Development of a fast and ultrasensitive black phosphorus-based colorimetric/photothermal dual-readout immunochromatography for determination of norfloxacin in tap water and river water.

A rapid and ultrasensitive method for colourimetric/photothermal dual-readout detection was developed using an 808 nm NIR laser and a thermal imaging app on mobile phone. Norfloxacin was used as a model contaminant to demonstrate this universal rapid detection method. It is innovatively, to use the advanced two-dimensional material black phosphorus as a colourimetric/photothermal reagent for the first time. The samples were added to the strip, and the analytes were selectively captured on the conjugate pad by monoclonal antibody-modified magnetic/upconversion nanocomposites. The samples flowed through the strips by capillary action until reaching the control line, where immune complex formation occurred due to the presence of secondary antibody. The added black phosphorus could be captured by the the antigens which were directly exposed to the test line and a brown band could be observed by naked eye. Upon illumination by NIR light for 1 min, the real-time temperature is obtained for quantitative analysis through the thermal imaging performed by mobile phone camera. This method can achieve the detection of norfloxacin in water samples within 20 min, and the detection limits of colorimetric and photothermal readout can reach 45 pg mL-1. Compared with conventional strips, this method provided an increased sensitivity by about two orders of magnitude, with a integrated portable laser and a mobile phone. It is a valuable method for rapid detection and can be applied to other environmental contaminants as well.