Abstract

An Automated Digital Microfluidic Platform Integrated with Electrochemical Biosensor to Detect Circulating PD-L1 in Extracellular Vesicle and Soluble Forms

Yuqian Zhang, Postdoctoral Research Fellow, Mayo Clinic

PD1/PD-L1 immune checkpoint inhibitors are at the forefront of cancer immunotherapy. However, the overall response remains low; among many initial responders, drug resistance develops. Closely monitoring patients’ responsiveness is vital to prompt personalized therapies. Circulating PD-L1 molecules are increasingly recognized as a non-invasive key indicator of therapeutic responsiveness, whether in extracellular vesicle (EV) or soluble forms. Conventional methods to measure PD-L1 molecules involve ultracentrifugation to separate EVs and soluble PD-L1 (sPD-L1) and detect them with ELISA. These are tedious processes that require trained technologists in centralized facilities. Therefore, we develop a proof-of-concept digital microfluidic (DMF) device integrated with electrochemical biosensors to separate EVs directly from biofluids (culture media at this stage), and quantify PD-L1-positive EVs and sPD-L1 automatedly. In this device, EVs are captured by immunomagnetic beads, and the PD-L1 expression level are quantified with the electrochemical sensor < 2 hours. Meanwhile, sPD-L1 is detected by functionalizing a reduced graphene oxide-based 3D matrix structure on the sensor surface to increase binding sites. We dynamically incubate the sample by continuously moving the droplets, enabling detection sensitivity as low as 1 pg/mL. The integrated system is portable and automated, which makes it suitable for monitoring their dynamic changes regularly.