Real-time, label-free impedimetric monitoring of insulin secretion from three-dimensional stem cell-derived islets.

Functional assessment of insulin secretion is essential for the development and application of stem cell-derived β-cell products. Conventional glucose-stimulated insulin secretion (GSIS) assays rely on end-point, batch-averaged enzyme-linked immunosorbent assays (ELISA), limiting temporal resolution and masking functional heterogeneity at the level of individual islet-like clusters. Here, we present a label-free, non-invasive impedance spectroscopy-based approach for real-time monitoring of insulin secretion from individual stem cell-derived islets (SC-islets) cultured on microcavity microelectrode array (MEA) chips. Human induced pluripotent stem cells were differentiated into SC-islets and integrated into microcavity MEAs, enabling three-dimensional confinement and parallel electrical recordings. Impedance measurements during on-chip GSIS revealed characteristic glucose-responsive dynamics that correlated with insulin secretion quantified by ELISA and were suppressed by pharmacological inhibition. Impedance spectroscopy resolved functional responses at the level of individual SC-islets, uncovering cluster-to-cluster variability that was obscured by pooled secretion assays. High-density microcavity MEAs further enabled spatially resolved impedance measurements, revealing intra-cluster heterogeneity of insulin secretion. While impedance spectroscopy provides an indirect readout and glucose stimulation was applied as stepwise changes, this platform enables real-time, scalable, and cluster-resolved functional assessment of three-dimensional islet tissues. The approach establishes a foundation for functional screening of SC-islets, differentiation optimization, drug testing, and future potency assessment workflows.