No abstract

Electrochemically polymerised riboflavin (PRf) film was applied in development of glutamate and hypoxanthine biosensors using appropriate oxidases as recognition elements. PRf served as an enzyme immobilisation matrix composed of natural monomer and as a redox mediator. The PRf film was deposited on glassy carbon electrode (GCE) or on the laser‐designed microstructures of the chitosan‐graphene oxide (Chit‐GO) film deposited on glass slide, which served as a chip sensor. The redox polymer was stable and efficient mediator, however, Chit‐GO was placed on the top of PRf/GCE in order to increase the response signal. Such an approach allowed to extend the stability of glutamate and hypoxanthine biosensors to at least 1 month and 15 days, respectively. The chip microelectrode was a single use disposable biosensor due to insufficiently good Chit‐GO adhesion on the top of the cover‐glass. The glutamate microbiosensor had extremely high sensitivity of 16 μA cm−2 μmol L−1.

The melt of H3BO3 was used to reach a controllable reduced graphene oxide (rGO) synthesis protocol using a graphene oxide (GO) precursor. Thermogravimetric analysis and differential scanning calorimetry (TG/DSC) investigation and scanning electron microscopy (SEM) images have shown that different from GO powder, reduction of GO in the melt of H3BO3 leads to the formation of less disordered structure of basal graphene planes. Threefold coordinated boron atom acts as a scavenger of oxygen atoms during the process of GO reduction. Fourier-transform infrared (FTIR) spectra of synthesized products have shown that the complex of glycerol and H3BO3 acts as a regioselective catalyst in epoxide ring-opening reaction and suppress the formation of ketone C=O functional groups at vacancy sites. Thermal treatment at 800 °C leads to the increased concentration of point defects in the backbone structure of rGO. Synthesized materials were tested electrochemically. The electrochemical performance of these materials essentially differs depending on the preparation protocol. The highest charge/discharge rate and double-layer capacitance were found for a sample synthesized in the melt of H3BO3 in the presence of glycerol and treated at 800 °C. The effect of optimal porosity and high electrical conductivity on the electrochemical performance of prepared materials also were studied.

Folic acid was polymerised electrochemically at a glassy carbon electrode surface from 0.1 mol L−1 phosphate buffer saline solution, pH 5.0, containing 0.1 mmol L−1 monomer. The obtained thin film was porous with a pore size of 50–60 nm. Since its electrochemical stability was rather short, the polyfolate film was covered with a graphene‐chitosan composite layer which increased its stability significantly. The best strategy to immobilise the enzyme was crosslinking with glutaraldehyde. The lifetime of this glucose biosensor in use was at least 12 days, on‐shelf life time was at least 30 days. The linear range was up to 1 mmol L−1 and the LOD was 0.6 µmol L−1. The first polyfolate‐based biosensor was applied to analysis of natural samples.

No abstract