Sulfamethazine detection with direct-binding optical waveguide lightmode spectroscopy-based immunosensor

A direct-binding optical waveguide lightmode spectroscopy-based immunosensor detecting sulfamethazine (SMZ) was prepared, followed by the measurement of its specificity and sensitivity. System construction was undertaken with a peristaltic pump, an injector and the main unit comprising a sensor holder, two signal-harvesting photodiodes, a beam mirror, shutter and He–Ne laser source emitting a monochrome light (λ = 632.8 nm), plus a PC. Antibody immobilization was performed in situ by covalent binding of an anti-SMZ antibody over the surface of a glutaraldehyde-activated 3-aminopropyltriethoxysilane-treated sensor chip. The reaction buffer for the system was 4 mM Tris–HCl (pH 7.2) that showed a medium surface coverage and stable baseline. Sensor response was quite specific to antibody–antigen complexation, as judged from no sensor response caused by bovine serum albumin immobilization. The sensor responses according to SMZ concentrations from 10−8 to 10−2 M increased linearly in a semi-logarithmic scale, with the limit of detection of 10−8 M. The immunosensor was favorably reusable for SMZ screening.