Perfecting and extending the near-infrared imaging window

Multi-dimensional donor engineering of NIR-II AIEgens for multimodal phototheranostics of orthotopic breast cancer

"One-for-all" multimodal phototheranostic agents, which integrate multiple photodiagnostic and phototherapeutic functionalities into a single component, have emerged as promising platforms for advancing cancer treatment. Among these, agents featuring second near-infrared (NIR-II) emission are particularly appealing due to their superior tissue penetration depth and high signal-to-background ratio (SBR). However, most reported NIR-II fluorophores suffer from severely imbalanced radiative and non-radiative excited-state energy dissipation in biological environments, resulting in extremely low fluorescence quantum yields (QYs) and limited diagnostic efficacy. This highlights the urgent need for innovative molecular design strategies to develop high-performance NIR-II "one-for-all" multimodal phototheranostic agents. Herein, we present, for the first time, a multi-dimensional donor engineering protocol that optimizes donor design at the molecular, aggregated, and solvent-interaction levels. By introducing 2,4,4-trimethylpentan-2-yl groups into the diphenylamine indeno[1,2-b]thiophene donor unit, we developed a donor-acceptor-donor (D-A-D) type NIR-II aggregation-induced emission-active luminogen (AIEgen), i.e. OPITBT. When formulated into nanoparticles (NPs), OPITBT NPs exhibited a 16-fold enhancement in fluorescence QY compared to OPITBT in tetrahydrofuran, along with excellent photothermal conversion efficiency (PCE) and acceptable type-I reactive oxygen species (ROS) generation. When further fabricated into tumor-targeting NPs, the resulted OPITBT-R NPs effectively eliminated orthotopic breast cancer through fluorescence-photoacoustic-photothermal multimodal imaging-guided photodynamic-photothermal synergistic therapy under single 808 nm laser irradiation. Notably, the exceptional NIR-II fluorescence brightness of OPITBT-R NPs enables high-resolution NIR-IIb whole-body vascular imaging in living mice. This work provides a versatile strategy to enhance radiative dissipation of NIR-II fluorophores for balanced phototheranostic performance and advances the development of "one-for-all" phototheranostic systems.

High-contrast in vivo fluorescence imaging exploiting wavelengths beyond 1880 nm

The second near-infrared (NIR-II) window is widely acknowledged for its excellent potential in in vivo fluorescence imaging. Currently, NIR-II fluorescence imaging predominantly operates within the 900-1880 nm spectral range, while the region beyond 1880 nm has been disregarded due to the large light absorption of water. Based on a refined understanding of the effect of light absorption on imaging, we propose an approach that utilizes the previously neglected region surrounding the water absorption peak at ~1930 nm for imaging. Both simulations and experiments confirm that the water absorption contributes positively to imaging, enabling high-contrast in vivo fluorescence imaging in the 1880-2080 nm window. To further assess the applicability of this approach in different biological media, we extend our focus to fluorescence imaging in adipose tissue. This leads to the expansion of the imaging window to 1700-2080 nm, owing to the unique light absorption characteristics of adipose tissue. Our results demonstrate that the 1700-2080 nm region provides optimal imaging quality in adipose tissue, attributing to its moderate absorption and low scattering. This work advances our understanding of the interplay between light absorption and photon scattering in bioimaging, providing an insight for selecting optimal imaging windows to achieve high-contrast fluorescence imaging.

High-Resolution Multicolor Shortwave Infrared Dynamic In Vivo Imaging with Chromenylium Nonamethine Dyes

Imaging in the shortwave infrared (SWIR) region offers fast, high-resolution visualization of in vivo targets in a multiplexed manner. These methods require bright, bathochromically shifted fluorescent dyes with sufficient emission at SWIR wavelengths-ideally above 1500 nm for high-resolution deep tissue imaging. Polymethine dyes are a privileged class of contrast agents due to their excellent absorption and high degree of modularity. In this work, we push flavylium and chromenylium dyes further into the SWIR region through polymethine chain extension. This panel of nonamethine dyes boasts absorbances as red as 1149 nm and tail emission beyond 1500 nm. These dyes are the brightest organic fluorophores at their respective bandgaps to date, with εmax ∼ 105 M-1 cm-1 and ΦF up to 0.5%. Using two nonamethine dyes, Chrom9 and JuloFlav9, we performed two-color all-SWIR multiplexed imaging (Excitation at 1060 and 1150 nm; Emission collection at >1500 nm), enhancing the depths and resolutions able to be obtained in multicolor SWIR imaging with small molecule contrast agents. Finally, we combine the nonamenthine dyes with other SWIR-emissive fluorophores and demonstrate five-color awake imaging in an unrestrained mouse, simultaneously pushing the multiplexing, resolution, and speed limits of in vivo optical imaging.

Molecular Rectangles Featuring Two Parallel NCN-Coordinated Platinum Units: Enhancing Near-Infrared Emission Through Excimer Formation

New macrocyclic molecules are described that incorporate Pt(NCN) units on opposite edges of a rectangular structure, with xanthene units constituting the other two sides. Here, NCN represents a cyclometallating tridentate ligand based on 2,6-di(2-pyridyl)benzene or its pyrimidine analog. The complexes display strong photoluminescence peaking in the near-infrared region of the spectrum in solution (λmax up to 761 nm). Photophysical data and DFT calculations indicate that the emission arises from "intramolecular excimers"-triplet excited states that form when the two Pt(NCN) units within the molecule are brought into close proximity to interact interfacially. In doped polymers, the necessary molecular distortion is inhibited, but related excited states that emit in a similar region can still form through intermolecular interactions.

Imaging-Guided Microscale Photothermal Stereolithography Bioprinting

Stereolithography bioprinting relies heavily on costly photoinitiators for polymerization, limiting its potential for further technical advancement to meet growing needs in tissue engineering and regenerative medicine. Thermal initiators, in contrast, are low cost, and rapid growth of the photothermal conversion field offers a wide range of materials and tools to convert light into heat. However, high-resolution photothermal stereolithography bioprinting remains unattainable due to the difficulty of confining heat in an aqueous environment. Here, this challenge has been fully addressed by establishing imaging-guided microscale photothermal stereolithography bioprinting (ImPSB). This technique is achieved through building a novel imaging-guided stereolithography system that provides depth-resolved visualization of the printing dynamics, creating a unique photothermal initiator in the second near-infrared window, and developing a new bioink by seeing and controlling the photothermal gelation process. ImPSB achieves a printing resolution of ≈47 µm and generates smooth lines of arbitrarily designed shapes with a cross-sectional diameter as small as ≈104 µm, representing an unprecedented scale from photothermal aqueous stereolithography. Its cellular biocompatibility in printing both bioscaffold and cell-laden hydrogel is demonstrated, and its feasibility of transdermal printing is also shown. This work sets a new path for high-resolution stereolithography bioprinting where the vast photothermal resources can be utilized.

Synergistic Comprehensive Activation Methods for Dual-Modality PDT and Hypoxia-Triggered Chemotherapy Guided by NIR-II Imaging beyond 1700 nm in Deep Tumors

Although photodynamic therapy (PDT) holds great promise for applications in cancer treatment, it has limited effectiveness against deep hypoxic tumors. Moreover, the lack of visualization guidance for precision theranostics poses additional challenges, hindering its broader clinical adoption. By combining NIR-IIc (1800 nm) imaging guidance with internally and externally activatable dual-modality PDT and hypoxia-triggered chemotherapy, this study proposes a conceptual framework to overcome these limitations. This approach involves the use of photoswitchable lanthanide-doped nanoparticles featuring Tm3+-activated upconversion/downshifting emissions coupled with carboxyl-terminated Ir(III) complex-based Type I/II photosensitizer to form a nanophotosensitizer. The findings demonstrate that this system enabled NIR-IIc imaging guidance upon 808/980 nm excitation while selectively activating external PDT under 980 nm irradiation, thereby ensuring accurate therapy and minimizing phototoxicity risk. The Ir(III) complex conjugates with luminol to form a self-illuminating Type I/II photosensitizer, which can respond to the elevated H2O2 levels in the tumor microenvironment, effectively catalyzing chemiluminescence-assisted PDT. Moreover, PDT aggravates tumor hypoxia, which in turn activates the hypoxia-activatable prodrugs like tirapazamine, resulting in a synergistic antitumor effect. With NIR-IIc imaging-guided dual-modality PDT, this study introduces a groundbreaking approach that unites Type I/II PDT with chemotherapy, significantly advancing the precise and effective treatment of deep hypoxic tumors.

Research progress of near-infrared fluorescence imaging in accurate theranostics in bladder cancer

BACKGROUND

With among the highest 5-year recurrence rate, bladder cancer is a relatively common type of malignancy that typically originates from the urothelial cells lining the bladder. Additionally, bladder cancer is one of the most financially burdensome neoplasms to medical institutions in terms of management. Hence, prompt identification and accurate handling of bladder cancer are pivotal for enhancing patient prognosis. Optical imaging has experienced remarkable advancements in fundamental medical research owing to its cost-effectiveness and capacity for real-time imaging. The utilization of near-infrared imaging techniques has also become a prominent area of research in recent times. By effectively decreasing the adverse effects of light scattering and tissue autofluorescence, this technique offers a deeper penetration depth, a better signal-to-noise ratio of images, and a clear resolution for imaging. Thus, this article introduces the application of near-infrared fluorescence imaging in diagnosing and treating bladder cancer. Furthermore, the paper delves into the field's obstacles, possibilities, and upcoming prospects.

RESULTS

Near-infrared fluorescence has advantages over white or blue light in theory and in most articles. However, the lack of penetration depth of NIR fluorescence imaging is still a challenge.

CONCLUSION

Despite notable improvements in the depth of near-infrared fluorescence imaging, the penetration of deeper tissues remains a barrier. It is our hope and pursuit that NIR fluorescence imaging technology can achieve good depth and precision in surgery.

From Optical Fiber Communications to Bioimaging: Wavelength Division Multiplexing Technology for Simplified in vivo Large-depth NIR-IIb Fluorescence Confocal Microscopy

Near-infrared II (NIR-II, 900-1880 nm) fluorescence confocal microscopy offers high spatial resolution and extensive in vivo imaging capabilities. However, conventional confocal microscopy requires precise pinhole positioning, posing challenges due to the small size of the pinhole and invisible NIR-II fluorescence. To simplify this, a fiber optical wavelength division multiplexer (WDM) replaces dichroic mirrors and traditional pinholes for excitation and fluorescence beams, allowing NIR-IIb (1500-1700 nm) fluorescence and excitation light to be coupled into the same optical fiber. This streamlined system seamlessly integrates key components-excitation light, detector, and scanning microscopy-via optical fibers. Compared to traditional NIR-II confocal systems, the fiber optical WDM configuration offers simplicity and ease of adjustment. Notably, this simplified system successfully achieves optical sectioning imaging of mouse cerebral blood vessels up to 1000 µm in depth. It can discern tiny blood vessels (diameter: 4.57 µm) at 800 µm depth with a signal-to-background ratio (SBR) of 5.34. Additionally, it clearly visualizes liver vessels, which are typically challenging to image, down to a depth of 300 µm.

Rationally designed NIR-II excitable and endoplasmic reticulum-targeted molecular phototheranostics for imaging-guided enhanced photoimmunotherapy of triple-negative breast cancer

Triple-negative breast cancer (TNBC) is a highly aggressive subtype of breast cancer characterized by an extremely poor prognosis. Photoimmunotherapy has emerged as a promising strategy for the treatment of TNBC. This approach works by selectively destroying tumor cells, releasing tumor-associated antigens, activating the immune system, and effectively inhibiting tumor proliferation and metastasis. However, the majority of current phototheranostic approaches are hindered by limited tissue penetration in the first near-infrared (NIR-I) and ultraviolet-visible (UV-Vis) regions. Additionally, due to the lack of specific subcellular targets, it may be difficult to effectively treat deep-seated lesions with ambiguous and extensive boundaries caused by TNBC metastases. Consequently, the development of effective, deep-penetrating, organelle-targeted phototheranostics is essential for enhancing treatment outcomes in TNBC. This work proposes a novel molecular design strategy of NIR-II phototheranostics to realize planar rigid conjugation and alkyl chain functionalization. The di-hexaalkyl chains in a vertical configuration on the donor (4H-cyclopenta[2,1-b:3,4-b'] dithiophene) and shielding units (fluorene) are introduced to construct a S-D-A-D-S type NIR-II phototheranostics (IR-FCD). The planar and rigid structure of IR-FCD exhibits a robust intramolecular charge transfer capability, a lower band gap, enhanced photon absorption properties, and significant steric hindrance from vertically arranged alkyl chains to minimize non-radiative energy loss. By incorporating N-(but-3-yn-1-yl)-4-methylbenzenesulfonamide at the terminus of an elongated alkyl chain, followed by self-assembly into DSPE-S-S-PEG2000, NIR-II excitable phototheranostics (IR-FCD-Ts NPs) with endoplasmic reticulum (ER) targeting capability were successfully synthesized for imaging-guided photoimmunotherapy of TNBC. The IR-FCD-Ts NPs demonstrate exceptional optical characteristics, with maximum absorption at 1068 nm (extending to 1300 nm) and emission at 1273 nm (extending to 1700 nm), along with a high molar absorption coefficient of 2.76*104 L/mol·c at 1064 nm in aqueous solution. Under exposure to 1064 nm laser irradiation, IR-FCD-Ts NPs exhibit superior photothermal properties and have the potential for photodynamic therapy. By targeting ER, thereby inducing ER stress and significantly enhancing immunogenic cell death (ICD) in tumor cells, it triggers a strong antitumor immune response and inhibits the proliferation and metastasis of TNBC.

Two-plex in vivo molecular imaging in the second near-infrared window for immunotherapeutic response

Tumor-infiltrating CD8+ T cells and programmed death-1 (PD1) levels are critical indicators for tumor immunophenotyping and therapeutic decision-making. Noninvasive optical imaging in the second near infrared window (NIR-II) is particularly well-suited for investigating the biological processes within tumors in live mammals, thanks to its deep-tissue penetration and superior spatiotemporal resolution. However, in vivo NIR-II imaging has primarily been restricted to a single probe at a time. Methods: Herein, we developed a two-plex NIR-II molecular imaging method utilizing the non-overlapping fluorescence emission of indocyanine green (ICG) in the NIR-IIa window (1000-1200 nm) and PbS/CdS core-shell quantum dots (QDs) in the NIR-IIb window (1500-1700 nm). By integrating PD1 aptamer-labeled ICG (ICG-Apt-PD1, targeting PD1) and CD8 aptamer-labeled QDs (QDs@Apt-CD8, targeting CD8+ T cells), our two-plex NIR-II molecular imaging enabled simultaneous and noninvasive monitoring of the number of CD8+ T cells and PD1 levels in tumors. Results: QDs@Apt-CD8 demonstrated the excellent ability for in vivo imaging of tumor infiltrating CD8+ T cells, owing to its strong NIR-IIb luminescence and the high selectivity and specificity. This two-plex in vivo molecular imaging allowed for dynamic monitoring for PD1 levels and the number of CD8+ T cells in tumors. We observed the heterogeneous bio-distributions of PD1 and CD8+ T cells across different tumor types and revealed the tumor immunophenotypes. Moreover, our findings indicated that the low PD1 and high CD8+ T cells levels in tumors predicted a better anti-tumor effect. Conclusions: Such in vivo noninvasive NIR-II molecular imaging would complement ex vivo biopsy-based diagnostic techniques, and it could contribute to developing an in vivo tumor immune-scoring algorithm to offer a more precise prediction for immunotherapeutic response.

Achieving Ultrabright NIR-II Nanofluorophore for In Vivo Imaging by Inhibiting H-Aggregates Formation

Small molecules with an acceptor-donor-acceptor (A-D-A) structure, featuring a fused-ring core as the donor and two electron-withdrawing end groups as acceptor units, represent a potential option for NIR-II fluorophores, benefiting from their narrow bandgaps, superior light-harvesting capabilities, and exceptional photostabilities. However, their planar conformations predispose them to forming H-aggregates during self-assembly, leading to significantly reduced fluorescence quantum yield (QY) of the resulting nanofluorophores. Herein, we report a small molecule, PF8CN, with a terminal unit-A-D-A-terminal unit structure. The terminal units of 3,5-bis(octyloxy)phenyl group result in a twisted conformation for PF8CN, preventing face-to-face stacking and thereby inhibiting the formation of H-aggregates. Consequently, the NIR-II fluorescence QY of PF8CN NPs is 3.8 times that of the model nanofluorophore (F8CN NPs), which contains a substantial amount of H-aggregates. The NIR-II brightness of PF8CN NPs is 5.3- and 14.9-times that of F8CN NPs and ICG/FBS, respectively, at an equal molar concentration. Such ultrahigh NIR-II brightness of PF8CN NPs allows us to perform long-term and real-time NIR-II fluorescence imaging of cerebral and hindlimb vessels, as well as the thrombolytic process. This work provides an effective method for producing nanofluorophores with ultrahigh NIR-II brightness, positioning PF8CN NPs as a strong contender in the field of NIR-II nanofluorophores.

Alleviating NIR-II emission quenching in ring-fused fluorophore via manipulating dimer populations for superior fluorescence imaging

Emission quenching resulting from fluorophore aggregation has long been a significant challenge in optimizing emission-based technologies, such as fluorescence imaging and optoelectronic devices. Alleviating this quenching in aggregates is crucial, yet progress is impeded by the limited understanding of the nature and impact of aggregates on emission. Here, we elucidate the critical role of dimeric aggregate (dimer) in alleviating second near-infrared (NIR-II, 900-1700 nm) emission quenching from ring-fused fluorophore 4F for superior fluorescence imaging. Spectral decomposition and molecular dynamics simulations demonstrate the predominance of dimer populations in 4F aggregates. Notably, dimers exhibit significantly weaker emission but intense intermolecular nonradiative (interNR) decay compared to monomers, as demonstrated by ultrafast spectra and quantum calculation. Therefore, the predominant population of dimers with weak emission and pronounced interNR feature underlies the emission quenching in 4F aggregates. This discovery guides the preparation of ultrabright NIR-II 4F nanofluorophore (4F NP3s) by decreasing dimer populations, which show 5-fold greater NIR-II brightness than indocyanine green, enabling superior resolution in visualizing blood vessels. This work offers valuable insights into aggregation-caused quenching, with broad implications extending far beyond NIR-II fluorescence imaging.

Cyclodextrins as nanocarriers of hydrophobic silicon phthalocyanine dichloride for the enhancement of photodynamic therapy effect

In this study, silicon phthalocyanine dichloride (SiCl2Pc) was successfully encapsulated in β-cyclodextrin (β-CD) and hydroxy-propyl-β-cyclodextrin (HP-β-CD) using the kneading method. Dynamic Light Scattering (DLS) demonstrated complexes of various hydrodynamic diameters with moderate stability in aqueous solutions. Their structural characterization by Infrared Spectroscopy (FT- IR) indicated that a part of phthalocyanine is located inside the cyclodextrin cavity. Both photophysical and photochemical studies showed that phthalocyanine's encapsulation in cyclodextrins increased its aqueous solubility. The photodynamic studies against A431 cancer cell line indicated that the complexes are more effective than pure SiCl2Pc. Pure SiCl2Pc's photodynamic effect is characterized as dose-dependent, whereas both complexes presented a biphasic dose-response photodynamic effect. For the highest energy dose of 3.24 J/cm2, pure SiCl2Pc induced mild cell toxicity. SiCl2Pc-β-CD complex was the most promising photosensitizer, exhibiting the highest photodynamic effect when irradiated at 2.16 J/cm2.

From X- To J-Aggregation: Subtly Managing Intermolecular Interactions for Superior Phototheranostics with Precise 1064 nm Excitation

The stacking mode in aggregate state results from a delicate balance of supramolecular interactions, which closely affects the optoelectronic properties of organic π-conjugated systems. Then, managing these interactions is crucial for advancing phototheranostics, yet remains challenging. A subtle strategy involving peripheral phenyl groups is debuted herein to transform X-aggregated SQ-H into J-aggregated SQ-Ph, reorienting intermolecular dipole interactions while rationally modulating π-π interactions. Co-assembled with liposomes (DSPE-PEG2000), SQ-Ph nanoparticles (NPs) exhibit low toxicity, superior biocompatibility, and a bathochromic shift to the 1064 nm match-excited NIR-II region, with a fluorescence brightness (ε1064 nm ΦNIR-II) of 4129 M-1 cm-1 and a photothermal conversion efficiency (PCE) of 48.3%. Preliminary in vivo experiments demonstrate that SQ-Ph NPs achieve a signal-to-background ratio (SBR) of up to 14.29 in NIR-II fluorescence imaging (FLI), enabling highly efficient photothermal therapy (PTT) of tumors guided by combined photoacoustic imaging (PAI). This study not only enriches the J-aggregation library but also provides a paradigm for optimizing photosensitizers at the supramolecular level.

Near-Infrared II Fluorescence Imaging Highlights Tumor Angiogenesis in Hepatocellular Carcinoma with a VEGFR-Targeted Probe

Hepatocellular carcinoma (HCC) is typically characterized by rich vascularity, with angiogenesis playing a crucial role in its growth and invasion. Molecular imaging of specific receptors in blood vessels is crucial in HCC diagnosis. In particular, in vivo imaging utilizing the second near-infrared (NIR-II) window offers improved tissue penetration, reduced light scattering, and lower autofluorescence. Despite the great potential of the NIR-II window, developing safe and effective probes to provide better imaging performance for HCC is urgently needed. In this study, NIR-II imaging integrated with a vascular endothelial growth factor receptor (VEGFR)-targeted probe generated by combining a VEGFR-targeted peptide with indocyanine green (ICG) is used to characterize HCC-related angiogenesis at a resolution of 56.0 µm. For the first time, liver metabolic curves and parameters of liver function reserve (LFR) are obtained by fitting NIR-II fluorescence signals with high spatiotemporal resolution, showing significant differences between HCC mice and controls. Moreover, unlike ICG, the targeting probe has a targeted effect on blood vessels in vivo. The tumor-to-normal (T/N) ratio in NIR-II imaging reaches up to 3.30 after post-injection of the targeting probe. The results indicate that the VEGFR-targeted probe is a powerful tool for NIR-II fluorescence imaging to enhance early diagnosis of HCC.

Xanthene-based NIR organic phototheranostics agents: design strategies and biomedical applications

Fluorescence imaging and phototherapy in the near-infrared window (NIR, 650-1700 nm) have attracted great attention for biomedical applications due to their minimal invasiveness, ultra-low photon scattering and high spatial-temporal precision. Among NIR emitting/absorbing organic dyes, xanthene derivatives with controllable molecular structures and optical properties, excellent fluorescence quantum yields, high molar absorption coefficients and remarkable chemical stability have been extensively studied and explored in the field of biological theranostics. The present study was aimed at providing a comprehensive summary of the progress in the development and design strategies of xanthene derivative fluorophores for advanced biological phototheranostics. This study elucidated several representative controllable strategies, including electronic programming strategies, extension of conjugated backbones, and strategic establishment of activatable fluorophores, which enhance the NIR fluorescence of xanthene backbones. Subsequently, the development of xanthene nanoplatforms based on NIR fluorescence for biological applications was detailed. Overall, this work outlines future efforts and directions for improving NIR xanthene derivatives to meet evolving clinical needs. It is anticipated that this contribution could provide a viable reference for the strategic design of organic NIR fluorophores, thereby enhancing their potential clinical practice in future.

Design strategies and biomedical applications of organic NIR-IIb fluorophores

The introduction of fluorescence imaging (FLI) in near-infrared II sub-channels (NIR-IIb, 1500-1700 nm) has revolutionized the ability to explore complex patho-physiological settings in vivo. Despite the transformative potentials, the development of organic NIR IIb dyes encounters considerable difficulties, and only a limited number of such fluorophores have been developed so far. This review systematically introduces design strategies of organic NIR-IIb fluorophores classified by molecular scaffolds, mainly including cyanine dyes and D-A-D small molecule dyes. The design strategies of cyanine dyes involve repurposing of the existing NIR dyes, conjugate reinforcement and regulation of the aggregation state. For D-A-D small molecule dyes, strategies mainly incorporate the extension of the conjugate skeleton, introduction of shielding units, and acceptor/donor engineering. We further describe recent biomedical applications including biomedical imaging and imaging-guided therapy, and conclude by clarifying the current challenges and prospects of NIR-IIb FLI.

In situ albumin tagging for targeted imaging of endothelial barrier disruption

The endothelial barrier (EB) is a critical component of the body's homeostatic mechanisms, thus developing effective imaging techniques to visualize its integrity is essential. The EB disruption is accompanied by the alternations in permeability and even the breakdown of tight junctions (TJs), leading to the leakage of albumin; thus, albumin can serve as a biomarker for EB disruption. Herein, we develop an albumin-specific, covalently tagged near-infrared II (NIR-II) dye, with its high selectivity for endogenous albumin, for targeted imaging EB disruption. Our albumin-tagging dye serves as a chromophore to construct NIR-II fluorescent proteins in situ, with substantially improved brightness. Thus, through in situ dye tagging of endogenous albumin as the efficient "targeting agent," we can precisely image disruptions in various endothelial barriers. Unlike the traditional exogenous targeting agents (e.g., dye-labeled antibodies) with enzymatic degradation or immune system capture issues, in situ albumin tagging demonstrates superhigh performance for targeted imaging.

Enhanced brightness and photostability of dye-sensitized Nd-doped rare earth nanocomposite for in vivo NIR-IIb vascular and orthotopic tumor imaging

Rare-earth doped nanoparticles (RENPs) have shown promise in biomedical imaging, particularly within the NIR-IIb region, due to their deep tissue penetration and minimal light scattering. However, challenges such as low extinction coefficients, narrow excitation spectra, and prone to quenching in aqueous environments limit their effectiveness. To overcome these obstacles, we developed a novel dye-sensitized, onion-like Nd-doped RENP nanocomposite to enhance NIR-IIb imaging performance. The onion-like Nd-RENP nanocomposite markedly enhances emission intensity at 1525 nm within the NIR-IIb range by reducing quenching and improving spectral overlap. The integration of an IR783-containing micellar layer further stabilizes the NIR dye, mitigating quenching and photobleaching. In vivo imaging studies demonstrated a 75-fold increase in luminance and a 9-fold improvement in photostability compared to free NIR dyes in aqueous solutions. Time-dependent in vivo studies confirmed the nanocomposite's capability for prolonged imaging of vascular and tumor tissues, maintaining high-resolution images for over an hour. Additionally, the nanocomposite supported successful 3D imaging reconstruction of biological tissues. The dye-sensitized onion-like Nd-RENP nanocomposite presents a significant advancement in NIR-IIb imaging, providing enhanced brightness and photostability. Its ability to maintain clear and stable imaging over extended periods suggests potential applications in dynamic vascular and tumor-targeted imaging. This innovation holds promise for future biomedical imaging technologies, particularly in areas requiring high-resolution and long-duration monitoring.

Dual-Ligand Assisted Anisotropic Assembly for the Construction of NIR-II Light-Propelled Mesoporous Nanomotors

The advent of autonomous nanomotors presents exciting opportunities for nanodrug delivery. However, significant potential remains for enhancing the asymmetry of nanomotors and advancing the development of second near-infrared (NIR-II) light-propelled nanomotors capable of operating within deep tissues. Herein, we developed a dual-ligand assisted anisotropic assembly strategy that enables precise regulation of the interfacial energy between selenium (Se) nanoparticle and periodic mesoporous organosilica (PMO). This strategy facilitates the controllable anisotropic growth of PMO on the Se nanoparticle, leading to the formation of Se&PMO Janus nanohybrids. The exposure ratio of the Se subunit within the Janus nanohybrids can be finely tuned from 0% to 75%. Leveraging the transformability of the Se subunit, a variety of functional MxSe&PMO Janus nanocomposites (MxSe denotes metal selenide) were further derived. As a proof of concept, CuSe&PMO Janus nanohybrids, with NIR-II photothermal properties, were employed as NIR-II light-driven nanomotors. By precisely controlling the exposure ratio of the CuSe subunit within the Janus nanostructure, these CuSe&PMO nanomotors achieved optimal self-propulsion, thus enhancing cellular uptake and promoting deep tumor penetration. Furthermore, the high loading capacity and hydrophobic framework of the PMO subunit enabled the incorporation of hydrophobic disulfiram, thereby significantly boosting the efficacy of synergistic active-motion photothermal therapy.

PET-Based Dual-Modal Probes for In Vivo Imaging

Molecular imaging has significantly advanced the detection and analysis of in vivo metabolic processes, while single-modal techniques remain limited. Dual-modal imaging, particularly positron emission tomography (PET)-based combinations has emerged as a powerful solution, offering enhanced capabilities through integration with magnetic resonance imaging (MRI) or near-infrared fluorescence (NIRF) imaging. This review highlights recent progress in PET-based dual-modal imaging, focusing on the development of various bimodal probes derived from antibodies, nanoparticles, and peptides, and key applications including image-guided surgery and disease assessment. PET-based dual-modal imaging holds substantial potential for advancing research and diagnostics by improving resolution and providing functional insights. By combining complementary modalities, these systems deliver a more comprehensive view of disease processes, leading to more accurate diagnoses and targeted treatments. Future research prioritizes optimizing probe design for enhanced biocompatibility and safety, facilitating clinical translation, and broadens applications beyond cancer. Through interdisciplinary collaboration, PET-based dual-modal probes are poised to play a pivotal role in improving patient outcomes, particularly in diagnosing and managing complex diseases.

Photoacoustic imaging of rat kidney tissue oxygenation using second near-infrared wavelengths

Significance

Conventionally, spectral photoacoustic imaging (sPAI) to assess tissue oxygenation (sO 2 ) uses optical wavelengths in the first near-infrared (NIR-I) window. This limits the maximum photoacoustic imaging depth due to the high spectral coloring of biological tissues and has been a major barrier to the clinical translation of the technique.

Aim

We demonstrate the second near-infrared (NIR-II) tissue optical window (950 to 1400 nm) for the assessment of blood and tissuesO 2 .

Approach

The NIR-II PA spectra of oxygenated and deoxygenated hemoglobin were first characterized using a phantom. Optimal wavelengths to minimize spectral coloring were identified. The resulting NIR-II PA imaging methods were then validated in vivo by measuring kidneysO 2 in adult female rats.

Results

sPAI of whole blood, in a phantom, and of blood in kidneys in vivo produced PA spectra proportional to wavelength-dependent optical absorption. Using the NIR-II wavelengths for spectral unmixing resulted in a ∼ 50 % decrease in the error of the estimated bloodsO 2 , compared with conventional NIR-I wavelengths. In vivo measurements of kidneysO 2 validated these findings, with a similar 50% reduction in error when using NIR-II wavelengths versus NIR-I wavelengths at larger illumination depths.

Conclusions

sPAI using NIR-II wavelengths improved the accuracy of tissuesO 2 measurements. This is likely due to reduced scattering, which reduces the attenuation and, therefore, the impact of spectral coloring in this wavelength range. Combined with the increased safe skin exposure fluence limits in this wavelength range, these results demonstrate the potential to use NIR-II wavelengths for quantitative sPAI ofsO 2 from deep heterogeneous tissues.

NIR-II scattering gold superclusters for intravascular optical coherence tomography molecular imaging

Currently, intravascular optical coherence tomography (IV-OCT) is limited to anatomical imaging, providing structural information about atherosclerotic plaque morphology, thrombus and dissection. Earlier detection and risk stratification would be possible through molecular characterization of endothelium but necessitates a purpose-engineered IV-OCT contrast agent. Here we developed gold superclusters (AuSCs) tailored to clinical instrumentation and integrated into clinically relevant workflows. AuSCs are aqueously dispersible clusters of closely packed small gold nanoparticles, affording plasmon hybridization to maximize light scattering at the IV-OCT laser line (~1,350 nm). A polymer coating fosters AuSC uniformity and provides a functionalizable handle, which we targeted to intravascular P-selectin, an early vascular endothelial marker of inflammation. In a rat model of intravascular inflammation, P-selectin-targeted AuSC facilitated IV-OCT molecular imaging, where the strength of the signal correlates with the severity of vascular inflammation.

NIR-activated multifunctional agents for the combined application in cancer imaging and therapy

Anticancer therapies that combine both diagnostic and therapeutic capabilities hold significant promise for enhancing treatment efficacy and patient outcomes. Among these, agents responsive to near-infrared (NIR) photons are of particular interest due to their negligible toxicity and multifunctionality. These compounds are not only effective in photodynamic therapy (PDT), but also serve as contrast agents in various imaging modalities, including fluorescence and photoacoustic imaging. In this review, we explore the photophysical and photochemical properties of NIR-activated porphyrin, cyanine, and phthalocyanines derivatives as well as aggregation-induced emission compounds, highlighting their application in synergistic detection, diagnosis, and therapy. Special attention is given to the design and optimization of these agents to achieve high photostability, efficient NIR absorption, and significant yields of fluorescence, heat, or reactive oxygen species (ROS) generation depending on the application. Additionally, we discuss the incorporation of these compounds into nanocarriers to enhance their solubility, stability, and target specificity. Such nanoparticle-based systems exhibit improved pharmacokinetics and pharmacodynamics, facilitating more effective tumor targeting and broadening the application range to photoacoustic imaging and photothermal therapy. Furthermore, we summarize the application of these NIR-responsive agents in multimodal imaging techniques, which combine the advantages of fluorescence and photoacoustic imaging to provide comprehensive diagnostic information. Finally, we address the current challenges and limitations of photodiagnosis and phototherapy and highlight some critical barriers to their clinical implementation. These include issues related to their phototoxicity, limited tissue penetration, and potential off-target effects. The review concludes by highlighting future research directions aimed at overcoming these obstacles, with a focus on the development of next-generation agents and platforms that offer enhanced therapeutic efficacy and imaging capabilities in the field of cancer treatment.

NIR-II Anti-Stokes Luminescence Nanocrystals with 1710 nm Excitation for in vivo Bioimaging

Anti-Stokes luminescence (ASL) based on lanthanide nanocrystals holds immense promise for in vivo optical imaging and bio-detection, which benefits from filtered autofluorescence. However, the current longest emission and excitation wavelengths of lanthanide ASL system were shorter than 1200 nm and 1532 nm, respectively, which limited tissue penetration depth and caused low signal-to-noise ratio (SNR) of in vivo imaging due to tissue scattering and water absorption. In this work, we extended the excitation wavelength to 1710 nm with the second near-infrared (NIR-II, 1000-1700 nm) emission up to 1650 nm through a novel ASL nanocrystal LiYF4 : 10 %Tm@LiYF4 : 70 %Er@LiYF4. Compared with 1532 nm excited ASL nanoprobes, the 1710 nm excited nanocrystals could improve in vivo imaging SNR by 12.72 folds. Based on this excellent imaging performance of the proposed ASL nanoprobes, three-channel in vivo dynamic multiplexed imaging was achieved, which quantitatively revealed metabolic rates of intestinal dynamics and liver enrichment under anesthetized and awake states. This innovative ASL nanoprobes and dynamic multiplexed imaging technology would be conducive to optimizing dosing regimen and treatment plans across various physiological conditions.

Aggregation-Induced Emission Luminogens Realizing High-Contrast Bioimaging

A revolutionary transformation in biomedical imaging is unfolding with the advent of aggregation-induced emission luminogens (AIEgens). These cutting-edge molecules not only overcome the limitations of traditional fluorescent probes but also improve the boundaries of high-contrast imaging. Unlike conventional fluorophores suffering from aggregation-caused quenching, AIEgens exhibit enhanced luminescence when aggregated, enabling superior imaging performance. This review delves into the molecular mechanisms of aggregation-induced emission (AIE), demonstrating how strategic molecular design unlocks exceptional luminescence and superior imaging contrast, which is crucial for distinguishing healthy and diseased tissues. This review also highlights key applications of AIEgens, such as time-resolved imaging, second near-infrared window (NIR-II), and the advancement of AIEgens in sensitivity to physical and biochemical cue-responsive imaging. The development of AIE technology promises to transform healthcare from early disease detection to targeted therapies, potentially reshaping personalized medicine. This paradigm shift in biophotonics offers efficient tools to decode the complexities of biological systems at the molecular level, bringing us closer to a future where the invisible becomes visible and the incurable becomes treatable.

High-Definition, Video-Rate Triple-Channel NIR-II Imaging Using Shadowless Lamp Excitation and Illumination

Multichannel imaging in the second near-infrared (NIR-II) window offers vital and comprehensive information for complex surgical environments, yet a simple, high-quality, video-rate multichannel imaging method with low safety risk remains to be proposed. Centered at the superior NIR-IIx window of 1400-1500 nm, triple-channel imaging coordinated with 1000-1100 and 1700-1880 nm (NIR-IIc) achieves exceptional clarity and an impressive signal-to-crosstalk ratio as high as 22.10. To further simplify the light source and lower the safety risk, we develop a type of in vivo multichannel imaging-assisted surgical navigation mode at a video frame rate of 25 fps under shadowless lamp excitation and illumination instead of extra excitation light sources. This work provides a reference for real-time, high-imaging-performance multichannel imaging with minimal crosstalk and introduces a practical fluorescence surgical navigation paradigm.

mPatch: A Wearable Hydrogel Microneedle Patch for In Vivo Optical Sensing of Calcium

This study presents an in vivo optical hydrogel microneedle platform that measures levels of analytes in interstitial fluid. The platform builds on a previously published technique for molding hydrogel microneedles by developing a composite hydrogel (i.e., PEGDA and polyacrylamide) that is sufficiently stiff to penetrate skin in the hydrated state and whose fluorescence changes dynamically-via a conjugated aptamer-depending on level of analyte. In a demonstration relevant to hypercalcemia, the hydrogel microneedle distinguished varying concentrations of calcium (within a range of 0 to 2 mM, which spans physiologically meaningful variations for hypoparathyroidism) within 10 minutes. In rats, a compact CMOS sensor measuring fluorescence from microneedles distinguished low hypercalcemic (1.7 mM) from high hypercalcemic (2.3 mM) ionized calcium levels as determined from reference blood measurements. Overall, this work demonstrates in vivo feasibility of a concept-which we call mPatch-for an optical hydrogel microneedle to measure small changes in levels of analytes in interstitial fluid, which does not rely on extraction of interstitial fluid out of the dermis.

Mild Focused Ultrasound-Induced Microscopic Heating of Nanoparticles Observed by Lanthanide Luminescence for Precise Sonothermal Cancer Therapy

Focused ultrasound (FUS) is a recognized tool that can be used clinically for the thermal ablation of tumors. However, excessive heat can cause side effects on the ultrasound transmission path and normal tissues around the tumor. To address the issue, this work detected for the first time the effect of microscopic heating of nanoparticles under the action of FUS through the luminescence intensity ratio (LIR) and luminescence lifetime of temperature-responsive lanthanide-doped nanoparticles. When FUS is applied to the tissue embedded with nanoparticles, the increase in the microscopic temperature of the nanoparticles synchronously monitored by LIR is more obvious than the increase in the macroscopic temperature. Based on this phenomenon, the intensity of focused ultrasound can be finely regulated to avoid overheating while ensuring a therapeutic effect. This work achieves the measurement of the microscopic heating of nanoparticles under FUS, which is of great significance for the development of sonothermal cancer therapy.

Extended Short-Wave Infrared Colloidal Quantum Dot Lasers with Nanosecond Excitation

Solution-processed gain media have great technological potential as lasers due to their ease of integration with on-chip photonics, scalability and tuneable optoelectronic properties. Currently, the spectral coverage of solution-processed lasers extends from visible up to telecom wavelengths in the short-wave infrared (SWIR) (<1650 nm). Here, the optical gain in the extended SWIR from 1600 nm to 2500 nm is demonstrated, using PbSbased colloidal quantum dots (CQDs). This spectral region has many applications such as in LIDAR, biological imaging and environmental monitoring and is currently served by exotic, costly materials with limitedscalability. Using the CQDs in distributed feedback laser cavities, lasing with emission tuned between 2150 nm and 2500 nm is reported. We show that due to the increased absorption cross-section of larger CQDs, the optical gain threshold is reduced by a factor of 36 compared to smaller-sized CQDs, reaching an amplified spontaneous emission (ASE) threshold down to 42 µJ cm-2. Furthermore, gain and lasing under nanosecond excitation are demonstrated for the first time from PbS CQDs and use transient absorption spectroscopy data to model nanosecond gain thresholds. This paves the way for realizing compact and practical CQD infrared lasers and potentially toward electrically driven laser diodes.

Nanographene-Based Polymeric Nanoparticles as Near-Infrared Emissive Neuronal Tracers

Precise tracking of axonal transport is key to deciphering neuronal functions. To achieve long-term imaging at both ultrastructural and macroscopic resolutions, it is critical to develop fluorescent transport tracers with high photostability and biocompatibility. Herein, we report the investigation of nanographene (NG)-based polymeric nanoparticles (NPs) as near-infrared (NIR)-emissive neuronal tracers. Dibenzo[a,m]dinaphtho[3,2,1-ef:1',2',3'-hi]coronene (DBDNC) was employed as the NG, which exhibited a broad NIR emission with a maximum at 711 nm inside the NPs. DBDNC-NPs displayed high photostability and low cytotoxicity, enabling live tracing of retrograde axonal transport in mouse sensory neurons cultured in microfluidic chambers. We also elucidated how DBDNC-NPs undergo retrograde axonal transport following the endolysosomal pathway. This work provides a proof of concept for NIR-emissive, NG-based neuronal tracers with potential for applications in neurobiology.

A comprehensive review on nanoparticle-based photo acoustic: current application and future prospective

In vivo, molecular imaging is prevalent for biology research and therapeutic practice. Among advanced imaging technologies, photoacoustic (PA) imaging and sensing is gaining interest around the globe due its exciting features like high resolution and good (~ few cm) penetration depth. PA imaging is a recent development in ultrasonic technology that generates acoustic waves by absorbing optical energy. However, poor light penetration through tissue continues to be the key obstacle in the field. The NPs as contrast agents can assist in overcoming tissue penetration depth as NPs can produce high signal to noise (SNR) PA signal which aids reconstruction of high resolution of the PA images in deep tissue sights. Subsequently, NPs are very effective in PA based targeted and precise theranostic applications. This article detail about various NPs (organic, inorganic and hybrid) used in PA imaging and spectroscopy applications including various disease diagnosis, therapy and theranostic. It also features optical property, advantages and limitations of various NPs utilised in PA techniques which would comprehend readers about the potential of NPs in evolving PA technique from laboratory to clinical modality in future.

Tm3+-Based Downshifting Nanoprobes with Enhanced Luminescence at 1680 nm for In Vivo Vascular Growth Monitoring

Optical imaging in the 1500-1700 nm region, known as near-infrared IIb (NIR-IIb), shows potential for noninvasive in vivo detection owing to its ultrahigh tissue penetration depth and spatiotemporal resolution. Rare earth-doped nanoparticles have emerged as widely used NIR-IIb probes because of their excellent optical properties. However, their downshifting emissions rarely exhibit sufficient brightness beyond 1600 nm. This study presents tetragonal-phase thulium-doped nanoparticles (Tm3+-NPs) with core-shell-shell structures (CSS, LiYbF4:3%Tm@LiYbF4@LiYF4) that exhibit bright downshifting luminescence at 1680 nm. Enhanced luminescence is attributed to (1) the promoted nonradiative relaxation between the doping ions and (2) the maximized sensitization process. Additionally, this strategy was validated for NIR-IIb luminescence enhancement of erbium (Er3+)-doped NPs. After surface modification with PEGylated liposomes, tetragonal-phase Tm3+-NPs exhibited a prolonged blood cycle time, high colloidal stability, and good biocompatibility. Owing to the advantages of Tm3+-based probes in NIR-IIb imaging, in vivo thrombus detection and monitoring of angiogenesis and arteriogenesis were successfully performed in a mouse model of ischemic hind limbs.

4T1 Cell Membrane-Coated Pdots with NIR-II Absorption and Fluorescence Properties for Targeted Phototheranostics of Breast Tumors

Designing highly biocompatible organic semiconducting conjugated polymer dots (Pdots) with bright fluorescence and superior absorption properties in the second near-infrared window (NIR-II: 1000-1700 nm) remains a huge challenge for tumor phototheranostics. In this study, we constructed 4T1 cell membrane-coated m-PBTQ4F Pdots (CPdots) with enhanced NIR-II photoacoustic (PA) and fluorescence (FL) imaging capability for NIR-II photothermal therapy (PTT) of breast tumors. Our findings demonstrated that CPdots could specifically target breast tumors, leading to enhanced tumor accumulation after systemic administration in living mice. In addition, CPdots can not only serve as contrast agents for NIR-II PA and FL imaging for improved breast tumor detection but also generate more cytotoxic heat to improve PTT efficacy. Therefore, this pilot study opens an option avenue for developing new NIR-II Pdots with homologous targeting capability for enhanced phototheranostics of breast tumors.

Advances in Lanthanide-Based NIR-IIb Probes for In Vivo Biomedical Imaging

The past decades have witnessed the significant development and practical interest of in vivo biomedical imaging technologies and optical materials in the second-near infrared (NIR-II, 1000-1700 nm) window. Imaging with the extended emission wavelength toward the long-wavelength end (NIR-IIb, 1500-1700 nm) further offers micrometer imaging resolution and centimeter tissue penetration depth by taking advantage of the much-reduced photon scattering and near-zero tissue autofluorescence background, which have become a very hot research area. This review focuses on the recent advances in the development of lanthanide-based NIR-IIb probes for in vivo biomedical applications. The progress including ratiometric imaging, multiplexed imaging for wide-field and microscopy, lifetime multiplexing and sensing, persistent luminescence, and multimodal imaging is summarized. Challenges and future directions concerning the investigation of the photophysical and photochemical properties of NIR-IIb probes, the selection of near-infrared cameras as well as the potential extension of the NIR-IIb imaging sub-window are pointed out. This review will inspire readers who have a strong interest in developing optical imaging technology and long-wavelength fluorescence probes for high-contrast in vivo biomedical applications.

Biodegradable ICG-Conjugated Germanium Nanoparticles for In Vivo Near-Infrared Dual-Modality Imaging and Photothermal Therapy

Theranostics, by integrating diagnosis and therapy on a single platform, enables real-time monitoring of tumors during treatment. To improve the accuracy of tumor diagnosis, the fluorescence and photoacoustic imaging modalities can complement each other to achieve high resolution and a deep penetration depth. Despite the superior performance, the biodegradability of theranostic agents plays a critical role in enhancing nanoparticle excretion and reducing chronic toxicity, which is essential for clinical applications. Herein, we synthesize biocompatible and biodegradable indocyanine green (ICG)-conjugated germanium nanoparticles (GeNPs) and investigate their biodistributions in nude mice and 4T1 tumor models after intravenous injections using near-infrared (NIR) dual-modality fluorescence and photoacoustic imaging. The ICG-conjugated GeNPs have strong NIR absorption due to the NIR-absorbing ICG and Ge in combination, emit strong NIR fluorescence due to the multilayered ICG coatings, and exhibit very low in vitro and in vivo toxicity. After tail vein injections, the ICG-conjugated GeNPs mainly accumulate in the liver and spleen as well as the tumor with the help of the enhanced permeability and retention effect. The tumor's fluorescence signal is much stronger than that of the control group injected with pure ICG solution, as the GeNPs can function as biodegradable carriers for efficiently delivering the ICG molecules to the tumor. Lastly, the ICG-conjugated GeNPs accumulated in the tumor can also be utilized for photothermal treatment under NIR laser irradiation, after which the tumor volume almost diminishes after 14 days. The experimental findings in this work demonstrate that the ICG-conjugated GeNPs are promising theranostic agents with exceptional biodegradability for in vivo NIR dual-modality imaging and photothermal therapy.

Lead-Free Perovskite Light-Emitting Diodes

Metal halide perovskites have been identified as a promising class of materials for light-emitting applications. The development of lead-based perovskite light-emitting diodes (PeLEDs) has led to substantial improvements, with external quantum efficiencies (EQEs) now surpassing 30% and operational lifetimes comparable to those of organic LEDs (OLEDs). However, the concern over the potential toxicity of lead has motivated a search for alternative materials that are both eco-friendly and possess excellent optoelectronic properties, with lead-free perovskites emerging as a strong contender. In this review, the properties of various lead-free perovskite emitters are analyzed, with a particular emphasis on the more well-reported tin-based variants. Recent progress in enhancing device efficiencies through refined crystallization processes and the optimization of device configurations is also discussed. Additionally, the remaining challenges are examined, and propose strategies that may lead to stable device operation. Looking forward, the potential future developments for lead-free PeLEDs are considered, including the extension of spectral range, the adoption of more eco-friendly deposition techniques, and the exploration of alternative materials.

Development of label-free light-controlled gene expression technologies using mid-IR and terahertz light

Gene expression is a fundamental process that regulates diverse biological activities across all life stages. Given its vital role, there is an urgent need to develop innovative methodologies to effectively control gene expression. Light-controlled gene expression is considered a favorable approach because of its ability to provide precise spatiotemporal control. However, current light-controlled technologies rely on photosensitive molecular tags, making their practical use challenging. In this study, we review current technologies for light-controlled gene expression and propose the development of label-free light-controlled technologies using mid-infrared (mid-IR) and terahertz light.

Switching from Molecules to Functional Materials: Breakthroughs in Photochromism With MOFs

Photochromic materials with properties that can be dynamically tailored as a function of external stimuli are a rapidly expanding field driven by applications in areas ranging from molecular computing, nanotechnology, or photopharmacology to programable heterogeneous catalysis. Challenges arise, however, when translating the rapid, solution-like response of stimuli-responsive moieties to solid-state materials due to the intermolecular interactions imposed through close molecular packing in bulk solids. As a result, the integration of photochromic compounds into synthetically programable porous matrices, such as metal-organic frameworks (MOFs), has come to the forefront as an emerging strategy for photochromic material development. This review highlights how the core principles of reticular chemistry (on the example of MOFs) play a critical role in the photochromic material performance, surpassing the limitations previously observed in solution or solid state. The symbiotic relationship between photoresponsive compounds and porous frameworks with a focus on how reticular synthesis creates avenues toward tailorable photoisomerization kinetics, directional energy and charge transfer, switchable gas sorption, and synergistic chromophore communication is discussed. This review not only focuses on the recent cutting-edge advancements in photochromic material development, but also highlights novel, vital-to-pursue pathways for multifaceted functional materials in the realms of energy, technology, and biomedicine.

Near-Infrared Emissive π-Conjugated Oligomer Nanoparticles for Three- and Four-Photon Deep-Brain Microscopic Imaging Beyond 1700 nm Excitation

High-resolution visualization of the deep brain is still a challenging and very significant issue. Multiphoton microscopy (MPM) holds great promise for high-spatiotemporal deep-tissue imaging under NIR-III and NIR-IV excitation. However, thus far, their applications have been seriously restricted by the scarcity of efficient organic probes. Herein, we designed and synthesized two donor-acceptor-donor-type conjugated small molecules (TNT and TNS) for in vivo mouse deep-brain imaging with three- and four-photon microscopy under 1700 and 2200 nm excitation. With a selenium (Se) substitution, we synthesized two conjugated small molecules to promote their emission into the deep near-infrared region with high quantum yields of 55% and 20% in THF solvent, respectively, and their water-dispersive nanoparticles have relatively large absorption cross-sections in the 1700 and 2200 nm windows, respectively, with good biosafety. With these superiorities, these organic NPs achieve high-resolution deep-brain imaging via three-photon and four-photon microscopy with excitation at 1700 and 2200 nm windows, and 1620 μm deep in the brain vasculature can be visualized in vivo. This study demonstrates the efficiency of NIR-emissive conjugated small molecules for high-performance MPM imaging in the NIR-III and NIR-IV window and provides a route for the future design of organic MPM probes.

Dramatic Impact of Materials Combinations on the Chemical Organization of Core-Shell Nanocrystals: Boosting the Tm3+ Emission above 1600 nm

This article represents the first foray into investigating the consequences of various material combinations on the short-wave infrared (SWIR, 1000-2000 nm) performance of Tm-based core-shell nanocrystals (NCs) above 1600 nm. In total, six different material combinations involving two different types of SWIR-emitting core NCs (α-NaTmF4 and LiTmF4) combined with three different protecting shell materials (α-NaYF4, CaF2, and LiYF4) have been synthesized. All corresponding homo- and heterostructured NCs have been meticulously characterized by powder X-ray diffraction and electron microscopy techniques. The latter revealed that out of the six investigated combinations, only one led to the formation of a true core-shell structure with well-segregated core and shell domains. The direct correlation between the downshifting performance and the spatial localization of Tm3+ ions within the final homo- and heterostructured NCs is established. Interestingly, to achieve the best SWIR performance, the formation of an abrupt interface is not a prerequisite, while the existence of a pure (even thin) protective shell is vital. Remarkably, although all homo- and heterostructured NCs have been synthesized under the exact same experimental conditions, Tm3+ SWIR emission is either fully quenched or highly efficient depending on the type of material combination. The most efficient combination (LiTmF4/LiYF4) achieved a high photoluminescence quantum yield of 39% for SWIR emission above 1600 nm (excitation power density in the range 0.5-3 W/cm2) despite significant intermixing. From now on, highly efficient SWIR-emitting probes with an emission above 1600 nm are within reach to unlock the full potential of in vivo SWIR imaging.

Near-Infrared II Agent with Excellent Overall Performance for Imaging-Guided Photothermal Thrombolysis

Near-infrared II (NIR-II) imaging and photothermal therapy hold tremendous potential in precision diagnosis and treatment within biological organisms. However, a significant challenge is the shortage of NIR-II fluorescent probes with both high photothermal conversion coefficient (PCE) and fluorescence quantum yield (ΦF). Herein, we address this issue by integrating a large conjugated electron-withdrawing core, multiple rotors, and multiple alkyl chains into a molecule to successfully generate a NIR-II agent 4THTPB with excellent PCE (87.6%) and high ΦF (3.2%). 4THTPB shows a maximum emission peak at 1058 nm, and the emission tail could extend to as long as 1700 nm. These characteristics make its nanoparticles (NPs) perform well in NIR-II high-resolution angiography, thereby allowing for precise diagnosis of thrombus through NIR-II imaging and enabling efficient photothermal thrombolysis. This work not only furnishes a NIR-II agent with excellent overall performance but also provides valuable guidance for the design of high-performance NIR-II agents.

New Insights in Luminescence and Quenching Mechanisms of Ag2S Nanocrystals through Temperature-Dependent Spectroscopy

Bright near-infrared-emitting Ag2S nanocrystals (NCs) are used for in vivo temperature sensing relying on a reversible variation in intensity and photoluminescence lifetime within the physiological temperature range. Here, to gain insights into the luminescence and quenching mechanisms, we investigated the temperature-dependent luminescence of Ag2S NCs from 300 to 10 K. Interestingly, both emission and lifetime measurements reveal similar and strong thermal quenching from 200 to 300 K, indicating an intrinsic quenching process that limits the photoluminescence quantum yield at room temperature, even for perfectly passivated NCs. The low thermal quenching temperature, broadband emission, and multiexponential microsecond decay behavior suggest the optical transition involves strong lattice relaxation, which is consistent with the recombination of a Ag+-trapped hole with a delocalized conduction band electron. Our findings offer valuable insights for understanding the optical properties of Ag2S NCs and the thermal quenching mechanism underlying their temperature-sensing capabilities.

Designing SERS nanotags for profiling overexpressed surface markers on single cancer cells: A review

This review focuses on the chemical design and the use of Surface-Enhanced Raman Scattering (SERS)-active nanotags for measuring surface markers that can be overexpressed at the surface of single cancer cells. Indeed, providing analytical tools with true single-cell measurements capabilities is capital, especially since cancer research is increasingly leaning toward single-cell analysis, either to guide treatment decisions or to understand complex tumor behaviour including the single-cell heterogeneity and the appearance of treatment resistance. Over the past two decades, SERS nanotags have triggered significant interest in the scientific community owing their advantages over fluorescent tags, mainly because SERS nanotags resist photobleaching and exhibit sharper signal bands, which reduces possible spectral overlap and enables the discrimination between the SERS signals and the autofluorescence background from the sample itself. The extensive efforts invested in harnessing SERS nanotags for biomedical purposes, particularly in cancer research, highlight their potential as the next generation of optical labels for single-cell studies. The review unfolds in two main parts. The first part focuses on the structure of SERS nanotags, detailing their chemical composition and the role of each building block of the tags. The second part explores applications in measuring overexpressed surface markers on single-cells. The latter encompasses studies using single nanotags, multiplexed measurements, quantitative information extraction, monitoring treatment responses, and integrating phenotype measurements with SERS nanotags on single cells isolated from complex biological matrices. This comprehensive review anticipates SERS nanotags to persist as a pivotal technology in advancing single-cell analytical methods, particularly in the context of cancer research and personalized medicine.

Room-Temperature Near-Infrared Phosphorescence from C64 Nanographene Tetraimide by π-Stacking Complexation with Platinum Porphyrin

Near-Infrared (NIR) phosphorescence at room temperature is challenging to achieve for organic molecules due to negligible spin-orbit coupling and a low energy gap leading to fast non-radiative transitions. Here, we show a supramolecular host-guest strategy to harvest the energy from the low-lying triplet state of C64 nanographene tetraimide 1. 1H NMR and X-ray analysis confirmed the 1 : 2 stoichiometric binding of a Pt(II) porphyrin on the two π-surfaces of 1. While the free 1 does not show emission in the NIR, the host-guest complex solution shows NIR phosphorescence at 77 K. Further, between 860-1100 nm, room temperature NIR phosphorescence (λmax=900 nm, τavg=142 μs) was observed for a solid-state sample drop-casted from a preformed complex in solution. Theoretical calculations reveal a non-zero spin-orbit coupling between isoenergetic S1 and T3 of π-stacked [1 ⋅ Pt(II) porphyrin] complex. External heavy-atom-induced spin-orbit coupling along with rigidification and protection from oxygen in the solid-state promotes both the intersystem crossing from the first excited singlet state into the triplet manifold and the NIR phosphorescence from the lowest triplet state of 1.

Multifunctional Near-Infrared Phosphors Cr3+/Ni2+ Codoped Mg3Ga2GeO8 Based on Energy Transfer from Cr3+ to Ni2

Currently, near-infrared (NIR) light-emitting materials have been widely used in many fields, such as night vision, bioimaging, and nondestructive analysis. However, it is difficult to achieve multifunction in certain NIR light emitting phosphor. Herein, we propose a new near-infrared phosphor Mg3Ga2GeO8:Cr3+,Ni2+ that can be applied to at least three fields, i.e., identification of compounds, temperature sensing, anticounterfeiting, and other applications. The multifunctional material exhibited efficient broadband emission of 650-1650 nm under 420 nm excitation. The emission intensity of Ni2+ in Mg3Ga2GeO8:Cr3+,Ni2+ is enhanced by two times compared with that of Ni2+ in Mg3Ga2GeO8:Ni2+ due to the energy transfer process. Compared with phosphor single doped with Ni2+, Mg3Ga2GeO8:Cr3+,Ni2+ is more convincing in organic compound recognition because it is based on two emission bands: 600-1100 nm and 1100-1650 nm. As a temperature sensor, Mg3Ga2GeO8:Cr3+,Ni2+ is an ideal temperature-sensing material. This work not only provides a super broadband NIR emitting phosphor with multiple functions but also presents a practical approach for the development of high-efficiency and multifunctional NIR phosphors.

Noninvasive in vivo microscopy of single neutrophils in the mouse brain via NIR-II fluorescent nanomaterials

In vivo microscopy of single cells enables following pathological changes in tissues, revealing signaling networks and cell interactions critical to disease progression. However, conventional intravital microscopy at visible and near-infrared wavelengths <900 nm (NIR-I) suffers from attenuation and is typically performed following the surgical creation of an imaging window. Such surgical procedures cause the alteration of the local vasculature and induce inflammation in skin, muscle and skull, inevitably altering the microenvironment in the imaging area. Here, we detail the use of near-infrared fluorescence (NIR-II, 1,000-1,700 nm) for in vivo microscopy to circumvent attenuation in living tissues. This approach enables the noninvasive visualization of cell migration in deep tissues by labeling specific cells with NIR-II lanthanide downshifting nanoparticles exhibiting high physicochemical stability and photostability. We further developed a NIR-II fluorescence microscopy setup for in vivo imaging through the intact skull with high spatiotemporal resolution, which we use for the real-time dynamic visualization of single-neutrophil behavior in the deep brain of a mouse model of ischemic stroke. The labeled downshifting nanoparticle synthesis takes 5-6 d, the imaging system setup takes 1-2 h, the in vivo cell labeling takes 1-3 h, the in vivo NIR-II microscopic imaging takes 3-5 h and the data analysis takes 3-8 h. The procedures can be performed by users with standard laboratory training in nanomaterials research and appropriate animal handling.

An ultra-small organic dye nanocluster for enhancing NIR-II imaging-guided surgery outcomes

PURPOSE

The accuracy of surgery for patients with solid tumors can be greatly improved through fluorescence-guided surgery (FGS). However, existing FGS technologies have limitations due to their low penetration depth and sensitivity/selectivity, which are particularly prevalent in the relatively short imaging window (< 900 nm). A solution to these issues is near-infrared-II (NIR-II) FGS, which benefits from low autofluorescence and scattering under the long imaging window (> 900 nm). However, the inherent self-assembly of organic dyes has led to high accumulation in main organs, resulting in significant background signals and potential long-term toxicity.

METHODS

We rationalize the donor structure of donor-acceptor-donor-based dyes to control the self-assembly process to form an ultra-small dye nanocluster, thus facilitating renal excretion and minimizing background signals.

RESULTS

Our dye nanocluster can not only show clear vessel imaging, tumor and tumor sentinel lymph nodes definition, but also achieve high-performance NIR-II imaging-guided surgery of tumor-positive sentinel lymph nodes.

CONCLUSION

In summary, our study demonstrates that the dye nanocluster-based NIR-II FGS has substantially improved outcomes for radical lymphadenectomy.

Ultrabright Dibenzofluoran-Based Polymer Dots with NIR-IIa Emission Maxima and Unusual Large Stokes Shifts for 3D Rotational Stereo Imaging

Emerging organic molecules with emissions in the second near-infrared (NIR-II) region are garnering significant attention. Unfortunately, achieving accountable organic emission intensity over the NIR-IIa (1300 nm) region faces challenges due to the intrinsic energy gap law. Up to the current stage, all reported organic NIR-IIa emitters belong to polymethine-based dyes with small Stokes shifts (<50 nm) and low quantum yield (QY; ≤0.015%). However, such polymethines have proved to cause self-absorption with constrained emission brightness, limiting advanced development in deep-tissue imaging. Here a new NIR-IIa scaffold based on rigid and highly conjugated dibenzofluoran core terminated by amino-containing moieties that reveal emission peaks of 1230-1305 nm is designed. The QY is at least 10 times higher than all synthesized or reported NIR-IIa polymethines with extraordinarily large Stokes shifts of 370-446 nm. DBF-BJ is further prepared as a polymer dot to demonstrate its in vivo 3D stereo imaging of mouse vasculature with a 1400 nm long-pass filter.