Unlocking the power of optical imaging in the second biological window: Structuring near‐infrared II materials from organic molecules to nanoparticles

Abstract

Biomedical imaging techniques play a crucial role in clinical diagnosis, surgical intervention, and prognosis. Fluorescence imaging in the second biological window (second near‐infrared [NIR‐II]; 1000–1700 nm) has attracted attention recently. NIR‐II fluorescence imaging offers unique advantages in terms of reduced photon scattering, deep tissue penetration, high sensitivity, and many others. A host of materials, including small organic molecules, single‐walled carbon nanotubes, polymeric and rare‐earth‐doped nanoparticles, have been explored as NIR‐II emitting fluorescent probes. Efficient and viable approaches to design and develop fluorescence probes with tunable photophysical properties without compromising other key features are of paramount importance. Various chemical strategies are explored to increase the quantum yield of these imaging agents without compromising their spatiotemporal resolution, specificity, and tissue penetration capabilities. This review summarizes the strategies implemented to design and synthesize NIR‐II emitting nanoparticles and small organic molecule‐based fluorescent probes for applications in the biomedical field. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Implantable Materials and Surgical Technologies > Nanoscale Tools and Techniques in Surgery

Rational Design of NIR-II AIEgens with Ultrahigh Quantum Yields for Photo- and Chemiluminescence Imaging

“…Many inorganic NIR-II fluorescent materials have been developed with narrow emission bands and high photostability. However, their applications are still impeded by inevitable drawbacks like low quantum yields (QYs), poor reproducibility, and high toxicity. − Organic small molecules with NIR-II emission are potential candidates for bioimaging because of good biocompatibility, well-defined molecular structures, and ease of synthetic modification. To red-shift the emission wavelength of NIR-II dyes, two strategies are commonly used. , The first strategy is to enlarge the conjugation length.…”

“…However, their applications are still impeded by inevitable drawbacks like low quantum yields (QYs), poor reproducibility, and high toxicity. − Organic small molecules with NIR-II emission are potential candidates for bioimaging because of good biocompatibility, well-defined molecular structures, and ease of synthetic modification. To red-shift the emission wavelength of NIR-II dyes, two strategies are commonly used. , The first strategy is to enlarge the conjugation length. However, it cannot always work practically because of tedious synthesis, unsatisfactory processability, and instability (especially for cyanine dyes with extended double bonds).…”

“…To red-shift the emission wavelength of NIR-II dyes, two strategies are commonly used. 7,14 The first strategy is to enlarge the conjugation length. However, it cannot always work practically because of tedious synthesis, unsatisfactory processability, and instability (espe- cially for cyanine dyes with extended double bonds).…”

Rational Design of NIR-II AIEgens with Ultrahigh Quantum Yields for Photo- and Chemiluminescence Imaging

“…However, their applications are still impeded by inevitable drawbacks like low quantum yields (QYs), poor reproducibility, and high toxicity. [7][8][9][10][11][12][13] Organic small molecules with NIR-II emission are potential candidates for bioimaging because of good biocompatibility, well-defined molecular structures, and ease of synthetic modification. To red-shift the emission wavelength of NIR-II dyes, two strategies are commonly used.…”

“…To red-shift the emission wavelength of NIR-II dyes, two strategies are commonly used. 7,14 The first strategy is to enlarge the conjugation length. However, it cannot always work practically because of tedious synthesis, unsatisfactory processability, and instability (especially for cyanine dyes with extended double bonds).…”