Spiropyran-Functionalized Gold Nanoclusters with Photochromic Ability for Light-Controlled Fluorescence Bioimaging.

Fluorescent gold nanoclusters with unique luminescence properties have drawn great attention in bioimaging. The gold nanoclusters with controlled multicolor fluorescence may benefit accurate fluorescence imaging. In this work, gold-nanocluster-engineered spiropyran ligands (AuNC-SP) were reported to achieve controlled dual-color imaging under single excitation. Through switching the Förster resonance energy transfer from the gold nanocluster segment to the open-ring state merocyanine by UV-vis irradiation, AuNC-SP possesses reversibly dual-color fluorescence. After AuNC-SP combined with chitosan to form AuNC-SP@CS nanoparticles, the steric protection of chitosan largely improved the oxidative stability of AuNC-SP upon UV irradiation. Moreover, the AuNC-SP@CS could be internalized within cancer cells and released AuNC-SP that further underwent transportation into the nucleus. Thus, the AuNC-SP@CS exhibits excellent and reversible dual-color fluorescence to label not only the cytoplasm but also the nucleus. We envisage the AuNC-SP@CS as an ideal probe for fine subcellular assays in the cell interior.