Study on the interaction between oxolinic acid aggregates and protein and its analytical application

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.

Rapid and sensitive determination of trace chloride ion in drinks using resonance light scattering technique

A resonance light scattering (RLS) technique to determine chloride ions in drinks was developed. Chloride ions were found to bind Ag(+) forming AgCl aggregates that produced intense resonance scattering light. Effects of factors such as acidity, ionic strength, and coexistent interferents on the RLS of AgCl aggregates were investigated. The pH of solution almost did not affect the production of RLS and few foreign species interfered with the detection of chloride ions. The resonance scattering light intensity at the maximum peak of 571 nm was linear to the concentration of chloride ions in the range of 1.42-8.52 ng mL(-1) with a detection limit of 0.71 ng mL(-1). To determine the feasibility of the proposed method, some samples of water and drinks were analyzed. The attained results were in agreement with that of ion-selective electrode method. Good recovery results were also obtained with the range of 94.08-105.63%. The sensitivity and selectivity of the RLS method are high enough to determine trace amounts of chloride ions without any significant interference from high concentration of other components such as common anions and cations.