Bioorthogonally activatable cyanine dye with torsion-induced disaggregation for in vivo tumor imaging

Enhanced π-conjugation in hybridized local and charge transfer emitters for efficient red OLEDs and bioimaging

Red-emitting materials have significantly advanced the development of materials for OLEDs and bioimaging. However, traditional red dyes often suffer from the 5 % external quantum efficiency (EQE) limit and aggregation-caused quenching (ACQ), which impede their practical applications. Herein, two red-emitting materials, TPA-QP and Cz-Ph-QP were designed and synthesized with donor-acceptor (D-A) structures. The ratio of localized π-conjugation to intramolecular charge transfer components was rationally adjusted due to the different spatial configurations of the donor units. Both emitters exhibited hybridized local and charge transfer (HLCT) characteristics and the higher planarity of the TPA-QP molecular structure enhanced π-conjugation and facilitated effective hybridization between the locally excited (LE) and charge transfer (CT), resulting in deep-red (DR) emission at 680 nm and high photoluminescence quantum yields of 15.6 %. Furthermore, TPA-QP-based OLED demonstrated emission closer to the standard saturated red (λ = 657 nm, CIE coordinates of (0.65, 0.33)) with an excellent maximum EQE of 6.47 % and low efficiency roll-off. Additionally, the fabricated nanoparticles (TQ NPs) showed deep-red emission (λ = 682 nm) and were successfully applied in cellular imaging. The results provide deeper insights into the effects of spatial configuration changes on promoting the luminescence performance of the long-wavelength HLCT molecules.

Constructing J-aggregates of cyanine dye for NIR-II in vivo dynamic vascular imaging and long-term targeting of tumors

Cyanine molecules with the second near-infrared (NIR-II) emission hold great potential for bioimaging owing to their great biocompatibility, but the scissor-like structure of these molecules poses a major bottleneck in obtaining efficient NIR-II fluorescence probes. Constructing J-aggregates represents a promising strategy for obtaining biomedical NIR-II emissive materials. However, achieving J-aggregates in cyanine dyes with large torsion angles between the heterocyclic rings poses a challenge. In this study, we introduced the guanidine of tumor molecular targeted peptide 1 (TMTP1) to increase steric hindrance of IR-783 and reduce the angle of IR-783 scissors. The near-coplanar structure of IR-783@peptide TMTP1 composite facilitates the formation of a novel J-aggregates (IR-783-LP-TMTP1) with super-stable effect for NIR-II in vivo dynamic vascular imaging and remarkable tumor targeting capability. The stable emission wavelength and high spatial resolution of J-aggregates was demonstrated for brain and ear vasculature bioimaging under 808 nm laser excitation. Additionally, J-aggregates exhibits robust tumor-targeting capability towards cervical tumors, indicating their potential in cervical cancer diagnosis. This work develops a molecular design strategy to construct bright NIR-II J-aggregates with super-stable and robust tumor-targeting properties and paving the way for improving bioimaging performance of similar molecules.

Ischemic Myocardium Targeting Peptide-Guided Nanobubbles for Multimodal Imaging and Treatment of Coronary Microvascular Dysfunction

Coronary microvascular dysfunction (CMD) refers to clinical symptoms caused by structural and functional damage to coronary microcirculation. The timely and precise diagnosis of CMD-related myocardial ischemia is essential for improving patient prognosis. This study describes a method for the multimodal (fluorescence, ultrasonic, and photoacoustic) noninvasive imaging and treatment of CMD based on ischemic myocardium-targeting peptide (IMTP)-guided nanobubbles functionalized with indocyanine green (IMTP/ICG NBs) and characterizes their basic characteristics and in vitro imaging and targeting abilities. The IMTP/ICG NBs enable the accurate location of myocardial ischemia via photoacoustic imaging, and when loaded with tannic acid (TA), can be used to effectively treat myocardial ischemia and fibrosis in CMD mice, achieving an effect superior to that of free TA. The origin of this high therapeutic efficiency is revealed by transcriptomic and proteomic analyses. This investigation lays the groundwork for visual monitoring and the drug-targeted treatment of CMD.

Bioorthogonal SERS-bioluminescence dual-modal imaging for real-time tracking of triple-negative breast cancer metastasis

Triple-negative breast cancer (TNBC) represents an aggressive subtype of breast cancer, characterized by early metastasis and a poor prognosis. Traditional imaging modalities often lack the sensitivity and molecular specificity required for the early detection of metastatic lesions. In this study, we developed a dual-modal imaging strategy that integrates surface-enhanced Raman scattering (SERS) and bioluminescence imaging probes, utilizing bioorthogonal labeling to track TNBC organ metastasis. The SERS probes were encapsulated with azide-labeled macrophage membranes to extend circulation time and enhance targeting efficiency. Additionally, bioorthogonal metabolic glycolengineering was employed to modify luciferase-labeled tumor cells (4T1-Luc) with bicyclo[6.1.0]nonyne (BCN) groups, facilitating precise binding between the probes and 4T1-Luc cells through click chemistry reactions. This dual-modal imaging approach enabled real-time monitoring of small metastatic lesions with high sensitivity, providing a non-invasive and accurate method for assessing tumor metastasis and therapeutic response in vivo. Our findings indicate that the dual-modal imaging technique, combining SERS and bioluminescence with bioorthogonal labeling, holds significant potential for advanced applications in oncology. STATEMENT OF SIGNIFICANCE: This study devised a surface-enhanced Raman scattering (SERS) and bioluminescence dual-modal imaging strategy integrated with a bioorthogonal label to address the challenge of tracking the metastasis of aggressive triple-negative breast cancer (TNBC). In contrast to conventional methods, this approach facilitated real-time, whole-body monitoring of tumor dissemination through bioluminescence. Simultaneously, it achieved the detection of micro-metastases in organs using SERS, thereby exceeding the sensitivity limitations of existing imaging techniques. Clinical validation with human samples further demonstrated its potential for non-invasive therapeutic assessment and early intervention. By bridging preclinical innovation and clinical requirements, this research offered a transformative tool for precision oncology. It is expected to attract the interest of researchers in the fields of biomedicine, nanotechnology, and cancer therapeutics.

Photodynamic and Photothermal Co-Induced Efficient Anti-Tumor Immunotherapy

Currently, immunotherapy based on photothermal and the application of photodynamic therapy in anti-tumor treatment is showing great potential. Its uniqueness lies in the critical role of small molecule immunomodulators in promoting effective immune responses against tumors, and the use of laser-activated biophysical mechanisms to precisely trigger the swift demise of cancer cells, avoiding damage to surrounding normal tissues. However, the use of photodynamic therapy (PDT) alone is hampered by the tumors' hypoxic environment, resulting in poor antitumor effects, while photothermal therapy (PTT) alone cannot arouse enough antigen presentation. It is of great significance to design photosensitizers (PSs) that possess both PDT and PTT effects. Herein, a series of PSs with both PDT and PTT efficacy are reported, ultimately selecting Cy7-Naph as the star molecule due to its best overall phototherapeutic effect. Upon reactive oxygen species (ROS) production and thermogenesis in tumor cells, Cy7-Naph induced significant apoptosis and eventually boosted the release of damage-associated molecular patterns (DAMPs) under near-infrared (NIR) light irradiation. By combining Cy7-Naph with the Toll-like receptor agonist Resiquimod (R848), a synergistic treatment for bilateral tumor-bearing mice is achieved. This combination promotes dendritic cell (DC) maturation and increases the infiltration of cytotoxic T lymphocytes (CTLs), leading to significant inhibition of both primary and distant tumors.

A Nonconsumptive Fluorescent Probe for Precise Detection of Hydrogen Peroxide in Nonalcoholic Fatty Liver Disease and Inflammation

Hydrogen peroxide (H2O2) plays a vital role in various physiological and pathological processes. Thus, fluorescent probes of H2O2 are powerful tools for the investigation of H2O2-related diseases. However, developing fluorescent probes that do not irreversibly consume H2O2 presents a significant challenge. In this work, we introduce carbonate ester as a nonconsumptive recognizing molecule to construct RES-6C as a novel fluorescent probe of H2O2. RES-6C exhibited a selective and sensitive turn-on fluorescence response to H2O2, enabling the detection of H2O2 in cells without disturbing the cellular redox status. RES-6C has been applied to study nonalcoholic fatty liver disease, revealing that peroxisomes and mitochondria contribute to H2O2 production to a similar extent during very-long-chain fatty acid metabolism for the first time. It has also enabled fluorescent imaging of H2O2 in the LPS-induced inflammation mouse model. Overall, RES-6C serves as a versatile tool to monitor H2O2 in tissues and in vivo, providing new insights into the design of probes for H2O2.

Design strategies for tetrazine fluorogenic probes for bioorthogonal imaging

Tetrazine fluorogenic probes play a critical role in bioorthogonal chemistry, selectively activating fluorescence upon reaction to enhance precision in imaging and sensing within complex biological environments. Recent structural innovations-such as varied fluorophore choices, spacer optimization, and direct tetrazine integration within a fluorophore's π-conjugated system-have expanded their spectral range from visible to NIR, enhancing adaptability across various applications. This review examines advancements in the rational design and synthesis of these probes. We examine key fluorogenic mechanisms, such as energy transfer, internal conversion, and electron/charge transfer, that significantly influence fluorescence activation. We also highlight representative applications in live-cell imaging, super-resolution microscopy, and therapeutic monitoring, underscoring the expanding role of tetrazine probes in biomedical research and diagnostics. Collectively, these insights provide a strategic foundation for developing next-generation tetrazine probes with tailored properties to address evolving diagnostic and therapeutic challenges.

Unveiling the photophysical mechanistic mysteries of tetrazine-functionalized fluorogenic labels

Tetrazine-based fluorogenic labels are widely utilized in medical and biological studies, exhibiting substantial fluorescence enhancement (FE) following tetrazine degradation through bio-orthogonal reactions. However, the underlying mechanisms driving this fluorogenic response remain only partially resolved, particularly regarding the diminished FE efficiency in the deep-red and near-infrared (NIR) regions. This knowledge gap has impeded efforts to optimize these labels for extended emission wavelengths and improved FE ratios. This review offers a photophysical perspective, discussing the fluorescence quenching pathways (i.e., energy flows and charge separation) that regulate the fluorogenic properties exhibited in various types of tetrazine labels. Moreover, this work examines the emerging role of intramolecular rotations in certain tetrazine-based structures and the integration of additional quencher units. The proposed alternative quenching channel offers the potential to surpass traditional wavelength constraints while achieving improved FE. By examining these photophysical mechanisms, this review aims to advance the understanding of tetrazine-functionalized fluorogenic labels and provide guiding principles for their future design and practical applications.

Bioorthogonal Reaction of β-Chloroacroleins with meta-Aminothiophenol to Develop Near-Infrared Fluorogenic Probes for Simultaneous Two-color Imaging

Highly fluorogenic probe based bioorthogonal chemistry has become a promising tool in biomedical applications. However, the majority of fluorogenic probes are designed by introducing a bioorthogonal partner as a fluorescence quencher into classical fluorophores, and these probes exhibit a deteriorating fluorogenicity as the emission wavelength shifts toward the near-infrared (NIR) region, greatly limiting their applications in vivo. Herein, we report a novel fluorogenic bioorthogonal reaction involving β-chloroacroleins (β-CAs) and meta-aminothiophenol (m-AT1), whose fluorescence increases more than 500-fold upon in situ generating fluorophores. β-CAs are stable under physiological conditions and react rapidly (β-CA9, k2 = 2.2 × 102 M-1 s-1, in H2O) and chemoselectively with m-AT1 in the presence of biological nucleophiles, and delightfully, the reaction proceeds swiftly even under solvent-free conditions. Furthermore, manipulating the conjugate length of β-CAs enables the emission wavelength of the probes to be fine-tuned from 627 to 778 nm. These probes allow the simultaneous labeling of multiple cellular organelles without washing steps, and two-color tumor visualization is achieved in living mice. We believe this study not only provides new insights for the development of NIR fluorogenic probes with superior turn-on behaviors but also presents a promising fluorogenic bioorthogonal reaction CA-AT with widespread potential applications in biomedical research.

Fluorogenic Tetrazine Bioorthogonal Probes for Advanced Application in Bioimaging and Biomedicine

A variety of bioorthogonal chemical tools have been developed and widely used in the study of biological phenomena in situ. Tetrazine bioorthogonal chemistry exhibits ultrafast reaction kinetics, excellent biocompatibility, and precise optical regulatory capabilities. Fluorogenic tetrazine bioorthogonal probes have achieved particularly diverse applications in bioimaging and disease diagnosis and treatment. This Viewpoint briefly introduces the characteristics and advantages of tetrazine bioorthogonal chemistry, some design strategies of fluorogenic tetrazine probes, and the status of applications of these tools to in vivo imaging, as well as disease diagnosis and treatment. Finally, we discuss challenges and propose future trends in the field of fluorogenic tetrazine probes. This Viewpoint offers insights into the development of new bioorthogonal tools for chemical biology research and for the design of new drugs.

Bioorthogonally activated probes for precise fluorescence imaging

Over the past two decades, bioorthogonal chemistry has undergone a remarkable development, challenging traditional assumptions in biology and medicine. Recent advancements in the design of probes tailored for bioorthogonal applications have met the increasing demand for precise imaging, facilitating the exploration of complex biological systems. These state-of-the-art probes enable highly sensitive, low background, in situ imaging of biological species and events within live organisms, achieving resolutions comparable to the size of the biomolecule under investigation. This review provides a comprehensive examination of various categories of bioorthogonally activated in situ fluorescent labels. It highlights the intricate design and benefits of bioorthogonal chemistry for precise in situ imaging, while also discussing future prospects in this rapidly evolving field.

Tumor microenvironment-modulated nanoparticles with cascade energy transfer as internal light sources for photodynamic therapy of deep-seated tumors

Photodynamic therapy (PDT) is an appealing modality for cancer treatments. However, the limited tissue penetration depth of external-excitation light makes PDT impossible in treating deep-seated tumors. Meanwhile, tumor hypoxia and intracellular reductive microenvironment restrain the generation of reactive oxygen species (ROS). To overcome these limitations, a tumor-targeted self-illuminating supramolecular nanoparticle T-NPCe6-L-N is proposed by integrating photosensitizer Ce6 with luminol and nitric oxide (NO) for chemiluminescence resonance energy transfer (CRET)-activated PDT. The high H2O2 level in tumor can trigger chemiluminescence of luminol to realize CRET-activated PDT without exposure of external light. Meanwhile, the released NO significantly relieves tumor hypoxia via vascular normalization and reduces intracellular reductive GSH level, further enhancing ROS abundance. Importantly, due to the different ROS levels between cancer cells and normal cells, T-NPCe6-L-N can selectively trigger PDT in cancer cells while sparing normal cells, which ensured low side effect. The combination of CRET-based photosensitizer-activation and tumor microenvironment modulation overcomes the innate challenges of conventional PDT, demonstrating efficient inhibition of orthotopic and metastatic tumors on mice. It also provoked potent immunogenic cell death to ensure long-term suppression effects. The proof-of-concept research proved as a new strategy to solve the dilemma of PDT in treatment of deep-seated tumors.

Research Progress of Cyanine-Based Near-Infrared Fluorescent Probes for Biological Application

Cyanine-based near-infrared (NIR) fluorescent probes have played vital roles in biological application due to their low interference from background fluorescence, deep tissue penetration, high sensitivity, and minimal photodamage to biological samples. They are widely utilized in molecular recognition, medical diagnosis, biomolecular detection, and biological imaging. Herein, we provide a review of recent advancements in cyanine-based NIR fluorescent probes for the detection of pH, cells, tumor as well as their application in photothermal therapy (PTT) and photodynamic therapy (PDT).

Bypassing Ca2+ Influx for Antimetastasis Photodynamic Therapy via Robust Nucleus-Targeted Near-Infrared Cyanines

Hypoxia-induced tumor metastasis severely hinders the efficacy of photodynamic therapy (PDT) in cancer treatment. Current strategies predominantly offer palliative suppression of the HIF-1α pathway, emphasizing the urgent need for innovative PDT approaches to prevent metastasis from the outset. Our study revealed that typical PDT triggers an increase in cytoplasmic Ca2+ levels, activating HIF-1α, and that reducing Ca2+ levels can, in turn, mitigate metastasis. Considering cytoplasm's role in Ca2+ storage and regulation, we propose that PDT-induced metastasis can be addressed at its source by precise intracellular localization of photosensitizers (PSs). We developed near-infrared (NIR) cyanine PSs with inherent nucleus targeting capabilities. These PSs effectively inhibit cytoplasmic Ca2+ elevation and reduce HIF-1α activity upon irradiation, achieving remarkable antimetastatic effects in 4T1 tumors. Consequently, our findings highlight the pivotal role of Ca2+ in PDT-induced metastasis and provide a robust approach for circumventing metastasis from the outset using new nucleus-targeting organic PSs.

J-aggregates of strong electron-donating groups linked Aza-BODIPY adjusting by polypeptide for NIR-II phototheranostics

The commonly employed strategies for engineering second near-infrared (NIR-II) organic phototheranostic agents are based on expanding conjugated backbone length, strengthening donor (D)-acceptor (A) effect, or forming J-aggregates. We constructed the D-A-D' structure by incorporating strong electron-donating methoxy and tetraphenylethene (TPE) moieties on the electron-deficient Aza-BODIPY core, and simultaneously expanded the π-conjugation effect by introducing thiophene groups, to obtain a dye BDP-TPE. Next, the nanoparticles P-TPE were prepared via the assembly of BDP-TPE with amphiphilic polypeptides (mPEG2000-P(Asp)10), and successfully constructed the J-aggregates. The obtained P-TPE exhibited strong absorption and fluorescence with maxima at 808 and 1018 nm, respectively, with a conspicuous absolute quantum yield of 0.241 %. Moreover, P-TPE also showed excellent biocompatibility, and high photothermal conversion efficiency of 61.15 %, and excellent resistance to pH, long-term storage, and photobleaching. In vitro and in vivo experiments revealed that P-TPE exhibited good biocompatibility and effectively achieved NIR-II fluorescence imaging-guided PTT with complete tumor ablation under 808 nm laser irradiation. These results provided good evidence for the use of P-TPE as a NIR-II fluorescence imaging-guided PTT therapeutic agent in vivo.

Dual-Locked Enzyme-Activatable Bioorthogonal Fluorescence Turn-On Imaging of Senescent Cancer Cells

Bioorthogonal pretargeting optical imaging shows the potential for enhanced diagnosis and prognosis. However, the bioorthogonal handles, known for being "always reactive", may engage in reactions at unintended sites with their counterparts, resulting in nonspecific fluorescence activation and diminishing detection specificity. Meanwhile, despite the importance of detecting senescent cancer cells in cancer therapy, current methods mainly rely on common single senescence-associated biomarkers, which lack specificity for differentiating between various types of senescent cells. Herein, we report a dual-locked enzyme-activatable bioorthogonal fluorescence (DEBOF) turn-on imaging approach for the specific detection of senescent cancer cells. A dual-locked bioorthogonal targeting agent (DBTA) and a bioorthogonally activatable fluorescent imaging probe (BAP) are synthesized as the biorthogonal pair. DBTA is a tetrazine derivative dually caged by two enzyme-cleavable moieties, respectively, associated with senescence and cancer, which ensures that its bioorthogonal reactivity ("clickability") is only triggered in the presence of senescent cancer cells. BAP is a fluorophore caged by trans-cyclooctane (TCO), whose fluorescence is only activated upon bioorthogonal reaction between its TCO and the decaged tetrazine of DBTA. As such, the DEBOF imaging approach differentiates senescent cancer cells from nonsenescent cancer cells or other senescent cells, allowing noninvasive tracking of the population fluctuation of senescent cancer cells in the tumor of living mice to guide cancer therapies. This study thus provides a general molecular strategy for biomarker-activatable in vivo bioorthogonal pretargeting imaging with the potential to be applied to other imaging modalities beyond optics.

Homo-Dyad with Outer Hydration Layer Approach for Developing NIR-II Chromophore of High Stability and Water-Solubility as Injectable and Sprayable Optical Probe

Dyes with extended conjugate structures are the focus of extensive design and synthesis efforts, aiming to confer unique and improved optical and electronic properties. Such advancements render these dyes applicable across a wide spectrum of uses, ranging from second-window near-infrared (NIR-II) bioimaging to organic photovoltaics. Nevertheless, the inherent benefits of long conjugation are often accompanied by persistent challenges like aggregation, fluorescence quenching, absorption blueshift, and low stability and poor water solubility. Herein, a unique structural design strategy termed "homo-dyad with outer hydration layer" is introduced to address these inherent problems, tailored for the development of imaging probes exhibiting long absorption/emission wavelengths. This approach involves bringing two heptamethine cyanines together through a flexible linker, forming a homo-dyad structure, while strategically attaching four polyethylene glycol (PEG9) chains to the terminal heterocycles. This approach imparts excellent water solubility, biocompatibility, and enhanced chemical, photo-, and spectral stability for the dyes. Utilizing this strategy, a biomarker-activatable probe (HD-FL-4PEG9-N) for NIR-II fluorescent and 3D multispectral optoacoustic tomography imaging is developed, and its effectiveness in disease visualization. It can not only serve as an injectable probe for acute kidney injury imaging due to its high water solubility, but also a sprayable probe for imaging bacterial-infected wounds.

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.

A Dual-Cascade Activatable Near-Infrared Fluorescent Probe for Precise Intraoperative Imaging of Tumor

Accurate intraoperative tumor delineation is critical to achieving successful surgical outcomes. However, conventional techniques typically suffer from poor specificity and low sensitivity and are time-consuming, which greatly affects intraoperative decision-making. Here, we report a cascade activatable near-infrared fluorescent (NIRF) probe IR780SS@CaP that can sequentially respond to tumor acidity and elevated glutathione levels for accurate intraoperative tumor localization. Compared with nonactivatable and single-factor activatable probes, IR780SS@CaP with a cascade strategy can minimize nonspecific activation and false positive signals in a complicated biological environment, affording a superior tumor-to-normal tissue ratio to facilitate the delineation of abdominal metastases. Small metastatic lesions that were less than 1 mm in diameter can be precisely identified by IR780SS@CaP and completely excised under NIRF imaging guidance. This study could benefit tumor diagnosis and image-guided tumor surgery by providing real-time information and reliable decision support, thus reducing the risk of both recurrence and complications to improve patient outcomes.

A β-Galactosidase-Activated Fluorogenic Reporter for the Detection of Gastric Cancer In Vivo and in Urine

Although gastric cancer (GC) is one of the most frequent malignant tumors in the digestive tract with high morbidity and mortality, it remains a diagnostic dilemma due to its reliance on invasive biopsy or insensitive assays. Herein, we report a fluorescent gastric cancer reporter (FGCR) with activatable near-infrared fluorescence (NIRF) signals and high renal-clearance efficiency for the detection of orthotopic GC in a murine model via real-time imaging and remote urinalysis. In the presence of gastric-tumor-associated β-galactosidase (β-Gal), FGCR can be fluorescently activated for in vivo NIRF imaging. Relying on its high renal-clearance efficiency (∼95% ID), it can be rapidly excreted through kidneys to urine for the ultrasensitive detection of tumors with a diameter down to ∼2.1 mm and for assessing the prognosis of oxaliplatin-based chemotherapy. This study not only provides a new approach for noninvasive auxiliary diagnosis and prognosis of GC but also provides guidelines for the development of fluorescence probes for cancer diagnosis.

Filamentous-Actin-Mimicking Nanoplatform for Enhanced Cytosolic Protein Delivery

Despite the potential of protein therapeutics, the cytosolic delivery of proteins with high efficiency and bioactivity remains a significant challenge owing to exocytosis and lysosomal degradation after endocytosis. Therefore, it is important to develop a safe and efficient strategy to bypass endocytosis. Inspired by the extraordinary capability of filamentous-actin (F-actin) to promote cell membrane fusion, a cyanine dye assembly-containing nanoplatform mimicking the structure of natural F-actin is developed. The nanoplatform exhibits fast membrane fusion to cell membrane mimics and thus enters live cells through membrane fusion and bypasses endocytosis. Moreover, it is found to efficiently deliver protein cargos into live cells and quickly release them into the cytosol, leading to high protein cargo transfection efficiency and bioactivity. The nanoplatform also results in the superior inhibition of tumor cells when loaded with anti-tumor proteins. These results demonstrate that this fusogenic nanoplatform can be valuable for cytosolic protein delivery and tumor treatment.

Suppressing ACQ of molecular photosensitizers by distorting the conjugated-plane for enhanced tumor photodynamic therapy

Non-AIE-type molecular photosensitizers (PSs) suffer from the aggregation-caused-quenching (ACQ) effect in an aqueous medium due to the strong hydrophobic and π-π interactions of their conjugated planes, which significantly hinders the enhancement of tumor photodynamic therapy (PDT). So far, some ionic PSs have been reported with good water-solubility, though the ACQ effect can still be induced in a biological environment rich in ions, leading to unsatisfactory in vivo delivery and fluorescence imaging performance. Hence, designing molecular PSs with outstanding anti-ACQ properties in water is highly desirable, but it remains a tough challenge for non-AIE-type fluorophores. Herein, we demonstrated a strategy for the design of porphyrin-type molecular PSs with remarkable solubility and anti-ACQ properties in an aqueous medium, which was assisted by quantum chemical simulations. It was found that cationic branched side chains can induce serious plane distortion in diphenyl porphyrin (DPP), which was not observed for tetraphenyl porphyrin (TPP) with the same side chains. Moreover, the hydrophilicity of the chain spacer is also crucial to the plane distortion for attaining the desired anti-ACQ properties. Compared to ACQ porphyrin, anti-ACQ porphyrin displayed type-I ROS generation in hypoxia and much higher tumor accumulation efficacy by blood circulation, leading to highly efficient in vivo PDT for hypoxic tumors. This study demonstrates the power of sidechain chemistry in tuning the configuration and aggregation behaviors of porphyrins in water, offering a new path to boost the performance of PSs to fulfill the increasing clinical demands on cancer theranostics.

J-Aggregation Strategy toward Potentiated NIR-II Fluorescence Bioimaging of Molecular Fluorophores

Molecular fluorophores emitting in the second near-infrared (NIR-II, 1000-1700 nm) window with strong optical harvesting and high quantum yields hold great potential for in vivo deep-tissue bioimaging and high-resolution biosensing. Recently, J-aggregates are harnessed to engineer long-wavelength NIR-II emitters and show unique superiority in tumor detection, vessel mapping, surgical navigation, and phototheranostics due to their bathochromic-shifted optical bands in the required slip-stacked arrangement aggregation state. However, despite the preliminary progress of NIR-II J-aggregates and theoretical study of structure-property relationships, further paradigms of NIR-II J-aggregates remain scarce due to the lack of study on aggregated fluorophores with slip-stacked fashion. In this effort, how to utilize the specific molecular structure to form slip-stacked packing motifs with J-type aggregated exciton coupling is emphatically elucidated. First, several molecular regulating strategies to achieve NIR-II J-aggregates containing intermolecular interactions and external conditions are positively summarized and deeply analyzed. Then, the recent reports on J-aggregates for NIR-II bioimaging and theranostics are systematically summarized to provide a clear reference and direction for promoting the development of NIR-II organic fluorophores. Eventually, the prospective efforts on ameliorating and promoting NIR-II J-aggregates to further clinical practices are outlined.

Strategies for quantifying the enzymatic activities of glycoside hydrolases within cells and in vivo

Within their native milieu of the cell, the activities of enzymes are controlled by a range of factors including protein interactions and post-translational modifications. The involvement of these factors in fundamental cell biology and the etiology of diseases is stimulating interest in monitoring enzyme activities within tissues. The creation of synthetic substrates, and their use with different imaging modalities, to detect and quantify enzyme activities has great potential to propel these areas of research. Here we describe the latest developments relating to the creation of substrates for imaging and quantifying the activities of glycoside hydrolases, focusing on mammalian systems. The limitations of current tools and the difficulties within the field are summarised, as are prospects for overcoming these challenges.

An Activatable Near-Infrared Fluorescent Probe for Precise Detection of the Pulmonary Metastatic Tumors: A Traditional Molecule Having a Stunning Turn

An accurate detection of lung metastasis is of great significance for making better treatment choices and improving cancer prognosis, but remains a big challenge in clinical practice. In this study, we propose a reinventing strategy to develop a pH-activatable near-infrared (NIR) fluorescent nanoprobe, pulmonary metastasis tracer (denoted as PMT), based on assembly of NIR dye IR780 and calcium phosphate (CaP). By delicately tuning the intermolecular interactions during the assembly process and dye doping content, as well as the synthetic condition of probe, the fluorescence of PMT could be finely adjusted via the tumor acidity-triggered disassembly. Notably, the selected PMT9 could sharply convert subtle pH variations into a distinct fluorescence signal to generate high fluorescence ON/OFF contrast, dramatically reducing the background signals. Benefiting from such preferable features, PMT9 is able to precisely identify not only the tumor sites in orthotopic lung cancer models but also the pulmonary metastases in mice with remarkable signal-to-background ratio (SBR). This study provides a unique strategy to turn shortcomings of traditional dye IR780 during in vivo imaging into advantages and further expand the application of fluorescent probe to image lung associated tumor lesions.

A Protocol for Activated Bioorthogonal Fluorescence Labeling and Imaging of 4-Hydroxyphenylpyruvate Dioxygenase in Plants

4-Hydroxyphenylpyruvate dioxygenase (HPPD) plays a crucial role in the synthesis of nutrients needed to maintain optimal plant growth. Its level is closely linked to the extent of abiotic stress experienced by plants. Moreover, it is also the target of commercial herbicides. Therefore, labeling of HPPD in plants not only enables visualization of its tissue distribution and cellular uptake, it also facilitates assessment of abiotic stress of plants and provides information needed for the development of effective environmentally friendly herbicides. In this study, we created a method for fluorescence labeling of HPPD that avoids interference with the normal growth of plants. In this strategy, a perylene-linked dibenzyl-cyclooctyne undergoes strain-promoted azide-alkyne cycloaddition with an azide-containing HPPD ligand. The activation-based labeling process results in a significant emission enhancement caused by the change in the fluorescent forms from an excimer to a monomer. Notably, this activated bioorthogonal strategy is applicable to visualizing HPPD in Arabidopsis thaliana, and assessing its response to multiple abiotic stresses. Also, it can be employed to monitor in vivo levels and locations of HPPD in crops. Consequently, the labeling strategy will be a significant tool in investigations of HPPD-related abiotic stress mechanisms, discovering novel herbicides, and uncovering unknown biological functions.

New cationic spiropyrans with photoswitchable NIR fluorescence

Visible-light-mediated photochromic compounds with NIR absorption and fluorescence are of great interest for use in different biomedical applications. In this work, new representatives of spiropyrans with conjugated cationic 3H-indolium substituents in different positions of 2H-chromene moiety were synthesized. The electron-donating methoxy groups were introduced in the uncharged indoline and charged indolium cycles to form the effective conjugation chain between the hetarene moiety and the cationic fragment for reaching NIR absorption and fluorescence. The molecular structure and the effects of cationic fragment position on the mutual stability of the spirocyclic and merocyanine forms of compounds were carefully studied in the solutions and solid state by NMR, IR, HRMS, single-crystal XRD, and quantum chemical calculations. It was found that the obtained spiropyrans demonstrate positive or negative photochromism depending on the cationic fragment's position. One of spiropyrans has shown bidirectional photochromic properties induced exclusively by visible light of different wavelengths in both directions. The photoinduced merocyanine forms of compounds possessed far-red shifted absorption maxima and NIR fluorescence, which makes them prospective fluorescent probes for bioimaging.

The Application of Bio-orthogonality for In Vivo Animal Imaging

The application of bio-orthogonality has greatly facilitated numerous aspects of biological studies in recent years. In particular, bio-orthogonal chemistry has transformed biological research, including in vitro conjugate chemistry, target identification, and biomedical imaging. In this review, we highlighted examples of bio-orthogonal in vivo imaging published in recent years. We grouped the references into two major categories: bio-orthogonal chemistry-related imaging and in vivo imaging with bio-orthogonal nonconjugated pairing. Lastly, we discussed the challenges and opportunities of bio-orthogonality for in vivo imaging.

Live-Cell Mitochondrial Targeted NIR Fluorescent Covalent Labeling of Specific Proteins Using a Dual Localization Effect

Here, our designed water-soluble NIR fluorescent unsymmetrical Cy-5-Mal/TPP+ consists of a lipophilic cationic TPP+ subunit that can selectively target and accumulate in a live-cell inner mitochondrial matrix where a maleimide residue of the probe undergoes faster chemoselective and site-specific covalent attachment with the exposed Cys residue of mitochondrion-specific proteins. On the basis of this dual localization effect, Cy-5-Mal/TPP+ molecules remain for a longer time period even after membrane depolarization, enabling long-term live-cell mitochondrial imaging. Due to the adequate concentration of Cy-5-Mal/TPP+ reached in live-cell mitochondria, it facilitates site-selective NIR fluorescent covalent labeling with Cys-exposed proteins, which are identified by the in-gel fluorescence assay and LC-MS/MS-based proteomics and supported by a computational method. This dual targeting approach with admirable photostability, narrow NIR absorption/emission bands, bright emission, long fluorescence lifetime, and insignificant cytotoxicity has been shown to improve real-time live-cell mitochondrial tracking including dynamics and interorganelle crosstalk with multicolor imaging applications.

Ultralow Background Near-Infrared Fluorophores with Dual-Channel Intraoperative Imaging Capability

Two of the most pressing challenges facing bioimaging are nonspecific uptake of intravenously administered contrast agents and incomplete elimination of unbound targeted agents from the body. Designing a targeted contrast agent that shows fast clearance from background tissues and eventually the body after complete targeting is key to the success of image-guided interventions. Here, this work describes the development of renally clearable near-infrared contrast agents and their potential use for dual-channel image-guided tumor targeting. cRGD-ZW800-PEG (800 nm channel) and ZW700-PEG (700 nm channel) are able to visualize tumor margins and tumor vasculature simultaneously and respectively. These targeted agents show rapid elimination from the bloodstream, followed by renal clearance, which together significantly lower off-target background signals and potential toxicity. To demonstrate its applicability, this multispectral imaging is performed in various tumor-bearing animal models including lung cancer, pancreatic neuroendocrine tumors, breast, and ovarian cancer.

New "Destruction Seek to Survive" Strategy Based on a Serum Albumin Assembly with a Squaraine Molecule for the Detection of Peroxynitrite

Peroxynitrite (ONOO^-), a kind of active nitrogen species, plays an important role in biological systems. Overproduction of ONOO^- is closely related to the pathogenesis of many diseases. Therefore, it is necessary to quantify intracellular ONOO^- for differentiating health and disease states. Fluorescent probes with near-infrared (NIR) fluorescence can detect ONOO^- with high sensitivity and selectivity. However, there is an inevitable problem that many NIR fluorophores are easily oxidized by ONOO^- to give a false-negative result. To avoid this problem, herein, we ingeniously propose a "destruction to seek to survive" strategy to detect ONOO^-. Two NIR squaraine (SQ) dyes were connected together to form a fluorescent probe (SQDC). This method utilizes the destructive effect of peroxynitrite on one of the SQ moieties of SQDC to eliminate the steric hindrance, enabling the other "survived" SQ segment to enter the hydrophobic cavity of bovine serum albumin (BSA) via the well-known host-guest interactions. The encapsulation of albumin protects the "survived" SQ from further attack of ONOO^-. As a result, a NIR fluorescence turn-on response coming from the host-guest interaction between BSA and the "survived" SQ escaped from SQDC was found, which can be used for the detection of ONOO^-. The assembly of SQDC mixed with BSA can be located in mitochondria to detect endogenous and exogenous ONOO^- sensitively in living cells. As a proof-of-concept method, it is envisioned that this novel detection strategy with a simple assembly would become a powerful means for the detection of ONOO^- when employing NIR fluorophores.

Renal-Clearable Probe with Water Solubility and Photostability for Biomarker-Activatable Detection of Acute Kidney Injuries via NIR-II Fluorescence and Optoacoustic Imaging

Acute kidney injuries (AKI) have serious short-term or long-term complications with high morbidity and mortality rate, thus posing great health threats. Developing high-performance NIR-II probes for noninvasive in situ detection of AKI via NIR-II fluorescent and optoacoustic dual-mode imaging is of great significance. Yet NIR-II chromophores often feature long conjugation and hydrophobicity, which prevent them from being renal clearable, thus limiting their applications in the detection and imaging of kidney diseases. To fully exploit the advantageous features of heptamethine cyanine dye, while overcoming its relatively poor photostability, and to strive to design a NIR-II probe for the detection and imaging of AKI with dual-mode imaging, herein, we have developed the probe PEG3-HC-PB, which is renal clearable, water soluble, and biomarker activatable and has good photostability. As for the probe, its fluorescence (900-1200 nm) is quenched due to the existence of the electron-pulling phenylboronic group (responsive element), and it exhibits weak absorption with a peak at 830 nm. Meanwhile, in the presence of the overexpressed H₂O₂ in the renal region in the case of AKI, the phenylboronic group is converted to the phenylhydroxy group, which enhances NIR-II fluorescent emission (900-1200 nm) and absorption (600-900 nm) and eventually produces conspicuous optoacoustic signals and NIR-II fluorescent emission for imaging. This probe enables detection of contrast-agent-induced and ischemia/reperfusion-induced AKI in mice using real-time 3D-MSOT and NIR-II fluorescent dual-mode imaging via response to the biomarker H₂O₂. Hence, this probe can be used as a practicable tool for detecting AKI; additionally, its design strategy could provide insight into the design of other large-conjugation NIR-II probes with multifarious biological applications.

Toward Precise Antitumoral Photodynamic Therapy Using a Dual Receptor-Mediated Bioorthogonal Activation Approach

Targeted delivery and specific activation of photosensitizers can greatly improve the treatment outcome of photodynamic therapy. To this end, we report herein a novel dual receptor-mediated bioorthogonal activation approach to enhance the tumor specificity of the photodynamic action. It involves the targeted delivery of a biotinylated boron dipyrromethene (BODIPY)-based photosensitizer, which is quenched in the native form by the attached 1,2,4,5-tetrazine unit, and an epidermal growth factor receptor (EGFR)-targeting cyclic peptide conjugated with a bicycle[6.1.0]non-4-yne moiety. Only for cancer cells that overexpress both the biotin receptor and EGFR, the two components can be internalized preferentially where they undergo an inverse electron-demand Diels-Alder reaction, leading to restoration of the photodynamic activity of the BODIPY core. By using a range of cell lines with different expression levels of these two receptors, we have demonstrated that this stepwise "deliver-and-click" approach can confine the photodynamic action on a specific type of cancer cells.