Metal nanoclusters (NCs), typically consisting of a few to tens of metal atoms, bridge the gap between organometallic compounds and crystalline metal nanoparticles. As their size approaches the Fermi wavelength of electrons, metal NCs exhibit discrete energy levels, which in turn results in the emergence of intriguing physical and chemical (or physicochemical) properties, especially strong fluorescence. In the past few decades, dramatic growth has been witnessed in the development of different types of noble metal NCs (mainly AuNCs and AgNCs). However, compared with noble metals, copper is a relatively earth-abundant and cost-effective metal. Theoretical and experimental studies have shown that copper NCs (CuNCs) possess unique catalytic and photoluminescent properties. In this context, CuNCs are emerging as a new class of nontoxic, economic, and effective phosphors and catalysts, drawing significant interest across the life and medical sciences. To highlight these achievements, this review begins by providing an overview of a multitude of factors that play central roles in the fluorescence of CuNCs. Additionally, a critical perspective of how the aggregation of CuNCs can efficiently improve the florescent stability, tunability, and intensity is also discussed. Following, we present representative applications of CuNCs in detection and bioimaging. Finally, we outline current challenges and our perspective on the development of CuNCs.When decreasing the size of nanoparticles so that it approaches the Fermi wavelength of an electron, novel optical, electrical and magnetic properties appear (Deng et al. 2018a; Li et al. 2016b;Moghadam and Rahaie 2019;Wang et al. 2018c). Commonly termed nanoclusters (NCs), these ultra-small nanoparticles, bridging the missing link between atoms and nanocrystals, have attracted considerable attention in both fundamental research and practical applications (Bagheri et al. 2017;Basu et al. 2019;Sun et al. 2019;Wang et al. 2016b). Benefiting from the great progress in nanosynthetic chemistry, high-quality Copper NCs (CuNCs) with tailored size and good stability can be easily obtained. CuNCs, therefore, constitute an active research direction due to their unique properties, such as high luminous efficiency, long fluorescence lifetime, good optical and chemical stability, and large stokes displacement, which distinguish them as a new type of fluorescent probe for optical sensing and bioimaging/labeling (Cao et al. 2014;Wang et al. 2017).In this review, we highlight recent developments of CuNCs, with a particular emphasis on the multiple factors affecting fluorescent properties of CuNCs, as well as the aggregation-induced emission enhancement (AIEE) effect. To appreciate these advances, applications focused on the detection of ions, macromolecules and bioimaging are summarized. Lastly, we will provide a brief conclusion, and will address future challenges in the rapidly growing field of fluorescent CuNCs.
Multiple factors that govern the fluorescence of CuNCsDue to the size of CuNCs falls w...
