Fig. 4: Simultaneous detection of calcium and insulin in beta TC6 cells.

The microfluidic platform was first tested for GSIR under normoxic conditions at a single location without spatial oxygen gradients. Boluses of 1–3 mM glucose were injected into the aqueous reservoir during observation via microscopy for 25 min before flushing with Krebs–Ringer buffer to return to baseline. Intracellular calcium was monitored using Fura-2 AM dye, while insulin release was detected using the hydrogel assay. a Beta TC6 cells responded to glucose stimuli and demonstrated intracellular calcium flux, with 3 mM resulting in the highest Fura measurements. Here, Fura was sampled at 15 s intervals. At this sampling rate, cyclic oscillation was observed at the 3 mM concentration. However, at lower concentrations, the noise averaged out the oscillations. b The change in the Fura ratio from baseline to peak was plotted for the three concentrations. Significant increases were seen in 3 mM over 1 mM stimulation. c Corresponding fluorescence micrographs on the right show increased insulin detection with increasing glucose stimulation (scale bar denotes 100 µm). d Insulin release detected using the built-in sensor demonstrated significant increases at all concentrations. *p < 0.05, **p < 0.01, and ***p < 0.001