A multifunctional micro-fluidic system for dielectrophoretic concentration coupled with immuno-capture of low numbers of Listeria monocytogenes

In this study, we demonstrated a micro-fluidic system with multiple functions, including concentration of bacteria using dielectrophoresis (DEP) and selective capture using antibody recognition, resulting in a high capture efficiency of bacterial cells. The device consisted of an array of oxide covered interdigitated electrodes on a flat silicon substrate and a similar to 16 mu m high and similar to 260 mu m wide micro-channel within a PDMS cover. For selective capture of Listeria monocytogenes from the samples, the channel surface was functionalized with a biotinylated BSA streptavidin-biotinylated monoclonal antibody sandwich structure. Positive DEP (at 20 V-pp and 1 MHz) was used to concentrate bacterial cells from the fluid flow. DEP could collect similar to 90% of the cells in a continuous flow at a flow rate of 0.2 mu l min(-1) into the micro-channel with concentration factors between 10(2)-10(3), in sample volumes of 5-20 mu l. A high flow rate of 0.6 mu l min(-1) reduced the DEP capture efficiency to similar to 65%. Positive DEP attracts cells to the edges of the electrodes where the field gradient is the highest. Cells concentrated by DEP were captured by the antibodies immobilized on the channel surface with efficiencies of 18 to 27% with bacterial cell numbers ranging from 10(1) to 10(3) cells. It was found that DEP operation in our experiments did not cause any irreversible damage to bacterial cells in terms of cell viability. In addition, increased antigen expression ( antigens to C11E9 monoclonal antibody) on cell membranes was observed following the exposure to DEP.