Electrochemical aptasensor for Staphylococcus aureus by stepwise signal amplification.

An electrochemical aptasensor for ultrasensitive detection of Staphylococcus aureus (SA) has been developed based on stepwise signal amplification. In the sample processing stage, the specific recognition between SA and aptamer triggers the enzyme-assisted cyclic cleavage to produce a large amount of target DNA (tDNA), realizing the first-level signal amplification. In the sensor assembly stage, tDNA induces a catalytic hairpin assembly (CHA) cycle to capture much more hairpin DNA H2 labeled by the electrochemical tag ferrocene, bringing the second-level signal amplification. In the signal detection stage, ferrocene is quasi-adsorbed on the electrode surface, and a high redox peak current linearly increasing with the scan rate up to 1000 V/s has been obtained by fast scan cyclic voltammetry (FSCV), achieving the third-level signal amplification. Under the optimized experimental conditions, the linear range and detection limit are 1 ~ 10 8  CFU/mL and 0.3 CFU/mL, respectively. The sensor has good reproducibility, stability, and sensitivity, affording practical sample detection. This detection principle is widely applicable to other pathogens, and provides a new path for the establishment of highly sensitive detection strategies.