Fast and accurate detection of microorganisms is of key importance in clinical analysis and in food and water quality monitoring. S. Typhimurium is responsible for about a third of all cases of foodborne diseases worldwide and its fast detection is of great importance for ensuring the safety of food stuffs. 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 key aspect of the process. Results showed that electrochemical immobilisation on the diazonium grafting layer allowed the formation of a denser aptamer layer, which resulted in higher sensitivity. The developed aptamer-biosensor responded linearly, in 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 the ability of the aptamer biosensor to discriminate S. Typhimurium from different 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.
