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

Abstract

Recently, second near-infrared (NIR-II) fluorescent imaging has been widely applied in biomedical diagnosis, due to its high spatiotemporal resolution and deep tissue penetration. In contrast to the “always on” NIR-II fluorescent probes, the activatable NIR-II fluorescent probes have specific targeting to biological tissues, showing a higher imaging signal-to-background ratio and a lower detection limit. Therefore, it is of great significance to utilize disease-associated endogenous stimuli (such as pH values, enzyme existence, hypoxia condition and so on) to activate the NIR-II probes and achieve switchable fluorescent signals for specific deep bioimaging. This review introduces recent strategies and mechanisms for activatable NIR-II fluorescent probes and their applications in biosensing and bioimaging. Moreover, the potential challenges and perspectives of activatable NIR-II fluorescent probes are also discussed.

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“…Representative NIR-II fluorescent probes including carbon nanotubes, organic dyes, quantum dots (QDs), lanthanide (Ln 3+ )-doped nanoparticles, and aggregation-induced emission (AIE) nanoparticles have enlarged the library of luminescent materials for biomedical application. However, most NIR-II fluorescent probes are “always-on” probes, which can accumulate in both the target and background tissues owing to their nonspecific effects, leading to a low signal-to-noise ratio (SNR). , Compared with always-on probes, our interest is to develop NIR-II fluorescent probes that are specifically activated by the target and simultaneously increase the target signal while greatly reducing the background signal to achieve a higher SNR. , …”