Strategies for fabricating a biorecognition interface for a label free electrochemical immunosensor

An electrochemical interface for a label-free electrochemical immuno-biosensor was prepared by modifying electrodes with a mixed layer comprising a molecular wire (MW) and oligo(ethylene glycol) (OEG) molecules derived from in situ-generated aryl diazonium salts. The in situ-generated aryl diazonium salts were prepared in two different ways using either organic solvents or aqueous solutions. For organic phase surface modification, the corresponding amines of MW and OEG were dissolved in acetonitrile while for aqueous phase surface modification the corresponding amines of MW and OEG were dissolved in 0.5 M HCl acidic solution. Reduction of the aryl diazonium cations generates the corresponding aryl radicals which react with the carbon substrate, resulting in a covalent bond. Our results show that the interface generated in acidic aqueous conditions not only produced denser layers on the electrode surfaces, as determined by the passivation of the electrode towards the redox active species such as Fe(CN)₆^3-/4- and Ru(NH₃)₆^2+/3+, but also has good responses for the detection of small molecules such as biotin.