Detection of E. coli using SERS active filters with silver nanorod array

Silver nanorod (AgNR) arrays fabricated by oblique angle deposition technique has been demonstrated as a highly reproducible and sensitive substrate for intrinsic surface-enhanced Raman spectroscopy (SERS) detection of various types of small molecules, but its application in bacterial detection has been largely limited due to low sensitivity. In this study, we introduce a new type of AgNR substrates based on filter membranes for potential improvements in assay sensitivity. AgNRs are successfully deposited on the smooth surface of Anodisc and GA-8 filters (pore size = 0.2 μm), and the resultant AgNR filter substrates are used for pre-concentration of bacterial cells and subsequent on-chip SERS detection. With such AgNR filters, improved bacterial SERS signal is observed with the increase of sample volume, and the limit of detection (LOD) for Escherichia coli is reduced by at least two orders of magnitude compared with the standard glass AgNR substrates after 10 mL of samples are concentrated and dried on the filter for 10-20 min. Lower LODs could potentially be achieved by adopting larger sample volumes or further improvements in the surface morphology of the filter substrates.