Disposable Amperometric Sensors for Thiols with Special Reference to Glutathione

Halogen mediated voltammetric oxidation of biological thiols and disulfides

The electrochemical generation of the halides, bromine and iodine, in the presence of biologically relevant organosulfur is demonstrated to result in an analytically useful response. In the case of the iodide/iodine redox couple only the thiol causes an increase in the electrochemical oxidative peak current. Conversely, the formed bromine may catalytically oxidise both thiols and disulfides. Hence, the differing reactivities of the halide ions readily allow discrimination between the closely related thiol and disulphide species. For all of the organosulfur species investigated (glutathione, cysteine and homocysteine) micromolar limits of detection are attainable. In the case of the bromine mediated oxidation this sensitivity at least partially arises from the large catalytic amplification, such that, for each disulphide molecule up to ten electrons may be transferred. Ultimately this bromine oxidation results in the formation of the sulfonate species. For the iodine mediated oxidation of the thiols the oxidation proceeds no further than to the formation of the associated disulfide.

In vivo detection of glutathione disulfide and oxidative stress monitoring using a biosensor

A highly sensitive in vivo biosensor for glutathione disulfide (GSSG) is developed using covalently immobilized-glutathione reductase (GR) and -β-nicotinamide adenine dinucleotide phosphate (NADPH) on gold nanoparticles deposited on poly[2,2':5',2″-terthiophene-3'-(p-benzoic acid)] (polyTTBA). The fabricated biosensor was characterized with SEM, TEM, XPS, and QCM. Analytical parameters affecting the biosensor performance were optimized in terms of applied potential, NADPH:GR ratio, temperature, and pH. A linear calibration plot is obtained using chronoamperometry in the dynamic range between 0.1 μM and 2.5 mM of GSSG, with a detection limit of 12.5 ± 0.5 nM. The developed biosensor is applied to detect GSSG in a real plasma sample. A microbiosensor was applied to detect the in vivo GSSG concentration to monitor the oxidative stress caused by diquat and t-butyl hydroperoxide. The results obtained are reliable, implying a promising approach for a GSSG biosensor in clinical diagnostics and oxidative stress monitoring.

Anti-aggregation of gold nanoparticle-based colorimetric sensor for glutathione with excellent selectivity and sensitivity

For the widely used Au nanoparticles (AuNPs)-based colorimetric probe, AuNPs generally change from the dispersion to the aggregation state and corresponding colors turn from red to blue concomitantly. In previous studies, there are few probes based on the anti-aggregation of AuNPs though anti-aggregation of AuNPs is preferable to aggregation to achieve higher selectivity. In this manuscript, a fast and simple but sensitive and selective sensor suitable for on-site and real-time detection of glutathione (GSH) has been developed based on the anti-aggregation of AuNPs. The sensor has a LOD of 8 nM and excellent selectivity toward GSH by a factor of 200-fold or more relative to natural amino acids as well as homocysteine (Hcys) and glutathione disulfide (GSSG). The dynamic range of the sensor can be tuned simply by adjusting the amount of aggregation agent used.

Electrochemical sensing systems for arsenate estimation by oxidation of L-cysteine

In this study, rapid electrochemical sensing systems for detection of arsenate by oxidation of L-cysteine are proposed. Three different sensing systems comprising of screen-printed electrode and standard electrodes were used for this study. The detector element i.e. L-cysteine was immobilized on the working electrodes of the transducers by in-situ polymerization of acylamide. The electrocatalytic oxidation of L-cysteine was performed by cyclic voltammentry and amperometry. All the systems presented linear response range up to 30 microgL(-1) of arsenic. The sensors were able to estimate arsenic below 10 microgL(-1) with a detection limit of 1.2-4.6 microgL(-1).