Integration of a nanostructured dielectrophoretic device and a surface-enhanced Raman probe for highly sensitive rapid bacteria detection.

This work reports a synergistic approach to the concentration, detection and kinetic monitoring of pathogens through the integration of nanostructured dielectrophoresis (DEP) with nanotag-labelled Surface Enhanced Raman Spectroscopy (SERS). A nanoelectrode array made of embedded Vertically Aligned Carbon Nanofibers (VACNFs) at the bottom of a microfluidic chip was used to effectively capture and concentrate nanotag-labelled E. coli DHα5 cells into a 200 μm × 200 μm area on which a Raman laser probe was focused. The SERS nanotags were based on iron oxide-gold (IO-Au) core-shell nanoovals (NOVs) of ∼50 nm size, which were coated with a QSY21 Raman reporter and attached to E. coli through specific immunochemistry. The combination of the greatly enhanced Raman signal by the SERS nanotags and the effective DEP concentration significantly improved the detection limit and speed. The SERS signal was measured with both a confocal Raman microscope and a portable Raman probe during DEP capture, and was fully validated with fluorescence microscopy measurements under all DEP conditions. The SERS measurements were sensitive enough to detect a single bacterium. A concentration detection limit as low as 210 cfu ml(-1) using a portable Raman system was obtained with a DEP capture time of only ∼50 s. These results demonstrate the potential to develop a compact portable system for rapid and highly sensitive detection of specific pathogens. This system is reusable, requires minimum sample preparation, and is amenable to field applications.