Fast and accurate detection of microorganisms is of key importance in clinical analysis and in food and water quality monitoring. Salmonella typhimurium is responsible for about a third of all cases of foodborne diseases and consequently, its fast detection is of great importance for ensuring the safety of foodstuffs. 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 × 10(1) to 1 × 10(8)CFU mL(-1), with a limit of quantification (LOQ) of 1 × 10(1) 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 × 10(2), 1 × 10(4) and 1 × 10(6) CFU mL(-1)) apple juice samples.

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We designed an electrochemical platform by modifying a carbon paste electrode (CPE) with platinum nanoparticles to study the interaction between ketamine and the G‐quadruplex structure of human telomeric DNA (G4HTD). The drug ketamine (Kt) was used as the model ligand and its ability for stabilizing the G‐quadruplex structure was examined. The modified CPE (NPtCPE) was characterized by differential pulse voltammetry (DPV) and atomic force microscopy (AFM). The interaction of Kt with G4HTD was studied by DPV and the DPV current decreased with increasing Kt concentration. The results from UV‐vis and circular dichroism (CD) spectroscopy showed a prominent intercalation mode between G4HTD and Kt.