'Traffic light' immunochromatographic test based on multicolor quantum dots for the simultaneous detection of several antibiotics in milk.

An immunochromatographic test was developed for the simultaneous detection of several compounds in a complex sample matrix. The system was designed in a 'traffic light' format comprising three lines of different colors on a test strip, thereby providing an easy tool with which to identify an analyte of interest based on the visible color of the line formed (qualitative analysis), and to determine the amount of the analytes present based on the fluorescence intensity of the lines (quantitative analysis). For the development of the multicolor immunochromatographic test, we used antibodies against antibiotics of three different classes as selective binders. Each antibody was labeled with water-soluble quantum dots with emission maximum at either 525, 585, or 625 nm. The test system exhibited high sensitivity, with limits of detection for ofloxacin, chloramphenicol, and streptomycin of 0.3, 0.12, and 0.2 ng mL(-1), respectively. These values are 80-200 times lower than those achievable with ELISA using the same antibodies. Using the 'traffic light' assay, these antibiotics could be detected in milk samples within 10 min without any sample preparation. The 'traffic light' assay also demonstrated a high degree of analyte detection when testing spiked milk samples (92-101%) and accuracy (quantitation error <8% of the mean).

Highly Sensitive Immunochromatographic Identification of Tetracycline Antibiotics in Milk.

A rapid immunochromatographic assay was developed for the control of tetracycline (TC). The assay is based on the competition between immobilized TC-protein conjugate and TC in a tested sample for binding with polyclonal anti-TC antibodies conjugated to colloidal gold during the flow of the sample along a membrane strip with immobilized reactants. Conjugation of colloidal gold and the total immunoglobulin (IgG) fraction of polyclonal antibodies was used to increase the assay sensitivity to ensure low content of specific antibodies in the conjugate. This allowed effective inhibition of free TC and conjugate binding in the strip test zone. Photometric marker registration allows control of the reduction of binding, thereby enhancing detection sensitivity. The proposed assay allows TC to be detected at concentrations up to 20 ng/mL, exceeding the limit of detection of the known analogues, in a wide working range (more than two orders) of 60 pg/mL to 10 ng/mL, ensured through the use of polyclonal antibodies. The assay time is 10 min. The efficiency of the designed assay is shown to identify TC in milk; the degree of recovery of TC ranges from 90 to 112%. The precision of the concentrations measurements was no more than 10%.