pH‐Responsive Near‐Infrared Emitting Gold Nanoclusters
Shaochen Zhou, Lotta Gustavsson, Grégory Beaune, Sourov Chandra, Jukka Niskanen, Janne Ruokolainen, Jaakko V. I. Timonen, Olli Ikkala, Bo Peng, Robin H. A. Ras
Abstract
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.