Direct fluorimetric sensing of UV-excited analytes in biological and environmental samples using molecularly imprinted polymer nanoparticles and fluorescence polarization.

A rapid, robust, sensitive and economic sensing method, based on a molecularly imprinted polymer (MIP) synthetic antibody mimic, and fluorescence polarization analysis, for the direct detection of UV-excited fluorescent analytes in food and environmental samples was developed. Fluoroquinolone (FQ) antibiotics were used as fluorescent model analytes. Water-compatible MIP nanoparticles were synthesized with enrofloxacin (ENRO) as the imprinting template. Fluorescence polarization measurements then allow the direct determination of the amount of ENRO and other structurally related piperazine-based fluoroquinolones that bind to the MIP. No separation step was required since this technique distinguishes in situ analyte molecules bound to the MIP from the free analyte in solution. This assay was successfully applied for the first time to determine FQs in real samples, i.e. tap water and milk, without any prior concentration step, by simply adding a known amount of MIP. No interference by the sample components was observed even though the excitation was in the UV region. In tap water, a low limit of detection of 0.1 nM for ENRO was achieved with 5 μg mL(-1) of MIP. In milk, ENRO and danofloxacin, whose MRLs have been fixed at 0.28 μM and 0.08 μM, respectively, could be selectively measured and distinguished from other families of antibiotics. The procedure is very easy and practical as it consists of simply precipitating the milk proteins with acetonitrile and adding buffer and MIP to the supernatant before reading the polarization values with a spectrofluorimeter.