Fabrication and performance of monodisperse liquid crystal droplet-based microchips for the on-chip detection of bile acids

Liquid crystal (LC) droplets have been widely used in the detection of chemical and biological species due to their large surface area-to-volume ratio and stimuli-responsive configuration transitions. However, the wide size distribution and high mobility of LC droplets in current LC droplet-based platforms have limited their real-time and quantitative detection applications. Here, we report a novel monodisperse LC droplet-based polydimethylsiloxane (PDMS) microchip, in which monodisperse LC droplets are in situ generated and trapped on a single microfluidic device. A flow-focusing element and a hydrodynamic-based microstructure are designed for the generation and entrapment of monodisperse LC droplets, respectively. This miniatured monodisperse LC droplet-based microchip containing a fixed number of monodisperse LC droplets allows us to quantitatively and rapidly (<4 min) detect bile acids in real time by monitoring the collapse of LC droplets under a polarized optical microscope with small sample consumption (~1.5 μL). The detection limits for cholic acid and deoxycholic acid are 10 μM and 1 μM, respectively. This study provides a way to develop simple and portable LC droplet-based sensing devices for the quantitative, rapid and real-time detection applications.