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Featured Application: Measurement of glycerol content for wine safety and quality. This paper describes the design and development of a novel electrochemical biosensor for measuring glycerol in wine. Our initial detailed studies were aimed at deducing the optimum conditions for biosensor operation by conducting hydrodynamic voltammetric and amperometric studies. The resulting voltammograms revealed a maximum electrocatalytic current at 0.0 V vs. Ag/AgCl, which we used for all further studies. We also examined the effect of pH (8–10) on the amperometric responses of different glycerol concentrations over a range of 0.04 to 0.20 mM. Based on our findings, we propose that pH 9 would be suitable as the supporting electrolyte for further studies with the amperometric biosensor. The biosensor was constructed by immobilising 10 units of GLDH and 660 μg NAD+ onto the MB-SPCE surface using glutaraldehyde (GLA) as a cross-linking agent. Calibration studies were performed with glycerol over the 1.0–7.5 mM concentration range. Chronoamperometry was the electrochemical technique chosen for this purpose as it is convenient and can be performed with only 100 μL of sample directly deposited onto the biosensor's surface. In the current study, we observed linear calibration plots with the above standard solutions using current measurements at a selection of sampling times along the chronoamperograms (30–340 s). We have evaluated the glycerol biosensor by carrying out an analysis of commercially available red wine. Overall, these findings will form a platform for the development of novel rapid technology for point-of-test evaluation of glycerol in the production and quality control of wine. [ABSTRACT FROM AUTHOR]

Featured Application: Measurement of polyunsaturated fatty acids for food safety and quality. This paper describes the design, development and characterisation of an electrochemical biosensor for the measurement of linoleic and α-linolenic acid, as representative free polyunsaturated fatty acids (PUFAs), that may be implicated in food safety and food quality. Initial cyclic voltammetric studies were performed with solutions that contained enzyme-generated hydroperoxides of the two PUFAs. These were examined with plain screen-printed carbon electrodes (SPCEs) and screen-printed carbon electrodes containing the electrocatalyst cobalt phthalocyanine (CoPC). The electrocatalytic oxidation peaks obtained with the latter occurred at potentials about 300 mV lower than the those obtained by direct oxidation with the plain SPCEs and were better defined; as these attributes would lead to better selectivity and sensitivity for fatty acid determinations, the CoPC-SPCEs were used in the fabrication of amperometric biosensors. The enzyme lipoxygenase (LOX) was immobilised on the surface of these devices using the crosslinking agent glutaraldehyde. These biosensors were optimised for the measurement of linoleic and α-linolenic acid using amperometry in stirred solution; the optimum conditions were deduced by studying the effect of enzyme loading, pH and temperature on the amperometric responses. These responses were examined over the concentration range 2.0 to 20 µM and the results indicated that the following conditions were optimal: LOX loading 15 units; pH 8.0; temperature 37 °C. Low concentration calibration studies were performed with the two PUFAs and it was shown that the steady state currents were linear between 0.2 and 10 µM for linoleic acid and 0.2 and 10 µM for α-linolenic acid; the detection limits were 24 and 100 nM, respectively. The precision (coefficient of variation, n = 6) was 5.3% for α-linoleic acid and 3.3% for linoleic acid, which were calculated from the steady state current following additions (n = 6) of 0.2 µM PUFA. These results demonstrate that the novel amperometric biosensor holds promise for determining whether foods contain acceptable levels of free fatty acids. [ABSTRACT FROM AUTHOR]

An electrocatalytic screen-printed sensor has been investigated for the measurement of the biologically important biomolecule vitamin B1 (thiamine) for the first time in food supplements. Under basic conditions, the vitamin was converted to its electrochemically active thiolate anion species. It was shown that an electrocatalytic oxidation reaction occurred with the screen-printed carbon electrode containing the mediator cobalt phthalocyanine (CoPC-SPCE). This had the advantage of producing an analytical response current at an operating potential of 0 V vs. Ag/AgCl compared to +0.34 V obtained with plain SPCEs. This resulted in improved selectivity and limit of detection. Detailed studies on the underlying mechanism occurring with the sensor are reported in this paper. A linear response was obtained between 0.1 and 20 µg mL−1, which was suitable for the quantification of the vitamin in two commercial products containing vitamin B1. The mean recovery for a multivitamin tablet with a declared content of 5 mg was 101% (coefficient of variation (CV) of 9.6%). A multivitamin drink, which had a much lower concentration of vitamin B1 (0.22 mg/100 mL), gave a mean recovery of 93.3% (CV 7.2%). These results indicate that our sensor holds promise for quality control of food supplements and other food types. [ABSTRACT FROM AUTHOR]