Most recent advances on enzyme-activatable optical probes for bioimaging

Enzymes are essential biological elements that play vital roles in many key cellular events and physiological processes. The dysregulation of enzyme activity broadly occurs in a large number of diseases ranging from inflammation to neurodegenerative disorders to tumors. Molecular imaging allows accurate and noninvasive visualization of biological analytes/physiological processes of interest closely linked to human health at different levels. Among various imaging modalities, optical imaging stands out benefited from its high sensitivity, excellent spatiotemporal resolution, real-time mode, and facile accessibility. Diverse optical probes specifically activatable by disease-relevant enzymes have sprung up. In comparison to the "always-on" counterparts, the "off-on" imaging probes activated by enzymes hold great promise for precise diagnosis of diseases at early stage with high target-to-background ratio, dramatically improved specificity, and significantly enhanced sensitivity. Herein, the most recent advances in optical probes activatable by enzymes for biosensing and bioimaging are briefly reviewed emphasizing their molecular design, working mechanism, and biomedical applications. Besides, some important prospects and the current challenges to fully implement the potential of enzyme-activatable probes for precise and efficient theranostics in life science are also pointed out to hopefully arouse new insights into the development of new generation of theranostics.