A novel fluorescent “on-off-on” sensor for monohydrogen phosphate based on the 5, 10, 15, 20-(4-sulphonatophenyl) porphyrin (TSPP) in nutrient solution and DFT calculation

We successfully synthesized the 5, 10, 15, 20-(4-sulphonatophenyl)porphyrin (TSPP) by the most environmentally friendly method, afterwhich, we proposed a novel fluorescent “on-off-on” sensor for monohydrogen phosphate (HPO[Formula: see text] in the nutrient solution using the appealing fluorescence of TSPP. The switchable sensor based on TSPP was developed to determine HPO[Formula: see text] via fluorescence quenching of TSPP solution by Fe[Formula: see text] (off) and recovery by HPO[Formula: see text] (on). Under optimal conditions, the limit of detection (LOD) for HPO[Formula: see text] was 0.31 [Formula: see text]M (S/N=3), and a good linearity is showed in the range of 0–54.7 [Formula: see text]M with R 2 =0.9989. This method displayed several excellent properties including convenience, high selectivity and fast fluorescence response.