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[Display omitted] • Correlating metal nanocluster's physicochemical properties to sensing applications. • The main synthetic strategies for luminescent metal nanoclusters (MNCs). • The conventional configurations of MNCs-based luminescent sensors. • The sensing mechanisms of MNCs-based luminescent sensors. • The challenges and prospects related to MNCs-based luminescent sensors. Metal nanoclusters (MNCs) have ultrasmall size (≤3 nm), precise molecular structure, strong luminescence, size-sensitive physicochemical properties, engineerable metallic composition, and rich yet tailorable surface chemistry, enabling them to be promising for the construction of luminescent sensors for diversified sensing applications in fields of environmental protection, food safety, agriculture, disease diagnosis, biomarker identification, etc. However, a systematic summary is urgently needed to correlate the physicochemical properties of MNCs with their influences on sensing applications, to summarize the synthetic strategies of highly luminescent MNCs towards sensor construction, and to discuss the general configurations and sensing mechanisms of MNCs-based luminescent probes. In this review, we first discuss relevant physicochemical properties of MNCs that may have major influences on the sensing mechanisms/performance of MNCs-based luminescent sensors, and then summarize the main synthetic strategies of highly luminescent MNCs. Then, we briefly illustrate the general configurations of MNCs-based sensors, and elaborately clarify their sensing mechanisms with the exemplification of representative sensing applications. We conclude the review with our perspectives on the opportunities/challenges of MNCs-based luminescent sensors. It is believed that this review will shed light on the design of MNCs-based luminescent sensors for future sensing applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • An overview of the two-phase strategies for ultrasmall metal nanoclusters. • The two-phase synthesis, processing, functionalization, and application of metal nanoclusters. • The challenges and prospects related to the two-phase strategies for metal nanoclusters. Ultrasmall metal nanoclusters (NCs) are a sub-class of metal nanoparticles (NPs) with a metal core size of ≤3 nm, and display interesting molecule-like properties. Atomically precise metal NCs can be synthesized by many solution chemistry methods in polar and non-polar reaction environments. Among these methods, two-phase based strategies involving a water-oil binary reaction system have emerged as a facile means to synthesize, process, functionalize, and apply metal NCs. This Review firstly presents an overview of the two-phase based strategies in the synthesis of hydrophobic and hydrophilic metal NCs, and aims to elucidate the underlying working principles of these strategies. Then, how a two-phase system could process metal NCs for size/composition tailoring, luminescence generation, sorting and purification is discussed. Subsequently, several examples that utilizing a two-phase system to efficiently functionalize metal NCs with different surface chemistry are highlighted. Finally, two-phase based applications of metal NCs in catalysis and self-assembly are also reviewed. The fundamentals and the advances of the two-phase based strategies in the synthesis, processing, functionalization, and application of metal NCs summarized in this Review may increase the acceptance of two-phase based strategy in the metal NC field. [ABSTRACT FROM AUTHOR]