Glycated albumin (GA) is an important glycemic control marker for diabetes mellitus. This study aimed to develop a highly sensitive disposable enzyme sensor strip for GA measurement by using an interdigitated electrode (IDE) as an electrode platform. The superior characteristics of IDE were demonstrated using one microelectrode of the IDE pair as the working electrode (WE) and the other as the counter electrode, and by measuring ferrocyanide/ferricyanide redox couple. The oxidation current was immediately reached at the steady state when the oxidation potential was applied to the WE. Then, an IDE enzyme sensor strip for GA measurement was prepared. The measurement of fructosyl lysine, the protease digestion product of GA, exhibited a high, steady current immediately after potential application, revealing the highly reproducible measurement. The sensitivity (2.8 nA µM−1) and the limit of detection (1.2 µM) obtained with IDE enzyme sensor strip were superior compared with our previously reported sensor using screen printed electrode. Two GA samples, 15 or 30% GA, corresponding to healthy and diabetic levels, respectively, were measured after protease digestion with high resolution. This study demonstrated that the application of an IDE will realize the development of highly sensitive disposable-type amperometric enzyme sensors with high reproducibility.
Currently available enzymatic methods for the measurement of glycated proteins utilize fructosyl amino acid/peptide oxidases (FAOXs/FPOXs) as sensing elements. FAOXs/FPOXs oxidize glycated amino acids or glycated dipeptides but they are not able to accept longer glycated peptides or intact glycated proteins as substrates. Therefore, pretreatment via proteolytic digestion is unavoidable with the current enzymatic methods, and there remains a need for simpler measurement methods for glycated proteins. In this study, in order to develop a novel sensing system for glycated albumin (GA), a marker for diabetes, with no requirement for proteolytic digestion, we created an electrochemical sensor based on fructosamine 6-kinase (FN6K) from Escherichia coli. Uniquely, FN6K can react directly with intact GA unlike FAOXs/FPOXs. The concentration of GA in samples was measured using a carbon-printed disposable electrode upon which FN6K as well as two additional enzymes, pyruvate kinase and pyruvate dehydrogenase were overlaid. A clear correlation between the response current and the concentration of GA was observed in the range of 20-100 µM GA, which is suitable for measurement of GA in diluted blood samples from both healthy individuals and patients with diabetes. The sensing system reported here could be applied to point-of-care-testing devices for measurement of glycated proteins.
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