pH-Responsive Near-Infrared Emitting Gold Nanoclusters

Near-infrared (NIR) fluorophores with pH-responsive properties suggest merits in biological analyses. This work establishes a general and effective method to obtain pH-responsive NIR emissive gold nanoclusters by introducing aliphatic tertiary amine (TA) groups into the ligands. Computational study suggests that the pH-responsive NIR emission is associated with electronic structure change upon protonation and deprotonation of TA groups. Photo-induced electron transfer between deprotonated TA groups and the surface Au-S motifs of gold nanoclusters can disrupt the radiative transitions and thereby decrease the photoluminescence intensity in basic environments (pH=7-11). By contrast, protonated TA groups curb the electron transfer and restore the photoluminescence intensity in acidic environments (pH=4-7). The pH-responsive NIR-emitting gold nanoclusters serve as a specific and sensitive probe for the lysosomes in the cells, offering non-invasive emissions without interferences from intracellular autofluorescence. Near-infrared emitting gold nanoclusters with reversible pH responsiveness have been developed by the incorporation of tertiary amine groups in the surface ligands. The amine groups change the highest occupied molecular orbital upon their pH-induced protonation and deprotonation, resulting in photoluminescence quenching.image

Automated summary

This work presents a general and efficient method to synthesize pH-responsive near-infrared (NIR) emitting gold nanoclusters by introducing aliphatic tertiary amine (TA) groups as ligands. The pH-responsive NIR emission is achieved through the protonation and deprotonation of TA groups, which induce electronic structure changes. The pH-responsive gold nanoclusters can serve as specific and sensitive probes for lysosomes in cells, offering non-invasive emissions without interference from intracellular autofluorescence.