Quantitative Assays on Endocrine Tissue Every Few Seconds using Droplet-Based Microfluidic Analog-to-Digital Converters
Christopher Easley,
C. Harry Knowles Professor,
Auburn University
The scale of microfluidic systems is well-matched to those of cellular systems, multi-cellular tissues, and even some small organisms. Ex vivo endocrine tissues—taken directly from animals such as mice—can be analyzed precisely and effectively with continuous flow microdevices. However, most micro-analytical systems to date have been limited to temporal resolutions in the 2-10 minute range. Our group has leveraged droplet-based microfluidics for rapid sampling of two ex vivo murine tissues (adipose tissue, pancreatic islets) with integrated on-chip assays to achieve sampling every few seconds, and these devices have been termed as microfluidic analog-to-digital converters (µADCs). Here, we use valve-automated droplet generators and salt-water electrode mergers to rapidly sample ex vivo endocrine tissues every few seconds, then quantitatively assay secreted metabolites within nanoliter droplets on-chip. Custom tissue-culture interfaces from 3D-printed templates allow proximal sampling into droplets with minimal dispersion. While continuous flow microfluidic sampling has been limited to temporal resolutions (Deltat) of about 2 minutes, our µADC devices have been validated with Deltat as low as 3.5 seconds. These novel tools have revealed new biological information on the dynamic functions of both adipose tissue (lipolytic oscillations) and pancreatic islets (acute incretin effects).
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