Supramolecules‐Guided Synthesis of Brightly Near‐Infrared Au₂₂ Nanoclusters with Aggregation‐Induced Emission for Bioimaging

Abstract

Protein‐protected gold nanoclusters with emission in the near‐infrared wavelength range have been widely considered for applications in biomedical fields. However, their quantum yield (QY) remains low, thus limiting their practical applications. Herein, a novel strategy to synthesize bovine serum albumin–encapsulated gold nanoclusters (BSA‐AuNCs) with QY of 23% is developed. Assembled coordination polymers (supramolecules) of Au(I)‐BSA complexes are initially formed because of the intermolecular forces between BSA ligands. The forces are easily controlled by pH level during the reaction, leading to significant change in the photoluminescence of BSA‐AuNCs. By regulating the pH and reaction temperature, Au(0)@Au(I) core‐shell structured BSA‐AuNCs are fabricated in 2 h. Importantly, such AuNCs are in a rigidified state with high Au(I) content in the shell, offering an explanation for their high luminescence character. Further increasing QY to 29% is achieved by confining BSA‐AuNCs into a cationic polymer, poly(allylamine) hydrochloride (AuNCs@PAH). Enhanced cellular uptake and improved sensitivity of AuNCs@PAH to glutathione compared to BSA‐AuNCs is demonstrated. These findings may give insights into the synergistic effect of pH level and reaction temperature on the properties of protein‐encapsulated AuNCs and provide a possible way for up‐scaled fabrication of brighter AuNCs protected by other protein templates.

Integrating gold nanoclusters, folic acid and reduced graphene oxide for nanosensing of glutathione based on “turn-off” fluorescence

“…To the best of our knowledge, there are no reports on the addition of GSH directly onto BSA/AuNCs. BSA/AuNCs are normally coupled with MnO 2 nanosheets 78 , peptide 79 , polymer or subjected to growth process 80 before using as an activatable fluorescence probe for GSH sensing. A possible justification for the modification of BSA/AuNCs was to enhance aurophilic interactions of Au(I)-thiolate complexes on the surface of Au(0) core and rigidify the ligand shell.…”

“…A possible justification for the modification of BSA/AuNCs was to enhance aurophilic interactions of Au(I)-thiolate complexes on the surface of Au(0) core and rigidify the ligand shell. This allows AuNCs to undergo aggregation-induced emission mechanism with enhanced fluorescence intensity 80 while retaining the intrinsic structure of BSA/AuNCs surface and biological functions of BSA 78 , 79 . In addition, the surface modification of BSA/AuNCs reduces unwanted intramolecular vibration and rotation 80 , enhances biocompatibility and stability, as well as diversifies the potential of BSA/AuNCs in biological applications 79 .…”

Nanomaterials with Supramolecular Assembly Based on AIE Luminogens for Theranostic Applications

“…[46] For example, Luan and co-workers synthesized Au 22 nanoclusters guided by the supramolecular assembly with bright near-infrared AIE fluorescence for bioimaging, thus providing a new strategy to prepare different kinds of protein-protected Au nanoclusters for biomedical application. [47]…”

Potassium-Induced Emission Enhancement of Bovine Serum Albumin-Stabilized Red-Emitting Au Nanoclusters: Mechanism and Application to Blood Plasma

“…Potential application of AuNCs in cell imaging have been demonstrated in recent years thus emission intensity of BSA-rAuNCs was also investigated upon mixing with bovine blood plasma [11,43]. The emission spectrum acquired with the custom-built uorescence set-up is shown in Fig.…”