A general purpose programmable microfluidic platform for screening and optimization of biological assays
Screening is a fundamental process in today’s medicine and clinical diagnostics, comprising of several processes ranging from finding new target molecules having the desired therapeutic potential to identifying biomarkers for accurate diagnosis of a spectrum of diseases. Current high throughput screening (HTS) platforms leverage sophisticated robotics to perform a large number of experiments very quickly, an otherwise unmanageable task with manual labor. However, these systems are capital intensive which limit their use to large pharmaceutical companies or larger research labs. Additionally, reagent consumption is of the order of 10-100 µL per assay, which leads to substantial consumables cost. Recently proposed droplet microfluidic technologies have the potential to substantially reduce assay costs by performing reactions using nanoliter volumes at very rapid rates. However, their incorporation into screening workflows is limited owing to various technological challenges such as on-chip droplet storage for long incubation assays, fluid waste due to large dead volumes, lack of programmable control over individual assay droplets, etc.^ To address aforementioned problems, three novel microfluidic designs are proposed in this work which not only facilitates assay miniaturization but also enable extraction of high information content, compared to the existing methodologies. First, an on-demand droplet generator is developed which enables complete spatiotemporal control over individual droplets. It consists of programmable on-chip pumps that convert pipetted samples into nanoliter sized droplets surrounded by an immiscible oil phase, each of which can be used as an independent reaction chamber. The design enables variable volume mixing of multiple droplets and long term droplet storage inside the microfluidic chip, making it an excellent candidate for pharmaceutical co-crystal screenings. Second, an on-chip droplet dilution scheme is developed which generates a train of droplets with a tunable concentration gradient, a feature highly desired for high definition profiling of pharmaceutical drug molecules. Finally, a microfluidic device is developed for delivering nanoliter quantities of reagents over paraffin embedded tissue sections mounted on microscopic slides. This attribute demonstrates the feasibility of programmable microfluidics for seamless integration within tissue diagnostics workflow for biomarker discovery.^
Steven T. Wereley, Purdue University.