A novel fluorescence method for detection of phosphate anions based on porphyrin metalation

In this work, a novel fluorescence method for the detection of phosphate anions (PO₄^3-) was developed based on porphyrin metalation. Through catalysis by G-quadruplex (G4), Cu²⁺ could insert into the porphyrins to quench their fluorescence. G4 simultaneously improved the fluorescence of the porphyrins but not that of Cu²⁺-porphyrin. In the absence of PO₄^3-, the porphyrins were metallized by Cu²⁺, and no fluorescence was observed. In the presence of PO₄^3-, PO₄^3- could coordinate with Cu²⁺ to prevent porphyrin metalation. Free porphyrin could bind with G4 to emit strong fluorescence. By comparing four common porphyrins, we found that G4 had the greatest effect on increasing the fluorescence intensity of N-methylmesoporphyrin IX (NMM). Thus, NMM/G4 was chosen for the design of a biosensor. Under optimal experimental conditions, this method showed high sensitivity and satisfactory selectivity for PO₄^3- with a detection limit of 44 nM in a linear range of 0.01-1.0 μM. The recovery experiments showed recovery rates of 93.75-106.00%, suggesting a great potential for measuring PO₄^3- in real samples.