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.