DEVELOPMENT OF ACCELERATED BACTERIAL COLLECTION AND DETECTION (ABCD) PLATFORMS USING AC ELECTROKINETICS
MEMS, AC Electrokinetics, Biosensor, Microconcentrator, Microcantilever
Real-time detection of low concentrations of bacteria is essential in health and environmental monitoring, and biosensors are promising tools for this. However, the limited number of analytes and the time required for diffusion and Brownian motion to transport them to the sensing surface highlight the importance of using particle concentration. Particle concentration could be done during the pre-sensing sample preparation and/or by accelerating the analytes' movement towards the sensing surface and locally concentrating them there. In this thesis, individual components were designed and developed based on AC electrokinetics for both pre-sensing and local concentration of particles. Particles were concentrated inside microchannels as pre-sensing particle enrichment in two designed platforms. A coil embedded in a PDMS channel is one novel design. Particles are pushed to the centre of the channel by dielectrophoresis force when electric potentials are applied to the wires that make up the coil. The other design consists of two coplanar asymmetric electrodes on the walls of a microchannel, and a floating potential electrode is placed at the bottom of the channel. By using AC electrothermal and dielectrophoresis effects, this design concentrates the particles in the channel's centre. Furthermore, gap method microcantilever biosensors were used to detect E. coli and P. aeruginosa bacteria in water in real time and with high sensitivity. In this method, a fixed structure connected to an AC signal is placed near the free end of a vibrating microcantilever that is grounded. We developed this technique by making longer and thinner gaps between the free end of the cantilever and the fixed structure. The goal was to expand the area where dielectrophoresis is effective and to strengthen this force by making the gap thinner. Based on this, two designs were created: a V-shaped and a rectangular microcantilever. In this thesis, detection of 10 cells/mL was achieved in a 7-min period. The developed microcantilever biosensors offer real-time, sensitive, low-noise, and repeatable biosensing with a very low limit of detection (1–9 cells/mL). Moreover, experiments investigated functionalizing the gap method microcantilever biosensor's surface to enhance specificity.