Scalable static droplet array for biochemical assays based on concentration gradients

Abstract

Many important biological assays demand rapid and low-cost screening systems. In this study, we present a scalable static droplet array (SDA) that can generate a high-resolution concentration gradient. The system consists of discrete sample dispensing channels, array units, and microvalves for droplet generation and droplet storage. We utilize negative pressure on a suction valve located below array chambers to enhance the capacity of droplet filling. The size of the droplets is controlled by valve actuation time, and array chambers can contain up to 32 droplets with a 20-millisecond valve actuation time. We present various profiles of concentration gradients generated by the combined storage of binary concentrations of droplets. As a proof of concept, we performed an enzymatic inhibition assay for validating our system with IC50 and the Hill coefficient using β–galactosidase (β-gal), di(β-d-galactopyranoside) (FDG) and 2-Phenylethyl β-d-thiogalactoside (PETG), and achieved an IC50 value of 2.18 μM and a Hill coefficient of 1.11, which agrees well with results in the literature. We anticipate that this system will serve as a general assay platform that is capable of high-throughput screening for various biological assays and imaging.