Flow-amperometric biosensor for respiratory toxins using myoglobin-adsorbed carbon-felt, based on an inhibitory effect on bioelectrocatalytic reduction of oxygen

Shield, Anchor, and Adhesive Roles of Methylene Blue in Tyrosinase Adsorbed on Carbon Felt for a Flow Injection Amperometric Enzyme Biosensor for Phenolic Substrates and Inhibitors

Methylene blue (MB) acted as a stabilizer for preventing surface-induced denaturation of tyrosinase (TYR) adsorbed on a carbon felt (CF) surface, which is based on shield and anchor roles preventing the unfavorable conformational change of TYR on the hydrophobic CF surface. Furthermore, MB acted as an effective adhesive for TYR immobilization on CF. The resulting TYR and MB coadsorbed CF (TYR/MB-CF) worked as an excellent working electrode unit in an electrochemical detector in a flow injection amperometric biosensor, which allowed highly sensitive consecutive determination of not only TYR substrates but also competitive inhibitors. Simultaneous adsorption of TYR and MB from their mixed solution was much useful as compared with step-wise separated adsorption of TYR on the MB-adsorbed CF, which suggests that the binding interaction of MB with TYR in the solution phase is important for this phenomenon. Fluorescence and UV-vis spectroscopy revealed that not only electrostatic forces between the cationic MB and anionic amino acid residues of TYR but also hydrophobic interactions via the phenothiazine ring of MB play a principal binding driving force of MB with TYR at the surface of the TYR molecules. Synchronous fluorescence, three-dimensional fluorescence, and circular dichroism (CD) spectroscopy clarified that the conformation and the secondary structure of TYR slightly changed upon the MB binding, implying that MB binding leads to the modification of the original intramolecular bonding in part.

Cyanide sensitivity in direct electron transfer-type bioelectrocatalysis by membrane-bound alcohol dehydrogenase from Gluconobacter oxydans

An overexpression system of membrane-bound alcohol dehydrogenase (ADH) from Gluconobacter oxydans was constructed to examine its bioelectrocatalytic characteristics. The effects of cyanide (CN-) addition on the kinetics of direct electron transfer (DET)-type bioelectrocatalysis by ADH were analyzed. CN- enhanced the bioelectrocatalytic activity, while the catalytic activity in the solution remained unchanged, even in the presence of CN-. Electrochemical methods and electron spin resonance spectroscopy showed the detailed electron transfer pathway in the DET-type bioelectrocatalysis by ADH. Briefly, ADH is suggested to communicate with an electrode via a CN--insensitive and H+-sensitive heme c in DET. These characteristics of ADH with respect to CN- suggest the involvement of ADH in CN--insensitive respiration in G. oxydans.

Biosensors in forensic analysis. A review

Forensic analysis is an important branch of modern Analytical Chemistry with many legal and socially relevant implications. Biosensors can play an important role as efficient tools in this field considering their well known advantages of sensitivity, selectivity, easy functioning, affordability and capability of miniaturization and automation. This article reviews the latest advances in the use of biosensors for forensic analysis. The different methodologies for the transduction of the produced biological events are considered and the applications to forensic toxicological analysis, classified by the nature of the target analytes, as well as those related with chemical and biological weapons critically commented. The article provides several Tables where the more relevant analytical characteristics of the selected reported methods are gathered.

Sensitive voltammetric and amperometric responses of respiratory toxins at hemin-adsorbed carbon-felt

A hemin [iron-Fe(III) protoporphyrin IX chloride] was adsorbed onto a carbon-felt (CF), which is a microelectrode ensemble of micro carbon fiber (ca. 7 microm diameter). The resulting hemin-adsorbed-CF (hemin-CF) showed a well-defined redox wave based on the hemin-Fe(III)/Fe(II) redox process with the formal potential of -0.225 V vs. Ag/AgCl in deoxygenated phosphate/citrate buffer solution (0.1 mol/L, pH 5.0). The apparent heterogenous electron transfer rate constant was estimated to be 8.6 sec(-1). In air-saturated electrolyte solution, the hemin-CF exhibited an excellent electrocatalytic activity for the reduction of dioxygen (O2). This activity was reversibly inhibited by respiratory toxins such as cyanide and azide, which bind sixth coordination position of iron active center of hemin. The electrocatalytic 02 reduction current at the hemin-CF was modulated by the toxins in a concentration-depending manner. Based on the relationship between the %inhibition and the toxin concentration, apparent inhibition constants of cyanide and azide were evaluated to be 4.52 and 1.98 micromol/L, respectively. When the hemin-CF was used as a working electrode unit of the CF-based electrochemical flow-through detector with air-saturated carrier, the injection of the azide induced peak-shape current responses, which allowed rapid and continuous flow-amperometric determination of azide with high sensitivity.