Ultrasensitive biosensing pathogenic bacteria by combining aptamer-induced catalysed hairpin assembly circle amplification with microchip electrophoresis

Because foodborne pathogenic bacteria are in a great variety and may cause many infectious diseases even at low concentrations, a highly sensitive and selective method has long-been desired for bacteria detection. In this study, a microchip electrophoretic method for biosensing E. coli O157:H7 was developed by using E. coli O157:H7 aptamer (apt-E) for specific bacteria recognition together with aptamer-induced catalysed hairpin assembly (CHA) for significantly improving the sensitivity of bacteria detection. Briefly, three nucleic acid strands (apt-E, hairpin H1, and H2) were used in the CHA amplification. Because different quantities of H1/H2 complexes were formed due to the circle amplification induced with different amounts of apt-E and the correlation between the concentrations of apt-E and E. coli O157:H7, E. coli O157:H7 thus could be quantified by the detection of H1/H2 complexes with microchip electrophoresis (MCE). Under the optimal conditions, the limit of detection was 75 CFU mL⁻¹. This method was also applied to detect E. coli O157:H7 in defatted milk with a satisfying recovery rate. The proposed strategy for E. coli O157:H7 detection is label-free, enzyme-free, ultra-sensitive, and cost-effective. It is also practical and could be applied to detect other bacteria in food samples.