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ABSTRACT
An easily prepared fluorescent bioconjugate colloidal solution based on gold nanoparticles is reported for the detection of Salmonella. This bioconjugate was prepared by conjugation of staphylococcal protein A on the surface of gold nanoparticles, followed by biofunctionalization over this layer with fluorescein isothiocyanate-labeled antibodies. The surface plasmon resonance band observed in the ultraviolet–visible spectrum of the gold nanoparticles showed a shift to low energy after covering the surface with protein A and a broadening of the band after biofunctionalization with the antibody. Surface-enhanced infrared spectroscopy showed the absorption bands of the conjugate and bioconjugate due to their proximity to the nanoparticles. In particular, vibrations at 1649, 1588, and 1400 cm−1 were from C˭O, N–H, and C–NH2 groups from the staphylococcal protein A covering the gold nanoparticles. The final bioconjugate colloidal solution was also used as probe to detecting Salmonella by confocal microscopy of solutions containing 1E3 and 1E5 CFU/ml. The total time required to detect these bacteria was less than 1 h. Fluorescent emission of the bacillus suggests that this methodology may have potential to develop a universal method for detecting different bacteria.