An integrated digital microfluidic electrochemical impedimetric lipopolysaccharide sensor based on toll-like receptor-4 protein

The spread of infectious diseases poses a global threat to human health and the economy. Conventional laboratory-based pathogen detection analytical techniques are reliable, but are labour and time consuming. Decentralized, rapid pathogen detection and classification devices are essential to boost biosecurity efforts and can aid in the advancement of modern medicine. Here, we describe the development of an integrated digital microfluidic (DMF) electrochemical impedimetric sensor for rapid and on-site detection of lipopolysaccharide (LPS), a molecular signature of Gram-negative bacteria. The sensor was fabricated by immobilizing toll-like receptor protein (TLR4) onto a gold sensing electrode that was fabricated on an indium tin oxide (ITO) DMF top plate. The top plate also housed lithographically patterned ITO pseudo-reference and auxiliary electrodes for a three-electrode electrochemical impedance (EIS) detection system. We exploited the unique feature of DMF to manipulate droplets consisting of samples, buffers, wash solutions and reagents to perform automated EIS measurements due to the interaction of TLR4 with LPS. The integrated sensor platform showed a detection limit of 35 ng/mL LPS and a linear range of up to 400 ng/mL. The small size and ease of operation of the integrated system holds great prospect for the development of portable, and automated generic pathogen detection and classification platform for point-of-need applications.