Increasing insulin measurement throughput by fluorescence anisotropy imaging immunoassays

Insulin secreted from islets of Langerhans is the main hormone to reduce blood glucose. Examination of insulin secretion patterns at the single islet level reveals functional differences in the timings and patterns of release. This heterogeneous response highlights the importance of developing systems to measure dynamic release from small numbers of islets in parallel. Toward this, we describe fluorescence anisotropy imaging immunoassays as a relatively simple method for increased throughput of islet secretion measurements. In this system, vacuum pressure from a syringe pump pulled perfusate from 12 islet chambers and reagents into 12 parallel mixing channels for a competitive immunoassay. Light from a Xe arc lamp was filtered and polarized prior to focusing on the microfluidic device at the region where the 12 mixing channels converged. Emission was collected and passed through vertical and horizontal emission polarizers housed in an automated filter wheel before being imaged with a sCMOS camera for the determination of anisotropy. This microfluidic system was tested by monitoring insulin release from groups of murine and human islets. Heterogeneity was observed in the islet traces; however, the presence of islets affected the resistance of the islet chambers, hampering insulin quantification. Nonetheless, this microfluidic system is a step towards increasing the throughput of hormone release measurements from islets of Langerhans.