It is essential to monitor the long-term glucose concentration in the blood of diabetic patients, and glycated hemoglobin (HbA1c) has become one of the most prominent markers of glycemic control in diabetes. This study presents an on-chip biosensor for detecting HbA1c as a ratio to total hemoglobin (Hb) based on impedance measurement, which allows for a label-free low-volume sample. The ring-shaped interdigital electrodes were coated with the self-assembled monolayer (SAM) to immobilize the proteins and measure the impedance deviations. The roughness of the glass substrates was further improved by buffer oxide etchant (BOE), while distribution uniformity of the proteins was also improved and verified by fluorescent images. Various concentrations of Hb and HbA1c were measured via before-after impedance deviations. After the HbA1c separation process, the ratio of HbA1c to total Hb was measured by the differential capacitance (ΔC) of the proteins calculated from the equivalent circuit model. ΔC rises with the volume percent of HbA1c from 1% to 15% in 200 ng/μL Hb and 200 ng/μL HbA1c. The proposed detection method is very close to actual point-of-care diagnostics for diabetic patients, and features the advantages of low-cost and easy fabrication.
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