NIR-II Fluorescence Imaging and Photothermal Theranostics

Fluorescence imaging in the second near-infrared window (NIR-II, 1000–1700 nm) offers unprecedented opportunities for visualising deep-seated tissues with enhanced spatial resolution, minimal autofluorescence and reduced light scattering. By operating at longer wavelengths, NIR-II probes penetrate several millimetres to centimetres into biological media, facilitating precise delineation of vascular networks, tumour margins and organ microstructures. Photothermal theranostics combines such imaging with the non-radiative conversion of absorbed light into heat, enabling simultaneous diagnostic visualisation and targeted thermal ablation of diseased tissue. Central to this approach is the rational design of small-molecule and nanoparticulate agents that balance high fluorescence quantum yield with efficient photothermal conversion. Structural motifs such as donor–acceptor–donor frameworks and aggregation-induced emission luminogens (AIEgens) have emerged as key strategies for maximising brightness, tunability and biocompatibility. This dual functionality holds immense promise for image-guided surgery, real-time treatment monitoring and minimally invasive interventions across oncology, vascular medicine and inflammatory disease models.

Research from Nature Portfolio

Recent studies have demonstrated the value of ultralong molecular packing in small-molecule NIR-II fluorophores. By engineering aggregation-induced emission motifs and extending donor–acceptor distances, novel dyes emit beyond 1200 nm with a signal-to-background ratio exceeding 100 through 4–6 mm of tissue, enabling high-contrast detection of deep lesions with virtually zero background. In parallel, acceptor engineering has produced a sulfonated dye featuring a robust thiadiazoloquinoxaline core that resists alkaline degradation while exhibiting a two-fold increase in quantum yield compared to conventional analogues. Complexation with serum proteins further amplifies fluorescence intensity, permitting real-time cerebral and tumour vessel imaging with micrometre-scale resolution. Foundational work on pure organic NIR-IIb AIEgens has also revealed molecular and morphological guidelines for extending emission to 1500–1700 nm, achieving quantum yields above 10 % in vivo and visualising fine vascular and intestinal structures in live models.

NIR-II Fluorescence Imaging and Photothermal Theranostics publication trend

The graph below shows the total number of articles in nir-ii fluorescence imaging and photothermal theranostics across all publications each year (not limited to Nature Index journals).

Technical terms

NIR-II window: The spectral region between 1000 and 1700 nm used for deep-tissue optical imaging with reduced scattering and autofluorescence.

Aggregation-Induced Emission (AIE): A photophysical phenomenon where certain luminogens exhibit enhanced fluorescence in aggregated or solid states due to restricted intramolecular motions.

Donor–Acceptor–Donor (D-A-D) structure: A molecular architecture featuring electron-donating units flanking an electron-accepting core to facilitate intramolecular charge transfer and tune optical properties.

Quantum Yield: The ratio of emitted photons to absorbed photons, indicating fluorescence efficiency.

Photothermal Conversion Efficiency: The proportion of absorbed light energy converted into heat, determining the effectiveness of thermal ablation.

Signal-to-Background Ratio: The intensity of target fluorescence relative to non-specific background emission, crucial for imaging contrast.

Twisted Intramolecular Charge Transfer (TICT): A process in which excited-state molecules adopt a twisted geometry, often promoting non-radiative decay and heat generation.

References

1. Engineered NIR-II fluorophores with ultralong-distance molecular packing for high-contrast deep lesion identification. Nature Communications (2023).
2. Acceptor engineering for NIR-II dyes with high photochemical and biomedical performance. Nature Communications (2022).
3. Albumin tailoring fluorescence and photothermal conversion effect of near-infrared-II fluorophore with aggregation-induced emission characteristics. Nature Communications (2019).
4. Design of AIEgens for near-infrared IIb imaging through structural modulation at molecular and morphological levels. Nature Communications (2020).
5. Tunable Nanoparticles with Aggregation‐Induced Emission Heater for Precise Synergistic Photothermal and Thermodynamic Oral Cancer Therapy of Patient‐Derived Tumor Xenograft. Advanced Science (2023).
6. Incorporation of Robust NIR‐II Fluorescence Brightness and Photothermal Performance in a Single Large π‐Conjugated Molecule for Phototheranostics. Advanced Science (2022).
7. Structural and process controls of AIEgens for NIR-II theranostics. Chemical Science (2021).