In Situ Depletion-Guided Engineering of Nanoshell-like Gold Nanocluster Assemblies with Enhanced Peroxidase-like Nanozyme Activity.

Functional superstructures constructed from metal nanoclusters (MNCs) hold great promise in providing highly tunable photoluminescence (PL), catalytic activity, photothermal stability, and biological functionality. However, their controlled synthesis with well-defined size, structure, and properties remains a significant challenge. Herein, we introduce a novel approach that combines depletion attraction and thermal activation to induce the in situ formation of spherical superclusters (AuSCs) from Au(I)-thiolate complexes within the assembly. Extensive characterization and electron tomographic reconstruction reveal that Au(I)-thiolate complexes can be sequentially transitioned into metallic Au0, resulting in hollow nanoshell-like structures with consistent size (∼110 nm) and diverse shell configurations. Our results demonstrate that AuSCs with thinner shells, containing a high concentration of Au(I)-thiolate complexes, exhibit the highest PL, while AuSCs with thicker shells, containing high concentrations of metallic gold atoms and low ligand density, show remarkable peroxidase-like nanozyme activity in the 3,3',5,5'-tetramethylbenzidine (TMB) oxidation reaction.

Switchable catalysis and CO2 sensing by reduction resistant, luminescent copper-thiolate complexes.

Metal-thiolate complexes have been the focus of research for several years because of their unique photophysical properties and their use as a precursor for synthesizing various well-defined metal nanoclusters. A rational understanding of their structure-property relationship is necessary to realize their full potential in practical applications. Herein, we demonstrate the synthesis of a unique copper-thiolate complex with reversibly switchable catalytic and photoluminescence (PL) properties. The as-synthesized complex at basic pH (Complex B) showed cyan PL with a strong peak at ∼488 nm (cyan) and a small shoulder peak at ∼528 nm (green). When the pH of the complex was changed to acidic (Complex A), the PL was switched to light green. Such pH-responsive PL properties were demonstrated to be useful for pH and CO2 sensing. The switchable properties originate from their two distinct structural states at two different pHs. We found that Complex A was resistant to high concentrations of a strong reducing agent, and had an intermediate oxidation state of copper (Cu+) with good thermodynamic stability. Furthermore, the switchable catalytic property was investigated with a 4-nitrophenol reduction and 3,3',5,5'-tetramethylbenzidine (TMB) oxidation reaction. The reduction kinetics followed pseudo-first-order, where the catalytic activity was enhanced by more than 103 times when Complex B was switched to Complex A. A similar trend was also observed for TMB oxidation. Our design strategy demonstrates that redox switchable metal-thiolate complexes could be a powerful candidate for a plethora of applications.

Depletion Driven Assembly of Ultrasmall Metal Nanoclusters: From Kinetically Arrested Assemblies to Thermodynamically Stable, Spherical Superclusters.

Nanoscale assembly of ultrasmall metal nanoclusters (MNCs) by means of molecular forces has proven to be a powerful strategy to engineer their molecule-like properties in multiscale dimensions. By leveraging depletion attraction as the guiding force, herein, we demonstrate the formation of kinetically trapped NCs assemblies with enhanced photoluminescence (PL) and excited state lifetimes and extend the principle to cluster impregnated cationic nanogels, nonluminescent Au(I)-thiolate complexes, and weakly luminescent CuNCs. We further demonstrate a thermal energy driven kinetic barrier breaking process to isolate these assemblies. These isolated assemblies are thermodynamically stable, built from a strong network among several discrete, ultrasmall AuNCs and exhibit several unusual properties such as high stability in various pH, strong PL, microsecond lifetimes, large Stocks shifts, and higher accumulation in the lysosome of cancer cells. We anticipate our strategy may find wider use in creating a large variety of MNC-based assemblies with many unforeseen arrangements, properties, and applications.

Driving Forces and Routes for Aggregation-Induced Emission-Based Highly Luminescent Metal Nanocluster Assembly.

The development of ultrasmall, luminescent metal nanoclusters (MNCs) with aggregation-induced emission (AIE) characteristics is a relatively new research area that has gained significant attention in various multidisciplinary applications such as optoelectronics, sensing, imaging, and therapy. The numerous scientific breakthroughs in the AIE field provide many tools that, if incorporated into MNCs design strategies, could help realize various new and exciting MNC-based avenues that maximize the utilization of the AIE phenomenon. Indeed, leveraging the aggregation strategies from the AIE community with the judicious use of various covalent and noncovalent interactions has been demonstrated to be effective for constructing several MNC-based hybrid assemblies with enhanced AIE characteristics. In this Perspective, we summarize the key driving forces and routes of MNC assembly together with their impact on deciphering the working mechanism behind the AIE process. These strategies can inspire the design of highly luminescent MNC-based hierarchical functional materials across multiple length scales.