Activatable NIR‐II Fluorescent Probes Applied in Biomedicine: Progress and Perspectives

Abstract

With the advantage of inherent responsiveness that can change the spectroscopic signals from “off” to “on” state in responding to targets (e. g. biological analytes/microenvironmental factors), activatable fluorescent probes have attracted extensive attention and made significant progress in the field of bioimaging and biosensing. Due to the high depth of tissue penetration, minimal tissue damage and negligible background signal at longer wavelengths, the development of second near‐infrared window (NIR‐II) fluorescent materials provides a new opportunity to develop activable fluorescent probes. Here, we summarized properties, advantages and disadvantages of mainly NIR‐II fluorophores (such as rare earth‐doped nanoparticles, quantum dots, single‐walled carbon nanotubes, small molecule dyes, conjugated polymers and gold nanoclusters), then overviewed current role and development of activatable NIR‐II fluorescent probes (AFPs) for biomedical applications including biosensing, bioimaging and therapeutic. The potential challenges and perspectives of AFPs in deep‐tissue imaging and clinical application are also discussed.

Dithieno[3,2-b:2′,3′-d]silole-based conjugated polymers for bioimaging in the short-wave infrared region

“…† To our best knowledge, the fluorescence quantum efficiency of P1 and P2 is higher than majority of organic SWIR fluorescent materials. 48 Thus, P1 and P2 are very suitable for in vivo imaging. The high quantum efficiency of P1 and P2 should be attributed to their structural characteristics.…”

Advances of gold nanoclusters for bioimaging

“…In the NIR region, including the NIR I region (700–900 nm) and the NIR II region (1000–1700 nm), the human body exhibits low absorption and no interference from biological tissues, showing its great potential for bioimaging. Compared with other NIR materials, AuNCs have the advantages of simple preparation, high biocompatibility, easy surface modification, significant Stokes shifts and rapid elimination ( Gong et al., 2021a ). Therefore, modulation of the FL emission wavelength of AuNCs has been a hot research topic, and selecting suitable ligands for modification is one of the most commonly used strategies, such as proteins, polymers, and peptides ( Figure 4 ) ( Kumar and Tseng, 2020 ; Wu et al., 2010 ).…”

Activatable Second Near-Infrared Fluorescent Probes: A New Accurate Diagnosis Strategy for Diseases

“…Enzymes are an extremely important class of biocatalysts which are involved in a great number of biological reactions in living organisms, and abnormalities in their concentrations are often associated with the development of various diseases [ 64 , 65 , 66 ]. For example, β-galactosidase (β-Gal), an enzyme that can hydrolyze substances containing a β-glycoside bond, exists widely in living organisms [ 67 , 68 ].…”