the contrary, the current intensity was not markedly affected by KCl concentrations with the NRT-treated Au electrode (Figure 2b). Namely, significant contrasts in the signals with bare and NRT-treated Au electrodes could be obtained with 1 mM KCl. A linear correlation between current intensity and the square root of the scan rate was observed, even for the NRT-treated electrode (Figure 2c). This behavior suggests that the observed redox currents are derived not from the adsorbed species but from the diffusible species. NRT itself is not redox active (within this voltage window) but promotes the electron transfer between ferricyanide marker anions in solution and the Au electrode. The rate constants of the electron transfer obtained by digital simulation are summarized in Figure 2d. We can see that the rate constants for the bare Au, represented as closed circles, fell rapidly with decreasing KCl concentration, whereas the decline for the NRT-treated Au (open circles) was relatively low. At a KCl concentration of 1 mM, the rate constant for the bare Au was too small to be estimated precisely. We performed the following experiments under these conditions.

Figure 2. Electrochemical behavior of bare and NRT-treated electrodes. All CV measurements were performed with 0.5 mM ferricyanide marker ion at room temperature. (a) Typical CVs obtained with the bare Au electrode in the presence of

various concentrations of KCl: solid curve, 1 mM; dashed curve, 10 mM; and dotted curve, 100 mM KCl. (b) CVs obtained with the NRT-treated Au electrode in the same KCl solutions as in (a). The electrode was treated with 100 µg/mL (670 µM) of NRT aqueous solution for 10 min. (c) Cathodic current intensities plotted versus the square root of the scan rates with NRT-treated Au electrode. (d) Rate constants of the electron transfer measured at various concentrations of KCl: closed circles, bare Au electrode; open circles, NRT-treated electrode.

This NRT-directed acceleration of electron transfer at low ionic strength could be explained considering the potential profiles in electric double layer (EDL). We assumed that this effect was derived from the protonated NRTs on the Au surface. According to the theoretical study based on GouyChapman model, the thickness of the EDL (κ–1) on the bare Au surface was 9.6 nm with 1 mM KCl, while it was 0.96 nm in the presence of 100 mM KCl. The thickness of the EDL increases to 10 times with weakening ionic strength, resulting in the loss of a sufficient potential gradient for effective electron transfer. While the electron transfer on the bare electrode was seriously suppressed by this effect, the NRT molecules conjugated to the Au electrode appear to make the potential gradient around the electrode surface almost constant regardless of the changing in the electrolyte concentration. Additionally, the cationic charge on the termini of NRTs would concentrate anionic marker ion [Fe(CN)6]3– close to the electrode by electrostatic interaction (Scheme 1). The weak ionic strength would also enhance the electrostatic interaction and contribute to making the contrast more pronounced. The more details of the EDL model studies are summarized in the Supporting Information. Scheme 1. Schematic of the promotion effect of NRT on the redox reaction of ferricyanide ions.

To confirm the involvement of electrostatic interactions on the electrode surface, an MPA-modified Au electrode was prepared and was subjected to electrochemical measurement under the same conditions. As expected, the electrochemical response based on the redox couple of [Fe(CN)6]3–/4– was not observed with the MPA-modified Au electrode (Figure 3a). The access of the marker anion to the electrode surface would be completely restricted by electrostatic repulsion with the carboxylate group in MPA. The effect of pH on the electrochemical measurements was examined using an NRTmodified electrode by varying the pH of the electrolysis solution. The current signals observed by DPV were plotted versus pH of the solutions (Figure 3b). No current signal was observed at pH values higher than 10, which corresponds to the pKa of aliphatic amines. The suppression of the redox reaction



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would derive from the tertiary amino group of NRT existing as a free base that makes the electrode surface hydrophobic and inhibits the access of the marker anions to the electrode surface. It is noteworthy that significant electric currents were observed with the NRT-modified electrode at pH > 10 and even with the MPA-modified electrode under standard conditions using abundant electrolyte (100 mM KCl). These results show that an extremely low ionic strength can restrict electron transfer at the interface and impart selectivity towards the reactions.

Figure 3. Studies on the effect of the conditions of electrode surface in the presence of 1 mM KCl. (a) CVs of 0.5 mM ferricyanide with NRT-treated (solid curve) and MPA-treated Au electrode (dotted curve). (b) Current signals obtained with DPV in electrolysis solutions of various pH. The electrode was treated with NRT or MPA aqueous solution (670 µM) for 10 min

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Figure 4. Preliminary studies for NRT determination with DPV. (a) Effects of exposure time to NRT solution (1.0 µg/mL) on electrochemical response. (b) Calibration curve for NRT in acidic (pH 3) solution. (c) Electric current intensities obtained by DPV measurements for electrodes treated with solutions at various pH and NRT concentrations. The error bars indicate the SD (n=3).

To fabricate an electrochemical NRT sensor based on this principle, we examined the conditions of exposure of the Au electrode to the sample solutions containing NRT. All electrochemical measurements were carried out using 0.5 mM [Fe(CN)6]3– in 1 mM KCl solution. First, we investigated the effect of time of exposure to the solution at 1.0 µg/mL (6.7 µM) NRT. The redox current was observed in 5 sec exposure, as shown in Figure 4a. The current increased with exposure time, reaching a maximum at 60 sec. Even in a solution of 0.1 µg/mL NRT, significant current was detected in 5 min (data not shown). The pH dependence of the sample solutions was investigated for several NRT concentrations. Figure 4b shows the calibration curve for NRT measurement at pH 3 and the results are summarized in Figure 4c. The electric currents for all of the solutions were measured after 30 sec exposure of the electrode to NRT solutions. The red, green, purple and blue bars represent 0.5, 1.0, 5.0 and 10 µg/mL NRT, respectively. Higher electric current signals were obtained from NRT solutions at higher pH. This behavior would be caused by the hydrophobicity of NRTs at higher pH accelerating their deposition onto the Au electrode and/or the electrostatic repulsion between the protonated NRTs reducing their assembly on the electrode at lower pH. The time required for signal saturation depended on pH and NRT concentration of the sample solutions. Therefore, considering the general trend of the response observed here, we can choose an appropriate exposure time, depending on pH and the concentration of NRT. This choice is expected to widen the dynamic range of this technique through rational design of the measurement protocol. To check the feasibility of this method, we applied it to commercially available NRT derivatives. It was expected that NRT derivatives could be determined using this method after converting them to NRT. The NRT derivatives were subjected to hydrolysis and reduction using KOH and TCEP, respectively. Cartap is readily hydrolyzed to give the NRT structure in aqueous solutions.31,32 In practice, moderate electric signals were observed without pretreatments. The signal increased with alkalization, which appears to complete the hydrolysis to NRT. Using both KOH and TCEP treatments, we presumed that NRT was first formed by hydrolysis, followed by reduction of the disulfide to form the dithiol structure (dihydro NRT). However, no electric current was observed following TCEP treatment alone, because the solution is acidic and the sulfur-carbamoyl bond is stable in acidic solution, 31,32 in addition to the reduced assembly of the molecules in acidic media (Figure 4c). In the case of Bensultap, both treatments were required to obtain the signal at the same level of NRT. It was reported that Bensultap is also hydrolyzed in aqueous solution, but that NRT monoxide forms as a major byproduct.33 Therefore, TCEP was needed to convert NRT monoxide to NRT and/or dihydro NRT. The formation of NRT monoxide and its reduction product generated by TCEP treatment were confirmed by LC/MS2 (see Supporting Information). The proposed pathways for the conversion of NRT derivatives to NRT are shown in Figure 5b. Other NRT derivatives such as Thiocyclam are expected to be detectable using the same strategy.


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Figure 6. Calibration curve for NRT in human serum, obtained through DPV measurement. The error bars indicate the SD (n=5).

Figure 5. Detection of NRT derivatives and the effects of TCEP and KOH treatments. (a) Current intensities obtained with DPV measurements. (b) Proposed conversion pathways of NRT derivatives to NRT and/or dihydro NRT: (i) hydrolysis and oxidization, (ii) reduction by TCEP, and (iii) adsorption on Au electrode. The error bars indicate the SD (n=3).

In the human body, NRT-related pesticides are metabolically hydrolyzed to NRT. Hence, finally, we applied this method to NRT detection in human serum. By exposing the Au electrode to NRT-spiked human serum for 30 sec, NRT was collected on the surface of the electrode. An unidentified electric current was observed after exposure to blank serum. This nonspecific signal could be removed by washing the electrode with NaOH solution (see Supporting Information). No further pretreatment or purification step was required and the sample consumption was only 5 µL. The signals were quantitatively detected in the range 1–25 µg/mL. This range covers the serum NRT level8,9,34 of patients who suffer from NRT poisoning, as reported previously.

CONCLUSIONS A unique technique for electrochemical sensing of small biologically active molecules was performed through NRT determination. The measurements were carried out at an unusually low ionic strength, using common instruments used for electrochemical studies in the laboratory. This approach involves structure-selective sensing; both sulfide and cationic substructures are essential as analytes. NRT is a small neurotoxin with a minimal structure consisting of disulfide and tertiary amines. In other examples, thiocholine and biothiols such as cysteine, homocysteine, and glutathione have both of these common substructures. Thiocholine is commonly used in the detection methods for nerve agents such as organophosphorus, based on their acetylcholinesterase inhibition activity. Biothiols play essential roles in human physiology, but abnormal levels are associated with many diseases. This study is expected to pave the way for simple and cost-effective electrochemical sensing of these biologically significant molecules.

ASSOCIATED CONTENT Supporting Information Supporting Information is available free of charge on the ACS Publications website. Raman spectra of NRT-modified Au electrode, results of EDL model studies, results of LC/MS2 analysis of NRT and Bensultap solutions with and without TCEP treatment, the effect of washing of the electrode with NaOH aqueous solution after exposing to blank serum (PDF)

AUTHOR INFORMATION Corresponding Author *Correspondence should be addressed to T.I. E-mail: [email protected]

Author Contributions H.S. considered the principles, applied the system to various samples and wrote the paper. S.N. optimized the conditions of the system. M.Y. performed the theoretical studies. K.N. and Y.K. analyzed and discussed the data. T.I. conceived the project and designed the system.



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ACKNOWLEDGMENT This work was partially supported by a Grant-in-Aid for Scientific Research (B) (15H03829) from MEXT, Japan.

REFERENCES (1) Xia, N.; Wang, Q.; Liu, L. Sensors 2015, 15, 499-514. (2) Watanabe, D.; Ohta, H.; Yamamuro, T. J. Chromatogr. B 2014, 969, 69-76. (3) Hashimoto, Y.; Okaichi, T. Ann. N.Y. Acad. Sci. 1960, 90, 667. (4) Okaichi, T.; Hashimoto, Y. Agric. Biol. Chem. 1962, 26, 224227. (5) Lee, S.-J.; Tomizawa, M, Casida, J. E. J. Agric. Food Chem. 2003, 51, 2646-2652. (6) Jeschke, P.; Nauen, R.; Beck, M. E. Angew. Chem. Int. Ed. 2013, 52, 9464-9485. (7) Fisher, D. H.; Xie, Y.; Loring, R Anal. Lett. 1993, 26, 10511063. (8) Namera, A.; Watanabe, T.; Yashiki, M.; Kojima, T.; Urabe, T. J. Chromatogr. Sci. 1999, 37, 77-82. (9) Park, Y.; Choe, S.; Lee, H.; Jo, J.; Park, Y.; Kim, E.; Pyo, J.; Jung, J. H. Forensic Sci. Int. 2015, 252, 143-149. (10) Ferrer, C.; Mezcua, M.; Martínez-Uroz, M. A.; Pareja, L.; Lozano, A.; Fernández-Alba, A. R. Anal. Bioanal. Chem. 2010, 398, 2299-2306. (11) Kmellár, B; Fodor, P; Pareja, L; Ferrer, C; Martínez-Uroz, M. A.;Valverde, A; Fernández-Alba, A. R. J. Chromatogr. A 2008, 1215, 37-50. (12) Hernando, M. D.; Ferrer. C.; Ulaszewska, M.; García-Reyes, J. F.; Molina-Díaz, A.; Fernández-Alba, A. R. Anal. Bioanal. Chem. 2007, 389, 1815-1831. (13) Liu, W.; Zhang, D.; Tang, Y.; Wang, Y.; Yan, F.; Li, Z.; Wang, J.; Zhou, H. S. Talanta 2012, 101, 382-387. (14) Liu, W.; Zhang, D.; Zhu, W.; Zhang, S.; Wang, Y.; Yu, S.; Liu, T.; Zhang, X.; Zhang, W.; Wang, J. Microchim. Acta 2015, 182, 401-408. (15) Wang, Z.; Wu, L.; Shen, B.; Jiang, Z. Talanta 2013, 114, 124130.

Page 6 of 7

(16) Love, J. C.; Estroff, L. A.; Kriebel, J. K; Nuzzo, R. G.; Whitesides G. M. Chem. Rev. 2005, 105, 1103-1169. (17) Ulman, A. Chem. Rev. 1996, 96, 1533-1554. (18) Gooding, J. J.; Mearns, F.; Yang, W.; Liu, J. Electroanalysis 2003, 15, 81-96. (19) Taniguchi, I.; Toyosawa, K.; Yamaguchi, H.; Yasukouchi, K. J. Chem. Soc., Chem. Commun., 1982, 1032-1033. (20) Wu, Y.; Lai, R. Y. Anal. Chem. 2016, 88, 2227-2233. (21) Chow, E; Wong, E. L. S.; Pascoe, O; Hibbert, D. B.; Gooding, J. J. Anal. Bioanal. Chem. 2007, 387, 1489-1498. (22) Xiao, Y.; Rowe, A. A.; Plaxco, K. W. J. Am. Chem. Soc. 2007, 129, 262-263. (23) Krause, K. J.; Yakushenko, A.; Schnitker, J.; Mayer, D.; Offenhäusser, A.; Wolfrun, B. Anal. Chem. 2016, 88, 3632-3637. (24) Tian, Y.; Ariga, T.; Takashima, N.; Okajima, T.; Mao, L.; Ohsaka, T. Electrochem. Commun. 2004, 6, 609-614. (25) Patil, B.; Kobayashi, Y.; Fujikawa, S.; Okajima, T.; Mao, L.; Ohsaka, T. Bioelectrochem. 2014, 95, 15-22. (26) Xiong, E.; Zhang, X.; Liu, Y.; Zhou, J.; Yu, P.; Li, X.; Chen, J. Anal. Chem. 2015, 87, 7291-7296. (27) Shi, K.; Dou, B.; Yang, C.; Chai, Y.; Yuan, R.; Xiang, Y. Anal. Chem. 2015, 87, 8578-8583. (28) Ihara, T.; Nakayama, M.; Murata, M.; Nakano, K.; Maeda, M. Chem. Commun. 1997, 1609-1610. (29) Nishiyama, K.; Tsuruta, K.; Ikeda, M.; Yoshimoto, S.; Shimada, H.; Kitamura, Y.; Ihara, T. Electrochemistry 2016, 84, 349353. (30) Rudolph, M.; Reddy, D. P.; Feldberg, S. W. Anal. Chem. 1994, 66, 589A-600A. (31) Asahi, Y.; Yoshida, T. Chem. Pharm. Bull. 1977, 25, 22112216. (32) Lee, S.-J.; Caboni, P.; Tomizawa, M.; Casida, J. E. J. Agric. Food Chem. 2004, 52, 95-98. (33) Inoue, M.; Yamamoto, A. J. Pesticide Sci. 1986, 11, 547-555. (34) Kurisaki, E.; Kato, N.; Ishida, T.; Matsumoto, A.; Shimohara, K.; Hiraiwa, K. Clinic. Toxicol. 2010, 48, 153-155.


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