Development of an electrochemical impedance spectroscopy immunosensor for insulin monitoring employing pyrroloquinoline quinone as an ingestible redox probe.

Contemporary electrochemical impedance spectroscopy (EIS)-based biosensors face limitations in their applicability for in vivo measurements, primarily due to the necessity of using a redox probe capable of undergoing oxidation and reduction reactions in solution. Although previous investigations have demonstrated the effectiveness of EIS-based biosensors in detecting various target analytes using potassium ferricyanide as a redox probe, its unsuitability for blood or serum measurements, attributed to its inherent toxicity, poses a significant challenge. In response to this challenge, our study adopted a unique approach, focusing on the use of ingestible materials, by exploring naturally occurring substances within the body, with a specific emphasis on pyrroloquinoline quinone (PQQ). Following an assessment of PQQ's electrochemical attributes, we conducted a comprehensive series of EIS measurements. This involved the thorough characterization of the sensor's evolution, starting from the bare electrode and progressing to the immobilization of antibodies. The sensor's performance was then evaluated through the quantification of insulin concentrations ranging from 1 pM to 100 nM. A single frequency was identified for insulin measurements, offering a pathway for potential in vivo applications by combining PQQ as a redox probe with EIS measurements. This innovative approach holds promise for advancing the field of in vivo biosensing based on the EIS method.