Fluorescent pH sensing and MnO2 nanosphere directed turn-on sensing of glutathione using pyridoxal 5′-phosphate modified polydopamine nanoparticles

Abstract

The water-soluble fluorescent organic nanoparticles (PDAPLP NPs) was synthesized by the oxidation of dopamine in the presence of vitamin B6 cofactor pyridoxal 5′-phosphate (PLP). The fluorescent intensity of PDAPLP NPs was quenched in the presence of MnO2 nanospheres due to the energy transfer process occurred from the PDAPLP NPs to MnO2 nanospheres. The fluorescence was restored upon addition of GSH to the PDAPLP_MnO2 nanocomposite due to the redox transformation of Mn(IV) to Mn(II). The fluorescence turn-on response allowed to detect GSH down to 0.31 µM. The developed nanoprobing approach was fast (response time < 2 min), simple and highly selective. The practical utility of the PDAPLP_MnO2 nanoprobe was validated by quantifying GSH in real saliva samples. In addition, the PDAPLP NPs was applied for the fluorescence sensing of pH. The cyan-blue fluorescent PDAPLP NPs between pH 2.0 to 7.0 turned to green-fluorescent above pH 7.0 in the basic pH.