The design of horseradish peroxidase mimicking catalysts is an emerging area of research for clinical diagnosis and biomedical application. Here, blue luminescent, pepsin-templated copper nanoclusters (Cu NCs) are synthesized, which act as an effective peroxidase mimic. The Cu NCs are composed of 23 Cu atoms within one pepsin molecule (Cu23@pepsin) and exhibit intense blue photoluminescence (PL) at 455 nm. The Cu23@pepsin catalyzes H2O2 reduction along with the oxidation of o-phenylenediamine (OPD) following Michaelis–Menten enzyme kinetics. The optimum enzymatic activity of recyclable Cu23@pepsin is obtained at neutral pH at 35 °C. When OPD is oxidized to yield yellow-colored diaminophenazine (DAP) with a PL maximum at 565 nm, a concurrent quenching of Cu23@pepsin emission at 455 nm takes place due to the energy transfer process. The dual PL response of the Cu23@pepsin-based probe is exploited in designing a ratiometric H2O2 sensor. The reactivity toward peroxide is utilized in specific and sensitive sensing of glucose with a limit of detection (LOD) of 7.56 μM. The development of Cu NC-based artificial enzymes will pave the way for versatile biomedical, environmental, and clinical applications.

Studies on self-assembly of metal nanoclusters (MNCs) are an emerging field of research owing to their significant optical properties and potential applications in many areas. Fabricating the desired self-assembly structure for specific implementation has always been challenging in nanotechnology. The building blocks organize themselves into a hierarchical structure with a high order of directional control in the self-assembly process. An overview of the recent achievements in the self-assembly chemistry of MNCs is summarized in this review article. Here, we investigate the underlying mechanism for the self-assembly structures, and analysis reveals that van der Waals forces, electrostatic interaction, metallophilic interaction, and amphiphilicity are the crucial parameters. In addition, we discuss the principles of template-mediated interaction and the effect of external stimuli on assembly formation in detail. We also focus on the structural correlation of the assemblies with their photophysical properties. A deep perception of the self-assembly mechanism and the degree of interactions on the excited state dynamics is provided for the future synthesis of customizable MNCs with promising applications.

Aggregation-induced emission (AIE) has been significantly explored to enhance luminescence properties. Here, we synthesized bimetallic AuCu nanoclusters (NCs) and studied their AIE by reconstructing the surface motif from −S–Au­(I)–S– Au­(I)–S– to −S–Au­(I)–S–Cu­(I)–S–, as evident from X-ray photoelectron spectroscopy (XPS) and microscopy studies. A significant blue shift in the emission band of Au NCs is observed with the change of the Au/Cu molar ratio. We observed enormous emission enhancement with decreasing temperature due to suppression of the intramolecular motion of surface ligands. A 200-fold emission enhancement occurs due to the aggregation of ultrasmall-sized AuCu NCs in a less polar medium of the water–ethanol mixture. An increase in the radiative rate supports the effect of the Au­(I)–Cu­(I) metallophilic interaction. A decrease in the nonradiative rate confirms the restriction of ligand motions in the aggregated state. Metal cluster-based AIE-type materials pave the way to design highly luminescent materials for potential applications in sensing, biolabeling, light-emitting diodes (LEDs), and other fields.

Precisely doped metal nanoclusters (NCs) are currently emerging nanomaterials for their unique photophysical properties. Here, we report the influence of single atom doping on the excited state relaxation dynamics of a series of MAg 24 (2,4-Me 2 PhS) 18 n− NCs where M is Ag, Au, Pd, and Pt. The NCs with a group 11 metal (Ag and Au) as central atoms exhibit dual emission at NIR and visible range, whereas it shows only NIR emission for group 10 metal (Pd and Pt) doped NCs. Global target analyses of transient absorption (TA) data reveal the three-state relaxation, i.e., initially excited state (S n ), ligand-centered charge transfer (CT) state (S L ), and metal-centered lowest excited state (S 1 ). Apart from the HOMO−LUMO (H−L) energy gap, the electron affinity of the central metal atom and rigidity of the NC structural framework influence the relaxation processes of the NCs. The extensive study into the relaxation dynamics will bestow the single atomic level modulation of photophysical properties.

Tailoring the hierarchical self-assembly of metal nanoclusters (NCs) is an emergent area of research owing to their precise structure and flexible surface environment. Herein, the morphological evolution from rod to...