Nanogap traps for passive bacteria concentration and single-point confocal Raman spectroscopy

A microfluidic device enabling the isolation and concentration of bacteria for analysis by confocal Raman spectroscopy is presented. The glass-on-silicon device employs a tapered chamber surrounded by a 500 nm gap that serves to concentrate cells at the chamber apex during sample perfusion. The sub-micrometer gap retains bacteria by size exclusion while allowing smaller contaminants to pass unimpeded. Concentrating bacteria within the fixed volume enables the use of single-point confocal Raman detection for the rapid acquisition of spectral signatures for bacteria identification. The technology is evaluated for the analysis of E. cloacae, K. pneumoniae, and C. diphtheriae, with automated peak extraction yielding distinct spectral fingerprints for each pathogen at a concentration of 10(3) CFU/ml that compare favorably with spectra obtained from significantly higher concentration reference samples evaluated by conventional confocal Raman analysis. The nanogap technology offers a simple, robust, and passive approach to concentrating bacteria from dilute samples into well-defined optical detection volumes, enabling rapid and sensitive confocal Raman detection for label-free identification of focused cells.

Automated summary

This paper presents a microfluidic device that enables the isolation and concentration of bacteria for analysis using confocal Raman spectroscopy. The device utilizes a glass-on-silicon structure with a tapered chamber and a surrounding nanogap to concentrate cells at the chamber apex during sample perfusion. The nanogap retains bacteria by size exclusion while allowing smaller contaminants to pass through. Concentrating bacteria within a fixed volume enables the use of single-point confocal Raman detection for rapid spectral analysis and identification. The technology was evaluated for the analysis of three pathogens, showing promising results for label-free bacteria identification.