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Glucagon exhibits insulinotropic ability by activating cAMP through glucagon or glucagon-like peptide-1 (GLP-1) receptors. To investigate the mechanism of endogenous and exogenous glucagon on insulin release, we studied the receptor selectivity on pancreatic islet beta-cells by switching the glucose concentration from 20 mmol/L to 0 mmol/L. To measure the exact temporal relationship between glucagon and insulin release, we developed a quick, small volume, multi-channel polydimethylsiloxane (PDMS) microchip. At 0 mmol/L glucose, we observed an insulinotropic effect in both INS-1 cells and islets. Meanwhile, we observed a 63 ± 6.27 s delay of endogenous glucagon-induced insulin release. After treatment with glucagon and GLP-1 receptor antagonists, we found that endogenous glucagon utilized the glucagon receptor, whereas exogenous glucagon primarily utilized the GLP-1 receptor to promote insulin secretion. The microchip can also be used to describe the “glucagonocentric” vision of diabetes pathophysiology. Taken together, the insulinotropic mechanism of different receptors should be taken into account in clinical treatments.

Microfluidic devices on CD have benefited from the advantages of centrifugal pumping. To date, only channels in the radial direction have been used in these devices. In this work, we have designed numerous spiral channels on CD. Through a two-step assembly process, these spiral channels intersect with pre-immobilized radial DNA probe line to form an array of DNA that covers the whole CD surface. In our experiments, 96 radial channels were used for the first step of DNA probe immobilizations. Then, 96 spiral channels were used for the second step of hydrodynamic DNA sample hybridizations. The 96 × 96 intersections between the spiral channels and radial lines of DNA probes created a multi-sample–multi-probe array on a CD.

An ideal microchip for single-cell experiments should be able to allow us to culture cells, to select any desired single cell from a group, to retain the cell for convenient cellular signal detection, and to deliver any buffer or reagent directly to the cell at any time during continual detection and observation. Most importantly, any negative impact on the live cell should be minimized. To accomplish all these functions, we developed a three-dimensional liquid flow control concept and employed special liquid flow fields to manipulate and retain a single yeast cell freely in the chip. A zero-speed point was controlled to retain the cell for three-dimensional cell balancing and cell scanning. A dispersive flow delivered reagents at a high speed to very near the cell and provided them to the cell at a low speed. No force stronger than its gravitational force was exerted on the cell, which could be balanced on different positions on an arc-sloping wall, thus minimizing any negative impact on the cell due to strong liquid flows. Specifically, we demonstrate on-chip single-cell culture, cell wall removal, and reagent delivery. Subsequently, single-cell fluorescence detection was performed, and noise filtering and background correction were applied for data processing.

Using a three-dimensional flow control concept to manipulate and retain a single yeast cell in a microchip, we were able to study the kinetics of intracellular metabolism and calcium mobilization at the single-cell level, as stimulated by glucose and pH changes. As a model study, the fluorogenic substrate fluorescein diacetate (FDA) was chosen to study how the intracellular carboxylesterase metabolize it. A single yeast cell was first cultured in the microchip. Thereafter, under a constant concentration of FDA, influx of FDA into the yeast cell occurred and FDA was hydrolyzed or metabolized. It was found that changes in both pH and glucose stimulated the FDA metabolism in a yeast cell, and the stimuli can elicit multiple responses from the cell. Since it was carried out within the microchip, the whole experiment on one single yeast cell could last for as long as 10 h. The dormant cell, budding cell, and pretreated budding cell (in low-pH buffer) of yeast resulted in different responses. Experimental data provided details on the FDA metabolism at the single-cell level and revealed strong correlations between FDA metabolism and calcium mobilization. Furthermore, efflux of the FDA metabolite fluorescein could start spontaneously if there was glucose in the medium. The experiments on a single cell were of the "human cell conservation" style because the cell responded to the reagent changes implemented by the human researcher. A mathematical model was also developed to study the influx-hydrolysis-efflux processes of the FDA metabolism using single-cell fluorescent data. These long overdue single-cell experiments are now rendered possible using the three-dimensional flow control in the microchip.