Semiquantitative immunochromatographic colorimetric biosensor for the detection of dexamethasone based on up-conversion fluorescent nanoparticles.

A low-cost bifunctional immunochromatographic colorimetric biosensor was developed that can be read visually or by using an optical density scanner. Five test lines (T lines) coated with different antigens were set on a nitrocellulose (NC) membrane to indicate the concentration of analyte. This method was applied for the detection of dexamethasone. The corresponding detection range was 0.1-9 ng mL-1, and the detection limit for dexamethasone in food supplements and cosmetic samples was 2.0 μg kg-1. For visual inspection of the colour the quantitative relative error range between the proposed method and liquid chromatography was -62 to -25%, with a detection time of only 10 min. More accurate assay results were obtained by using an optical density scanner with the relative error range of -31 to 20%. The results indicated that the proposed method has the potential of application for rapid and efficient screening of dexamethasone in cosmetics and food supplements. Graphical abstract.