Determination of the Fluoroquinolones Levofloxacin and Ciprofloxacin by a Piezoelectric Immunosensor Modified with Multiwalled Carbon Nanotubes (MWCNTs)

Abstract

Methods for the high-sensitivity determination of fluoroquinolones using a piezoelectric immunosensor based on multi-walled carbon nanotubes (MWCNTs) are developed. The use of MWCNTs in the formation of a stable piezoelectric sensor detection layer increases the active specific surface area which is necessary for receptor molecule binding. The concentrations of hapten-protein conjugates (35/65 serial concentration) and polyclonal antibodies are determined in the direct (15/85 for levofloxacin, 18/82 for ciprofloxacin) and in the competitive immunoassay formats (14/86 for levofloxacin, 10/90 for ciprofloxacin). Conditions for the analysis in the flow-injection mode were studied. The carrier flow rate was 30 and 50 µl/min depending on the detection layer formation method. The characteristics of MWCNTs-based piezoelectric immunosensors were characterized for the determination of fluoroquinolones in the static and in the flow-injection modes. The direct and competitive immunoassay formats (detection limit, linear range of target concentrations, reproducibility) were determined. The detection limits were 9 and 8 ng/ml for levofloxacin and ciprofloxacin in the competitive format and 25 and 21 ng/ml in the direct assay. The piezoelectric immunosensors were employed for the analysis of milk.