Aptamer-Based Glycated Albumin Sensor for Capacitive Spectroscopy

Glycated albumin (GA) is a candidate for glycemic indicator to control prediabetes, the half-life of which is about 2 weeks, which is neither too long nor too short, considering that there is no longer any need for daily fingerstick sampling but glucose levels can be controlled in a relatively short term. Its usefulness as a glycemic indicator must be widely recognized by developing a simple and miniaturized GA sensor for point-of-care testing (POCT) devices. In this study, we propose an aptamer-based capacitive electrode for electrochemical capacitance spectroscopy (ECS) to specifically detect GA in an enzyme-/antibody-free manner. As a component of the bioelectrical interface between the sample solution and the electrode, a densely packed capacitive polyaryl film coated on a gold electrode contributes to the detection of GA by the ECS method. In addition, the GA aptamer tethered onto the polyaryl-film-coated gold electrode is useful for not only specifically capturing GA but also inducing changes in the concentration of cations released from the cation/GA aptamer complexes by GA/GA aptamer binding. Also, hydrophilic poly(ethylene glycol) (PEG) coated on the polyaryl film electrode in parallel with the GA aptamer prevents interfering proteins such as human serum albumin (HSA) and immunoglobulin G (IgG) from nonspecifically absorbing on the polyaryl film electrode. Such a GA aptamer-based capacitive electrode produces significant signals of GA against HSA and IgG with the change in GA concentration (0.1, 1, and 10 mg/mL) detected by the ECS method. This indicates that the ECS method contributes to the evaluation of the GA level, which is based on the rate of glycation of albumin. Thus, a platform based on ECS measurement using the aptamer-based capacitive electrode is useful for protein analysis in an enzyme-/antibody-free manner.