Progress and Challenges of Water-soluble NIR-II Organic Fluorophores for Fluorescence Imaging In vivo

The small-molecule fluorophores for the second near-infrared(NIR-II,1000–1700 nm)window have attracted increasing attention in basic scientific research and preclinical practice owing to their deep-photo penetration,minimal physiological toxicity and simplicity of chemical modification.However,most of the reported small-molecule NIR-II fluorophores suffered from poor water solubility,which can easily cause organ toxicity.In addition,the aggregation caused by their poor water solubility in the aqueous solution would also result in weak fluorescence of these NIR-II fluorophores.Thus,it is highly desirable and valuable to develop water-soluble small-molecule NIR-II fluorophores with excellent photophysical properties for high-contrast in vivo imaging.In this review,we summarize the recent research advances in water-soluble small-molecule NIR-II fluorophores and highlight the representative bioimaging applications.Moreover,the potential challenges and perspectives of water-soluble small-molecule NIR-II fluorophores are discussed as well.We anticipate this review can help researchers to grab the latest information of water-soluble small-molecule fluorophores for NIR-II imaging,sequentially boosting their further development.

Self-assembled amphiphilic NIR-Ⅱ emissive nano-micelles for imaging-guided photothermal therapy of colorectal cancer

Colorectal cancer(CRC) is one of the major causes of cancer-related mortality worldwide. Most near-infrared(NIR) agents used in clinical CRC treatment are at NIR-I(700–900 nm) window, which has limitations on deep tissue, and fluorescent probes in the second NIR(1,000–1,700 nm) allow high-resolution bioimaging with deep tissue penetration. However, existing NIR-II fluorophores used in clinical are still rare. Herein, based on shielding-donor-acceptor-donor-shielding(S-D-A-D-S) scaffold, we developed an organic small-molecule fluorophore IR-BTGP with NIR-II emission for imaging-guided photothermal therapy(PTT) in CRC mice model. Amphiphilic IR-BTGP can be self-assembled into spherical nano-micelles, which presents reliable water solubility and photothermal conversion efficiency(30.2%). In vitro experiments indicate that cancer cells treated with IRBTGP were significantly killed upon 808 nm light irradiation. Furthermore, in vivo NIR-II fluorescence imaging confirms that IR-BTGP accumulates in the tumor region. Remarkably, a significant tumor inhibition rate(78.5%) was observed in tumorbearing mice when treated with IR-BTGP plus 808 nm irradiation. Therefore, this work shows that IR-BTGP holds great promise as an NIR-II fluorescence imaging-guided PTT platform for CRC in the future.

Biological imaging without autofluorescence in the second near-infrared region

Fluorescence imaging is capable of acquiring anatomical and functional infor- mation with high spatial and temporal resolution. This imaging technique has been indispensable in biological research and disease detection/diagnosis. Imaging in the visible and to a lesser degree, in the near-infrared （NIR） regions below 900 nm, suffers from autofluorescence arising from endogenous fluorescent molecules in biological tissues. This autofluorescence interferes with fluorescent molecules of interest, causing a high background and low detection sensitivity. Here, we report that fluorescence imaging in the 1,500-1,700-nm region （termed ＂NIR-IIb＂） under 808-nm excitation results in nearly zero tissue autofluorescence, allowing for background-free imaging of fluorescent species in otherwise notoriously autofluorescent biological tissues, including liver. Imaging of the intrinsic fluorescence of individual fluorophores, such as a single carbon nanotube, can be readily achieved with high sensitivity and without autofluorescence background in mouse liver within the 1,500-1,700-nm wavelength region.

Initial Experience of NIR-II Fluorescence Imaging-Guided Surgery in Foot and Ankle Surgery

Optical imaging in the second near-infrared(NIR-II;900-1880 nm)window is currently a popular research topic in the field of biomedical imaging.This study aimed to explore the application value of NIR-II fluorescence imaging in foot and ankle surgeries.A lab-established NIR-II fluorescence surgical navigation system was developed and used to navigate foot and ankle surgeries which enabled obtaining more high-spatial-frequency information and a higher signal-to-background ratio(SBR)in NIR-II fluorescence images compared to NIR-I fluorescence images;our result demonstrates that NIR-II imaging could provide higher-contrast and larger-depth images to surgeons.Three types of clinical application scenarios(diabetic foot,calcaneal fracture,and lower extremity trauma)were included in this study.Using the NIR-II fluorescence imaging technique,we observed the ischemic region in the diabetic foot before morphological alterations,accurately determined the boundary of the ischemic region in the surgical incision,and fully assessed the blood supply condition of the flap.NIR-II fluorescence imaging can help surgeons precisely judge surgical margins,detect ischemic lesions early,and dynamically trace the perfusion process.We believe that portable and reliable NIR-II fluorescence imaging equipment and additional functional fluorescent probes can play crucial roles in precision surgery.

靶向MC1R的NIR-Ⅱ聚集诱导发射纳米颗粒用于黑色素瘤成像

恶性黑色素瘤是最致命的皮肤癌,因此,早期诊断对提高生存率至关重要.黑色素皮质素-1受体(MC1R)在黑色素瘤细胞中过度表达,被认为是黑色素瘤检测的分子靶标.在本工作中,我们基于具有近红外二区(NIR-Ⅱ)发射的聚集诱导发光源TPE-BBT开发了一种新的MC1R靶向荧光探针,命名为MSH-TPE-BBT NPs,并评估了其在黑色素瘤体内成像的潜力.MSH-TPE-BBT NPs具有显著的组织穿透性、光稳定性和生物安全性,并在人类黑色素瘤细胞及其小鼠体内异种移植肿瘤中表现出特异性靶向特性.MSH-TPE-BBT NPs在黑色素瘤小鼠体内成像的成功应用及其良好的生物相容性表明其作为靶向MC1R的黑色素瘤成像探针具有临床应用潜力.

Repurposing organic semiconducting nanomaterials to accelerate clinical translation of NIR-II fluorescence imaging

Optical imaging possesses important implications for early disease diagnosis,timely disease treatment,and basic medical as well as biological research.Compared with the traditionary near-infrared(NIR-I)window(650-950 nm)optical imaging,the emerging second near-infrared(NIR-II)window optical imaging technology owns the great superiorities of non-invasiveness,nonionizing radiation,and real-time dynamic imaging with the low biological interference,can significantly improve the tissue penetration depth and detection sensitivity,thus expecting to achieve accurate and precise diagnosis of major diseases.Inspired by the conspicuous superiorities,an increasing number of versatile NIR-II fluorophores have been legitimately designed and engineered for precisely deep-tissue mapping-mediated theranostics of life-threatening diseases.Organic semiconducting nanomaterials(OSNs)are derived from organic conjugated molecules withπ-electron delocalized skeletons,which show greatly preponderant prospects in the biomedicine field due to the excellent photoelectric property,tunable energy bands,and fine biocompatibility.In this review,the superiorities of NIR-II fluorescence imaging using OSNs for brilliant visualization various of diseases,including tongue cancer,ovarian cancer,osteosarcoma,bacteria or pathogens infection,kidney dysfunction,rheumatoid arthritis,liver injury,and cerebrovascular function,are emphatically summarized.Finally,the reasonable prospects and persistent efforts for repurposing OSNs to facilitate the clinical translation of NIR-II fluorescence phototheranostics are outlined.

An activatable NIR-Ⅱ fluorescent probe for tracking heavy-metal ion and high-level salt-induced oxidative stress in plant sprouts

Humans and plants have become enfolded and inseparable.Abiotic stresses in particular oxidative stress caused by heavy-metal ions or high-level salt contamination deleteriously impact plants’growth process and have become a major threat to sustaining food security.Sprouting is the first step in plants’growth process.When plant sprouts endure oxidative stress induced by toxic heavy-metal ions or high-level salt,accelerated generation of reactive oxygen species(e.g.,H_(2)O_(2))occurs inside plant sprouts;hence in-situ H_(2)O_(2) in plant sprouts could serve as the in-vivo biomarker for tracking the oxidative stress in plant sprouts.Herein,we design an activatable probe CT-XA-H_(2)O_(2) to track the oxidative stress in plant sprouts via in vivo NIR-Ⅱ fluorescent imaging.In CT-XA-H_(2)O_(2),cyano-thiazole acts as the electron-accepting moiety and xanthane-aminodiphenyl as the electron-donating moiety,and dioxaborolane as the biomarker-responsive unit and fluorescence quencher.The probe CT-XA-H_(2)O_(2) shows weak fluorescent emission.When H_(2)O_(2) is present,the dioxaborolane in the probe is cleaved,consequently,the dye CT-XA-OH is generated and brings about significant fluorescent signals for detecting and imaging the in-situ biomarker.Moreover,the aminodiphenyl group endues the chromophore(the activated probe)with aggregation-induced emission characteristics,which ensures stronger fluorescence in the aggregated state in the aqueous milieu.The probe CT-XA-H_(2)O_(2) has been employed in the Cd^(2+)-ion or high-level salt(NaCl)induced oxidative stress models of soybean sprouts and peanut sprouts,and the experimental results evidently reveal the probe’s ability for in-situ biomarker-activatable in-vivo detection and imaging in the plants’sprouts.

High brightness NIR-Ⅱ nanofluorophores based on fused-ring acceptor molecules

It is challenging to develop molecular fluorophores in the second near-infrared(NIR-Ⅱ)window with long wavelength emission and high brightness,which can improve the performance of biological imaging.Herein,we report a molecular engineering approach to afford NIR-Ⅱ fluorophores with these merits based on fused-ring acceptor(FRA)molecules.Dioctyl 3,4-propylenedioxy thiophene(PDOT-C8)is utilized as the bridging donor to replace 3-ethylhexyloxy thiophene(3-EHOT),leading to more than 20 times enhancement of brightness.The nanofluorophores(NFs)based on the optimized CPTIC-4F molecule exhibit an emission peak of 1,110 nm with a fluorescence quantum yield(QY)of 0.39%(QY of IR-26 is 0.050%in dichloroethane as reference)and peak absorption coefficient of 14.5 x 10^4 M^-1·cm^-1 in aqueous solutions,which are significantly higher than those of 3-EHOT based COTIC-4F NFs.It is found that PDOT-C8 can weaken intermolecular aggregation,enhance protection of molecular backbone from water,and decrease backbone distortion,beneficial for the high brightness.Compared with indocyanine green with same injection dose,CPTIC-4F NFs show 10 times higher signal-to-background ratio for whole body vessels imaging at 1,300 nm long pass filters.