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.

Fluorometric discrimination of tyrosine isomers based on the inner filter effect of chiral Au nanoparticles on MoS2 quantum dots

A fluorescent chiral sensor is proposed based on the inner filter effect (IFE) of chiral Au nanoparticles (AuNPs) on MoS2 quantum dots (MoS2 QDs), which can be used for the discrimination of the isomers of tyrosine (Tyr). l-Tyrosine (l-Tyr) can induce obvious agglomeration of the chiral AuNPs, leading to an attenuated IFE of the chiral AuNPs and greatly restored fluorescence of the MoS2 QDs, and thus the enantioselective recognition of the Tyr isomers can be achieved. Also, l-Tyr but not d-Tyr induced agglomeration of the chiral AuNPs is confirmed by the larger association constant between l-Tyr and the chiral sensor.

Au25(SR)18: the captain of the great nanocluster ship

Noble metal nanoclusters are in the intermediate state between discrete atoms and plasmonic nanoparticles and are of significance due to their atomically accurate structures, intriguing properties, and great potential for applications in various fields. In addition, the size-dependent properties of nanoclusters construct a platform for thoroughly researching the structure (composition)-property correlations, which is favorable for obtaining novel nanomaterials with enhanced physicochemical properties. Thus far, more than 100 species of nanoclusters (mono-metallic Au or Ag nanoclusters, and bi- or tri-metallic alloy nanoclusters) with crystal structures have been reported. Among these nanoclusters, Au25(SR)18-the brightest molecular star in the nanocluster field-is capable of revealing the past developments and prospecting the future of the nanoclusters. Since being successfully synthesized (in 1998, with a 20-year history) and structurally determined (in 2008, with a 10-year history), Au25(SR)18 has stimulated the interest of chemists as well as material scientists, due to the early discovery, easy preparation, high stability, and easy functionalization and application of this molecular star. In this review, the preparation methods, crystal structures, physicochemical properties, and practical applications of Au25(SR)18 are summarized. The properties of Au25(SR)18 range from optics and chirality to magnetism and electrochemistry, and the property-oriented applications include catalysis, chemical imaging, sensing, biological labeling, biomedicine and beyond. Furthermore, the research progress on the Ag-based M25(SR)18 counterpart (i.e., Ag25(SR)18) is included in this review due to its homologous composition, construction and optical absorption to its gold-counterpart Au25(SR)18. Moreover, the alloying methods, metal-exchange sites and property alternations based on the templated Au25(SR)18 are highlighted. Finally, some perspectives and challenges for the future research of the Au25(SR)18 nanocluster are proposed (also holding true for all members in the nanocluster field). This review is directed toward the broader scientific community interested in the metal nanocluster field, and hopefully opens up new horizons for scientists studying nanomaterials. This review is based on the publications available up to March 2018.