Development of electrochemical Zn²⁺ sensors for rapid voltammetric detection of glucose-stimulated insulin release from pancreatic ?-cells

Diabetes is a chronic disease characterized by elevated blood glucose levels resulting from absent or ineffective insulin release from pancreatic ss-cells. ss-cell function is routinely assessed in vitro using static or dynamic glucose-stimulated insulin secretion (GSIS) assays followed by insulin quantification via time-consuming, costly enzyme-linked immunosorbent assays (ELISA). In this study, we developed a highly sensitive electrochemical sensor for zinc (Zn2+), an ion co-released with insulin, as a rapid and low-cost method for measuring dynamic insulin release. Different modifications to glassy carbon electrodes (GCE) were evaluated to develop a sensor that detects physiological Zn2+ concentrations while operating within a biological Krebs Ringer Buffer (KRB) medium (pH 7.2). Electrodeposition of bismuth and indium improved Zn2+ sensitivity and limit of detection (LOD), and a Nafion coating improved selectivity. Using anodic stripping voltammetry (ASV) with a pre-concentration time of 6 min, we achieved a LOD of 2.3 mu g/L over the wide linear range of 2.5-500 mu g/L Zn2+. Sensor performance improved with 10-min pre-concentration, resulting in increased sensitivity, lower LOD (0.18 mu g/L), and a bilinear response over the range of 0.25-10 mu g/L Zn2+. We further characterized the physicochemical properties of the Zn2+ sensor using scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Finally, we demonstrated the sensor's capability to measure Zn2+ release from glucose-stimulated INS-1 ss-cells and primary mouse islets. Our results exhibited a high correlation with secreted insulin and validated the sensor's potential as a rapid alternative to conventional two-step GSIS plus ELISA methods.