Synthesis of 1,8-naphthalimide-based fluorescent nano-probes and their application in pH detection

Two kinds of fluorescent nano-probes (pH-A and pH-B) with different diameters for the determination of H+ concentration, based on photo-induced electron transfer mechanism, were synthesized through click reaction. In which 1,8-naphthalimide was employed as the fluorophore and N,N-dimethylethylenediamine as the receptor. The effects of particle size and linker length on the photophysical properties of the probe were studied. The results revealed that the nano-probes were more sensitive toward pH with increasing particle size. The fluorescence intensity at 529 nm (I529) of the nano-probe pH-A of 120 nm exhibited good linear relationship with solution’s pH in the range of 6–8. The probe pH-A displayed excellent selectivity and competition toward proton over other possible coexisted ions, and it could be applied to detect pH in realistic samples (river water, urine).