Electrophoretically deposited carbon nanotubes as a novel support for electrogenerated silica–dehydrogenase bioelectrodes

Composite Silica-Based Films as Platforms for Electrochemical Sensors

Sol-gel-derived silica thin films generated onto electrode surfaces in the form of organic-inorganic hybrid coatings or other composite layers have found tremendous interest for being used as platforms for the development of electrochemical sensors and biosensors. After a brief description of the strategies applied to prepare such materials, and their interest as electrode modifier, this review will summarize the major advances made so far with composite silica-based films in electroanalysis. It will primarily focus on electrochemical sensors involving both non-ordered composite films and vertically oriented mesoporous membranes, the biosensors exploiting the concept of sol-gel bioencapsulation on electrode, the spectroelectrochemical sensors, and some others.

Electrochemical immobilization of glucose oxidase for the controlled production of H2O2 in a biocatalytic flow reactor

Electrochemical methods can be used to selectively modify the surfaces of electrodes, enabling the immobilisation of enzymes on defined areas on the surfaces of electrodes. Such selective immobilisation methods can be used to pattern catalysts on surfaces in a controlled manner. Using this approach, the selective patterning of the enzyme glucose oxidase on the electrodes was used to develop a flow reactor for the controlled delivery of the oxidant H₂O₂. GOx was immobilised on a glassy carbon electrode using polypyrrole, silica films, and diazonium linkers. The rate of production of H₂O₂ and the stability of the response was dependent on the immobilisation method. GOx encapsulated in polypyrrole was selected as the optimal method of immobilisation, with a rate of production of 91±11 μM h⁻¹ for 4 hours of continuous operation. The enzyme was subsequently immobilised on carbon rod electrodes (surface area of 5.76 cm²) using a polypyrrole/Nafion® film and incorporated into a flow reactor. The rate of production of H₂O₂ was 602±57 μM h⁻¹, with 100 % retention of activity after 7 h of continuous operation, demonstrating that such a system can be used to prepare H₂O₂ at continuous and stable rate for use in downstream oxidation reactions.

Blood sorbitol measurement in diabetic rats treated with an aldose reductase inhibitor using an improved fiber-optic sorbitol biosensor

Sorbitol is known as a biomarker for the evaluation of the progress of diabetic complications. We have developed a sorbitol biosensor using an optical fiber for rapid diagnosis and pathological evaluation of diabetic complications. In this paper, we measured blood sorbitol in diabetic rats using an improved biosensor, and discussed the effectiveness of the developed biosensor and the significance of sorbitol measurement. In order to investigate the effectiveness of the developed biosensor, the blood sorbitol level of type II diabetic rats prepared by streptozotocin administration was measured with the developed sensor. The values of sorbitol were highly correlated with the values measured by the F-kit of food analysis and that we confirmed the sorbitol concentration could be quantified using the developed biosensor. Furthermore, the aldose reductase inhibitor "eparlrestat", which is a therapeutic drug that suppresses the accumulation of sorbitol, was administered to diabetic rats, and the blood sorbitol level was measured with the developed biosensor. As a result, the blood glucose level was high in both the treated group and the non-treated group, but the blood sorbitol level in the treated group decreased. The results suggest that the measurement of the sorbitol level with the developed biosensor in addition to the blood glucose level enables evaluation of complications like diabetic neuropathy. In the future, we expected that the developed sorbitol biosensor will be miniaturized, the pretreatment method for blood samples will be simplified, and it will be applied to the development of therapeutic agents for diabetic complications and personalized medicine.

A fiber-optic sorbitol biosensor based on NADH fluorescence detection toward rapid diagnosis of diabetic complications

Accumulation of sorbitol in the tissue is known to cause microvascular diabetic complications. In this paper, a fiber-optic biosensor for sorbitol which is used as a biomarker of diabetic complications was developed and tested. The biosensor used a sorbitol dehydrogenase from microorganisms of the genus Flavimonas with high substrate specificity and detected the fluorescence of reduced nicotinamide adenine dinucleotide (NADH) by the enzymatic reaction. An ultraviolet light emitting diode (UV-LED) was used as the excitation light source of NADH. The fluorescence of NADH was detected using a spectrometer or a photomultiplier tube (PMT). The UV-LED and the photodetector were coupled using a Y-shaped optical fiber. In the experiment, an optical fiber probe with a sorbitol dehydrogenase immobilized membrane was placed in a cuvette filled with a phosphate buffer containing the oxidized form of nicotinamide adenine dinucleotide (NAD(+)). The changes in NADH fluorescence intensity were measured after adding a standard sorbitol solution. According to the experimental assessment, the calibration range of the sorbitol biosensor systems using a spectrometer and a PMT was 5.0-1000 μmol L(-1) and 1.0-1000 μmol L(-1), respectively. The sorbitol biosensor system using the sorbitol dehydrogenase from microorganisms of the genus Flavimonas has high selectivity and sensitivity compared with that from sheep liver. The sorbitol biosensor allows for point-of-care testing applications or daily health care tests for diabetes patients.

A review of production methods of carbon nanotube and graphene thin films for electrothermal applications

Electrothermal materials transform electric energy into heat due to the Joule effect. To date, resistive wires made of heavy metal alloys have primarily been used as the heat source in many appliances surrounding us. Recent discoveries in the field of carbon nanostructures revealed that they can offer a spectrum of advantages over the traditional materials. We review the production methods of thin films composed of carbon nanotubes or graphene and depict how they can be used as conductive coatings for electrothermal applications. We screen all reports from the field up to now and highlight the features of designed nanoheaters. A particular focus is placed on the analysis of general findings of how to tune their electrothermal properties, why carbon nanostructure devices operate the way they do and in what aspects they are superior to the currently available materials on the market.

Sol-gel Approaches for Elaboration of Polyol Dehydrogenase-Based Bioelectrodes

This review describes the input of sol-gel chemistry to the immobilization of polyol dehydrogenases on electrodes, for applications in bioelectrocatalysis. The polyol dehydrogenases are described and their application for biosensing, biofuel cell and electrosynthesis are briefly discussed. The immobilization of proteins via sol-gel approaches is described, including a discussion on the difficulty to maintain the activity of proteins in a silica matrix and the strategies developed to offer a proper environment to the proteins by developing optimal organic-inorganic hybrid materials. Finally, the co-immobilization of the NAD + co-factor and of mediators for the elaboration of reagentless devices is presented, based on published and original data. All-in-all, sol-gel approaches appear to be a very promising for development of original electrochemical applications involving dehydrogenases in near future.

Reagentless D-sorbitol biosensor based on D-sorbitol dehydrogenase immobilized in a sol-gel carbon nanotubes-poly(methylene green) composite

A reagentless D-sorbitol biosensor based on NAD-dependent D-sorbitol dehydrogenase (DSDH) immobilized in a sol-gel carbon nanotubes-poly(methylene green) composite has been developed. It was prepared by durably immobilizing the NAD(+) cofactor with DSDH in a sol-gel thin film on the surface of carbon nanotubes functionalized with poly(methylene green). This device enables selective determination of D-sorbitol at 0.2 V with a sensitivity of 8.7 μA mmol(-1) L cm(-2) and a detection limit of 0.11 mmol L(-1). Moreover, this biosensor has excellent operational stability upon continuous use in hydrodynamic conditions.