A single cell droplet microfluidic system for quantitative determination of food-borne pathogens

Single-cell detection methods are already of great significance for many bioanalysis applications, and droplet microfluidics technology is understood as particularly a powerful tool. Salmonella infection is a major hygienic problem worldwide that causes major public health and economic damage, and preventing Salmonella outbreaks requires detection food-borne detection methods that are rapid, portable, and reliable, ideally without the need for complicated pre-treatment protocol steps. Herein, we present a single-cell-level analysis method based on droplet microfluidics that can sensitively and rapidly detect Salmonella directly from food samples. Specifically, this method achieves single-cell encapsulation of Salmonella in droplets of a growth medium with resazurin that enables fluorescence-based detection of pathogens within 5 h. The ratio of positive droplets in a Poisson Distribution is used for quantitation, and the detection limit of our system determined to be 50 CFU/mL, a value lower than conventional analytical methods for assessing Salmonella contamination. Our experimental results demonstrate the precise and highly sensitive performance of a single-cell-precision, droplet-based microfluidic chip analytical method for monitoring pathogenic bacteria in food. Beyond our example case of Salmonella detection from milk samples, our work lays the foundation for a new generation of microfluidics-based analytical technologies for both public health and food safety applications which can undoubtedly benefit from increases in the sensitivity and rapidity of food-borne pathogen detection.