A copper(II) displacement approach for fluorescent turn-on sensing of glutathione using salicylaldehyde modified polydopamine nanoparticles

The salicylaldehyde modified green-fluorescent polydopamine nanoparticles (PDASA NPs) was synthesized, characterized and applied for the sensing of glutathione (GSH). The oxidative polymerization of dopamine in the presence of salicylaldehyde at pH = 8.5 (10 mM PBS solution) formed the spherical-shaped PDASA NPs with an average diameter of ∼ 150 nm. The addition of Cu(II) to the solution of PDASA NPs in HEPES buffer (10 mM, pH = 7.4) quenched the fluorescence at 490 nm (λex = 390 nm). Experimental evidence supported the fluorescence quenching was static in nature with the estimated Stern-Volmer constant (KSV) of 4.00 × 103 M−1. The fluorescence was restored upon addition of GSH to the solution containing PDASA NPs and Cu(II), among the other examined amino acids (alanine, aspartic acid, glutamic acid, arginine, glycine, cysteine, histidine, serine, leucine, proline, threonine, tryptophan, lysine and methionine). The nanoprobe Cu(II)-PDASA NPs showed a good linearity between 2.20 × 10−5 M and 2.49 × 10−6 M for GSH with an estimated limit of detection of 2.84 × 10−7 M. The Cu(II)-PDASA NPs was applied for the quantification of GSH in urine and saliva samples.