Fluorescent Gold Nanoclusters: Promising Fluorescent Probes for Sensors and Bioimaging

Abstract

Fluorescent gold nanoclusters (AuNCs) have recently emerged as a novel kind of promising fluorescent probes for high-performance sensors and bioimaging because of their ultrasmall size (\3 nm), strong luminescence, good photostability, and excellent biocompatibility. Over the past decade, we have witnessed growing popularity of AuNCs in analytical applications and enormous efforts have been devoted to their development. In this review, we provide an update on recent advances in the development of AuNCs in terms of physicochemical properties, synthesis strategies, and bioapplications. The optical, electrochemical, catalytical, and solvatochromic properties of AuNCs are first summarized, which are followed by different ligands or template-assisted controllable synthetic methods. Afterwards functionalization of AuNCs is described in terms of ligand exchange, bioconjugation, and noncovalent interaction. We then focus on the applications of AuNCs as fluorescent probes for detection of metal ions, inorganic anions, small biomolecules, proteins, nucleic acids, drug molecules, pH, and temperature. We also summarize the usage of metal NCs in cellular and in vivo targeting and imaging. Finally, we conclude with a brief look at the future challenges and prospects of the development of AuNCs.

Dynamic Structure of Metal Nanoclusters from Synchrotron X-ray Spectroscopy

“…The properties of MNCs are highly sensitive to their compositions, metal core structures, and ligand–core interactions . The excellent optical properties of MNCs have allowed these materials to be used in applications such as photothermal conversion, photodynamics, sensors, and bioimaging. , Accordingly, several mechanisms have been proposed to explain their optical properties. ,, One such theory proposes that surface rigidification of MNCs can significantly enhance their luminescence intensities . However, details on the rigidification mechanism at the atomic scale are still unknown.…”

Advances of gold nanoclusters for bioimaging

“…In the synthesis of AuNCs, stabilizers with exemplary terminal functional groups, such as alcohols, carboxylic acids, primary amines and thiols, are usually selected to prevent the aggregation of AuNCs. Then superior biomolecules are further selected to couple with them to achieve multi-functionalization of AuNCs ( Song et al., 2016 ; Wang et al., 2017 ; Zheng et al., 2017 ). For example, FA is conjugated to GSH capped AuNCs to achieve targeted recognition of cancer cells ( Zhang et al., 2013 ).…”

Ligand exchange reactions on thiolate-protected gold nanoclusters

“…The clusters had negligible inuence on the cell viability at the considered dose. 146 However, because of the synthesis method and the solubility of ligands, the diversity of the uorescent gold nanoclusters has been limited. LER is a very efficient strategy for preparing uorescent gold nanoclusters.…”