Ultrasensitive label-free ratiometric colorimetric sensor for free chlorine detection in tap water based on a novel brilliant blue-Au NCs

In this work, Au nanoclusters was prepared under the guidance of a synthetic colorant brilliant blue (BB-Au NCs). The microstructure and crystal structure of the resulting products were characterized by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The absorbance of BB-Au NCs at 247 nm was enhanced while the absorbance at 308 and 630 nm was reduced by free chlorine, an unavoidable and ubiquitous disinfection byproduct. The optical properties of BB-Au NCs and the influence of free chlorine were analyzed using computational chemistry methods based on density functional theory (DFT). The ratio of absorbance of BB-Au NCs at 247 and 630 nm was used for accurate quantitative determination of free chlorine in a range from 5 to 50 μM, with the detection limit is 1 μM. This method demonstrates potential application for simple and environmentally friendly detection of free chlorine in water samples. • A novel Au NCs is prepared by a simple method using BB as template. • The physicochemical and optical property of BB-Au NCs is discussed by DFT theory. • A ratio colorimetric sensor for free chlorine detection is fabricated based on BB-Au NCs. • The sensor combined the optical property of BB and catalytic property of Au NCs.