Rational Design of NIR-II Ratiometric Fluorescence Probes for Accurate Bioimaging and Biosensing In Vivo

Novel near-infrared 2H-chromene-based ratiometric fluorescent probe: Rapidly monitoring hydrazine in real samples

A novel near-infrared (NIR Ⅰ) fluorescent probe MCM-OMe with 2H-chromene scaffold was designed, synthesized and investigated it optical properties. MCM-OMe was identified as a novel hydrazine detector through nucleophilic substitution reaction with hydrazine, changing the color from red to blue. The emission spectra showed a clear intensity shift from MCM-OMe to its corresponding product MCH, indicating that MCM-OMe has ratiometric fluorescent property. Meanwhile, MCM-OMe exhibits acid-base tolerance with high selectivity and sensitivity to the residual N2H4. Moreover, the probe is equally suitable for the detection of residual hydrazine in water, soils and foods. Therefore, we provide a novel ratiometric fluorescent probe to detect hydrazine through a low-cost, easy-to-manufacture and easy-to-operate way.

Molecular Engineering of 2', 7'-Dichlorofluorescein to Unlock Efficient Superoxide Anion NIR-II Fluorescent Imaging and Tumor Photothermal Therapy

Although classical fluorescent dyes feature advantages of high quantum yield, tunable "OFF-ON" fluorescence, and modifiable chemical structures, etc., their bio-applications in deep tissue remains challenging due to their excessively short emission wavelength (that may lead to superficial tissue penetration depth). Therefore, there is a pressing need for pushing the wavelength of classical dyes from visible region to NIR-II window. As a representative classical dye, the 2',7'-Dichlorofluorescein (DCF), a derivative of Fluorescein, is selected and rationally engineered to develop a novel NIR-II platform, CR-OH, which exhibits a substantial red-shift in the wavelength from the visible region to the NIR-II region. This achievement is attributed to molecular modification strategies that include extending π-conjugation, enhancing molecular rigidity, and incorporating strong electron-withdrawing groups. Furthermore, based on this developed NIR-II platform, a NIR-II fluorescence probe and a photothermal nanoagent are successfully constructed to unlock its bio-application in the NIR-II fluorescence imaging of endogenous O2 ·- fluctuations in a CIRI model for the first time, as well as effective photothermal therapy for 4T1 tumors with a high photothermal conversion efficiency (44.0%). Significantly, this work overcomes the wavelength limitation of classical dyes, effectively unlocking their applications for the diagnosis and treatment of early disease in the NIR-II window.

Enabling Visible Light Sensitization of YbIII, NdIII and ErIII in Dimeric LnIII/GaIII Metallacrowns through Functionalization with RuII Complexes for NIR-II Multiplex Imaging

Multiplex imaging in the second near-infrared window (NIR-II, 1000-1700 nm) provides exciting opportunities for more precise understanding of biological processes and more accurate diagnosis of diseases by enabling real-time acquisition of images with improved contrast and spatial resolution in deeper tissues. Today, the number of imaging agents suitable for this modality remains very scarce. In this work, we have synthesized and fully characterized, including theoretical calculations, a series of dimeric LnIII/GaIII metallacrowns bearing RuII polypyridyl complexes, LnRu-3 (Ln=YIII, YbIII, NdIII, ErIII). Relaxed structures of YRu-3 in the ground and the excited electronic states have been calculated using dispersion-corrected density functional theory methods. Detailed photophysical studies of LnRu-3 have demonstrated that characteristic emission signals of YbIII, NdIII and ErIII in the NIR-II range can be sensitized upon excitation in the visible range through RuII-centered metal-to-ligand charge transfer (MLCT) states. We have also showed that these NIR-II signals are unambiguously detected in an imaging experiment using capillaries and biological tissue-mimicking phantoms. This work opens unprecedented perspectives for NIR-II multiplex imaging using LnIII-based molecular compounds.

Mitochondrial SO2-Activated NIR Photodiagnostic Agent Harnessing Hydroxyl Radicals for Efficient Inflammation Eradication and Tumor Suppression

At present, some progress has been made in developing NIR light-responsive free radical generators. However, the efficacy of theranostics continues to be hindered by tumor-associated inflammatory reactions. Hence, fulfilling the in situ release of free radicals upon NIR light excitation specifically activated by the inflammation microenvironment would be an ideal strategy for efficient inflammation eradication and tumor suppression but remains a challenge. Herein, a SO2 (overexpressed reactive sulfur species in inflamed site)-stimulated phototheranostic agent (CVS) is successfully developed. Through a specific response to both endogenous and exogenous SO2 with a low LOD (31.7 nM), CVS demonstrates the "switch on" two-photon activity as well as efficient OH· generation. Remarkably, in CVS-treated H22-tumor-bearing mice, the NIR light-activated accurate inflammation eradication and tumor suppression are accomplished. This reactive phototheranostic platform not only facilitates the quantification of SO2 during inflammation but also renders it a potent NIR antihypoxic tumor agent.

Recent advances of versatile fluorophores for multifunctional biomedical imaging in the NIR-II region

Fluorescence imaging in the second near-infrared region (NIR-II, 1000-1700 nm) enables high-resolution visualization of deep-tissue biological architecture and physiopathological events, due to the reduced light absorption, scattering and tissue autofluorescence. Numerous versatile NIR-II fluorescent probes have been reported over the past decades. In this review, we first provide a detailed account of the advantages of fluorescence imaging in the NIR-II region. Following this, the classification, design and performance optimization strategies of NIR-II fluorescent probes are systematically discussed, along with a broad range of biomedical applications in vivo. Finally, the discussion extends to the next generation of fluorescent probes for in vivo imaging and the challenges and perspectives for the clinical translation of fluorescence imaging technology in the NIR-II region.

Water-Soluble Lipophilic Near-Infrared Region II Fluorophores for High-Brightness Lipid Layer and Lipid Droplets Imaging Applications

Fluorescence imaging in the second near-infrared region (NIR-II, 1000-1700 nm) has garnered considerable attention for displaying the biological information of deep tissues. However, the lack of biocompatible contrast agents with bright NIR-II emission has hampered the precise clinical application of deep tissue imaging. Here, a lipophilic enhancement strategy employing donor-acceptor-donor (D-A-D) molecules, introducing long alkoxy chains and quaternary ammonium salts for the development of highly bright water-soluble NIR-II fluorophores (BBTD-2C-N), is described. Notably, liposome-encapsulated BBTD-2C-N nanoparticles (B-2C-N/DMPC) in aqueous solution exhibit a 1.8-fold increase in NIR-II fluorescence brightness compared to free BBTD-2C-N in methanol. Avoidance of the aggregation-caused quenching effect and enhanced NIR-II fluorescence are attributed to significantly attenuated π-π stacking interactions and maintained monodisperses in the hydrophobic liposome shell. Moreover, BBTD-2C-N demonstrates superior performance in visualizing lipid droplet-rich HeLa cells in vitro, as well as precise monitoring of adipose tissue and fatty liver in vivo. This study reveals a new avenue for the development of bright NIR-II fluorophores and precise in vivo imaging.

A Small-Molecule NIR-II Probe for the Diagnosis of Hemorrhagic Diseases

Numerous hemorrhagic disorders, particularly those presenting deep hemorrhage, pose diagnostic challenges, often leading to delayed treatment and severe outcomes. Near-infrared (NIR)-II fluorescence imaging offers advantages such as deep tissue penetration, real-time visualization, and a high signal-to-background ratio, making it highly suitable for diagnosing hemorrhagic diseases. In this study, an NIR-II fluorescent probe LJ-2P carrying carboxylic and phosphoric acid groups is successfully applied for imaging hemorrhagic diseases. LJ-2P demonstrates a strong affinity for fibrinogen and fibrin clots both computationally and experimentally, thus exhibiting increased brightness upon coagulation. As compared to Indocyanine Green, LJ-2P provides a longer imaging window, higher imaging specificity, and signal-to-background ratio, as well as superior photobleaching resistance in three disease models: gastric, pulmonary, and cerebral hemorrhages. These results reveal that LJ-2P demonstrates enhanced imaging capabilities, enabling precise identification of hemorrhagic sites.

Spacer Twisting Strategy to Realize Ultrabright Near-Infrared II Polymer Nanoparticles for Fluorescence Imaging-Guided Tumor Phototheranostics

Conjugated polymers are becoming popular near-infrared II (NIR-II) phototheranostic agents (PTAs) due to their numerous advantages, such as high photostability, large molar extinction coefficients, and excellent photothermal properties. However, the strong π-π interactions between the chains of the conjugated polymers resulted in their generally low NIR-II emission quantum yields (QY). Therefore, the synthesis of conjugated polymers with high QY is an interesting but challenging task. Herein, we proposed a spacer twisting strategy to realize ultrabright NIR-II polymer nanoparticles for fluorescence imaging-guided tumor phototheranostics. Theoretical calculations indicated that the polymer PY-IT has the largest dihedral angle between the largely π-conjugated skeleton and the spacer, which can effectively inhibit intermolecular π-π stacking, resulting in an improved QY as high as 16.5% in nanoparticles. In addition, PY-IT NPs can effectively perform NIR-II imaging and photothermal treatment of tumors. The work presents some valuable guides for achieving ultrabright NIR-II polymeric PTAs with high QY.

Supramolecular Nano-Tracker for Real-Time Tracking of Drug Release and Efficient Combination Therapy

Real-time tracking of drug release from nanomedicine in vivo is crucial for optimizing its therapeutic efficacy in clinical settings, particularly in dosage control and determining the optimal therapeutic window. However, most current real-time tracking systems require a tedious synthesis and purification process. Herein, a supramolecular nano-tracker (SNT) capable of real-time tracking of drug release in vivo based on non-covalent host-guest interactions is presented. By integrating multiple cavities into a single nanoparticle, SNT achieves co-loading of drugs and probes while efficiently quenching the photophysical properties of the probe through host-guest complexation. Moreover, SNT is readily degraded under hypoxic tumor tissues, leading to the simultaneous release of drugs and probes and the fluorescence recovery of probes. With this spatial and temporal consistency in drug loading and fluorescence quenching, as well as drug release and fluorescence recovery, SNT successfully achieves real-time tracking of drug release in vivo (Pearson r = 0.9166, R2 = 0.8247). Furthermore, the released drugs can synergize effectively with fluorescent probes upon light irradiation, achieving potent chemo-photodynamic combination therapy in 4T1-bearing mice with a significantly improved survival rate (33%), providing a potential platform to significantly advance the development of nanomedicine and achieve optimal therapeutic effects in the clinic.