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The detection of pathogenic bacteria remains a challenge for the struggle against biological weapons, nosocomial diseases, and for food safety. In this research, our aim was to develop an easy-to-use electrochemical immunosensor for the detection of pathogenic Staphylococcus aureus ATCC25923. The biosensor was elaborated by the immobilization of anti-S. aureus antibodies using a self-assembled monolayer (SAMs) of 3-Mercaptopropionic acid (MPA). These molecular assemblies were spontaneously formed by the immersion of the substrate in an organic solvent containing the SAMs that can covalently bond to the gold surface. The functionalization of the immunosensor was characterized using two electrochemical techniques: cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Here, the analysis was performed in phosphate buffer with ferro/ferricyanide as the redox probe. The EIS technique was used for affinity assays: antibody-cell binding. A linear relationship between the increment in the electron transfer resistance (RCT) and the logarithmic value of S. aureus concentration was observed between 10 and 106 CFU/mL. The limit of detection (LOD) was observed at 10 CFU/mL, and the reproducibility was calculated to 8%. Finally, a good selectivity versus E. coli and S. epidermidis was obtained for our developed immunosensor demonstrating its specificity towards only S. aureus.

International audiencePoly(oligoethylene glycol methacrylate), POEGMA, brushes were prepared by surface-initiated atom transfer radical polymerization (SI-ATRP) on gold-coated silicon wafers. Prior to ATRP, the substrates were grafted by brominated aryl initiators via the electrochemical reduction of a noncommercial parent diazonium salt of the formula BF4-, N-+(2)-C6H4-CH(CH3)Br. The diazonium-modified gold plates (Au-Br) served as macroinitiators for ATRP of OEGMA which resulted in hydrophilic surfaces (Au-POEGMA) that could be used for two distinct objectives: (i) resistance to fouling by Salmonella Typhimurium; (ii) specific recognition of the same bacteria provided that the POEGMA grafts are activated by anti-Salmonella. The Au-POEGMA plates were characterized by XPS, polarization modulation-infrared reflection-absorption spectroscopy (PM-IRRAS) and contact angle measurements. Both Beer-Lambert equation and Tougaard's QUASES software indicated a POEGMA thickness that exceeds the critical similar to 10 nm value necessary for obtaining a hydrophilic polymer with effective resistance to cell adhesion. The Au-POEGMA slides were further activated by trichlorotriazine (TCT) in order to covalently bind anti-Salmonella antibodies (AS). The antibody-modified Au-POEGMA specimens were found to specifically attach Salmonella Typhimurium bacteria. This work is another example of the diazonium salt/ATRP process to provide biomedical polymer surfaces

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