A scalable digital microfluidic platform for automation of onsite testing of dairy samples

Abstract

Antibiotic residues are regulated in commercially produced milk, with elevated concentrations being harmful. Detection of these antibiotic residues in milk pose a significant challenge for supply chain stakeholders due to the industry standard practice of low-interval off-site laboratory testing. This practice poses risk of non-compliant milk going undetected during on-site milk collection. On-site microfluidic technologies with integrated optical sensors are positioned to mitigate this challenge using increased screening intervals. Droplet-based (digital) microfluidic systems show promise to provide highthroughput screening in dairy applications with integrated fluorescence spectroscopy technologies. However, conventional digital microfluidic systems are subject to biofouling from the protein and fat content within milk. In this work, a biofouling-resistant digital microfluidic platform is introduced. The digital microfluidic platform leverages advancements in parafilm layers, and is demonstrated with actuation of milk and water microdroplets. Electrowetting-based microdroplet actuation is achieved via scalable grid arrays of uniplanar printed surface electrodes in open and closed system configurations. For this array technology, a reconfigurable firmware is developed for user control of automated microdroplet actuation at up to three hundred volts using a graphical computer interface. An exposition of the microdroplet actuation performance is demonstrated and assessed through an optical system for closed-open feedback and positioning of microdroplets. This optical closed-loop allows the actuation velocity of microdroplets to be characterized for polydimethylsiloxane and parafilm dielectric layers, for both water and milk as a function of frequency and voltage. Scalability and automation of the microfluidic platform is discussed, and future integration of fluorescence spectroscopy is investigated.