(213a) Immunoassay Sensors for Pathogen Detection Based on Ac Dielectrophoresis and Self-Assembly of Carbon Nanotubes

Carbon nanotubes, with extra-ordinary dielectrical properties, are integrated into a new electro-kinetic platform for bacteria detection. Because of their extremely small size and high aspect ratio, nanotubes exhibit high induced-dipole moments and large dielectrophoretic (DEP) mobility in an AC field. They hence self-assemble and transport rapidly to the high field regions on a diagnostic kit. These features are exploited to capture and concentrate small numbers of bacteria and other pathogens in a dilute sample. In our earlier work (Electrophoresis, 27(7), 1376-1385 (2006)), this design with single-wall nanotubes (SWNT) has been shown to reduce the transport time of the pathogen to the sensor by several orders of magnitude. In this report, we inject selectivity to our nanotube-enhanced DEP bacteria trap with anti-body functionalized gold electrodes sensors. The current design can rapidly (<10 minutes) capture and detect low numbers of bacteria (<10000 cells/ml) and sub-micron bioparticles. Concentrated SWNT solutions are mixed with the sample and a high-frequency AC field, with frequencies higher than the inverse RC time of a typical SWNT bundle, is applied by a micro-electrode array to enhance bulk docking between SWNT and the particles (bacteria or nanoparticle substitutes) by dipole-dipole interaction and by DEP. The conducting SWNT produces a high-field region around each suspended nanotube that can attract nearby bacteria that suffer positive DEP. The concentrated SWNT represents a much smaller diffusion length (by a factor of 1000) than the sample dimension. Moreover, DEP motion due to field concentration by SWNT increases the bacteria mobility by a factor of 10. As a result, the transport time to the electrode array, which drives the bulk docking and transportation as well as an electrode sensor, is reduced by four orders of magnitude. Within minutes, bacteria will be transported towards and trapped on the surface of the microelectrode arrays on which specific antibodies have been functionalized. The assembled SWNT disperse away when the field is turned off but bacteria that docked with the antibodies remain on the electrode surface and can be detected by the electrode sensor via impedance spectroscopic techniques with a subsequent frequency scan. The above electrokinetic strategy that exploits the high AC polarizability of SWNTs, leading to fast DEP capture and transport of the bacteria, and the reduced diffusion distance between bacteria and their SWNT transporters can hence achieve specific and rapid bacteria detection with the same electrode array on a chip.