In flow metal-enhanced fluorescence for biolabelling and biodetection

Abstract

Escherichia colibacteria were determined by in flow cytometry with laser excitation and fluorescence detection applying ultraluminescent core-shell nanoparticles based on Metal Enhanced Fluorescence (MEF). Core-shell nanoparticles consisted of a 40 nm core modified with a silica spacer grafted with Rhodamine B (RhB). The electromagnetic field in the near field of the core surface enhanced the fluorescence of RhB by plasmonic and fluorophore coupling. The hydrophilic silica spacer allowed the non-covalent interaction with the polarE. colisurface and thus ultraluminescent bacteria biolabelling was developed. Clearly, well defined and bright bacteria imaging was recorded by Laser Fluorescence Microscopy based on the non-covalent deposition of the ultraluminescent nano-emitters. Using these nano-labellers, it was possible to detect labelledE. coliby in flow cytometry. Higher values of Side-scattered light (SSC) and Forward-scattered light (FSC), and number of fluorescent event detections, were observed for labelled bacteria compared to those non-labelled. The sensitivity of the methodology was evaluated by varying bacteria concentration and acceptable analytical figures of merit were determined. Applying this methodology we could quantifyE. colifrom a synthetic real sample of fortified water. Similar results were obtained by bacteria counting with Laser Fluorescence Microscopy and with a cell-bacteria counter.