Near-Infrared-II Fluorescent Probes for Biomedical Imaging

The second near-infrared window (NIR-II; 1000–1700 nm) has emerged as a transformative modality for biological imaging, offering reduced photon scattering, minimal tissue autofluorescence and enhanced penetration depth compared with visible and first-window NIR techniques. A diverse toolkit of probes—from small-molecule cyanine dyes and anti-quenching polymethines to protein-based fluorophores and activatable nanoprobes—has been developed to address challenges such as low quantum yield, environmental quenching and limited biocompatibility. Recent strategies include molecular engineering to enhance brightness and photostability, genetic fusion to albumin domains for precise pharmacokinetics, and structural modifications that prevent nonspecific serum binding. Together, these innovations enable real-time lymphography, vascular mapping, tumour delineation and intraoperative guidance, paving the way for clinical translation of deep-tissue fluorescence imaging across oncology, neurology and cardiovascular research.

Research from Nature Portfolio

Biomimetic fluorescent proteins have been created by covalently attaching synthetic NIR-II dyes to serum albumin domains under mild physiological conditions. These chemogenic protein-seeking constructs exhibit enhanced brightness and photostability, and enable multicolour deep-tissue lymphography and angiography with high biocompatibility.

A bioengineering approach has generated albumin fragment–cyanine dye complexes via genetic editing, yielding size-tunable, covalently protected probes. These variants significantly improve quantum yield and permit precise control over circulation half-life and conjugation to targeting ligands, broadening prospects for clinical imaging.

A novel “pocket-escaping” acceptor design overcomes the common back-door binding of twisted intramolecular charge-transfer dyes to albumin pockets. By avoiding nonspecific capture, these probes deliver improved signal specificity and accuracy in live-animal imaging of liver fibrosis and other pathologies.

Near-Infrared-II Fluorescent Probes for Biomedical Imaging publication trend

The graph below shows the total number of articles in near-infrared-ii fluorescent probes for biomedical imaging across all publications each year (not limited to Nature Index journals).

Technical terms

NIR-II window: Spectral range from 1000 to 1700 nm with reduced tissue scattering and autofluorescence, enabling deeper optical penetration.

Quantum yield: Ratio of emitted to absorbed photons—a measure of fluorescence efficiency.

Polymethine cyanine dye: Organic fluorophore featuring conjugated methine chains, valued for high extinction coefficients and tunable NIR-II emission.

Photostability: Resistance of a probe to photobleaching under prolonged illumination.

Albumin binding: Interaction of fluorophores with serum albumin, influencing biodistribution, background signal and pharmacokinetics.

Activatable probe: Fluorescent agent that remains quenched until triggered by specific biological stimuli, improving imaging specificity.

References

1. Biomimetic NIR-II fluorescent proteins created from chemogenic protein-seeking dyes for multicolor deep-tissue bioimaging. Nature Communications (2024).
2. Anti-quenching NIR-II molecular fluorophores for in vivo high-contrast imaging and pH sensing. Nature Communications (2019).
3. Indocyanine green fluorescence in second near-infrared (NIR-II) window. PLOS ONE (2017).
4. A genetic engineering strategy for editing near-infrared-II fluorophores. Nature Communications (2022).
5. The pursuit of polymethine fluorophores with NIR-II emission and high brightness for in vivo applications. Chemical Science (2022).
6. A pocket-escaping design to prevent the common interference with near-infrared fluorescent probes in vivo. Nature Communications (2020).
7. NIR-II cell endocytosis-activated fluorescent probes for in vivo high-contrast bioimaging diagnostics. Chemical Science (2021).