Photostable and Biocompatible Luminescent Thiol-Terminated Organosilica Nanoparticles with Embedded Au(I)-Thiolate Complexes for Fluorescent Microscopic Imaging

Fluorescent silica nanoparticles (NPs) hold great promise in fluorescence microscopy (FM) owing to their high fluorescence intensity and photostability, multifunctionality, and biocompatibility. Conventionally, fluorescent silica NPs are synthesized from silica and fluorescent organic dyes or inorganic materials. This study focuses on photoluminescence (PL) exhibited by Au(I) complexes under specific conditions through a mechanism that is significantly different from that of the PL exhibited by transition-metal complexes. Luminescent thiol-terminated organosilica NPs with embedded Au(I)-thiolate complexes (thiol-OS/Au) produced under green synthetic conditions sustained the PL state of Au. Furthermore, the high Au content of thiol-OS/Au caused it to emit red PL detectable by FM imaging, exhibiting a PL emission peak at approximately 700 nm with a large Stokes shift. The size-tunable thiol-OS/Au was highly biocompatible, pH-stable (pH 2-12), and applicable to long-term cell imaging. Cells labeled using thiol-OS/Au did not exhibit photobleaching, following 30 min of excitation, encouraging the use of thiol-OS/Au as a stable fluorescent probe for FM bioimaging.