A SERS aptasensor based on HCR mediated signal conversion strategy for the rapid and reliable determination of Escherichia coli O157:H7

Abstract

Rapid and reliable determination of pathogenic bacteria is crucial for food safety and public health. Surface-enhanced Raman spectroscopy (SERS) based aptasensors have attracted increasing attention in the determination of pathogenic bacteria due to their high specificity and sensitivity. However, the sensitivity and reliability of the SERS aptasensors for the determination of pathogens were hindered by the uneven distribution of SERS tags. To tackle this limitation, a SERS aptasensor based on a hybridization chain reaction (HCR) mediated signal conversion strategy was fabricated for the determination of E. coli O157:H7. In the presence of E. coli O157:H7, the blocked aptamer specifically binds with it and releases the blocker DNA. Then the blocker DNA hybridizes with the capture DNA on the SERS probe and initiates the HCR reaction, which further leads to the formation of double stranded DNA and the reduction of the SERS signal intensity of 4-mercaptobenzonitrile (4-MBN). Under the optimal conditions, the SERS signal intensity at 1073.9 cm−1 and the logarithmic value of the concentration of E. coli O157:H7 in the range of 8 × 102–8 × 107 CFU·mL−1 exhibited a good linear relationship, with a coefficient of determination of 0.92. The limit of detection for E. coli O157:H7 was 409 CFU·mL−1. Besides, this aptasensor exhibited satisfactory specificity for E. coli O157:H7. In addition, it showed excellent stability in real sample analysis with relative standard deviations (RSDs) below 3.76 % (n = 3). The established SERS aptasensor employed a HCR mediated signal conversion strategy and overcame the drawback of unevenly distribution of SERS tags in classical SERS aptasensors for the determination of pathogenic bacteria. This study offered a new reference for the rapid and reliable detection of pathogens with a portable Raman spectrometer.