Surface IR applied to rapid and direct immunosensing of environmental pollutants

This paper describes the elaboration of a model immunosensor monitored by polarization modulation reflection absorption infrared spectroscopy (PM-RAIRS) and quartz crystal microbalance (QCM-D), as well as its reactivity using PM-RAIRS as transduction technique. To prove its relevance, this immunosensor was applied to the detection of benzo[a]pyrene (BaP), a carcinogenic polycylic aromatic hydrocarbon. Very few immunoassays, and even fewer immunosensors, have been described for the assay of BaP, making it an interesting target for analytical device development. The PM-RAIRS immunosensor was constructed on planar gold-coated sensors functionalized with cystamine then glutaraldehyde. Antibodies were immobilized through their affinity to protein G, covalently coupled to the aldehyde layer. In a first stage, a model mouse IgG was utilized to optimize the elaboration parameters; then, a monoclonal anti-PAH antibody was used and detection tests were performed, monitored by PM-RAIRS. The successive functionalization steps were monitored by PM-RAIRS and QCM-D. The binding of the proteins to gold surface, their saturation coverages and association constants, as well as their capture efficiencies were discussed. BaP capture by the antibody layer was evidenced by the appearance of a new ν(C–H) band at 3039 cm−1 typical of aromatic C–H bonds. The integrated area of this band varied linearly with the BAP concentration within the range of tested concentrations, with a limit of detection close to 3 μM. This represents the first example of direct, label-free immunodetection of a low molecular weight molecule by PM-RAIRS transduction. The simplicity and the rapid response of this IR sensor make it already very worthwhile to preliminary on-site measurements.