Diazonium-based impedimetric aptasensor for the rapid label-free detection of Salmonella typhimurium in food sample

We report the development of a label-free impedimetric aptamer-based biosensor for S. typhimurium detection. The aptamer biosensor was fabricated by grafting a diazonium-supporting layer onto screen-printed carbon electrodes (SPEs), via electrochemical or chemical approaches, followed by chemical immobilisation of aminated-aptamer. FTIR-ATR, contact angle and electrochemical measurements were used to monitor the fabrication process. Results showed that electrochemical immobilisation of the diazonium-grafting layer allowed the formation of a denser aptamer layer, which resulted in higher sensitivity. The developed aptamer-biosensor responded linearly, on a logarithm scale, over the concentration range 1×101 to 1×108 CFU mL−1, with a limit of quantification (LOQ) of 1×101 CFU mL−1 and a limit of detection (LOD) of 6 CFU mL−1. Selectivity studies showed that the aptamer biosensor could discriminate S. typhimurium from 6 other model bacteria strains. Finally, recovery studies demonstrated its suitability for the detection of S. typhimurium in spiked (1×102, 1×104 and 1×106 CFU mL−1) apple juice samples.