CySH Oxidation Research Articles

Microfluidic Reservoir Integrated with Optimized Screen-Printed Electrode for Simultaneous Detection of Ascorbic Acid and L-Cysteine

Abstract iomarker detection is crucial in the healthcare industry as it gives important insights into the field of disease diagnosis, prognosis, and treatment. This work demonstrates a flexible carbon-based screen-printed electrode (CSPE) modified with carboxylic acid functionalized multiwalled carbon nanotube (MWCNT-COOH) for simultaneous detection of Ascorbic acid (AA) and L-Cysteine (CySH). The electrochemical properties of the fabricated film are studied using the Cyclic voltammetry (CV) and Amperometry technique. The MWCNT-COOH/CSPE showed good electrocatalytic activity for oxidation of CySH and AA. Favorable ionic interaction, or electrostatic attraction, between the analytes and MWCNT-COOH increased the detection capability. The fabricated electrode is incorporated with a microfluidic reservoir to hold the analyte that can separately detect AA and CySH using the device. The device is tested for a linear range of 0.01 mM to 20 mM for both analytes. The detection limit for AA and CySH obtained using amperometry analysis is 3.07 µM and 5.72 µM, respectively. Also, the calculated quantification limits values are 9.11 µM and 17.3 µM, respectively for AA and CySH. Further, the device demonstrates appreciable results in both real sample analysis and interference analysis. The device, enabled with screen printed electrodes and microfluidic reservoir, opens a new method for simultaneous multiplexed detection enabling the detection of many different biomarkers on the same experimental setup.

A double-layered self-healing coating system based on the synergistic strategy of cysteine and iron polyacrylate for corrosion protection

Nanocontainers loaded with corrosion inhibitors are usually added to organic coatings to achieve self-healing of the coating. However, the amount of nanocontainers that the coating can accommodate is limited. Excessive addition of nanocontainers will damage the integrity of the coating, while too little addition will lead to its insufficient self-healing ability. Here, we prepared a double-layered self-healing coating system (C-DMS-EP/P-DMS-EP) consisting of a bottom epoxy coating containing cysteine (CysH) loaded dendritic mesoporous silica (DMS) (C-DMS-EP) and an upper epoxy coating containing iron polyacrylate (PAAFe) loaded DMS (P-DMS-EP) based on the synergistic effect of CysH and PAAFe. It can achieve more efficient self-healing ability for Q235 steel. The experimental results exhibit that PAAFe can not only accelerate the oxidation of CysH but also capture the hydrogen ions generated during the oxidation process, thereby exhibiting excellent corrosion resistance. Electrochemical impedance spectroscopy (EIS) results show that the low frequency impedance modulus (|Z|0.01 Hz) of C-DMS-EP/P-DMS-EP is nearly-two orders of magnitude higher than that of pure epoxy coating (EP) after 40 days of immersion in 3.5 wt% NaCl solution. Moreover, the self-healing efficiency (ηs) of C-DMS-EP/P-DMS-EP with an artificial scratch (C-DMS-EP/P-DMS-EP@AS) gradually changes from negative to positive as the immersion time increases. The preparation method for this double-layered self-healing coating system proposed in this work will provide a new idea for constructing high-performance self-healing coatings.

An electrochemical sensor based on copper nanowires-PDDA modified glassy carbon electrode for amperometric detection of cysteine in alkaline medium

The development of highly efficient and stable electrocatalysts for their application in electrochemical detection is desirable. Herein, a new copper nanowires (CuNWs) modified electrode was fabricated by coating poly(dimethyl diallyl ammonium chloride) (PDDA) stabilized CuNWs composite onto the the glassy carbon electrode (GCE), and used for electro-catalyze and determination of cysteine (CySH). The morphology, structure, and surface property of fabricated CuNWs were tested using SEM, XRD, and XPS, separately. Electrocatalytic behavior of the modified electrode (CuNWs-PDDA/GCE) for CySH oxidation in alkaline medium was researched by cyclic voltammetry (CV) and chronoamperometry (CA) thoroughly, displaying excellent electrocatalytic oxidation activity and sensing ability towards CySH with a rapid and sensitive anodic current response at low oxidation potential. In the amperometric detection of CySH, the as-prepared electrode displayed a significantly wide linear range from 2 μM to 260 μM and a detection limit of 0.19 μM with a sensitivity of 1.430 μAμM−1cm−2. The proposed CySH sensor exhibited good reproducibility, stability, and anti-interference ability, and has been used to detect CySH in human plasma samples successfully with good applicability.

Molecular orientation and dynamics of ferricyanide ion-bearing copoly(ionic liquid) modified glassy carbon electrode towards selective mediated oxidation reaction of cysteine versus ascorbic acid: A biomimicking enzyme functionality

Understanding the electron-transfer (ET) functionality of enzymes in relation to their molecular orientation and dynamics is a cutting-edge research interest in the interdisciplinary areas of chemistry and biology. In this work, we demonstrate how the molecular structure and orientation of a redox polymer influence the ET behavior and specific catalytic functionality to target substance, ascorbic acid (AA) or cysteine (CySH) in a physiological condition. In the literature, Fe(CN)63−, a well-known benchmarking redox system, based chemically modified electrodes (CME) prepared by the ion-exchange method, has been widely used as an electrocatalyst for ascorbic acid oxidation reaction without the interference of CySH. In this work, a Fe(CN)63− bearing copoly(ionic liquid)-ethanol solution modified glassy carbon electrode, designated as GCE@{Fe(CN)63−}-coPIL, prepared as a homogenous solution followed by CME formation, has shown a unique and selective CySH oxidation reaction, rather than expected AA mediation, similar to the Thiol Oxidase enzyme-based biomimetic functionality. Andrieux and Saveant and Michaelis-Menten kinetic models were adopted to explain the reaction mechanism. The polymer network orientation and dynamics are found to influence strongly on the electrocatalytic functionality of the new CME. It has been revealed that underlying surface, functional groups, and solvent nature impact the molecular architectures of the {Fe(CN)63−}-caped polymer back-bone (insulating) network as a fully (H2O and CHCl3) or partially (C2H5-OH and CH3CN) shielded structures and decide its electron-transfer and selective mediated oxidation reaction functionalities. This observation is similar to the protein folding of enzymes at various external stimuli conditions and its unfolded structures for direct electron transfer and selective mediated oxidation/reduction reaction. As a proof of concept, electroanalytical application of thiol functional group (CySH) oxidation to disulfide bond (CyS-SyC) catalyzed by the GCE@{Fe(CN)63−}-coPIL in neutral pH solution has been demonstrated.

Biomimetic oxidation of benzo[a]pyrene to a quinone metabolite as a cysteine-oxidation mediator on MWCNT-modified electrode surface

Bay-region containing polyaromatic hydrocarbons (PAHs) like Benzo(a)pyrene (BaP), which comprise several strained benzenoid rings, are representative organic compounds for the carcinogenic and mutagenic activities in physiological system. In general, cytochrome c, peroxidase and certain soil-bacteria oxidize these compounds to respective hydroxylated metabolites like BaP-7,8-diol (BaP–2OH), that can interact with DNA, RNA and protein, and in turn makes the cellular system dysfunctional. The structure - activity relationship of these compounds is still unclear and therefore, it is necessary for a new analytical approach to delineate the intricate mechanism behind the oxidation of the PAHs. Herein, we report, a simple electrochemical approach of surface-confined oxidation of BaP on multiwalled carbon nanotube (MWCNT) modified glassy carbon electrode (GCE/MWCNT) in physiological condition (pH 7 phosphate buffer solution). It has been found that MWCNT-surface adsorbed BaP (electro-inactive compound) gets electro-oxidized to highly redox active BaP–2OH compound at high positive potential, 1.2 V vs Ag/AgCl, in which, the water molecule was oxidized to molecular oxygen via hydroxyl radical intermediate. From the collective electrochemical and physicochemical studies using Raman, FTIR, GC-MS and 1,2-dihydroxy redox active probe, cysteine (CySH), it has been observed that the hydroxyl radical species produced on the surface has assisted the BaP oxidation to BaP-7,8-diol product, which is similar to the biocatalyzed oxidation of BaP observed in the physiological system. The BaP-7,8-diol surface confined MWCNT modified GCE showed a well-defined and stable redox peak at an apparent standard electrode potential, Eo’ = 0 V vs Ag/AgCl. The redox process is found to be proton-coupled electron-transfer in nature. As an independent study, selective electrocatalytic oxidation of CySH has been demonstrated as an application.

3D pothole-rich hierarchical carbon framework-encapsulated Ni nanoparticles for highly selective nonenzymatic cysteine detection

3D pothole-rich hierarchical amorphous carbon network-encapsulated Ni nanoparticles (Ni NPs) electrocatalytic material (3D-Ni@AC) is successfully designed and synthesized via a facile in-situ NaCl template-removal method for electrochemical non-enzymatic cysteine (CySH) detection. 3D-Ni@AC assembled from the carbon nanosheet encapsulated Ni NPs layer-by-layer interlaced possesses interconnected porous network structure, the network structure of carbon nano-layer can effectively prevent the agglomeration of Ni NPs, ensuring full utilization of active materials. Cyclic voltammetric (CV) study showed that 3D-Ni@AC/GCE displayed high electrocatalytic activity toward the oxidation of CySH compared to template-free Ni@AC/GCE. The unique structure, the enlarged specific surface area and the synergistic effects from the excellent conductivity of carbon frame and Ni NPs provide fast electrons/ions transfer and favorable electrocatalytic activity for the electro-oxidation of CySH. In an electrolyte solution of 0.1 M NaOH, the constructed CySH sensor offered a high sensitivity (0.079 mA/cm2 μM), a low detection limit (0.15 μM) and a wide linear range (from 0.8 to 85 μM). The fabricated high electrocatalytic performance sensor was utilized to monitor the CySH levels in urine and serum, and satisfactory results were gained. Moreover, 3D-Ni@AC electrode showed good reproducibility, stability, and anti-interference ability, indicating that 3D-Ni@AC can be used as a good electrocatalytic material in practical biological applications.

A high-performance electrochemical sensor for biologically meaningful l-cysteine based on a new nanostructured l-cysteine electrocatalyst

As a new class of l-cysteine electrocatalyst explored in this study, Au/CeO2 composite nanofibers (CNFs) were employed to modify the screen printed carbon electrode (SPCE) to fabricate a novel l-cysteine (CySH) electrochemical sensor with high performance. Its electrochemical behavior and the roles of Au and CeO2 in the composite toward electro-oxidation of CySH were elucidated and demonstrated using cyclic voltammetry and amperometry techniques for the first time through the comparison with pure CeO2 NFs. More specifically, the Au/CeO2 CNFs modified SPCE possessed greatly enhanced electrocatalytic activity toward CySH oxidation. An ultra high sensitivity of 321 μA mM−1cm−2 was obtained, which is almost 2.7 times higher than that of pure CeO2 NFs, revealing that the presence of Au imposed an important influence on the electrocatalytic activity toward CySH. The detailed reasons on such high performance were also discussed. In addition, the as-prepared sensor showed a low detection limit of 10 nM (signal to noise ratio of 3), a wide linear range up to 200 μM for the determination of CySH, an outstanding reproducibility and good long-term stability, as well as an excellent selectivity against common interferents such as tryptophan, tyrosine, methionine, ascorbic acid and uric acid. All these features indicate that the Au/CeO2 composite nanofiber is a promising candidate as a new class of l-cysteine electrocatalyst in the development of highly sensitive and selective CySH electrochemical sensor.

Photoelectrochemical properties of bare fluorine doped tin oxide and its electrocatalysis and photoelectrocatalysis toward cysteine oxidation

We first revealed that the bare fluorine doped tin oxide (FTO) under the cathodic polarization over −0.7V (vs.SCE) shows very sensitive to the irradiating light in a wide wavelength region 850–400nm in the aqueous solution free of a redox couple, and its band gap of energy Eg is determined to be 1.38eV via the photoelectrochemical method. The bare FTO can effectively catalyze electrochemically L-cysteine (CySH) oxidation and especially shows the photocatalytic ability toward CySH oxidation. Thus the bare FTO electrode can be directly used for determination of CySH concentration using cyclic voltammetry in both the dark and light illumination and it can be used to recognize CySH among 20 α-amino acids found in proteins, based on the low oxidation peak potential and unique photoelectric response. The rate-determining step for the photocatalytic oxidation of CySH on the bare FTO electrode is controlled by supply of charge inside the FTO film to the electrode surface, which exhibits the typical characteristics of semiconductors.

The Electrochemical Behavior of Au/AuNPs/PNA/ZnSe-QD/ACA Electrode Towards CySH Oxidation

This work describes the electrochemical behavior of azodicarboxamide (ACA) film immobilized on the surface of penicillamine (PNA)/ZnSe-quantum dot (ZnSe-QD) gold nanoparticle (AuNPs) Au electrode. Electrocatalytic activity of modified electrode toward the oxidation of cysteine (CySH) was investigated. The surface structure and composition of the sensor were characterized by scanning electron microscopy (SEM). Oxidation of CySH on the surface of modified electrode was investigated with cyclic voltammetry, electrochemical impedance spectroscopy (EIS), hydrodynamic voltammetry and chronoamperometry methods. The results show that the PNA/ZnSe-QD/ACA film displays excellent electrochemical catalytic activities towards CySH oxidation. The modified electrode shows reproducible behavior and high level of stability during the electrochemical experiments. Also it has short response time, low detection limit, high sensitivity and low operation potential, which can be used as an amperometric sensor for monitoring of CySH. The proposed modified electrode was successfully used for determination of CySH in real sample such as human serum.

A nonenzymatic l-cysteine sensor based on SnO2-MWCNTs nanocomposites

In the present work, a SnO2-coated multiwall carbon nanotubes (MWCNTs) modified glassy carbon electrode (SnO2-MWCNTs/GCE) was fabricated and was used for amperotemetric detection of l-cysteine (CySH). The surface morphology and structure of the prepared nanocomposite modified electrode were investigated by transmission electron microscope (TEM), X-ray diffraction (XRD), and Raman spectroscopy. Electrochemical investigation indicated that the nanocomposites possess an excellent performance towards the electrocatalytic oxidation of CySH in phosphate buffer solution (pH7.4). The current response of the SnO2-MWCNTs/GCE was linearly related to the CySH concentration in the range from 0.1 to 55.6μM and 55.6 to 554.5μM, respectively. The detection limit was 0.03μM at a signal-to-noise ratio of 3, and the response time was as short as 4s. Additionally, the sensor exhibits long-term stability, good reproducibility and anti-interference.

Electrocatalytic Oxidation of Cysteine at a CoSalophen/ n‐(butyl)4SiW12O40 Carbon Paste Electrode

AbstractIn the present study, a novel mixture consisting of N,N′‐bis(salicylidene)‐1,2‐phenylenediamino cobalt (CoSalophen, CoSal) complex and (n‐butyl)4SiW12O40 (SiW12), have been used to chemically modify a carbon paste electrode (CPE) for sensitive determination of cysteine (CySH). The electrocatalytic effect of the newly developed modified CPE towards oxidation of CySH was evaluated by comparing cyclic and differential pulse voltammograms in the presence of cysteine at bare, CoSal, SiW12 and CoSal/SiW12 modified CPE. The differential pulse voltammetry method was applied as a sensitive method for quantitative detection of CySH trace amounts, the experimental conditions being optimized in order to evaluate the best analytical parameters of the sensor. Reproducibility and stability studies were also performed and the sensor was applied for the determination of CySH in a pharmaceutical sample and in human blood serum and urine samples.

The electrochemical determination of l-cysteine at a Ce-doped Mg–Al layered double hydroxide modified glassy carbon electrode

Abstract A Ce-doped Mg–Al layered double hydroxide modified glassy carbon electrode (Mg–Al–Ce LDH/GCE) was fabricated for the detection of l -cysteine (CySH). The electrochemical behavior of CySH on the as-prepared electrode was investigated by cyclic voltammetry. Our results show that Mg–Al–Ce LDHs gave an enhanced oxidation wave of CySH at the modified electrode. The effect of pH value and scan rate on CySH oxidation was studied in detail, and the mechanism of CySH oxidation on the Mg–Al–Ce LDH/GCE was also addressed. The amperometric current of the electrode is proportional to the concentration of CySH over the range of 10–5400 μM, with a detection limit of 4.2 μM at a signal-to-noise ratio of 3. The low cost, fast amperometric response, wide linear range, excellent stability, good selectivity and easy preparation are some of the notable advantages of this electrode.

Highly sensitive and selective electrochemical detection of L-cysteine using nanoporous gold

Nanoporous gold (NPG) with uniform pore sizes and ligaments was prepared by using a simple dealloying method. NPG electrodes exhibit excellent electrocatalytic activity towards the oxidation of CySH and the mechanism for the electrochemical reaction of CySH on NPG has been discussed. Interestingly, if the operating potential is fixed at 0.65 V, a strong current is observed and interferences by tryptophan and tyrosine are avoided. The calibration plot is linear in the concentration range from 1 μM to 400 μM (R2 = 0.994), and the quantification limit is as low as 50 nM. The NPG-modified electrode has good reproducibility, high sensitivity and selectivity, can be used to sense CySH in aqueous solution.

Oxidation and detection of L-cysteine using a modified Au/Nafion/glass carbon electrode

In this work, the electrochemical oxidation of L-cysteine (CySH) was investigated on a composite film modified electrode with Au nanoparticles dispersed in the fluorocarbon polymer (Nafion). The excellent electrocatalytic effect on CySH oxidation was attributed to the role of Au nanoparticles. The voltammetric studies revealed two anodic peaks for the oxidation of CySH in the pH range of 2.0–8.0. The electrode was used to detect cysteine at pH 2.0 and pH 7.0. At pH 2.0, a determination range of 3.0–50.0 μmol/L was obtained with the detection sensitivity of 22.7 μA/(mmol L−1), while at pH 7.0, a determination range of 2.0–80.0 μmol/L was obtained with the detection sensitivity of 4.08 μA/(mmol L−1). The detection limits were estimated to be as low as 1.0 μmol/L at both pH 7.0 and pH 2.0. Additionally, at pH 7.0, the interferences of ascorbic acid and uric acid were reduced for the detection of cysteine. These made the Au/Nafion/GC electrode a promising candidate for efficient electrochemical sensors for the detection of CySH.

Sputtering deposition of Pt nanoparticles on vertically aligned multiwalled carbon nanotubes for sensing L-cysteine

A highly sensitive electrochemical sensor for determination of L-cysteine (CySH) is presented. It is based on vertically aligned multiwalled carbon nanotubes modified with Pt nanoparticles by magnetron sputtering deposition. The morphology of the nanocomposite was characterized by scanning electron microscopy, transmission electron microscopy and energy-dispersive. The electrochemistry of CySH was investigated by cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The mechanism for the electrochemical reaction of CySH at the modified electrode at different pH values is discussed. The electrode exhibits a higher electrocatalytic activity towards the oxidation of CySH than comparable other electrodes. It displays a linear dependence (R2 = 0.9980) on the concentration of CySH in the range between 1 and 500 μM and at an applied potential of +0.45 V, a remarkably low detection limit of 0.5 μM (S/N = 3), and an outstandingly high sensitivity of 1.42 × 103 μA mM−1 cm−2, which is the highest value ever reported. The electrode also is highly inert towards other amino acids, creatinine and urea. The sensor was applied to the determination of CySH in urine with satisfactory recovery, thus demonstrating its potential for practical applications.

Pt–NiCo Nanostructures with Facilitated Electrocatalytic Activities for Sensitive Determination of Intracellular Thiols with Long‐Term Stability

A Pt-NiCo nanomaterial has been synthesized for developing the sensitive electrochemical determination of biological thiols that include L-cysteine (CySH), homocysteine (HCySH), and gluthione (GSH) with high sensitivity and long-term stability, in which the Pt nanoparticles are well supported on amorphous NiCo nanofilms. The electrochemical oxidation of thiols has been successfully facilitated on the optimized Pt-NiCo nanostructures, that is, two oxidation peaks of CySH have been clearly observed at potentials of +0.06 and +0.45 V. The experimental results demonstrate that the first peak for CySH oxidation may be attributed to a direct oxidation from CySH to L-cystine (CySSCy), whereas the second peak possibly results from a sequential oxidation from CySSCy to cysteic acid (CySO(3)H), together with a direct oxidation of CySH into CySO(3)H. The enhanced electrocatalytic activities at the Pt(23)-NiCo nanostructures have provided a methodology to determine thiols at a very low potential of 0.0 V with relatively high sensitivity (637 nA μM cm(-2)), a low detection limit (20 nM), and a broad linear range. The striking analytical performance, together with the characteristic properties of the Pt-NiCo nanomaterial itself, including long-term stability and strong antipoisoning ability, has established a reliable and durable approach for the detection of thiols in liver cancer cells, Hep G2.

Electrochemical determination of l-Cysteine by an elbow shaped, Sb-doped ZnO nanowire-modified electrode

Elbow shaped Sb-doped ZnO nanowires (SZO NWs) have been synthesized via thermal evaporation and thoroughly characterized. A glassy carbon (GC) electrode was modified by these NWs for the determination of L-cystein (L-CySH). Detailed electrochemical measurements of the modified electrode towards L- CySH oxidation are investigated. The response current of L-CySH oxidation at the SZO/GC electrode is found to be much higher than that of the bare GC and ZnO/GC electrodes. This change in the electrochemical properties of the modified electrode is due to the reduction in band gap and an increased amount of deep-level defects in SZO NWs, which leads to a significant role in the L-CySH determination. The modified electrode exhibits a reproducible sensitivity of 400 nA μM−1, within a response time of less than 6s, a detection limit of 0.025 μM and a linear range of 0.075 to 100 μM. Furthermore, the modified electrode shows high stability and good resistance to interference. Our investigation demonstrates that SZO NWs are very sensitive to L-CySH and can be employed in the development of biosensors for future biological and medical applications.

Side-chain oxidative damage to cysteine on a glassy carbon electrode

In this paper, oxidative damage to the cysteine (CySH) side-chain on a glassy carbon electrode (GCE) was investigated. Voltammetric studies show that there are three anodic peaks for the oxidation of CySH, which arise from (1) the oxidation of the -SH side-chain, forming cystine (0.71 V, vs. SCE) and (2) CySO( x )H, x = 2, 3 (0.98 V vs. SCE), and (3) the oxidation of the amino acid carboxyl group (around 1.51 V vs. SCE). The influence of dissolved oxygen, pH, scan rate, scan time, temperature and CySH concentration were investigated and the oxidative mechanism proposed. The peaks near 0.71 and 0.98 V are the promising candidates for measuring the oxidation of CySH on the GCE. This paper provides a new strategy for researching oxidative damage of amino acids, sulfur-containing peptides and proteins.

Oxidation of l-Cysteine at a Fluorosurfactant-Modified Gold Electrode: Lower Overpotential and Higher Selectivity

We describe the oxidation of L-cysteine (CySH) at a fluorosurfactant (i.e., Zonyl FSO)-modified gold electrode (FSO-Au). Significantly reduced anodic overpotential of CySH was observed. The FSO layer inhibited the adsorption of CySH and its oxidation products at the gold electrode surface, and the low coverage of the adsorbed thiol-containing species might account for the more facile electron-transfer kinetics of free CySH at low potentials. An electrochemical impedance spectroscopy study revealed the lower charge-transfer resistance of CySH oxidation at the FSO-Au electrode as compared to that at a bare gold electrode. Interestingly, although the FSO layer facilitated CySH oxidation, the anodic responses of other electroactive biological species such as glucose, uric acid, and ascorbic acid were generally suppressed. Furthermore, the modified electrode was capable of differentiating CySH from other low-molecular-mass biothiols such as homocysteine and glutathione. The unique features of the FSO-Au electrode allowed for the development of a highly selective method of detecting CySH in complex biological matrices. The direct determination of free reduced and total CySH in human urine samples has been successfully carried out without the assistance of any separation techniques.

Electrochemical Behavior of l-Cysteine and Its Detection at Ordered Mesoporous Carbon-Modified Glassy Carbon Electrode

In this paper, the electrochemical behavior of L-cysteine (CySH) was investigated thoroughly at an ordered mesoporous carbon-modified glassy carbon (OMC/GC) electrode. The voltammetric studies showed there were three anodic peaks for the electrooxidation of CySH in the pH range of 2.00-5.00; however, one peak disappeared above pH 5.00. This behavior has never been reported before. Through the studies of the effect of pH on the distribution fractions (delta) of the four chemical species of CySH, we conclude only CySH2+ (H3A+) and CyS- (HA-) are the electroactive substances and should be responsible for the electrooxidation of CySH. And for the first time, we successfully established the exact and systemic mechanisms based on the electroactive species to explain CySH oxidation at different pH values. On the other hand, a sensitive CySH sensor was developed based on an OMC/GC electrode, which shows a large determination range (18-2500 micromol L(-1)), a high sensitivity (23.6 microA mmol L(-1)), and a remarkably low detection limit (2.0 nmol L(-1), which is the lowest value ever reported for direct CySH determination on the electrodes) at pH 2.00. At pH 7.00, the modified electrode can be still used to readily detect CySH in the range of the physiological levels. These make OMC/GC electrode a promising candidate for efficient electrochemical sensors for the detection of CySH.