Fast, Tiny, Bioanalytical Tools for Dynamic Studies of Endocrine Tissue Function Seminar

Pancreatic islets secrete the dominant endocrine hormone, insulin, which controls the metabolic function of nearly all other organ systems. Additionally, adipose tissue (fat) is now understood to be a complex, multicellular endocrine organ with similarly profound, systemic effects. In studies of obesity, diabetes, and metabolic syndrome, there has been a renewed interest in insulin secretion and adipose tissue dynamics in response to various nutrients and hormones. However, using standard approaches, we unfortunately have a limited view of the temporal relationships between important players—glucose, gut hormones, insulin, various adipokines—which points to a need for better methodology that can interface with the cells and tissues of interest. In this work, we present microfluidic approaches that can meet these needs, particularly when combined with our customizable, mix-and-read immunoassay platforms using fluorescence and electrochemistry.

Microfluidic systems have been shown to provide exquisite volumetric and temporal control, and recent breakthroughs in organ-on-a-chip platforms reveal the scale and operation in these systems to be well-matched with organized biological tissues. Until now, the development of compatible, simple-readout protein assays has lagged behind these fluidic advancements. Our group has developed several versions of DNA-driven proximity immunoassays that are well-matched with microfluidic sampling volumes, i.e. the picoliter to nanoliter scale.  Using thermofluorimetric analysis (TFA) or electrochemical proximity assays (ECPA), antibody-oligonucleotide conjugates can be applied for generalizable, small-volume protein quantification in the attomoles range, often with a mix-and-read workflow. These assay formats were combined with droplet microfluidics, precisely controlled by on-chip valving, to permit less than five-second temporal resolution on secretions from single pancreatic islets or adipose tissue explants extracted from mice. In these first-of-their-kind measurements, the high-resolution sampling has revealed rapid oscillations in insulin secretion from islets—an expected result—but also in lipolysis and hormone secretion from adipose tissue. Overall, these results show that our microanalytical systems, combined with small-volume compatible assays, should provide the means to further improve our understanding of the dynamics of endocrine biology.