Organic Dots with Large π-Conjugated Planar for Cholangiography beyond 1500 nm in Rabbits: A Non-Radioactive Strategy

NIR-II light in clinical oncology: opportunities and challenges

Novel strategies utilizing light in the second near-infrared region (NIR-II; 900-1,880 nm wavelengths) offer the potential to visualize and treat solid tumours with enhanced precision. Over the past few decades, numerous techniques leveraging NIR-II light have been developed with the aim of precisely eliminating tumours while maximally preserving organ function. During cancer surgery, NIR-II optical imaging enables the visualization of clinically occult lesions and surrounding vital structures with increased sensitivity and resolution, thereby enhancing surgical quality and improving patient prognosis. Furthermore, the use of NIR-II light promises to improve cancer phototherapy by enabling the selective delivery of increased therapeutic energy to tissues at greater depths. Initial clinical studies of NIR-II-based imaging and phototherapy have indicated impressive potential to decrease cancer recurrence, reduce complications and prolong survival. Despite the encouraging results achieved, clinical translation of innovative NIR-II techniques remains challenging and inefficient; multidisciplinary cooperation is necessary to bridge the gap between preclinical research and clinical practice, and thus accelerate the translation of technical advances into clinical benefits. In this Review, we summarize the available clinical data on NIR-II-based imaging and phototherapy, demonstrating the feasibility and utility of integrating these technologies into the treatment of cancer. We also introduce emerging NIR-II-based approaches with substantial potential to further enhance patient outcomes, while also highlighting the challenges associated with imminent clinical studies of these modalities.

Planar-structured thiadiazoloquinoxaline-based NIR-II dye for tumor phototheranostics

Second near-infrared (NIR-II) fluorescence imaging shows huge application prospects in clinical disease diagnosis and surgical navigation, while it is still a big challenge to exploit high performance NIR-II dyes with long-wavelength absorption and high fluorescence quantum yield. Herein, based on planar π-conjugated donor-acceptor-donor systems, three NIR-II dyes (TP-DBBT, TP-TQ1, and TP-TQ2) were synthesized with bulk steric hindrance, and the influence of acceptor engineering on absorption/emission wavelengths, fluorescence efficiency and photothermal properties was systematically investigated. Compared with TP-DBBT and TP-TQ2, the TP-TQ1 based on 6,7-diphenyl-[1,2,5]thiadiazoloquinoxaline can well balance absorption/emission wavelengths, NIR-II fluorescence brightness and photothermal effects. And the TP-TQ1 nanoparticles (NPs) possess high absorption ability at a peak absorption of 877 nm, with a high relative quantum yield of 0.69% for large steric hindrance hampering the close π-π stacking interactions. Furthermore, the TP-TQ1 NPs show a desirable photothermal conversion efficiency of 48% and good compatibility. In vivo experiments demonstrate that the TP-TQ1 NPs can serve as a versatile theranostic agent for NIR-II fluorescence/photoacoustic imaging-guided tumor phototherapy. The molecular planarization strategy provides an approach for designing efficient NIR-II fluorophores with extending absorption/emission wavelength, high fluorescence brightness, and outstanding phototheranostic performance.

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.

Ultrabright NIR-II Nanoprobe for Image-Guided Accurate Resection of Tiny Metastatic Lesions

Fluorescence imaging is a vital way to delineate the tumor boundaries. Here, we achieve a NIR-II aggregation-induced emission luminogen (AIEgen) with a fluorescence quantum yield (QY) of 12.6% in water through straightforward alkyl side chain modification. After loading of NIR-II AIEgen into polystyrene (PS) nanospheres, the thermal deactivation pathway is extremely limited, thereby concentrating absorption excitation on fluorescence emission. The fluorescence intensity is further enhanced by 5.4 times, the QY increases to 21.1%, and the NIR-II imaging signal is accordingly enhanced by 8.7 times, surpassing conventional DSPE-PEG carriers. The NIR-II@PS nanoprobe showcases superior resolution and tissue penetration depth compared to indocyanine green (ICG) and short-range near-infrared AIEgens. In vivo investigations underscore its tumor-to-normal tissue ratio (3.9) at 24 h post intravenous injection, enabling complete resection of ≤1 mm metastases under NIR-II bioimaging guidance. Additionally, the PS carrier-nanoparticles exhibit low toxicity in vivo, laying a promising foundation for the future design of medical nanomaterials.

Promoting the Near-Infrared-II Fluorescence of Diketopyrrolopyrrole-Based Dye for In Vivo Imaging via Donor Engineering

Small-molecule dyes for fluorescence imaging in the second near-infrared region (NIR-II, 900-1880 nm) hold great promise in clinical applications. Constructing donor-acceptor-donor (D-A-D) architectures has been recognized to be a feasible strategy to achieve NIR-II fluorescence. However, the development of NIR-II dyes via such a scheme is hampered by the lack of high-performance electron acceptors and donors. Diketopyrrolopyrrole (DPP), as a classic organic optoelectronic material, enjoys strong light absorption, high fluorescence quantum yield (QY), and facile derivatization. Nevertheless, its application in the NIR-II imaging field has been hindered by its limited electron-withdrawing ability and the aggregation-caused quenching (ACQ) effect resulting from the planar structure of DPP. Herein, with DPP as an electron acceptor and through donor engineering, we have successfully designed and synthesized a DPP-based dye named T-27, in which the strong D-A interaction confers excellent NIR absorption and high-brightness NIR-II fluorescence tail emission. By strategically introducing long alkyl chains on the donor unit to increase intermolecular spacing and reduce the influence of solvent molecules, T-27 exhibits an improved anti-ACQ effect in aqueous solutions. After being encapsulated into DSPE-PEG2000, T-27 nanoparticles (NPs) show a relative NIR-II fluorescence QY of 3.4% in water, representing the highest value among the DPP-based NIR-II dyes reported to date. The outstanding photophysical properties of T-27 NPs enable multimode NIR-IIa bioimaging under 808 nm excitation. As such, the T-27 NPs can distinguish mouse femoral vein and artery and achieve cerebral vascular microscopic imaging with a penetrating depth of 800 μm, demonstrating the capability for high-resolution deep-tissue imaging. This work holds significant potential in the field of bioimaging and provides a new strategy for developing bright NIR-II dyes.

Nanotechnology for brain tumor imaging and therapy based on π-conjugated materials: state-of-the-art advances and prospects

In contemporary biomedical research, the development of nanotechnology has brought forth numerous possibilities for brain tumor imaging and therapy. Among these, π-conjugated materials have garnered significant attention as a special class of nanomaterials in brain tumor-related studies. With their excellent optical and electronic properties, π-conjugated materials can be tailored in structure and nature to facilitate applications in multimodal imaging, nano-drug delivery, photothermal therapy, and other related fields. This review focuses on presenting the cutting-edge advances and application prospects of π-conjugated materials in brain tumor imaging and therapeutic nanotechnology.

Novel NIR-II fluorescent probes for biliary atresia imaging

Biliary atresia is a rare infant disease that predisposes patients to liver transplantation and death if not treated in time. However, early diagnosis is challenging because the clinical manifestations and laboratory tests of biliary atresia overlap with other cholestatic diseases. Therefore, it is very important to develop a simple, safe and reliable method for the early diagnosis of biliary atresia. Herein, a novel NIR-II fluorescence probe, HZL2, with high quantum yield, excellent biocompatibility, low cytotoxicity and rapid excretion through the liver and gallbladder was developed based on the oil/water partition coefficient and permeability. A simple fecal sample after injection of HZL2 can be used to efficiently identify the success of the mouse model of biliary atresia for the first time, allowing for an early diagnosis of the disease. This study not only developed a simple and safe method for the early diagnosis of biliary atresia with great potential in clinical translation but also provides a research tool for the development of pathogenesis and therapeutic medicines for biliary atresia.

Blood Circulation Assessment by Steadily Fluorescent Near-Infrared-II Aggregation-Induced Emission Nano Contrast Agents

The dysfunction of the blood circulation system typically induces acute or chronic ischemia in limbs and vital organs, with high disability and mortality. While conventional tomographic imaging modalities have shown good performance in the diagnosis of circulatory diseases, multiple limitations remain for real-time and precise hemodynamic evaluation. Recently, fluorescence imaging in the second region of the near-infrared (NIR-II, 1000-1700 nm) has garnered great attention in monitoring and tracing various biological processes in vivo due to its advantages of high spatial-temporal resolution and real-time feature. Herein, we employed NIR-II imaging to carry out a blood circulation assessment by aggregation-induced emission fluorescent aggregates (AIE nano contrast agent, AIE NPs). Thanks to the longer excited wavelength, enhanced absorptivity, higher brightness in the NIR-II region, and broader optimal imaging window of the AIE NPs, we have realized a multidirectional assessment for blood circulation in mice with a single NIR-II imaging modality. Thus, our work provides a fluorescence contrast agent platform for accurate hemodynamic assessment.

Synthesis of an aggregation-induced emission-based fluorescent probe based on rupestonic acid

Chinese herbal medicine and Chinese patent medicine have been widely applied for cancer care in China. Rupestonic acid, an active ingredient of Artemisia rupestris L., has recently been confirmed to have certain anti-tumor effects in vitro. In this study, we employed the application of a commonly devoted triphenylamine as a fluorophore and the addition of 2,4-thiazolidinedione as a bridge to integrate rupestonic acid into the AIE system to create an fluorescent probe with anti-tumor properties. The spectral, cytotoxic, and cellular imaging properties of the probe were measured. Its promising responses make possible the application of the probe in antitumor theragnostic systems.

Engineered NIR-II fluorophores with ultralong-distance molecular packing for high-contrast deep lesion identification

The limited signal of long-wavelength near-infrared-II (NIR-II, 900-1880 nm) fluorophores and the strong background caused by the diffused photons make high-contrast fluorescence imaging in vivo with deep tissue disturbed still challenging. Here, we develop NIR-II fluorescent small molecules with aggregation-induced emission properties, high brightness, and maximal emission beyond 1200 nm by enhancing electron-donating ability and reducing the donor-acceptor (D-A) distance, to complement the scarce bright long-wavelength emissive organic dyes. The convincing single-crystal evidence of D-A-D molecular structure reveals the strong inhibition of the π-π stacking with ultralong molecular packing distance exceeding 8 Å. The delicately-designed nanofluorophores with bright fluorescent signals extending to 1900 nm match the background-suppressed imaging window, enabling the signal-to-background ratio of the tissue image to reach over 100 with the tissue thickness of ~4-6 mm. In addition, the intraluminal lesions with strong negatively stained can be identified with almost zero background. This method can provide new avenues for future long-wavelength NIR-II molecular design and biomedical imaging of deep and highly scattering tissues.

Aggregation-Induced Emission (AIE), Life and Health

Light has profoundly impacted modern medicine and healthcare, with numerous luminescent agents and imaging techniques currently being used to assess health and treat diseases. As an emerging concept in luminescence, aggregation-induced emission (AIE) has shown great potential in biological applications due to its advantages in terms of brightness, biocompatibility, photostability, and positive correlation with concentration. This review provides a comprehensive summary of AIE luminogens applied in imaging of biological structure and dynamic physiological processes, disease diagnosis and treatment, and detection and monitoring of specific analytes, followed by representative works. Discussions on critical issues and perspectives on future directions are also included. This review aims to stimulate the interest of researchers from different fields, including chemistry, biology, materials science, medicine, etc., thus promoting the development of AIE in the fields of life and health.

NIR-II and visible fluorescence hybrid imaging-guided surgery via aggregation-induced emission fluorophores cocktails

Fluorescence imaging-guided surgery is one of important techniques to realize precision surgery. Although second near-infrared window (NIR-II) fluorescence imaging has the advantages of high resolution and large penetration depth in surgical navigation, its major drawback is that NIR-II images cannot be detected by our naked eyes, which demands a high hand-eye coordination for surgeons and increases the surgical difficulty. On the contrary, visible fluorescence can be observed by our naked eyes but has poor penetration. Here, we firstly propose a kind of NIR-II and visible fluorescence hybrid navigation surgery assisted via a cocktail of aggregation-induced emission nanoparticles (AIE NPs). NIR-II imaging helps to locate deep targeted tissues and judge the residual, and visible fluorescence offers an easily surgical navigation. We apply this hybrid navigation mode in different animals and systems, and verify that it can accelerate surgical process and compatible with a visible fluorescence endoscopy. To deepen the understanding of lymph node (LN) labelling, the distribution of NPs in LNs after local administration is initially analyzed by NIR-II fluorescence wide-filed microscopy, and two fates of the NPs are summarized. An alternative strategy which combines indocyanine green and berberine is also reported as a compromise for rapidly clinical translation.

BOIMPY-Based NIR-II Fluorophore with High Brightness and Long Absorption beyond 1000 nm for In Vivo Bioimaging: Synergistic Steric Regulation Strategy

Fluorescence imaging in the second near-infrared (NIR-II, 1000-1700 nm) region holds great promise for in vivo bioimaging. However, it is challenging to develop a brilliant donor-acceptor-donor (D-A-D) type NIR-II fluorophore with maximal absorption beyond 1000 nm in aqueous solution. Herein, we report a bright D-A-D type BOIMPY-based NIR-II dye (NK1143) with peak absorption/emission at 1005/1143 nm for in vivo bioimaging. Co-assembly of NK1143, SC12 (intermolecular steric hindrance modulator), and DSPE-PEG2000 effectively inhibits H-aggregation of NK1143 in aqueous solution and enhances the brightness simultaneously up to 53-fold by leveraging synergistic steric regulation strategy. Notably, this strategy allows for deep optical penetration of 8 mm and high-resolution blood vessels imaging in vivo, displaying high signal-to-background ratio of 7.8/1 under 980 nm excitation. More importantly, the BOIMPY-based nanoprobe can passively target and clearly visualize broad types of tumor xenografts, further improving intraoperative NIR-II fluorescence-guided resection of tiny metastases of less than 1 mm. This work provides an effective strategy for the development of BOIMPY-based NIR-II organic fluorophores with broad applications.

Imaging the Deep Spinal Cord Microvascular Structure and Function with High-Speed NIR-II Fluorescence Microscopy

The spinal cord (SC) is crucial for a myriad of somatosensory, autonomic signal processing, and transductions. Understanding the SC vascular structure and function thus plays an integral part in neuroscience and clinical research. However, the dense layers of myelinated ascending axons on the dorsal side inconveniently grant the SC tissue with high optical scattering property, which significantly hinders the imaging depth of the SC vasculature in vivo. Commonly used antiscattering techniques such as multiphoton fluorescence microscopy have low imaging speed and cannot capture the rapid vascular particle flow without significant motion blur. Here, advantage of the high penetration of near-infrared (NIR)-II fluorescence is taken to demonstrate a deep SC vascular structural image stack up to 350 µm, comparable to two-photon microscopy. Furthermore, the red blood cells are labelled with the clinically approved NIR dye indocyanine. The combination of a fast NIR camera and indocyanine green-red blood cells (RBCs) makes it possible to attain high-speed 100 frame-per-second NIR-II imaging to identify the corresponding changes in RBC velocity during the external hind leg stimulus. For the first time, it is established that the NIR-II region would be a promising spectral window for SC imaging. NIR-II fluorescence microscopy has excellent potential for clinical and basic science research on SC.

Molecular Crystal Engineering of Organic Chromophores for NIR-II Fluorescence Quantification of Cerebrovascular Function

Although molecular design strategies for highly bright near-infrared II (NIR-II) fluorophores were proposed, the lack of solid structural identification (single crystal) hinders the further development of this field. This thorny issue is addressed by performing the structure-function relationship of NIR-II dyes, as confirmed by molecular single crystal engineering. Single crystal structure analysis confirms that twisted architectures (large dihedral angles ∼70°) and loose packing patterns (intermolecular distance of ∼3.4-4.5 Å) are key elements to enhance the absolute quantum yield (QY) in the solid state. Through regulating donor-acceptor distance and donor-acceptor interactions, the resultant well-defined TBP-b-DFA fluorophore displays an absolute QY of 0.4% with an emission extending to 1400 nm, which is favorable for NIR-II bioimaging. The cerebrovascular function, including cerebral blood flow and cerebrovascular reactivity of different conditions, is accurately quantified by a NIR-II fluorescence wide-field microscope. Our study provides a sight for designing NIR-II fluorophores, which is useful for studying cerebrovascular function.

Aggregation-Induced Emission (AIE) Nanoparticles-Assisted NIR-II Fluorescence Imaging-Guided Diagnosis and Surgery for Inflammatory Bowel Disease (IBD)

The incidence of inflammatory bowel diseases (IBD), including Crohn's diseases and ulcerative colitis, is increasing by time and showing a trend of younger age. Precise diagnosis and effective treatments for IBD have attracted growing attention in recent years. However, diagnosing and locating inflammatory lesions remain a great challenge for IBD. In this study, assisted by a kind of aggregation-induced emission (AIE) nanoprobes (BPN-BBTD nanoparticles [NPs]), the second near-infrared (NIR-II) fluorescence imaging is first utilized to accurately trace inflammatory lesions, monitor inflammation severity and detect the response to the drug intervention in IBD mouse models. Through the advantages of high signal-to-background ratio (SBR) and sharp spatial resolution of bio-imaging in NIR-II region, the NIR-II fluorescence imaging-guided surgery can help to achieve a complete resection of severe inflammatory bowls and a secure surgical anastomosis. In addition, with the help of NIR-II fluorescence wide-field microscopy, the distribution of BPN-BBTD NPs can be directly detected in tissue level and found to be mainly accumulated in mucosa and submucosa layers. This study highlights that AIE NPs-assisted NIR-II fluorescence imaging hold a great potential value for future diagnosis and imaging-guided surgery in IBD.

Versatile Types of Inorganic/Organic NIR-IIa/IIb Fluorophores: From Strategic Design toward Molecular Imaging and Theranostics

In vivo imaging in the second near-infrared window (NIR-II, 1000-1700 nm), which enables us to look deeply into living subjects, is producing marvelous opportunities for biomedical research and clinical applications. Very recently, there has been an upsurge of interdisciplinary studies focusing on developing versatile types of inorganic/organic fluorophores that can be used for noninvasive NIR-IIa/IIb imaging (NIR-IIa, 1300-1400 nm; NIR-IIb, 1500-1700 nm) with near-zero tissue autofluorescence and deeper tissue penetration. This review provides an overview of the reports published to date on the design, properties, molecular imaging, and theranostics of inorganic/organic NIR-IIa/IIb fluorophores. First, we summarize the design concepts of the up-to-date functional NIR-IIa/IIb biomaterials, in the order of single-walled carbon nanotubes (SWCNTs), quantum dots (QDs), rare-earth-doped nanoparticles (RENPs), and organic fluorophores (OFs). Then, these novel imaging modalities and versatile biomedical applications brought by these superior fluorescent properties are reviewed. Finally, challenges and perspectives for future clinical translation, aiming at boosting the clinical application progress of NIR-IIa and NIR-IIb imaging technology are highlighted.

High-stability NIR-II fluorescence polymer synthesized by atom transfer radical polymerization for application in high-resolution NIR-II imaging

Near-infrared II (NIR-II, 1000-1700 nm) fluorescent imaging (FI) has been reported to achieve optical images with higher resolution and deeper penetration. Among the organic NIR-II small molecules, donor-acceptor-donor (D-A-D) type fluorescent agents have shown superior photophysical and biocompatible properties for FI applications but have ongoing limitations, such as the difficulty in further modifying them with drug-carrying functional groups or prodrugs. In this work, three D-A-D type NIR-II fluorophores with electron acceptors of 4,8-bis(5-bromo-4-(2-octyldodecyl)thiophen-2-yl)-1H,3H-benzo[1,2-c:4,5-c']bis([1,2,5]thiadiazole) (BBT), 6,7-bis(4-(hexyloxy)phenyl)-4,9-di(thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline (TTQ) and 4,6-bis(5-bromo-2-thienyl)thieno[3,4-c][1,2,5]thiadiazole (TTDT) have been successfully prepared. Their optical and imaging properties and stability were investigated via theoretical and experimental studies. The results demonstrated that TTDT-SF exhibited good NIR-II imaging ability. Importantly, TTDT-SF showed outstanding stability in an alkaline and redox environment. Subsequently, a stable atom transfer radical polymerization (ATRP) initiator, based on TTDT and its derivative water-soluble fluorescent polymer TTDT-TF-POEGMA, synthesized through ATRP, was successfully fabricated. It was demonstrated that TTDT-TF-POEGMA exhibited excellent fluorescence ability, great water solubility, effective light stability and great potential in tumor FI and image-guided surgery. In a word, this work has developed a new stable initiator with NIR-II fluorescent properties, which provides a platform for the development of water-soluble and multifunctional NIR-II fluorescent polymers for a broad range of applications.