Colorimetric sensor based on peroxidase-like activity of chitosan coated on magnetic nanoparticles for rapid detection of the total bacterial count in raw milk

Recently, frequent outbreaks of foodborne diseases have attracted increasing attention, and how to rapidly detect foodborne pathogens has also become an urgent issue. Herein, we reported the colorimetric sensor based on chitosan-coated magnetic nanoparticles (CS@MNPs) for rapidly broad-spectrum detection of the total bacterial count, whose color change can be visible to the naked eye without any other sophisticated instruments. CS@MNPs exhibited good capture ability (greater than 80%) for six model strains, including Escherichia coli O157:H7, Salmonella enterica serovar typhimurium, Staphylococcus aureus, Listeria monocytogenes, Bacillus cereus and Cronobacter sakazakii, due to their interaction with chitosan. Under optimized conditions, the colorimetric sensor showed a linear relationship of mixed bacteria within the concentration ranging from 2.30 × 10 to 2.30 × 10 CFU·mL in pure culture, and 8.50 × 10 to 8.50 × 10 CFU·mL in spiked raw milk within 15 min. Besides, compared with the traditional one, colorimetric method is a more rapid and efficient method that can be applied to the dairy industry to detect the total bacterial count. In our perception, the colorimetric sensor developed in this work provides a possibility for on-set detection of the total bacterial count in other research fields.