Lab-on-a-Chip Surface Plasmon Resonance Biosensor for Multiplex Bioassays

This thesis titled “Lab-on-a-Chip Surface Plasmon Resonance Biosensor for Multiplex Bioassays��? describes new developments in the integration of an SPR imaging based biosensor and electrokinetic lab-on-a-chip. This research was aimed to develop a strategy to multiplex a bioassays in combination with high-throughput, which not only saves a huge amount of time, but also reduces the cost of such assays while performing multiple assays simultaneously. The major advantage of using electrokinetic driven fluidics instead of conventional pressure driven flow is to avoid complex plumbing network, valves and pumps, especially when large number of microchannels (n > 10) are used. This thesis describes a successful operation of a newly developed integrated biosensor system which needs a single voltage supply only. This thesis also explores the possibilities of measuring (multiple) biomolecular interaction kinetics in a different way compared to the conventional approaches, taking the advantage of the microarray integrated SPR imaging system. The initial focus was on the development of a microfluidic lab-on-a-chip with the goal to demonstrate the feasibility of integrating both the biosensor microarray and applying electrokinetic pumping in a single device. After the demonstration of such an integrated biosensor, some of the observed practical and technical problems were addressed. Eg. higher current flow in the interaction chamber leads to electrolysis reactions near the gold metal layer giving additional unwanted effects as bubble formation, etching of the gold, pH shifts etc. A solution was found to protect the gold film by a hydrogel/dextran coating as well as usage of low conductivity buffers. In a new design of the chip the large interaction chamber was changed to individual microchannels (four microchannels operated in parallel) for guiding the sample flow. The modified chip (electrokinetic lab-on-a-biochip) was demonstrated with various types of biomolecular interaction experiments which includes multi-ligand/multianalyte detection which is the core of the thesis. Kinetics and affinity of the model biomolecular interactant pair (human IgG – a-IgG) was extracted from the integrated biosensor and compared with the conventional approaches. Both were in very good agreement with each other. The device was further scaled-up to 12 channels in combination with up to 9 times multiplexing per channel, which were demonstrated with well known interactant pairs. A recommendation for future work prior to the implementation of this newly developed chip for biological applications (for eg. drug screening) is firstly changing the titanium adhesion layer for the gold film to tantalum which withstands higher currents and secondly replacing the PDMS/glass hybrid chips with full glass chips although a low temperature bonding technique has still to be developed. With the modifications as suggested, it should be possible to screen ~ 80-90 drugs simultaneously with the extraction of its kinetics parameters straightaway from the measured SPR responses. The new device could be of further interest for not only drug discovery applications, but it also opens up a new dimension in the development of analytical tools in various application areas to measure many biomolecular interactions in multiplex format and at high throughput.