Integration of functional components into microfluidic chemical systems: bioimmobilization and electrochemiluminescent detection on-chip

We have investigated and implemented several general strategies in the development of microfluidics-based chemical/biochemical sensing systems. The research in this dissertation covers the immobilization of biological reagents inside microfluidic channels using polystyrene (PS) microbeads and photopolymerizable hydrogel, electrochemical sensing via electrochemiluminescence (ECL) reporting with bipolar and two-electrode configurations, and integration of these general functions to realize multiplexing and networking on-chip. Photopolymerizable hydrogel based on Poly(ethylene glycol) (PEG) and streptavidin-coated polystyrene (PS) microbeads were employed as building blocks as well as functional components in microfluidic system. PEG hydrogels can be used to define local microenvironments at different locations in the same microchannel, which enables the introduction of multiple sensing events on the same device. Monitoring of DNA hybridization and enzyme/substrate interaction were realized thereafter by using either fluorescence or electrochemistry as the detection method. Electrogenerated chemiluminescence based on Ru(bpy)32+ (bpy = 2,2??-bipyridine) and tripropylamine (TPA) was used to photonically report various redox events in microfluidic systems. By using microfluidic electrochemical cells based on either two-electrode or bipolar electrode (one-electrode), electroactive species that undergo reduction can be electrically linked to this anodic ECL process and thus be reported by the latter. This ECL sensing scheme essentially broadens the spectrum of redox compounds that can be detected by ECL since the analytes are not required to directly participate into the light-generating processes. Microfluidics offers some unique technical advantages of performing electrochemistry over conventional methods. In particular, laminar flow allows multiple analyte streams to be brought together in parallel with little mixing. Moreover, electrochemical signals can be generally utilized as a convenient means to link individual microchannels together hence to realize microfluidic networking and cross-communication. Electrochemical microfluidic devices can be used to mimic general functions of microelectronic devices such as diodes, transistors, and logic gates. These novel functions rendered by electrochemistry are believed to bring us closer to the final goals of micro total analysis systems and lab-on-a-chip.