  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.
