Silver nanoclusters with near-infrared-II emission: synthesis, properties, and biomedical applications

Optical imaging is playing an increasingly critical role in modern biomedical research. In particular, the second near-infrared window (NIR-II, 1000-1700 nm) has attracted widespread attention due to its significant advantages in tissue penetration depth, spatial resolution, and temporal resolution. In this cutting-edge field, silver nanoclusters (AgNCs) have emerged as highly promising NIR-II luminescent probes owing to their unique physicochemical properties. These intrinsic properties position AgNCs as a highly promising platform for engineering advanced NIR-II luminescent nanoprobes. This review aims to systematically summarize the research progress in AgNCs with NIR-II emission. Firstly, we will outline the main types of AgNCs with NIR-II emission, their synthesis strategies, and the theoretical foundations of their luminescence mechanisms. Secondly, we will focus on summarizing specific application examples of these materials in in vivo fluorescence imaging. Furthermore, the review will provide an in-depth analysis of the key challenges currently faced by these probes in practical biomedical applications, such as the need for further improvement in brightness, optimization of targeted functionalization strategies, and further clarification of in vivo metabolic behavior and long-term biosafety. The corresponding strategies for performance enhancement and novel material design approaches will also be discussed. Finally, we will prospect future development directions of NIR-II luminescent AgNCs, with the aim of promoting their broader application breakthroughs in areas such as deep-tissue imaging, multimodal theranostics, and precision medicine.