In this PhD thesis, the work is organised into separate articles that have been published. In the first part of the thesis, the electrocatalytic properties of o-aminophenol films grafted on glassy carbon surfaces have been employed for the electrochemical evaluation of hydrazine, NADH and ascorbic acid (AA). AA system was explored for clinical and food applications such as the determination of uric acid in presence of AA, and the detection of AA in real samples of fruits and vegetables using disposable screen printed electrodes. In the second part of the thesis, different surface engineering strategies of antibody immobilization for immunosensor construction using a linker (bipodal carboxylic acid terminated thiols) or via direct attachment of the SATA modified full length antibody, and their F(ab) fragments onto Au surface using a strategy of self assembly were evaluated and compared. The developed immunosensors were then applied to the detection of gliadin in commercial gluten-free and gluten-containing food products. An alternative strategy explored was the direct anchoring of the antibody with or without a linker via the electrochemical reduction of their diazonium cations.