NIR-II bioimaging of small molecule fluorophores: From basic research to clinical applications

Improving the fluorescence brightness of NIR-II fluorophores via intramolecular covalent bond locking: a theoretical perspective

Fluorescence imaging in the second near-infrared (NIR-II) region, characterized by deep tissue penetration and high spatial resolution, has emerged as a promising modality for biomedical applications. However, the majority of NIR-II fluorophores suffer from insufficient brightness primarily attributed to the limited fluorescence quantum yields. Herein, the mechanism of fluorescence brightness enhancement through an intramolecular covalent bond locking strategy for donor-acceptor-donor NIR-II fluorophores is investigated. Compared with the unlocked TQ-1, fusing phenyl rings on the acceptor moiety induces bathochromic shifts in both the photoabsorption and photoemission spectra, while the modification to the donor unit results in a hypsochromic effect. Notably, incorporating intramolecular covalent bonds within the acceptor segment facilitates structural relaxation during the electronic transitions, which is mainly responsible for the reduction in luminescence efficiency. In contrast, by locking the terminal phenyl groups of the fluorophore, the adiabatic excitation energy is increased and the electron-vibration coupling as well as nonadiabatic electronic coupling is decreased, resulting in a significant reduction in the nonradiative decay rate. Consequently, TQ-4 achieves an optimal fluorescence quantum yield and brightness while maintaining NIR-II emission, demonstrating its potential as a high-performance NIR-II chromophore. This work highlights the feasibility of constructing efficient NIR-II fluorophores via intramolecular covalent bond locking, providing rational design principles for developing novel NIR-II fluorophores toward biomedical applications.

Development of a Highly Efficient NIR-II Phototherapeutic Agent for Fluorescence Imaging-Guided Synergistic PTT/PDT/Chemotherapy of Colorectal Cancer

NIR-II-triggered phototherapy presents a noninvasive, resistance-free alternative therapeutic approach with deeper tissue penetration and improved imaging of deep tumors. However, many NIR-II phototherapeutic agents suffer from low fluorescence quantum yields, poor photothermal conversion efficiency (PCE), and reduced efficacy due to the upregulation of heat shock protein HSP70. This study develops a small-molecule NIR-II phototherapeutic agent (IRF) with a high fluorescence quantum yield (17.4%), excellent PCE (96.8%) for photothermal therapy (PTT), and photodynamic therapy (PDT) activity. To decrease thermal resistance during phototherapy, IRF and evodiamine (EVO) were loaded onto hyaluronic acid (HA)-modified nanoparticles, creating a multifunctional nanoplatform termed EVO/IRF@HA NPs. EVO/IRF@HA NPs can actively target tumors for NIR-II fluorescence imaging via the HA moiety. Upon 980 nm laser irradiation, IRF increases the temperature and content of reactive oxygen species for synergistic PTT/PDT. Importantly, EVO effectively inhibits the overexpression of HSP70, enabling combined PTT/PDT/chemotherapy for effective colorectal cancer (CRC) treatment.

Fluorescent probes in autoimmune disease research: current status and future prospects

Autoimmune diseases (AD) present substantial challenges for early diagnosis and precise treatment due to their intricate pathogenesis and varied clinical manifestations. While existing diagnostic methods and treatment strategies have advanced, their sensitivity, specificity, and real-time applicability in clinical settings continue to exhibit significant limitations. In recent years, fluorescent probes have emerged as highly sensitive and specific biological imaging tools, demonstrating substantial potential in AD research.This review examines the response mechanisms and historical evolution of various types of fluorescent probes, systematically summarizing the latest research advancements in their application to autoimmune diseases. It highlights key applications in biomarker detection, dynamic monitoring of immune cell functions, and assessment of drug treatment efficacy. Furthermore, this article analyzes the technical challenges currently encountered in probe development and proposes potential directions for future research. With ongoing advancements in materials science, nanotechnology, and bioengineering, fluorescent probes are anticipated to achieve higher sensitivity and enhanced functional integration, thereby facilitating early detection, dynamic monitoring, and innovative treatment strategies for autoimmune diseases. Overall, fluorescent probes possess substantial scientific significance and application value in both research and clinical settings related to autoimmune diseases, signaling a new era of personalized and precision medicine.

Isomerization enhanced fluorescence brightness of benzobisthiadiazole-based NIR-II fluorophores for highly efficient fluorescence imaging: A theoretical perspective

As a cutting-edge technique, fluorescence imaging in the second near-infrared window (NIR-II) is vital for both biomedical research and clinical applications. However, its intravital imaging capacity has been restricted by the extremely limited brightness of NIR-II fluorophores. To address this challenge, we elucidated the inner mechanism of constructing high-performance NIR-II chromophores based on molecular isomer engineering from detailed computational investigations. Herein, three pairs of cis-trans isomers (cis-1, 2, 3 and trans-1, 2, 3) are designed by attaching amino, methoxyl and nitro moieties to different positions on the donor-acceptor-donor molecular skeleton with benzobisthiadiazole as the acceptor and triphenylamine as the donor. All the compounds feature efficient NIR-II emission ranging in 1000-1164 nm, and the photophysical characterizations are regulated by molecular isomer manipulation. Interestingly, fluorescence quantum yields of cis-isomers are higher than those of their trans-counterparts. These enhancements can be attributed to the significant reduction in non-radiative transition, as evidenced by the non-adiabatic excitation energy, non-adiabatic electron coupling and electron-vibration coupling. Meanwhile, fluorophores with nitro terminal group exhibit superior performance facilitated by the prominently intramolecular charge transfer. As a result, cis-3 achieves an optimal brightness maxima of 196.36 M-1 cm-1 at 632 nm. Notably, the energy gap and the hole-electron related H index are respectively identified as strongly relevant to the emission wavelength and brightness, making them capable of evaluating the feasibility of fluorophores as effective NIR-II candidates. These findings highlight the correlations between molecular geometry and luminescent properties, which will inspire more insights into the development of highly efficient NIR-II fluorophores through rational isomer engineering for biomedical applications.

Activatable Molecular Probes With Clinical Promise for NIR-II Fluorescent Imaging

The second near-infrared window (NIR-II) fluorescence imaging has been widely adopted in basic scientific research and preclinical applications due to its exceptional spatiotemporal resolution and deep tissue penetration. Among the various fluorescent agents, organic small-molecule fluorophores are considered the most promising candidates for clinical translation, owing to their well-defined chemical structures, tunable optical properties, and excellent biocompatibility. However, many currently available NIR-II fluorophores exhibit an "always-on" fluorescence signal, which leads to background noise and compromises diagnostic accuracy during disease detection. Developing NIR-II activatable organic small-molecule fluorescent probes (AOSFPs) for accurately reporting pathological changes is key to advancing NIR-II fluorescence imaging toward clinical application. This review summarizes the rational design strategies for NIR-II AOSFPs based on four core structures (cyanine, hemicyanine, xanthene, and BODIPY). These NIR-II AOSFPs hold substantial potential for clinical translation. Furthermore, the recent advances in NIR-II AOSFPs for NIR-II bioimaging are comprehensively reviewed, offering clear guidance and direction for their further development. Finally, the prospective efforts to advance NIR-II AOSFPs for clinical applications are outlined.

Brightness Strategies toward NIR-II Emissive Conjugated Materials: Molecular Design, Application, and Future Prospects

Recent advances have been made in second near-infrared (NIR-II) fluorescence bioimaging and many related applications because of its advantages of deep penetration, high resolution, minimal invasiveness, and good dynamic visualization. To achieve high-performance NIR-II fluorescence bioimaging, various materials and probes with bright NIR-II emission have been extensively explored in the past few years. Among these NIR-II emissive materials, conjugated polymers and conjugated small molecules have attracted wide interest due to their native biosafety and tunable optical performance. This review summarizes the brightness strategies available for NIR-II emissive conjugated materials and highlights the recent developments in NIR-II fluorescence bioimaging. A concise, detailed overview of the molecular design and regulatory approaches is provided in terms of their high brightness, long wavelengths, and superior imaging performance. Then, various typical cases in which bright conjugated materials are used as NIR-II probes are introduced by providing step-by-step examples. Finally, the current problems and challenges associated with accessing NIR-II emissive conjugated materials for bright NIR-II fluorescence bioimaging are briefly discussed, and the significance and future prospects of these materials are proposed to offer helpful guidance for the development of NIR-II emissive materials.

Conceptually innovative fluorophores for functional bioimaging

Fluorophore chemistry is at the forefront of bioimaging, revolutionizing the visualization of biological processes with unparalleled precision. From the serendipitous discovery of mauveine in 1856 to cutting-edge fluorophore engineering, this field has undergone transformative evolution. Today, the synergy of chemistry, biology, and imaging technologies has produced diverse, specialized fluorophores that enhance brightness, photostability, and targeting capabilities. This review delves into the history and innovation of fluorescent probes, showcasing their pivotal role in advancing our understanding of cellular dynamics and disease mechanisms. We highlight groundbreaking molecules and their applications, envisioning future breakthroughs that promise to redefine biomedical research and diagnostics.

The Guardian of Vision: Intelligent Bacteriophage-Based Eyedrops for Clinical Multidrug-Resistant Ocular Surface Infections

Clinical multidrug-resistant Pseudomonas aeruginosa (MDR-PA) is the leading cause of refractory bacterial keratitis (BK). However, the reported BK treatment methods lack biosecurity and bioavailability, which usually causes irreversible visual impairment and even blindness. Herein, for BK caused by clinically isolated MDR-PA infection, armed phages are modularized with the type I photosensitizer (PS) ACR-DMT, and an intelligent phage eyedrop is developed for combined phagotherapy and photodynamic therapy (PDT). These eyedrops maximize the advantages of bacteriophages and ACR-DMT, enabling more robust and specific targeting killing of MDR-PA under low oxygen-dependence, penetrating and disrupting biofilms, and efficiently preventing biofilm reformation. Altering the biofilm and immune microenvironments alleviates inflammation noninvasively, promotes corneal healing without scar formation, protects ocular tissues, restores visual function, and prevents long-term discomfort and pain. This strategy exhibits strong scalability, enables at-home treatment of ocular surface infections with great patient compliance and a favorable prognosis, and has significant potential for clinical application.

Intraoperative Resection Guidance and Rapid Pathological Diagnosis of Osteosarcoma using B7H3 Targeted Probe under NIR-II Fluorescence Imaging

Complete removal of all tumor tissue with a wide surgical margin is essential for the treatment of osteosarcoma (OS). However, it's difficult, sometimes impossible, to achieve due to the invisible small satellite lesions and blurry tumor boundaries. Besides, intraoperative frozen-section analysis of resection margins of OS is often restricted by the hard tissues around OS, which makes it impossible to know whether a negative margin is achieved. Any unresected small tumor residuals will lead to local recurrence and worse prognosis. Herein, based on the high expression of B7H3 in OS, a targeted probe B7H3-IRDye800CW is synthesized by conjugating anti-B7H3 antibody and IRDye800CW. B7H3-IRDye800CW can accurately label OS areas after intravenous administration, thereby helping surgeons identify and resect residual OS lesions (<2 mm) and lung metastatic lesions. The tumor-background ratio reaches 4.42 ± 1.77 at day 3. After incubating fresh human OS specimen with B7H3-IRDye800CW, it can specifically label the OS area and even the microinvasion area (confirmed by hematoxylin-eosin [HE] staining). The probe labeled area is consistent with the tumor area shown by magnetic resonance imaging and complete HE staining of the specimen. In summary, B7H3-IRDye800CW has translational potential in intraoperative resection guidance and rapid pathological diagnosis of OS.

Global trends in the application of fluorescence imaging in pancreatic diseases: a bibliometric and knowledge graph analysis

Background

In recent years, with the continuous development of fluorescence imaging technology, research on its application in pancreatic diseases has surged. This area is currently of high research interest and holds the potential to become a non-invasive and effective tool in the diagnosis and treatment of pancreatic diseases. The objective of this study is to explore the hotspots and trends in the field of fluorescence imaging technology applications in pancreatic diseases from 2003 to 2023 through bibliometric and visual analysis.

Methods

This study utilized the Web of Science (core collection) to identify publications related to the application of fluorescence imaging technology in pancreatic diseases from 2003 to 2023. Tools such as CiteSpace (V 6.2.R6), VOSviewer (v1.6.20), and R Studio (Bibliometrix: R-tool version 4.1.4) were employed to analyze various dimensions including publication count, countries, institutions, journals, authors, co-cited references, keywords, burst words, and references.

Results

A comprehensive analysis was conducted on 913 papers published from January 1, 2003, to December 1, 2023, on the application of fluorescence imaging technology in pancreatic diseases. The number of publications in this field has rapidly increased, with the United States being the central hub. The University of California, San Diego emerged as the most active institution. "Biomaterials" was identified as the most influential journal. Authors with the most publications and the highest average citations per article are Hoffman, Robert M. and Luiken, George A., respectively. Keywords such as pancreatic cancer, cancer, expression, indocyanine green, and nanoparticles received widespread attention, with indocyanine green and nanoparticles being current active research hotspots in the field.

Conclusion

This study is the first bibliometric analysis in the field of fluorescence imaging technology applications in pancreatic diseases. Our data will facilitate a better understanding of the developmental trends, identification of research hotspots, and direction in this field. The findings provide practical information for other scholars to grasp key directions and cutting-edge insights.

Development of Polymethine Dyes for NIR-II Fluorescence Imaging and Therapy

Fluorescence imaging in the second near-infrared window (NIR-II) is burgeoning because of its higher imaging fidelity in monitoring physiological and pathological processes than clinical visible/the second near-infrared window fluorescence imaging. Notably, the imaging fidelity is heavily dependent on fluorescence agents. So far, indocyanine green, one of the polymethine dyes, with good biocompatibility and renal clearance is the only dye approved by the Food and Drug Administration, but it shows relatively low NIR-II brightness. Importantly, tremendous efforts are devoted to synthesizing polymethine dyes for imaging preclinically and clinically. They have shown feasibility in the customization of structure and properties to fulfill various needs in imaging and therapy. Herein, a timely update on NIR-II polymethine dyes, with a special focus on molecular design strategies for fluorescent, photoacoustic, and multimodal imaging, is offered. Furthermore, the progress of polymethine dyes in sensing pathological biomarkers and even reporting drug release is illustrated. Moreover, the NIR-II fluorescence imaging-guided therapies with polymethine dyes are summarized regarding chemo-, photothermal, photodynamic, and multimodal approaches. In addition, artificial intelligence is pointed out for its potential to expedite dye development. This comprehensive review will inspire interest among a wide audience and offer a handbook for people with an interest in NIR-II polymethine dyes.

Glutathione-triggered prodrugs: Design strategies, potential applications, and perspectives

The burgeoning prodrug strategy offers a promising avenue toward improving the efficacy and specificity of cytotoxic drugs. Elevated intracellular levels of glutathione (GSH) have been regarded as a hallmark of tumor cells and characteristic feature of the tumor microenvironment. Considering the pivotal involvement of elevated GSH in the tumorigenic process, a diverse repertoire of GSH-triggered prodrugs has been developed for cancer therapy, facilitating the attenuation of deleterious side effects associated with conventional chemotherapeutic agents and/or the attainment of more efficacious therapeutic outcomes. These prodrug formulations encompass a spectrum of architectures, spanning from small molecules to polymer-based and organic-inorganic nanomaterial constructs. Although the GSH-triggered prodrugs have been gaining increasing interests, a comprehensive review of the advancements made in the field is still lacking. To fill the existing lacuna, this review undertakes a retrospective analysis of noteworthy research endeavors, based on a categorization of these molecules by their diverse recognition units (i.e., disulfides, diselenides, Michael acceptors, and sulfonamides/sulfonates). This review also focuses on explaining the distinct benefits of employing various chemical architecture strategies in the design of these prodrug agents. Furthermore, we highlight the potential for synergistic functionality by incorporating multiple-targeting conjugates, theranostic entities, and combinational treatment modalities, all of which rely on the GSH-triggering. Overall, an extensive overview of the emerging field is presented in this review, highlighting the obstacles and opportunities that lie ahead. Our overarching goal is to furnish methodological guidance for the development of more efficacious GSH-triggered prodrugs in the future. By assessing the pros and cons of current GSH-triggered prodrugs, we expect that this review will be a handful reference for prodrug design, and would provide a guidance for improving the properties of prodrugs and discovering novel trigger scaffolds for constructing GSH-triggered prodrugs.

Exponential Amplification-Induced Activation of CRISPR/Cas9 for Sensitive Detection of Exosomal miRNA

As an important component of highly heterogeneous exosomes, exosomal microRNAs (miRNAs) have great potential as noninvasive biomarkers for cancer diagnosis. Therefore, a sensitive and simple sensor is the key for its clinical application. Herein, we designed an exponential amplification reaction (EXPAR) to induce the reactivation of the CRISPR-associated protein 9/small guide RNA (Cas9/sgRNA) complex, thus achieving sensitive and visual exosomal miRNAs-21 (miR-21) fluorescence sensing. In this design, we inactivated the sgRNA by hybridizing sgRNA and blocker DNA. Then, we used a trigger DNA to hybridize with miR-21 and produced a lot of activated DNA by EXPAR. Those activated DNA further hybridized with blocker DNA and released the free sgRNA to form the activated Cas9/sgRNA complex. Based on the quick cleavage of activated Cas9/sgRNA complex, the reporter DNA labeled by SYBR Green I was released from the surface of the magnetic nanoparticles (MNPs) into the supernatant, and thus was used to sensitively quantify the miRNAs concentration with a limit of detection of 3 × 103 particles/mL. In addition, this fluorescence sensor has also been successfully employed to distinguish healthy people and cancer patients by naked-eye observation of the fluorescence, thus demonstrating its great potential for accurate and point-of-care cancer diagnosis.

A selenium-based NIR-II photosensitizer for a highly effective and safe phototherapy plan

High efficiency, stability, long emission wavelength (NIR-II), and good biocompatibility are crucial for photosensitizers in phototherapy. However, current Food and Drug Administration (FDA)-approved organic fluorophores exhibit poor chemical stability and photostability as well as short emission wavelength, limiting their clinical usage. To address this, we developed Se-IR1100, a novel organic photosensitizer with a photostable and thermostable benzobisthiadiazole (BBTD) backbone. By incorporating selenium as a heavy atom and constructing a D-A-D structure, Se-IR1100 exhibits a maximum fluorescence emission wavelength of 1100 nm. Compared with FDA-approved indocyanine green (ICG), DSPE-PEGylated Se-IR1100 nanoparticles exhibit prominent photostability and long-lasting photothermal effects. Upon 808 nm laser irradiation, Se-IR1100 NPs efficiently convert light energy into heat and reactive oxygen species (ROS), inducing cancer cell death in cellular studies and living organisms while maintaining biocompatibility. With salient photostability and a photothermal conversion rate of 55.37%, Se-IR1100 NPs hold promise as a superior photosensitizer for diagnostic and therapeutic agents in oncology. Overall, we have designed and optimized a multifunctional photosensitizer Se-IR1100 with good biocompatibility that performs NIR-II fluorescence imaging and phototherapy. This dual-strategy method may offer novel approaches for the development of multifunctional probes using dual-strategy or even multi-strategy methods in bioimaging, disease diagnosis, and therapy.

Recent bio-applications of covalent organic framework-based nanomaterials

Appearing as a new class of functional organic materials, covalent organic frameworks (COFs) have aroused a huge wave of interest in versatile fields ever since they were first proposed in 2005. Thanks to but not limited to their ultralight weights, high surface areas, ordered channels, variable functional groups and well-defined crystal structures, the applications of COF-based biomaterials in the fields of drug loading and delivery, photodynamic therapy, photothermal therapy, bioimaging, etc. are comprehensively summarized and introduced. The existing challenges and future prospects for this emerging but hot research direction are also discussed. It is hoped that this review will serve as a guidance for future research on COFs as multifunctional bioplatforms.

Enhancing the inherent NIR photoluminescence in SrLaLiTeO6 through Cr3+-Yb3+ co-substitution for high performance pc-LEDs

Until now, double perovskite tellurates have not been reported to exhibit inherent NIR photoluminescence. Therefore, the current study's revelation of inherent NIR luminescence in SrLaLiTeO6 double perovskite centered at 970 nm under 340 nm excitation is particularly intriguing. This phenomenon is attributed to the photoluminescence of Te4+ ions. This study also examines the NIR luminescence of Cr3+-Yb3+ co-doped SrLaLiTeO6. The host and SrLaLiTeO6:3%Cr3+, y%Yb3+ (y = 1, 2, 4, 6, 8, 10 mol%) were synthesized using the solid-state ceramic route. The successful incorporation of Cr3+ and Yb3+ ions into the host lattice was confirmed through XRD, Raman, and diffuse reflectance spectral analyses. Under 270 nm excitation, the photoluminescence (PL) of SrLaLiTeO6:Cr3+ exhibits a blueshift of the PL band to 965 nm due to the 4T2(4F) → 4A2g(4F) emission component of Cr3+ ions. The excited-state lifetime of SrLaLiTeO6:0.5%Cr3+ was measured at 36 μs, but this decreased to 26 μs as the Cr3+ concentration reached 10 mol%, primarily due to the enhancement of non-radiative energy transfer between Cr3+ ions. Incorporating Yb3+ into the system results in additional spectral lines with an enhanced intensity in the range of 970 nm to 1125 nm when excited at 270 nm. These emission lines correspond to the 2F5/2 → 2F7/2 transitions of Yb3+ ions, indicating an efficient energy transfer from Cr3+ to Yb3+. Furthermore, the study also reveals that Yb3+ emission is observed even without Cr3+ ions in SrLaLiTeO6 under 340 nm excitation, suggesting the possibility of energy transfer from the host to Yb3+ ions. The thermal stability and crystal field parameters of the synthesized phosphors are also explained in detail. To explore the potential of these phosphors in practical applications, phosphor-converted NIR LEDs were fabricated using SrLaLiTeO6, SrLaLiTeO6:3% Cr3+, and SrLaLiTeO6:3% Cr3+, 1%Yb3+.

Near-infrared dye IRDye800CW-NHS coupled to Trastuzumab for near-infrared II fluorescence imaging in tumor xenograft models of HER-2-positive breast cancer

Near-infrared II fluorescent probes targeting tumors for diagnostic purposes have received much attention in recent years. In this study, a fluorescent probe for the NIR-II was constructed by using IRDye800CW-NHS fluorescent dye with Trastuzumab, which was investigated for its ability to target HER-2-positive breast cancer in xenograft mice models. This probe was compared with Trastuzumab-ICG which was synthesized using a similar structure, ICG-NHS. The results demonstrated that the IRDye800CW-NHS had significantly stronger fluorescence in the NIR-I and NIR-II than ICG-NHS in the aqueous phase. And the different metabolic modes of IRDye800CW-NHS and ICG-NHS were revealed in bioimaging experiments. IRDye800CW-NHS was mainly metabolised by the kidneys, while ICG-NHS was mainly metabolised by the liver. After coupling with Trastuzumab, Trastuzumab-800CW (TMR = 5.35 ± 0.39) not only had a stronger tumor targeting ability than Trastuzumab-ICG (TMR = 4.42 ± 0.10) based on the calculated maximum tumor muscle ratio (TMR), but also had a comparatively lower hepatic uptake and faster metabolism. Histopathology analysis proved that both fluorescent probes were non-toxic to various organ tissues. These results reveal the excellent optical properties of IRDye800CW-NHS, and the great potential of coupling with antibodies to develop fluorescent probes that will hopefully be applied to intraoperative breast cancer navigation in humans.

Recent advances on the construction of long-wavelength emissive supramolecular coordination complexes for photo-diagnosis and therapy

Recently, metal-based drugs have attracted relentless interest in the biomedical field. However, their short excitation/emission wavelengths and unsatisfactory therapeutic efficiency limit their biological applications in vivo. Currently, the second near-infrared window (NIR-II, 1000-1700 nm) provides more accurate imaging and therapeutic options. Thus, there has been a constant focus on developing multifunctional NIR metal agents for imaging and therapy that have deeper tissue penetration. Fortunately, supramolecular coordination complexes (SCCs) formed by the coordination-driven self-assembly of NIR-II emissive ligands can address the above issues. Importantly, metal receptors with chemotherapeutic properties in SCCs can bind to luminescent ligands, thus becoming a versatile therapeutic platform for chemotherapy, imaging and phototherapy. In this context, we systematically summarize the evolution of NIR-II emissive SCCs for biomedical applications and discuss future challenges and prospects.

Dye-Triplet-Sensitized Downshifting Nanoprobes with Ratiometric Dual-NIR-IIb Emission for Accurate In Vivo Detection

Despite the emerging near-infrared-IIb (NIR-IIb, 1500-1700 nm) bioimaging significantly improving the in vivo penetration depth and resolution, quantitative detection with accuracy remains challenging due to its inhomogeneous fluorescence signal attenuation in biological tissue. Here, ratiometric dual-NIR-IIb in vivo detection with excitation wavelengths of 808 and 980 nm is presented using analyte-responsive dye-triplet-sensitized downshifting nanoprobes (DSNPs). NIR cyanine dye IR-808, a recognizer of biomarker hypochlorite (ClO-), is introduced to trigger a triplet energy transfer process from the dye to Er3+ ions of DSNPs under 808 nm excitation, facilitating the formation of an analyte-responsive 1525 nm NIR-IIb assay channel. Meanwhile, DSNPs also enable emitting intrinsic nonanalyte-dependent downshifting fluorescence at the same NIR-IIb window under 980 nm excitation, serving as a self-calibrated signal to alleviate the interference from the probe amount and depth. Due to the two detected emissions sharing identical light propagation and scattering, the ratiometric NIR-IIb signal is demonstrated to ignore the depth of penetration in biotissue. The arthritis lesions are distinguished from normal tissue using ratiometric probes, and the amount of ClO- can be accurately output by the established detection curves.

Short-wave infrared fluorescence imaging of near-infrared dyes with robust end-tail emission using a small-animal imaging device

Commercially available near-infrared (NIR) dyes, including indocyanine green (ICG), display an end-tail of the fluorescence emission spectrum detectable in the short-wave infrared (SWIR) window. Imaging methods based on the second NIR spectral region (1,000-1,700 nm) are gaining interest within the biomedical imaging community due to minimal autofluorescence and scattering, allowing higher spatial resolution and depth sensitivity. Using a SWIR fluorescence imaging device, the properties of ICG vs. heptamethine cyanine dyes with emission >800 nm were evaluated using tissue-simulating phantoms and animal experiments. In this study, we tested the hypothesis that an increased rigidity of the heptamethine chain may increase the SWIR imaging performance due to the bathochromic shift of the emission spectrum. Fluorescence SWIR imaging of capillary plastic tubes filled with dyes was followed by experiments on healthy animals in which a time series of fluorescence hindlimb images were analyzed. Our findings suggest that higher spatial resolution can be achieved even at greater depths (>5 mm) or longer wavelengths (>1,100 nm), in both tissue phantoms and animals, opening the possibility to translate the SWIR prototype toward clinical application.

Preventing cation intermixing enables 50% quantum yield in sub-15 nm short-wave infrared-emitting rare-earth based core-shell nanocrystals

Short-wave infrared (SWIR) fluorescence could become the new gold standard in optical imaging for biomedical applications due to important advantages such as lack of autofluorescence, weak photon absorption by blood and tissues, and reduced photon scattering coefficient. Therefore, contrary to the visible and NIR regions, tissues become translucent in the SWIR region. Nevertheless, the lack of bright and biocompatible probes is a key challenge that must be overcome to unlock the full potential of SWIR fluorescence. Although rare-earth-based core-shell nanocrystals appeared as promising SWIR probes, they suffer from limited photoluminescence quantum yield (PLQY). The lack of control over the atomic scale organization of such complex materials is one of the main barriers limiting their optical performance. Here, the growth of either homogeneous (α-NaYF₄) or heterogeneous (CaF₂) shell domains on optically-active α-NaYF₄:Yb:Er (with and without Ce³⁺ co-doping) core nanocrystals is reported. The atomic scale organization can be controlled by preventing cation intermixing only in heterogeneous core-shell nanocrystals with a dramatic impact on the PLQY. The latter reached 50% at 60 mW/cm²; one of the highest reported PLQY values for sub-15 nm nanocrystals. The most efficient nanocrystals were utilized for in vivo imaging above 1450 nm.

Near-infrared metal agents assisting precision medicine: from strategic design to bioimaging and therapeutic applications

Metal agents have made incredible strides in preclinical research and clinical applications in recent years, but their short emission/absorption wavelengths continue to be a barrier to their distribution, therapeutic action, visual tracking, and efficacy evaluation. Nowadays, the near-infrared window (NIR, 650-1700 nm) provides a more accurate imaging and treatment option. Thus, there has been ongoing research focusing on developing multifunctional NIR metal agents for imaging and therapy that have deeper tissue penetration. The design, characteristics, bioimaging, and therapy of NIR metal agents are covered in this overview of papers and reports published to date. To start with, we focus on describing the structure, design strategies, and photophysical properties of metal agents from the NIR-I (650-1000 nm) to NIR-II (1000-1700 nm) region, in order of molecular metal complexes (MMCs), metal-organic complexes (MOCs), and metal-organic frameworks (MOFs). Next, the biomedical applications brought by these superior photophysical and chemical properties for more accurate imaging and therapy are discussed. Finally, we explore the challenges and prospects of each type of NIR metal agent for future biomedical research and clinical translation.

Activatable BODIPY-chromene NIR-II probes with small spectral crosstalk enable high-contrast in vivo bioimaging

Herein, we design a novel "crossbreeding" dye (BC-OH) within the second near-infrared (NIR-II) window based on BODIPY and chromene chromophores. BC-OH can serve as a platform to construct activatable NIR-II probes with small spectral crosstalk, thereby making a breakthrough in imaging in vivo H₂O₂ fluctuation in an APAP-induced liver injury model with high signal-to-background ratio.

NIR-II fluorescence imaging-guided colorectal cancer surgery targeting CEACAM5 by a nanobody

BACKGROUND

Surgery is the cornerstone of colorectal cancer (CRC) treatment, yet complete removal of the tumour remains a challenge. The second near-infrared window (NIR-II, 1000-1700 nm) fluorescent molecular imaging is a novel technique, which has broad application prospects in tumour surgical navigation. We aimed to evaluate the ability of CEACAM5-targeted probe for CRC recognition and the value of NIR-II imaging-guided CRC resection.

METHODS

We constructed the probe 2D5-IRDye800CW by conjugated anti-CEACAM5 nanobody (2D5) with near-infrared fluorescent dye IRDye800CW. The performance and benefits of 2D5-IRDye800CW at NIR-II were confirmed by imaging experiments in mouse vascular and capillary phantom. Then mouse colorectal cancer subcutaneous tumour model (n = 15), orthotopic model (n = 15), and peritoneal metastasis model (n = 10) were constructed to investigate biodistribution of probe and imaging differences between NIR-I and NIR-II in vivo, and then tumour resection was guided by NIR-II fluorescence. Fresh human colorectal cancer specimens were incubated with 2D5-IRDye800CW to verify its specific targeting ability.

FINDINGS

2D5-IRDye800CW had an NIR-II fluorescence signal extending to 1600 nm and bound specifically to CEACAM5 with an affinity of 2.29 nM. In vivo imaging, 2D5-IRDye800CW accumulated rapidly in tumour (15 min) and could specifically identify orthotopic colorectal cancer and peritoneal metastases. All tumours were resected under NIR-II fluorescence guidance, even smaller than 2 mm tumours were detected, and NIR-II had a higher tumour-to-background ratio than NIR-I (2.55 ± 0.38, 1.94 ± 0.20, respectively). 2D5-IRDye800CW could precisely identify CEACAM5-positive human colorectal cancer tissue.

INTERPRETATION

2D5-IRDye800CW combined with NIR-II fluorescence has translational potential as an aid to improve R0 surgery of colorectal cancer.

FUNDINGS

This study was supported by Beijing Natural Science Foundation (JQ19027), the National Key Research and Development Program of China (2017YFA0205200), National Natural Science Foundation of China (NSFC) (61971442, 62027901, 81930053, 92059207, 81227901, 82102236), Beijing Natural Science Foundation (L222054), CAS Youth Interdisciplinary Team (JCTD-2021-08), the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA16021200), the Zhuhai High-level Health Personnel Team Project (Zhuhai HLHPTP201703), the Fundamental Research Funds for the Central Universities (JKF-YG-22-B005) and Capital Clinical Characteristic Application Research (Z181100001718178). The authors would like to acknowledge the instrumental and technical support of the multi-modal biomedical imaging experimental platform, Institute of Automation, Chinese Academy of Sciences.

Iridium and Ruthenium Complexes Bearing Perylene Ligands

The present review summarizes the work carried out mostly in the last decade on iridium and ruthenium complexes bearing various perylene ligands, of particular interest for bioimaging, photodynamic therapy, and solar energy conversion. In these complexes, the absorption spectra and the electrochemical properties are those of the perylene subunit plus those of the metal moiety. In contrast, the emissions are completely changed with respect to perylenes considered alone. Thus, fully organic perylenes are characterized by a strong fluorescence in the visible region, lifetimes of a few nanoseconds, and luminescence quantum yields approaching 100%, whereas perylene Ir and Ru complexes usually do not emit; however, in few cases, weak phosphorescent emissions, with lifetimes in the range of microseconds and relatively low quantum yields, are reported. This is due to a strong interaction between the perylene core and the heavy metal center, taking place after the excitation. Nevertheless, an important advantage deriving from the presence of the heavy metal center is represented by the ability to generate large amounts of singlet oxygen, which plays a key role in photodynamic therapy.