Natural plant compounds in synthesis and luminescence modulation of metal nanoclusters: Toward sustainable nanoprobes for sensing and bioimaging

Luminescent metal nanoclusters (LMNCs) with a diameter of less than 3 nm have fascinated scientific community in the past two decades for facile synthesis, ultra-small size, and tunable optical properties. For the synthesis and luminescence modulation of LMNCs, the plant kingdom provides a great deal of natural compounds, including various polyphenols, carbohydrates, and proteins. Because of the cost-effective, sustainable, and hypo-allergenic features of the plant compounds, they are preferred over both synthetic chemicals and biomolecules isolated from animals and microorganisms for synthesis, modification, and application of LMNCs. In this review, we first highlighted recent advances in the use of natural plant compounds for the preparation of LMNCs including gold, silver, copper, and alloy nanoclusters. Moreover, we discussed how the plant compounds modulated the luminescence properties of pre-synthesized LMNCs. Furthermore, the application of plant compounds-capped LMNCs in metal ions sensing, pesticide detection, biomarkers analysis, and bioimaging was surveyed. Finally, we briefly discussed the challenging issues and future perspectives in the field of plant compounds-capped LMNCs. This review demonstrates the critical role of natural plant compounds in the synthesis, luminescence modulation, and application of LMNCs, and is expected to offer inspiration for the further design and practical use of LMNCs.