An on-site, highly specific immunosensor for Escherichia coli detection in field milk samples from mastitis-affected dairy cattle.

Bovine mastitis is the most economically important infectious disease in dairy industry, and Escherichia coli (E. coli) is one of the major causative pathogens. Rapid identification and quantitative detection of E. coli are of great importance for bovine mastitis control and milk quality monitoring. Capitalizing on dielectrophoresis and interphase capacitance sensing, we have developed an immunosensor for E. coli detection by modifying low cost commercial microelectrodes with an E. coli specific antibody. The limit of detection reaches as low as 775 cells/mL within a 15 s' response time, which can satisfy the requirement for on-site detection and field diagnosis of bovine mastitis. To demonstrate the sensor's specificity, tests against Staphylococcus aureus and Streptococcus uberis samples are performed showing negligible responses, and the selectivity is calculated to be 3063: 1. Furthermore, a simple pretreatment protocol is developed for on-site testing of raw milk, which only involves incubation, centrifugation and dilution steps. Then correct detection of E. coli is demonstrated for both artificially inoculated and infected field milk samples. This immunosensor and the corresponding protocol have advantages in speed, sensitivity, specificity, operability, and low cost, which make it highly promising for on-site pathogen detection of bovine mastitis.