Illuminating the metabolic sink: Optical probes for in vivo thermogenic fat imaging

As a metabolic sink, thermogenic fat plays a pivotal role in the pathogenesis of metabolic diseases, yet current techniques for assessing its location and activity in vivo face challenges, such as high costs and operational complexity. Optical imaging, encompassing label-free and labeled modalities, offers a relatively cost-effective and straightforward alternative. In comparison with the label-free modality, labeled optical imaging stands out for its superior performance, which is attributed to the utilization of advanced optical probes with enhanced specificity and sensitivity. Despite significant advancements in optical probes for thermogenic fat detection, systematic compilations related to these studies remain scarce. Hence, this review concentrates on four typical categories of optical probes and expounds their physicochemical properties, imaging benefits, and applications in thermogenic fat assessment. Their imaging targets, design strategies, translational challenges, and perspectives are also discussed. As a reference resource, this review will facilitate the development of more reliable and safer optical probes targeting thermogenic fat, thereby assisting in precise theranostics for metabolic diseases.