Test strips for detection of 4-nitrophenol based on fluorescence quenching and color change of black phosphorus quantum dots

Abstract

In this study, blue-fluorescent black phosphorus quantum dots (BPQDs) were synthesized through a combination of liquid-phase ultrasonication and solvothermal techniques. Black phosphorus (BP) crystal powder, isopropyl alcohol (IPA) and NaOH were employed as the precursor, as the solvent, and to adjust the reaction environment, respectively. The BPQDs exhibited optimal fluorescence characteristics, with excitation and emission wavelengths measured at 322 nm and 392 nm, respectively. Notably, 4-nitrophenol (4-NP) induced static fluorescence quenching of BPQDs, causing a reduction in their quantum yield from 7.8% to 4.4%. A linear correlation was observed between the fluorescence quenching intensity and 4-NP concentration, spanning a range from 0.1 μM to 120 μM, with a limit of detection as low as 43 nM. Furthermore, a portable test strip was developed, which undergoes a color change to yellow upon exposure to 4-NP, enabling selective detection. By analyzing the color of the strip through smartphone photography to obtain red, green and blue (RGB) values, a linear relationship was established between the R/B ratio and 4-NP concentration within the range of 10–150 μM, facilitating quantitative analysis. This study demonstrates the effectiveness of BPQD-based fluorescent probes and portable test strips for the detection of 4-NP in various water samples, including lake water, tap water and laboratory waste effluent.