Activity-based NIR fluorescent probes based on the versatile hemicyanine scaffold: design strategy, biomedical applications, and outlook

Fabrication of a carboxylesterases-activated near-infrared fluorescence probe for assisting hepatocellular carcinoma surgery in mice and clinical blood serum testing

Carboxylesterases (CES) is a family of hydrolases, which are mainly localized in the endoplasmic reticulum and cytosol in cells and can catalyze the hydrolysis of carboxylic esters to generate acids and alcohols. The changes of CES level are closely related to the liver disease, such as early onset liver injury induced diabetes and advanced liver cancer. Herein, a new activatable near-infrared (NIR) fluorescent probe PCES (Probe of Carboxylesterases) for imaging CES was rationally designed. The probe can not only specifically sense CES in buffer solution with a 49-fold fluorescence enhancement at 780 nm and a 2.5 mU/mL detection limit, but also can sensitively visualize CES changes with low cytotoxicity and good biocompatibility in living cells. Applying this agent, the fluctuation of CES levels was monitored under high glucose stimulation. The mechanism of ferroptosis in diabetes mellitus has also been preliminarily explored. Besides, PCES was utilized for imaging CES of hepatocellular carcinoma and effectively assisting the tumor surgical operation in vivo. In addition, the practical serum samples were detected from clinical patients suffered diabetes and liver cancer with the help of probe PCES, demonstrating the differentiated CES levels. With the favorable characteristics of fluorescence sensing and practicability of imaging CES in living cells, mice, and clinical serum samples, PCES can help the better understanding for the relationships of liver diseases with CES and has the potential as a useful agent for the diagnosis and treatment of clinical liver diseases.

Tumor-Targeted Exosome-Based Heavy Atom-Free Nanosensitizers With Long-Lived Excited States for Safe and Effective Sono-Photodynamic Therapy of Solid Tumors

Theranostic nanosensitizers with combined near-infrared (NIR) fluorescence imaging and sono-photodynamic effects have great potential for use in the personalized treatment of deep-seated tumors. However, developing effective nanosensitizers for NIR fluorescence image-guided sono-photodynamic therapy remains a considerable challenge, including the low generation efficacy of reactive oxygen species (ROS), poor photostability, and the absence of cancer specificity. Herein, a novel heavy atom-free nanosensitizer is developed, which exhibits intense NIR fluorescence, high ROS generation efficiency, and improved aqueous stability. By conjugating a bulky and electron-rich group, 4-(1,2,2-triphenylvinyl)-1,1'-biphenyl (TPE), to the IR820 backbone, the resulting IR820 bearing TPE (IR820-TPE) effectively generates ROS via type I and II photochemical mechanisms under 808 nm laser irradiation. Moreover, TPE conjugation considerably increases the sono-photodynamic performance of IR820. To improve the intracellular delivery and tumor-targeting ability of IR820-TPE, biotin-conjugated exosome (B-Exo) is used as a natural nanocarrier. In vitro studies demonstrate the outstanding therapeutic performance of IR820-TPE-loaded B-Exo (IR820-TPE@B-Exo) in synergistic sono-photodynamic cancer therapy. In vivo studies reveal that IR820-TPE@B-Exo shows enhanced tumor accumulation, strong fluorescence signals, and effective sono-photodynamic therapeutic activity with high biosafety. This work demonstrates that IR820-TPE@B-Exo is a promising sono-phototheranostic agent for safe and targeted cancer therapy and NIR fluorescence imaging.

Bifunctional fluorescent probe revealing viscosity and SO2 in cell, zebrafish and NASH model

Clarifying the presence of viscosity and endogenous sulfur dioxide (SO2) in mitochondria is crucial for advancing the diagnosis and treatment of illnesses. Nevertheless, the advancement of fluorescent probes that concurrently satisfy the criteria of mitochondrial viscosity and endogenous recognition of SO2 remains significantly insufficient. In this work, we have engineered and synthesized two probes ID-OH and BID-OH, which exhibit a ratio-type response to SO2 and an off-on fluorescence response to viscosity. Due to the superior selectivity coupled with its outstanding wavelength and fluorescence quantum yield, BID-OH has been effectively utilized for the detection of exogenous SO2, endogenous SO2 and viscosity within living HepG2 cells. Additionally, BID-OH demonstrates the capability to offer comprehensive insights into the distribution of endogenous SO2 as it traverses through the transfer pathway in zebrafish. Notably, the remarkable capacity of BID-OH to differentiate between normal mice and nonalcoholic steatohepatitis (NASH) mice has been demonstrated, indicating its potential as an excellent diagnostic tool for detecting SO2 levels and viscosity under physiological conditions. It is anticipated that BID-OH will emerge as a valuable instrument for diagnosing mitochondrial irregularities, thereby contributing to the advancement of related medical research in this field.

Selenenylsulfide Bond as a General Scaffold for Constructing Thiol Probes with Enhanced Response Rate

Leveraging disulfide (-S-S-) or diselenide (-Se-Se-) units as triggers in the design of small-molecule fluorescent probes for detecting intracellular reductive species has demonstrated high efficacy. However, selenenylsulfides, which exhibit reactivity between diselenides and disulfides, remain relatively unexplored. In this work, we compare the efficiency of -S-S-, seleno-sulfur (-Se-S-), and sulfur-selenium (-S-Se-) structural units in constructing thiol probes, disclose the scaffold of -Se-S- as a versatile recognition site for thiols, and successfully apply this unit to design a near-infrared (NIR) probe, ASC-SeS. The mechanism reveals that breaking the -Se-S- bond leads to a selenolate, which undergoes faster cyclization than the corresponding thiolate that is from the cleavage of the -S-S- or -S-Se- bond. Conjugation of this trigger unit with multiple NIR fluorophores validates the general applicability of linear selenenylsulfides in accelerating the response rate to thiols. By harnessing the superior thiol responsiveness of ASC-SeS, we employ this probe in live cells and in vivo, and elucidate a severe depletion of thiols in the drug-induced liver injury (DILI).

A near infrared light activated phenothiazine based cancer cell specific phototherapeutic system: a synergistic approach to chemo-photothermal therapy

In the pursuit of more effective cancer therapies, phototherapy has emerged as a promising approach due to its non-invasive nature and high precision. This study presents the development of a near-infrared (NIR) light-responsive phenothiazine (PTZ) based phototherapeutic system designed for targeted cancer treatment. This phototherapeutic system integrates four crucial elements for enhanced therapeutic efficacy: cancer cell-specific activity, mitochondrial targeting, photothermal conversion, and controlled drug release. The PTZ system utilizes the acidochromic 1,3-oxazine ring, which opens in the acidic tumor microenvironment, forming a positive iminium ion (CN+). This ionic species targets cancer cell mitochondria, ensuring precise localization. Under NIR light irradiation (640 nm), the phototherapeutic system undergoes a red shift in the absorption and reduction in the fluorescence intensity, demonstrating a significant photothermal effect that converts light to heat, thereby inducing tumor cell apoptosis. Furthermore, NIR light triggers the controlled release of the anticancer drug chlorambucil, enabling precise spatiotemporal drug delivery. The closed form of the phototherapeutic system also facilitates drug release upon visible light irradiation (≥410 nm) with high photochemical efficiency. This dual-mode photothermal and photocontrolled drug delivery offers a synergistic approach to cancer therapy, maximizing therapeutic outcomes while minimizing side effects. Our findings underscore the potential of this innovative phototherapeutic system to advance cancer treatment through targeted, controlled, and effective drug delivery.

Fluorescence enhancement of cyanine/hemicyanine dyes with adamantane as an auxochrome through host-guest inclusion with methylated cyclodextrin in water

Fluorescence of cyanine dyes is often quenched in aqueous solution, limiting their application in water or biological system. In this work, a novel strategy of host-guest interaction based on cyanine derivatives containing auxochromes was proposed to enhance fluorescence in aqueous solution and cell imaging. By using the host (methylated β-cyclodextrin, M-β-CD) to inclusion and suppress the TICT effect of the dye, the fluorescence was significantly enhanced at lower host concentration. Cyanine and hemicyanine dyes (Ad-NH-1a, Ad-NH-1b and Ad-NH-2) with adamantyl group as auxochrome were designed and prepared by using host-guest complexation to inhibit the TICT effect of dyes, thus realizing the purpose of significantly enhancing the fluorescence of dyes at lower concentration. After adding M-β-CD, the fluorescence quantum yields of these dyes increased to 15.9 %, 21.8 %, and 6.08 %, respectively. In comparison, the fluorescence quantum yield of the dyes Ad-CONH-1 and Ad-CONH-2 containing adamantyl groups, increased only modestly from 1.78 to 2.83 times. Encouraged by these satisfactory results, further cell experiments were conducted with Ad-NH-1a, Ad-NH-1b, and Ad-NH-2. The experiment showed that adding a lower concentration of M-β-CD significantly reduced the clear imaging dosage of the probe (0.3 μM) without altering the organelle targeting of the probes.

Near-infrared xanthene fluorescence probe for frequency upconversion fluorescence detection of HSO3- in evaluation of drug-induced hepatotoxicity

Bisulfite (HSO3-) plays an important role in life activities. Abnormal content of HSO3- may cause cardiovascular, cancer and other diseases. Frequency upconverted luminescent (FUCL) probes are a class of anti-Stokes luminescent materials with long-wavelength excitation and short-wavelength emission properties, which offer advantages in a range of applications due to their higher sensitivity and photostability. In addition, FUCL imaging has the advantages of high tissue penetration depth and low photo-damage, thus, it is more suitable for fluorescence imaging. In this work, a FUCL probe based on an xanthene fluorophore was designed and synthesised to detect HSO3-. The Probe PT-1 could respond to HSO3- and had high selectivity and sensitivity. It also exhibited a quenched FUCL signal. The detection limit of FUCL concerning HSO3- was 43 nM (λex = 730 nm), which is half the detection limit achieved under traditional excitation (93 nM, λex = 643 nm). Cell fluorescence imaging showed that PT-1 could effectively target mitochondria and monitor endogenous/exogenous HSO3- in living cells. More importantly, PT-1 was successfully used to monitor the level of HSO3- in mice with drug-induced liver injury through FUCL imaging.

Dual-Locked Fluorescence Probe for Monitoring the Dynamic Transition of Pulmonary Macrophages

Pulmonary macrophages undergo dynamic changes in population, proportion, and polarization during respiratory diseases. Monitoring these changes is critical for understanding their roles in pathology, improving the diagnosis, and guiding drug development. However, current analytic methods based on tissue biopsy are invasive and static, limiting their ability to provide such dynamic information. Herein, we report a dual-locked macrophage-specific renal-clearable probe (DMRPNOCas) for the dynamic monitoring of pulmonary macrophages during influenza A virus (IAV) infection. DMRPNOCas activates fluorescence in the presence of two biomarkers (caspase-1 and NO) only coexpressed by M1 macrophages. To optimize the NO reactivity, the scaffold of DMRPNOCas is screened from the hemicyanine derivatives with an o-phenylenediamine group positioned differently on the indole ring. Notably, the para-substituted o-phenylenediamine demonstrates a higher NO-activated fluorescence compared to its meta-substituted counterpart. This enhancement, as revealed by quantum chemical calculations, is attributed to differential inhibition of twisted intramolecular charge transfer induced by the NO reaction. DMRPNOCas specifically distinguishes M1 macrophages from other leukocytes including T cells, neutrophils, and M2 macrophages, a capability unmatched by single-locked control probes and other reported probes. Consequently, DMRPNOCas enables in vivo dynamic monitoring of pulmonary macrophages, uncovering extensive recruitment and M1 polarization of monocyte-derived macrophages within 48 h of IAV infection. This process is accompanied by a significant reduction in alveolar macrophages. These findings provide new insights into macrophage-mediated pulmonary inflammation and underscore the potential of dual-locked probes for precise diagnosis and monitoring of pathological processes.

Tetra-coordinated organoboron complexes with triaminoguanidine-salicylidene based ligands: aggregation induced enhanced emission and mechanoresponsive features

Organoboron complexes have garnered significant attention due to their remarkable optical properties and diverse applications. However, synthesizing stable fused five-, six- and seven-membered organoboron complexes possess significant challenges. In this study, we successfully developed novel mono-nuclear (6-8 & 10) and di-nuclear (9) organoboron complexes supported by triaminoguanidine-salicylidene based C3-symmetric Schiff base ligands via one-step condensation reaction with excess phenylboronic acid. Single-crystal X-ray diffraction analysis revealed that in the mononuclear complexes (6-8 & 10), boron atoms adopt tetrahedral geometry with fused five-membered N-B-N and six-membered O-B-N chelate ring whereas in the dinuclear complex (9), two boron atoms exist in distinct coordination environment, forming four fused boron-incorporated rings, including six-membered N-B-N, six-membered O-B-N, seven-membered N-B-O and five-membered N-B-N chelate rings. Our findings provide a unique family of mononuclear organoboron complexes and dinuclear organoboron complex with ESIPT unit. Aggregation induced enhanced emission features of the compounds were established in THF-water mixture and supported by DLS and SEM analyses. Interestingly, compound 6, 9 and 10 shows interesting mechanoresponsive features upon grinding.

pH-Activatable NIR Hemicyanine for Mitochondria-Targeted Cancer Phototheranostics

Photodynamic therapy (PDT) has garnered significant attention for cancer treatment due to its noninvasive nature, reduced drug resistance, and spatiotemporal controllability. However, traditional photosensitizers (PSs) face limitations such as severe systemic phototoxicity and shallow tissue penetration, which hinder the widespread clinical application of PDT. Capitalizing on the strong near-infrared (NIR) absorption and ease of structural modification of hemicyanine, we have designed a pH-activatable NIR hemicyanine PS (LET-15). It is specifically activated in the acid tumor microenvironment, subsequently targeting mitochondria and generating cytotoxic singlet oxygen under 660 nm laser irradiation, which selectively destroys tumor tissues while minimizing damage to healthy tissues. Additionally, it offers activatable fluorescence (FL) imaging with a high signal-to-noise ratio, enabling FL imaging-assisted tumor photoeradication. This study provides valuable guidance for designing tumor-specifically activated NIR PSs for precision PDT.

Anthracene carboxyimide-based selenide as a fluorescent probe for the ultrasensitive detection of hypochlorous acid

In situ detection of hypochlorous acid (HOCl) is critical for understanding its complex physiological and pathological roles. Fluorescent probes, known for their sensitivity and selectivity, are the preferred approach for such detections. Anthracene carboxyimide, an analog of naphthalimide, offers extended excitation and emission wavelengths, making it an excellent candidate for developing new fluorescent probes that address the limitations of naphthalimide. In this study, we designed a novel HOCl-specific fluorescent probe, AC-Se, by incorporating highly reactive selenium into anthracene carboxyimide. The probe exhibits a 104-fold fluorescence enhancement, a large Stokes shift of 72 nm, and a low detection limit of 36.2 nM. Moreover, AC-Se responds rapidly to HOCl within 4 seconds, enabling real-time intracellular monitoring of both exogenous and endogenous HOCl.

Metabolic Acidity/H2O2 Dual-Cascade-Activatable Molecular Imaging Platform Toward Metastatic Breast Tumor Malignancy

Fluorescence imaging in the second near-infrared window (NIR-II) is crucial for accurate tumor diagnosis, offering superior resolution and penetration capabilities. Current NIR-II probes are limited by either being "always on" or responding to one stimulus, leading to low signal-to-noise ratios and potential false positives. We introduced a dual-lock-controlled probe, HN-PBA, activated by both H2O2 and tumor acidic environment. This dual response ensures bright fluorescence at tumor sites, leading to higher tumor-to-normal tissue ratios (T/NT) compared to conventional "always on" probes and probes activated only by H2O2. This strategy allows precise tumor identification and removal of primary and metastatic tumors, achieving superior T/NT ratios (24.3/6.4 for orthotopic and lung metastasis, respectively). Our probe also effectively detected lung metastatic foci as small as≤0.7 mm and showed the capability for accurate lesion localization in clinical breast cancer specimens. This dual-stimuli-responsive strategy could aid future diagnostic probe design.

NIRFluor: A Deep Learning Platform for Rapid Screening of Small Molecule Near-Infrared Fluorophores with Desired Optical Properties

Small molecule near-infrared (NIR) fluorophores play a critical role in disease diagnosis and early detection of various markers in living organisms. To accelerate their development and design, a deep learning platform, NIRFluor, was established to rapidly screen small molecule NIR fluorophores with the desired optical properties. The core component of NIRFluor is a state-of-the-art deep learning model trained on 5179 experimental big data. First, novel hybrid fingerprints including Morgan fingerprints, physicochemical properties, and solvent properties were proposed. Then, a powerful deep learning model, multitask fingerprint-enhanced graph convolutional network (MT-FinGCN), was designed, which combines fingerprint information and molecule graph structure information to achieve accurate prediction of six properties (absorption wavelength, emission wavelength, Stokes shift, extinction coefficient, photoluminescence quantum yield, and lifetime) of different small molecule NIR fluorophores in different solvents. Furthermore, the "black-box" of the GCN model was opened through interpretability studies. Finally, the well-trained models were placed on the web platform NIRFluor for free use (https://nirfluor.aicbsc.com).

Discovery of an Enzyme-Activated Fluorogenic Probe for In Vivo Profiling of Acylaminoacyl-Peptide Hydrolase

Acylaminoacyl-peptide hydrolase (APEH), a serine peptidase that belongs to the prolyl oligopeptidase (POP) family, catalyzes removal of N-terminal acetylated amino acid residues from peptides. As a key regulator of protein N-terminal acetylation, APEH was involved in many important physiological processes while its aberrant expression was correlated with progression of various diseases such as inflammation, diabetics, Alzheimer's disease (AD), and cancers. However, while emerging attention has been attracted in APEH-related disease diagnosis and drug discovery, the mechanisms behind APEH and related disease progression are still unclear; thus, further investigating the physiological role and function of APEH is of great importance. To date, enzyme-activated fluorescent probes targeting POPs have been extensively reported and adopted in relevant medical research and applications. Nevertheless, as an important member of the POP family, APEH was rarely referred in the field of bioimaging while the fluorescent probe for in vivo sensing of APEH activity has not been reported yet. Thus, acquiring an efficient APEH-targeted probe is in urgent need. Herein, an enzyme-activated fluorogenic probe for in vivo profiling of APEH was first discovered via a substrate mimic-based strategy. By combination of stimulated molecular docking-based preliminary screening and experiment-based secondary screening, the optimal probe (named as TMN-AcA), which displayed high binding affinity, sensitivity, and specificity toward APEH, was screened out. Owing to the superior properties of TMN-AcA, endogenous APEH activity in various cell lines and transplanted tumor could be visualized while tissue distribution of APEH was revealed. Most importantly, APEH was first demonstrated to be a potential biomarker of multiple-organ injury via TMN-AcA-based bioimaging and immunohistochemistry (IHC) analysis while the newly developed probe could serve as a vital tool for APEH-related disease diagnosis and biological function study.

Glutathione-Driven Disassembly of Planar Organic Phototherapeutic Agents to Enhance Photodynamic-Photothermal Therapy Performance for Nasopharyngeal Carcinoma

The self-assembly of hydrophobic organic phototherapeutic agents (OPTAs) with expansive planar structures into nanoparticles (NPs) represents a pivotal strategy to bolster their biocompatibility. However, the tight molecular packing within these NPs significantly influences the generation of reactive oxygen species (ROS) and the photothermal conversion efficiency (PCE), posing a substantial hurdle to elevating the efficacy of photodynamic therapy (PDT) and photothermal therapy (PTT) for such NPs. In this article, three OPTAs by donor engineering are synthesized. Notably, 4,8-Bis (5-phenylthiophen-2-yl)-6-(2-ethylhexyl)-[1,2,5] thiadiazole [3,4-F] benzotriazole (BTBT), which incorporates a benzene ring as the donor, exhibits the highest ROS generation and optimal photothermal conversion capability. To further augment the overall phototheranostic potential of BTBT NPs, a glutathione (GSH)-driven disassembly strategy is employed. This strategy not only alleviates the aggregation-caused quenching (ACQ) effect on ROS but also facilitates enhanced free molecular rotation. As a result, the ROS production sees a tenfold increase, and the photothermal conversion temperature rises by 8.3 °C, achieving a PCE of 77.03%. In summary, a versatile disassembly strategy is proposed that concurrently enhances the performance of both PDT and PTT in planar OPTAs, while also advancing the state-of-the-art in nasopharyngeal carcinoma (NPC) treatment.

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

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

Dopamine-supported HPLC post-column derivatization to fluorescence: Simultaneous and sensitive detection of eight tea polyphenols

The effective differentiation and detection of multiple tea polyphenols are often challenging due to their subtle structural similarities. Although post-column derivatization HPLC strategies are commonly employed to distinguish multiple targets, the short physical distance between chromatographic column and detector limits reaction time, thereby reducing the derivatization efficiency. Dopamine (DA) reacts rapidly with resorcinol to form fluorescent azamonardine products, making fast fluorometric derivatization of tea polyphenols containing resorcinol motifs possible. In this study, a DA-driven rapid and post-column fluorescence derivatization method has been applied to sensitively detect eight tea polyphenols. This method is based on fluorescence derivatization and possesses low background interference, high sensitivity, and excellent reproducibility. Moreover, the practical application of this proposed fluorometric derivatization platform was further validated by simultaneous identification of multiple tea polyphenols in different tea samples. This work has great potential to become an alternative to the National Standard method for tea polyphenols determination.

Recent Advances in Strategies to Enhance Photodynamic and Photothermal Therapy Performance of Single-Component Organic Phototherapeutic Agents

Photodynamic therapy (PDT) and photothermal therapy (PTT) have emerged as promising treatment options, showcasing immense potential in addressing both oncologic and nononcologic diseases. Single-component organic phototherapeutic agents (SCOPAs) offer advantages compared to inorganic or multicomponent nanomedicine, including better biosafety, lower toxicity, simpler synthesis, and enhanced reproducibility. Nonetheless, how to further improve the therapeutic effectiveness of SCOPAs remains a challenging research area. This review delves deeply into strategies to improve the performance of PDT or PTT by optimizing the structural design of SCOPAs. These strategies encompass augmenting reactive oxygen species (ROS) generation, mitigating oxygen dependence, elevating light absorption capacity, broadening the absorption region, and enhancing the photothermal conversion efficiency (PCE). Additionally, this review also underscores the ideal strategies for developing SCOPAs with balanced PDT and PTT. Furthermore, the potential synergies are highlighted between PDT and PTT with other treatment modalities such as ferroptosis, gas therapy, chemotherapy, and immunotherapy. By providing a comprehensive analysis of these strategies, this review aspires to serve as a valuable resource for clinicians and researchers, facilitating the wider application and advancement of SCOPAs-mediated PDT and PTT.

Unravelling the recent advancement in fluorescent probes for detection against reactive sulfur species (RSS) in foodstuffs and cell imaging

Sulfur-containing representative HSO3-/SO32-, H2S, and biothiols (Cys, Hcy, and GSH) present in food items and biological organisms have raised substantial global concerns about food safety due to their reactivity and potential health implications. Adhering to international health standards is essential for these compounds; in particular, plenty of challenges exist in ensuring product quality in the beverage industry. Many fluorescent probes are being employed in various spectroscopic techniques and have developed rapidly to selectively detect sulfur-related species in food products and bio-sensing for cell imaging. This comprehensive review provides a detailed overview of a wide range of fluorescent probes designed using different fluorophores for detecting reactive sulfur species (RSS) using spectroscopic techniques. Additionally, the review explores the detection of RSS components (HSO3-/SO32-, H2S, and biothiols) in food products and cell imaging using different cell lines, highlighting the crucial role of fluorescent probes in swiftly detecting these analytes in both natural and biological contexts. Furthermore, the review discusses future trends and perspectives, emphasizing the on-going progress in detecting these analytes in food products and cell imaging using various fluorescent probes.

Modular Design and Scaffold-Synthesis of Multi-Functional Fluorophores for Targeted Cellular Imaging and Pyroptosis

Fluorophores are essential tools for optical imaging and biomedical research. Their synthetic modification to incorporate new functions, however, remains a challenging task. Conventional strategies rely on linear synthesis in which a parent framework is gradually extended. We here designed and synthesized a versatile library of multi-functional fluorophores via a scaffold-based Ugi four-component reaction (U-4CR). The adaptability of the scaffold is achieved through modification of starting materials. This allows to use a small range of starting materials for the creation of fluorogenic probes that can detect reactive-oxygen species and where the localization into subcellular organelles or membranes can be controlled. We present reaction yields ranging from 60 % to 90 % and discovered that some compounds can even function as imaging and therapeutic agents via Fenton chemistry inducing pyroptosis in living cancer cells. Our study underlines the potential of scaffold-based synthesis for versatile creation of functional fluorophores and their applications.

Near-Infrared Probes Designed with Hemicyanine Fluorophores Featuring Rhodamine and 1,8-Naphthalic Derivatives for Viscosity and HSA Detection in Live Cells

This paper presents the development of near-infrared (NIR) fluorescent probes, A and B, engineered from hemicyanine dyes with 1,8-naphthalic and rhodamine derivatives for optimized photophysical properties and precise mitochondrial targeting. Probes A and B exhibit absorption peaks at 737 nm and low fluorescence in phosphate-buffered saline (PBS) buffer. Notably, their fluorescence intensities, peaking at 684 (A) and 702 nm (B), increase significantly with viscosity, as demonstrated through glycerol-to-PBS ratio experiments. This increase is attributed to restricted rotational freedom in the fluorophore and its linkages to rhodamine or 1,8-naphthalic groups. Theoretical modeling suggests nonplanar configurations for both probes, with primary absorptions in the rhodamine and hemicyanine cores (A: 543; B: 536 nm), and additional transitions to 1,8-naphthalic (A: 478 nm) and rhodamine (B: 626 nm) groups. Probe A is also responsive to human serum albumin (HSA), a key biomarker, with fluorescence increasing in HeLa cells as HSA concentrations rise. In contrast, probe B shows no response to HSA, likely due to steric hindrance from its bulky rhodamine group, illustrating a selectivity difference between the probes. Probe B, however, excels in mitochondrial imaging, confirmed through cellular and in vivo studies. In HeLa cells, it tracked viscosity changes following treatment with monensin, nystatin, and lipopolysaccharide (LPS), with fluorescence increasing in a dose-dependent manner. In fruit flies, probe B effectively detected monensin-induced viscosity changes, demonstrating its stability and in vivo applicability. These findings highlight the versatility and sensitivity of probes A and B as tools in biological research, with potential applications in monitoring mitochondrial health, detecting biomarkers like HSA, and investigating mitochondrial dynamics in disease.

Nitrile-aminothiol bioorthogonal near-infrared fluorogenic probes for ultrasensitive in vivo imaging

Bioorthogonal chemistry-mediated self-assembly holds great promise for dynamic molecular imaging in living organisms. However, existing approaches are limited to nanoaggregates with 'always-on' signals, suffering from high signal-to-background ratio (SBR) and compromised detection sensitivity. Herein we report a nitrile-aminothiol (NAT) bioorthogonal fluorogenic probe (CyNAP-SS-FK) for ultrasensitive diagnosis of orthotopic hepatocellular carcinoma. This probe comprises a nitrile-substituted hemicyanine scaffold with a cysteine tail dually locked with biomarker-responsive moieties. Upon dual cleavage by tumor-specific cathepsin B and biothiols, the 1,2-aminothiol residue is exposed and spontaneously reacts with nitrile group for in situ intramolecular macrocyclization, enabling near-infrared fluorescence (NIRF) turn-on as well as self-assembly. In living male mice, such 'cleavage-click-assembly' regimen allows for real-time and ultrasensitive detection of small cancerous lesions (~2 mm in diameter) with improved SBR (~5) and extended detection window (~36 h), outperforming conventional clinical assays. This study not only presents NAT click reaction-based fluorogenic probes but also highlights a generic dual-locked design of these probes.

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

Intravital fluorescence imaging in the second near-infrared window (NIR-II, 900-1700 nm) has emerged as a promising method for non-invasive diagnostics in complex biological systems due to its advantages of less background interference, high tissue penetration depth, high imaging contrast, and sensitivity. However, traditional NIR-II fluorescence imaging, which is characterized by the "always on" or "turn on" mode, lacks the ability of quantitative detection, leading to low reproducibility and reliability during bio-detection. In contrast, NIR-II ratiometric fluorescence imaging can realize quantitative and reliable analysis and detection in vivo by providing reference signals for fluorescence correction, generating new opportunities and prospects during in vivo bioimaging and biosensing. In this review, the current design strategies and sensing mechanisms of NIR-II ratiometric fluorescence probes for bioimaging and biosensing applications are systematically summarized. Further, current challenges, future perspectives and opportunities for designing NIR-II ratiometric fluorescence probes are also discussed. It is hoped that this review can provide effective guidance for the design of NIR-II ratiometric fluorescence probes and promote its adoption in reliable biological imaging and sensing in vivo.

Covalent assembly-based two-photon fluorescent probes for in situ visualizing nitroreductase activities: From cancer cells to human cancer tissues

Nitroreductase (NTR) is widely regarded as a biomarker whose enzymatic activity correlates with the degree of hypoxia in solid malignant tumors. Herein, we utilized 2-dimethylamino-7-hydroxynaphthalene as fluorophore linked diverse nitroaromatic groups to obtain four NTR-activatable two-photon fluorescent probes based on covalent assembly strategy. With the help of computer docking simulation and in vitro assay, the sulfonate-based probe XN3 was proved to be able to identify NTR activity with best performances in rapid response, outstanding specificity, and sensitivity in comparison with the other three probes. Furthermore, XN3 could detect the degree of hypoxia by monitoring NTR activity in kinds of cancer cells with remarkable signal-to-noise ratios. In cancer tissue sections of the breast and liver in mice, XN3 had the ability to differentiate between healthy and tumorous tissues, and possessed excellent fluorescence stability, high tissue penetration and low tissue autofluorescence. Finally, XN3 was successfully utilized for in situ visualizing NTR activities in human transverse colon and rectal cancer tissues, respectively. The findings suggested that XN3 could directly identify the boundary between cancer and normal tissues by monitoring NTR activities, which provides a new method for imaging diagnosis and intraoperative navigation of tumor tissue.

Monitoring Endoplasmic Reticulum Peroxynitrite Fluctuations in Primary Tendon-Derived Stem Cells and Insights into Tendinopathy

Tendinopathy is one of the most prevalent musculoskeletal disorders, significantly affecting the quality of life of patients. Treatment outcomes can be improved with an early diagnosis and timely targeted interventions. Increasing evidence indicates that ROS and endoplasmic reticulum (ER) stress play key roles in modulating the differentiation processes of tendon-derived stem cells (TDSCs), thereby contributing to the initiation and progression of tendinopathy. However, the relationship between ONOO- and the differentiation process, as well as the various stages of tendinopathy, remains unexplored. Herein, we developed two highly specific and sensitive fluorescent probes (Rod-Cl and Rod-Br) for detecting ONOO- in the ER. Rod-Br can detect basal levels of ONOO- in the ER of TDSCs and measure ONOO- levels in primary TDSCs stimulated by interleukin-1β over various durations, allowing for comparisons between chondrogenic and osteogenic differentiation and ER stress levels. Additionally, we examined ONOO- variations in different stages of tendinopathy and treatment rat models in vivo and discussed the potential mechanisms. This research provides a robust tool for analyzing ONOO- dynamics in the tenogenic and osteogenic differentiation of TDSCs, offering new insights into the pathophysiology and treatment of tendinopathy.

An Activatable Heavy-Atom-Free Upconversion Photosensitizer for Targeted Imaging and Treatment of Tumors

Photodynamic therapy (PDT) is an innovative and promising method for treating tumors that has attracted significant interest but still faces several challenges, such as a lack of selectivity, deep penetration of light, and efficient ROS generation. To address these challenges, we optimized and synthesized a series of photosensitizers and successfully developed a heavy-atom-free near-infrared FUCL photosensitizer NFh-NMe-2. This photosensitizer can generate singlet oxygen (1O2) and induce cellular apoptosis under 808 nm light. For the safe ablation of microtumors in vivo, an activatable FUCL photosensitizer NFh-NTR was developed based on the overexpression of nitroreductase (NTR). NFh-NTR could be activated by NTR, leading to the release of the photosensitizer NFh-NMe-2, restoring the fluorescence signal, and effectively killing tumor cells under 808 nm light irradiation. This work opens new possibilities in the chemical design of an FUCL photosensitizer for cancer treatment.

A Mitochondria-Targeting and Peroxynitrite-Activatable Ratiometric Fluorescent Probe for Precise Tracking of Oxidative Stress-Induced Mitophagy

Mitochondria are the energy factory of cells and can be easily damaged by reactive oxygen species (ROS) because of the frequent occurrence of oxidative stress. Abnormality in mitophagy is often associated with many diseases including inflammation, cancer, and aging. While previously developed fluorescent probes mainly focus on detecting just ROS or mitophagy, quite rare studies have endeavored to comprehensively capture the entire mitophagic process, encompassing both the production of ROS and the induction of mitophagy. Herein, we report a new ratiometric fluorescent probe NA-DP for tracking peroxynitrite (ONOO-) as well as the subsequent oxidative stress-induced mitophagy. To a naphthalimide-based dye, an ONOO--responsive diphenyl phosphinate moiety and the mitochondria-targeting triphenylphosphonium group were attached. The probe showed a highly selective response to ONOO- through an addition-elimination reaction with diphenyl phosphinate. Owing to its outstanding pH stability and organelle-targeting ability, NA-DP was successfully used to detect mitophagy induced by oxidative stress after the generation of ONOO-. In the meantime, the probe was also used to track starvation-induced mitophagy and indicate that starvation-induced mitophagy is independent of ONOO-. Therefore, NA-DP has the ability to precisely track oxidative stress-induced mitophagy by distinguishing it from starvation-induced mitophagy. This study offers a new chemical tool to study the relationship between ROS generation and mitophagy.

Highly Efficient Near-Infrared Luminescent Radicals with Emission Peaks over 750 nm

Purely organic molecules exhibiting near-infrared (NIR) emission possess considerable potential for applications in both biological and optoelectronic technological domains, owing to their inherent advantages such as cost-effectiveness, biocompatibility, and facile chemical modifiability. However, the repertoire of such molecules with emission peaks exceeding 750 nm and concurrently demonstrating high photoluminescence quantum efficiency (PLQE) remains relatively scarce due to the energy gap law. Herein, we report two open-shell NIR radical emitters, denoted as DMNA-Cz-BTM and DMNA-PyID-BTM, achieved through the strategic integration of a donor group (DMNA) onto the Cz-BTM and PyID-BTM frameworks, respectively. We found that the donor-acceptor molecular structure allows the two designed radical emitters to exhibit a charge-transfer excited state and spatially separated electron and hole levels with non-bonding characteristics. Thus, the high-frequency vibrations are effectively suppressed. Besides, the reduction of low-frequency vibrations is observed. Collectively, the non-radiative decay channel is significantly suppressed, leading to exceptional NIR PLQE values. Specifically, DMNA-Cz-BTM manifests an emission peak at 758 nm alongside a PLQE of 55 %, whereas DMNA-PyID-BTM exhibits an emission peak at 778 nm with a PLQE of 66 %. Notably, these represent the pinnacle of PLQE among metal-free organic NIR emitters with emission peaks surpassing 750 nm.

Illuminating cisplatin-induced ferroptosis in non-small-cell lung cancer with biothiol-activatable fluorescent/photoacoustic bimodal probes

Ferroptosis modulation represents a pioneering therapeutic approach for non-small-cell lung cancer (NSCLC), where precise monitoring and regulation of ferroptosis levels are pivotal for achieving optimal therapeutic outcomes. Cisplatin (Cis), a widely used chemotherapy drug for NSCLC, demonstrates remarkable therapeutic efficacy, potentially through its ability to induce ferroptosis and synergize with other treatments. However, in vivo studies of ferroptosis face challenges due to the scarcity of validated biomarkers and the absence of reliable tools for real-time visualization. Biothiols emerge as suitable biomarkers for ferroptosis, as their concentrations decrease significantly during this process. To address these challenges, fluorescence/photoacoustic (PA) bimodal imaging offers a promising solution by providing more accurate in vivo information on ferroptosis. Therefore, the development of methods to detect biothiols using fluorescence/PA bimodal imaging is highly desirable for visualizing ferroptosis in NSCLC. In this study, we designed and constructed two activatable near-infrared (NIR) fluorescent/PA bimodal imaging probes specifically for visualizing ferroptosis by monitoring the fluctuations in biothiol levels. These probes exhibited excellent bimodal response performance in solution, cells, and tumors. Furthermore, they were successfully applied for real-time monitoring of biothiol changes during the ferroptosis process in NSCLC cells and tumors. Importantly, our findings revealed that the combined use of erastin and cisplatin exacerbates the consumption of biothiols, suggesting an enhancement of ferroptosis in NSCLC. This work not only provides powerful tools for monitoring in vivo ferroptosis but also facilitates the study of ferroptosis mechanisms and holds the potential to further advance the treatment of NSCLC.

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).

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.

An estrogen receptor β-targeted near-infrared probe for theranostic imaging of prostate cancer

Estrogen receptor β (ERβ) is aberrantly expressed in castration-resistant prostate cancer (CRPC). Therefore, a diagnostic and therapeutic ERβ probe not only helps to reveal the complex role of ERβ in prostate cancer (PCa), but also promotes ERβ-targeted PCa therapy. Herein, we reported a novel ERβ-targeted near-infrared fluorescent probe D3 with both imaging and therapeutic functions, which had the advantages of high ERβ selectivity, good optical performance, and strong anti-interference ability. In addition, it displayed excellent antiproliferative activity in CRPC cells. Finally, D3 was also successfully applied to the in vivo imaging of ERβ in the prostate cancer mouse model. Thus, this ERβ-targeted near-infrared fluorescent probe can be used as a potential tool for the study of ERβ-targeted diagnostic and therapeutic PCa.

Shortening the early diagnostic window of Hg2+-induced liver injury with a H2O2-activated fluorescence/afterglow imaging assay

Mercury ions (Hg2+) and mercury derivatives are a serious threat to ecosystems and human health due to their toxicity, and their toxicological effects are associated with a burst of reactive oxygen species (ROS) due to the oxidative stress. Endogenous hydrogen peroxide (H2O2), a featured ROS in vivo, plays an irreplaceable role in a significant number of pathological processes. However, the exact bioeffect role that H2O2 plays in Hg2+-induced oxidative stress in a specific disease has not been well answered. In particular, optical imaging probes for H2O2 endowed with afterglow emission properties are very rare. Here, the first fluorescence/afterglow probe (FA-H2O2) for accurate and specific detection of H2O2 in cells, zebrafish, and mice under Hg2+-induced oxidative stress is reported. Moreover, FA-H2O2 in its afterglow emission enables efficient monitoring of endogenous H2O2 with a higher signal-to-noise ratio (SNR) in comparison to its fluorescence signals. More importantly, by virtue of the merits of afterglow emission that can eliminate autofluorescence, thus for the first time, shortening the diagnostic window of Hg2+-induced liver injury with FA-H2O2 via noninvasive afterglow emission tracking of H2O2 is achieved, which definitely provides a new opportunity and promising tool for early diagnosis of Hg2+-induced liver injury.

Diaminonaphthalene Boronic Acid (DANBA): New Approach for Peroxynitrite Sensing Site

Selective detection of reactive oxygen species (ROS) is vital for studying their role in brain diseases. Fluorescence probes can distinguish ONOO- species from other ROS; however, their selectivity toward ONOO- species depends on the ONOO- recognition group. Aryl-boronic acids and esters, which are common ONOO- recognition groups, are not selective for ONOO- over H2O2. In this study, we developed a diaminonaphthalene (DAN)-protected boronic acid as a new ONOO- recognition group that selectively reacts with ONOO- over H2O2 and other ROS. Three DAN-protected boronic acid (DANBA)-based fluorophores that emit fluorescence over visible to near-infrared (NIR) regions, Cou-BN, BVP-BN, and HDM-BN, and their aryl-boronic acid-based counterparts (Cou-BO, BVP-BO, and HDM-BO), were developed. The DANBA-based probes exhibited enhanced selectivity toward ONOO- over that of their control group, as well as universality in solution assays and in vitro experiments with PC12 cells. The NIR-emissive HDM-BN was optimized to delineate in vivo ONOO- levels in mouse brains with Parkinson's disease. This DAN-protected boronic acid belongs to a new generation of recognition groups for developing ONOO- probes, and this strategy could be extended to other common hydroxyl-containing dyes to detect ONOO- levels in complex biological systems and processes.

Molecular Engineering of a Tumor-Targeting Thione-Derived Diketopyrrolopyrrole Photosensitizer to Attain NIR Excitation Over 850 nm for Efficient Dual Phototherapy

Photosensitizers with near-infrared (NIR) excitation, especially above 800 nm which is highly desired for phototherapy, remain rare due to the fast nonradiative relaxation process induced by exciton-vibration coupling. Here, a diketopyrrolopyrrole-derived photosensitizer (DTPA-S) is developed via thionation of carbonyl groups within the diketopyrrolopyrrole skeleton, which results in a large bathochromic shift of 81 nm, endowing the photosensitizer with strong NIR absorption at 712 nm. DTPA-S is then introduced with a functional biomolecule (N3-PEG2000-RGD) via click reaction for the construction of integrin αvβ3 receptor-targeted nano-micelles (NanoDTPA-S/RGD), which endows the photosensitizer with a further superlarge absorption redshift of 138 nm, thus extending the absorption maxima to ≈850 nm. Remarkably, thiocarbonyl substitution increases the nonbonding characters in frontier molecular orbitals, which can effectively suppress the nonradiative vibrational relaxation process via reducing the reorganization energy, enabling efficient reactive oxygen species (ROS) generation under 880 nm excitation. Screened by in vitro and in vivo assays, NanoDTPA-S/RGD with high water solubility, excellent tumor-targeting ability, and photodynamic/photothermal therapy synergistic effect exhibits satisfactory phototherapeutic performance. Overall, this study demonstrates a new design of efficient NIR-triggered diketopyrrolopyrrole photosensitizer with facile installation of functional biomolecules for potential clinical applications.

Engineering of Kidney-Targeting Fluorophores with Tunable Emission from NIR-I to NIR-II for Early Diagnosis of Kidney Disease

The development of rapidly distributed and retained probes within the kidneys is important for accurately diagnosing kidney diseases. Although molecular imaging shows the potential for non-intrusively interrogating kidney disease-related biomarkers, the limited kidney contrast of many fluorophores, owing to their relatively low distribution in the kidney, hinders their effectiveness for kidney disease detection. Herein, for the first time, an amino-functionalization strategy is proposed to construct a library of kidney-targeting fluorophores NHcy with tunable emissions from NIR-I to NIR-II. Among these, NHcy-8 is the first small-molecule NIR-II dye without a renal clearance moiety, designed specifically for kidney-targeting imaging. Building on this class of NIR-II fluorophore, the first NIR-II small-molecule kidney-targeting pH probe NIR-II-pH is developed, which exhibits a desirable kidney distribution after intravenous injection and is fluorescent only after activation by acidosis. NIR-II in vivo fluorescence/photoacoustic imaging of kidney disease models induced by cisplatin and renal I/R injury using NIR-II-pH reveals increasingly severe metabolic acidosis as the disease progressed, enabling sensitive detection of the onset of acidosis 36 h (cisplatin group) earlier than clinical methods. Thus, this study introduces a practical NIR-II kidney-targeting probe and provides a useful molecular blueprint for guiding kidney-targeting NIR-II fluorophores as diagnostic aids for kidney diseases.

Nanoprobe Based on Novel NIR-II Quinolinium Cyanine for Multimodal Imaging

NIR-II imaging has the advantages of high sensitivity, spatiotemporal resolution, and high penetration depth, thereby serving as a potential alternative to conventional imaging methods. Herein, a novel NIR-II dye IR-1010 (λex/λem = 1010/1058 nm) is reported with high quantum yield (3.08%) and good stability, by incorporating p-methoxyphenyl groups into a quinolinium cyanine dye. Then a multifunctional nanoprobe, termed IUFP NPs, is developed by the incorporation of upconversion (UC) nanoparticles (NPs), perfluoro-15-crown-5-ether (PFCE), and IR-1010, to display the novel performance of multimodal imaging. Under the single-wavelength excitation (980 nm), IUFP NPs simultaneously emit the NIR-II fluorescence of IR-1010 and visible UC luminescence of UCNPs, and thus realize the UC imaging for cells, and NIR-II fluorescence/photoacoustic/19F magnetic resonance imaging for blood vessels, lymph nodes and tumor in mice. This work affords a novel approach to NIR-II dyes and a general strategy for the design of multimodal imaging probes.

A hypoxia-activated and microenvironment-remodeling nanoplatform for multifunctional imaging and potentiated immunotherapy of cancer

Activatable theranostic systems combining precise diagnosis and robust immune activation have significant potential in cancer treatment. Herein, we develop a versatile nanoplatform integrating hypoxia-activatable molecular imaging with effective photoimmunotherapy for cancer treatment. Our molecular probe features turn-on near-infrared-II (NIR-II) fluorescence and photoacoustic signals in hypoxic tumor environments. It also induces hypoxia-triggered photodynamic and photothermal effects, promoting immunogenic cell death and activating the STING pathway, engaging both innate and adaptive immunity. The molecular probe is formulated with a vascular disrupting agent to amplify the hypoxia-responsive phototheranostic properties, on which M1-like macrophage membrane is camouflaged to shield against premature release while conferring cancer-targeting affinity. The activatable NIR-II fluorescence and photoacoustic imaging enable precise tumor delineation, while the enhanced phototherapy activates tumor-specific cytotoxic T cells, impeding both primary and distant tumor progression and providing protective immunity against rechallenge in 4T1 tumor-bearing female mice. This work advances activatable theranostic protocols for image-guided immunotherapy.

Suppressing ROS Production of AIE Nanoprobes by Simple Matrices Optimization for CNS Cell Observation and Minimized Influence of Cytoskeleton Morphology

The visualization of the central nervous system (CNS) has proposed stringent criteria for fluorescent probes, as the inevitable production of reactive oxygen species (ROS) or heat generated from most photoluminescent probes upon excitation can disturb the normal status of relatively delicate CNS cells. In this work, a red-emitting fluorogen with aggregation-induced emission (AIE) characteristics, known as DTF, was chosen as the model fluorogen to investigate whether the side effects of ROS and heat could be suppressed through easy-to-operate processes. Specifically, DTF was encapsulated with different amphiphilic matrices to yield AIE nanoprobes, and their photoluminescent properties, ROS production, and photothermal conversion rates were examined. BSA@DTF NPs possessed 1.3-fold brightness compared to that of DSPE-PEG@DTF NPs and F127@DTF NPs but its ROS generation efficiency is markedly decreased to only 2.4% of that produced by F127@DTF NPs. Meanwhile, BSA@DTF NPs showed a negligible photothermal effect. These features make BSA@DTF NPs favorable for long-term live cell imaging, particularly for fluorescent imaging of CNS cells. BSA@DTF NPs were able to sustain the normal state of HT-22 neuronal cells with continuous illumination for at least 25 min, and they also preserved the cytoskeleton of microglia BV-2 cells as the untreated control group. This work represents a successful but easy-to-operate process to suppress the ROS generation of red-emissive AIEgen, and it highlights the importance of minimizing the ROS generation of the fluorescent probes, particularly in the application of long-term imaging of CNS cells.

A Tandem-Locked Fluorescent Probe Activated by Hypoxia and a Viscous Environment for Precise Intraoperative Imaging of Tumor and Instant Assessment of Ferroptosis-Mediated Therapy

Noninvasive fluorescence detection of tumor-associated biomarker dynamics provides immediate insights into tumor biology, which are essential for assessing the efficacy of therapeutic interventions, adapting treatment strategies, and achieving personalized diagnosis and therapy evaluation. However, due to the absence of a single biomarker that effectively reflects tumor development and progression, the currently available optical diagnostic agents that rely on "always-on" or single pathological activation frequently show nonspecific fluorescence responses and limited tumor accumulation, which inevitably compromises the accuracy and reliability of tumor imaging. Herein, based on intramolecular charge transfer (ICT) and twisted intramolecular charge-transfer (TICT) hybrid mechanisms, we report a tandem-locked probe, NTVI-Biotin, for simultaneously specific imaging-guided tumor resection and ferroptosis-mediated tumor ablation evaluation under the coactivation of nitro reductase (NTR)/viscosity. The dual-stimulus-responsive design strategy ensures that NTVI-Biotin exclusively activates near-infrared (NIR) fluorescence signals upon interaction with both NTR and elevated viscosity levels through triggering ICT on while inhibiting the TICT process. Meanwhile, functionalization with a tumor-targeting hydrophilic biotin-poly(ethylene glycol) moiety enhances tumor accumulation. The probe's dual-response and tumor-targeting design minimizes nonspecific tissue activation, allowing for precise tumor identification and lesion removal with a superior tumor-to-normal tissue (T/N > 6) ratio. More importantly, NTVI-Biotin was capable of evaluating ferroptosis-mediated chemotherapeutics by real-time monitoring of the alternations of NTR/viscosity levels. The results reveal that the increased tumor signals of NTVI-Biotin following the combination of ferroptosis and chemotherapy correlate well with the tumor growth inhibition, demonstrating the potential of NTVI-Biotin to assess therapeutic efficacy.

Reactive oxygen species-mediated organic long-persistent luminophores light up biomedicine: from two-component separated nano-systems to integrated uni-luminophores

Organic luminophores have been widely utilized in cells and in vivo fluorescence imaging but face extreme challenges, including a low signal-to-noise ratio (SNR) and even false signals, due to non-negligible background signals derived from real-time excitation lasers. To overcome these challenges, in the last decade, functionalized organic long-persistent luminophores have gained much attention. Such luminophores could not only overcome the biological toxicity of inorganic long-persistent luminescent materials (metabolic toxicity and leakage risk of inorganic heavy metals), but also continue to emit long-persistent luminescence after removing the excitation source, thus effectively improving imaging quality. More importantly, organic long-persistent luminophores have good structure tailorability for the construction of activable probes, which is favorable for biosensing. Recently, the development of reactive oxygen species (ROS)-mediated long-persistent (ROSLP) luminophores (especially organic small-molecule ROSLP luminophores) is still in the rising stage. Notably, ROSLP luminophores for in vivo imaging have experienced from two-component separated nano-systems to integrated uni-luminophores, which obtained gradually better designability and biocompatibility. In this review, we summarize the progress and challenges of organic long-persistent luminophores, focusing on their development history, long-persistent luminescence working mechanisms, and biomedical applications. We hope that these insights will help scientists further develop functionalized organic long-persistent luminophores for the biomedical field.

Polydopamine-based surface coating fabrication on titanium implant by combining a photothermal agent and TiO2 nanosheets for efficient photothermal antibacterial therapy and promoted osteogenic activity

Developing titanium-based dental implants with both excellent antibacterial properties and good osseointegration is crucial for the success of the implant operation and the long-term durability of the implant. In this study, a polydopamine-based coating was created by attaching TiO2 nanosheets-cyanine composites onto the titanium surface, enabling the integration of effective photothermal antibacterial therapy with osseointegration. The exceptional dual-photothermal conversion abilities of polydopamine and cyanine in the coating resulted in outstanding photothermal antibacterial and antibiofilm therapy against four types of bacteria. Furthermore, TiO2 nanosheets promoted the adhesion, proliferation and early osteogenic differentiation of osteoblasts. In an infected dental implant model in rats, the developed coating exhibited potent antibacterial activity and remarkable osteogenic differentiation in the bone, leading to increased bone formation around the implants. This innovative approach, combining photothermal therapy with osteogenic two-dimensional nanomaterials, presents a novel method for surface functionalization of implants to achieve effective antibacterial and osseointegration capabilities.

Activatable Fluorescence and Bio/Chemiluminescence Probes for Aminopeptidases: From Design to Biomedical Applications

Aminopeptidases are exopeptidases that catalyze the cleavage of amino acid residues from the N-terminal fragment of protein or peptide substrates. Owing to their function, they play important roles in protein maturation, signal transduction, cell-cycle control, and various disease mechanisms, notably in cancer pathology. To gain better insights into their function, molecular imaging assisted by fluorescence and bio/chemiluminescence probes has become an indispensable method to their superiorities, including excellent sensitivity, selectivity, and real-time and noninvasive imaging. Numerous efforts are made to develop activatable probes that can effectively enhance efficiency and accuracy as well as minimize the side effects. This review is classified according to the type of aminopeptidases, summarizing some recent works on the design, work mechanism, and sensing, imaging, and theranostic performance of their activatable probe. Finally, the current challenges are outlined in developing activatable probes for aminopeptidases and provide possible solutions for future advancements.

Intramolecular Charge Transfer Inhibition Strategy toward a Desired Solvatochromic Fluorescent Platform: Visualization of Duple Organelles and Detection of Carbon Dioxide

Solvatochromic fluorescent probes are crucial molecular tools to investigate and aggregate proteins' fold, visualize fine structures in biomembranes, and label different organelles in dual emission colors. However, solvatochromic fluorogens often displayed a weak emission at high polarity, hindering their bioimaging applications. To resolve this problem, herein, we propose an intramolecular charge transfer (ICT) inhibition strategy. The probe was designed with a single electronic donor and two acceptors in order to split and inhibit the ICT procedure. As a result, the probe displayed an intense emission at both low and high polarities and showed a large emission shift (84 nm) upon polarity change. Using the probe, we successfully imaged lipid droplets and the endoplasmic reticulum in different fluorescence colors. Moreover, the different degrees of lipid accumulation by oleic acid, stearic acid, and cholesterol (oleic acid > stearic acid > cholesterol) have been revealed. The lipid accumulation induced by the three lipids could be rapidly consumed under lipid-less conditions, and the lipids with stearic acid were the most difficult to be consumed. The biological results could facilitate the understanding and treatment of lipid accumulation and obesity. Furthermore, utilizing the polarity increase of diethylamine after the reaction with CO2, the ratiometric detection of CO2 has been achieved for the first time with the probe.

Dissecting Exciton Dynamics in pH-Activatable Long-Wavelength Photosensitizers for Traceable Photodynamic Therapy

Tumor-specific activatable long-wavelength (LW) photosensitizers (PSs) show promise in overcoming the limitations of traditional photodynamic therapy (PDT), such as systemic phototoxicity and shallow tissue penetration. However, their insufficient LW light absorption and low singlet oxygen quantum yield (Φ 1O2) usually require high laser power density to produce thermal energy and synergistically enhance PDT. The strong photothermal radiation causing acute pain significantly reduces patient compliance and hinders the broader clinical application of LW PDT. Through the exciton dynamics dissection strategy, we have developed a series of pH-activatable cyanine-based LW PSs (LET-R, R = H, Cl, Br, I), among which the activated LET-I exhibits strong light absorption at 808 nm and a remarkable 3.2-fold enhancement in Φ 1O2 compared to indocyanine green. Transient spectroscopic analysis and theoretical calculations confirmed its significantly promoted intersystem crossing and simultaneously enhanced LW fluorescence emission characteristics. These features enable the activatable fluorescence and photoacoustic dual-modal imaging-escorted complete photodynamic eradication of tumors by the folic acid (FA)-modified LET-I probe (LET-I-FA), under the ultralow 808 nm laser power density (0.2 W cm-2) for irradiation, without the need for photothermal energy synergy. This research presents a novel strategy of dissecting exciton dynamics to screen activatable LW PSs for traceable PDT.

Turn-On Fluorescence Probe for Cancer-Related γ-Glutamyltranspeptidase Detection

The design and development of fluorescent materials for detecting cancer-related enzymes are crucial for cancer diagnosis and treatment. Herein, we present a substituted rhodamine derivative for the chromogenic and fluorogenic detection of the cancer-relevant enzyme γ-glutamyltranspeptidase (GGT). Initially, the probe is non-chromic and non-emissive due to its spirolactam form, which hinders extensive electronic delocalization over broader pathway. However, selective enzymatic cleavage of the side-coupled group triggers spirolactam ring opening, resulting in electronic flow across the rhodamine skeleton, and reduces the band gap for low-energy electronic transitions. This transformation turns the reaction mixture from colorless to intense pink, with prominent UV and fluorescence bands. The sensor's selectivity was tested against various human enzymes, including urease, alkaline phosphatase, acetylcholinesterase, tyrosinase, and cyclooxygenase, and showed no response. Absorption and fluorescence titration analyses of the probe upon incremental addition of GGT into the probe solution revealed a consistent increase in both absorption and emission spectra, along with intensified pink coloration. The cellular toxicity of the receptor was evaluated using the MTT assay, and bioimaging analysis was performed on BHK-21 cells, which produced bright red fluorescence, demonstrating the probe's excellent cell penetration and digestion capabilities for intracellular analytical detection. Molecular docking results supported the fact that probe-4 made stable interactions with the GGT active site residues.

Rational Molecular Design of a Fluorescent Probe for Selectively Sensing Human Cytochrome P450 2D6

Cytochrome P450 2D6 (CYP2D6) is a key enzyme that mediates the metabolism of various drugs and endogenous substances in humans. However, its biological role in drug-drug interactions especially mechanism-based inactivation (MBI), and various diseases remains poorly understood, owing to the lack of molecular tools suitable for selectively monitoring CYP2D6 in complex biological systems. Herein, using a tailored molecular strategy, we developed a fluorescent probe BDPM for CYP2D6. BDPM exhibits excellent specificity and imaging capability for CYP2D6, making it suitable for the real-time monitoring of endogenous CYP2D6 activity in living bio-samples. Therefore, our tailored strategy proved useful for constructing the highly selective and enzyme-activated fluorescent probes. BDPM as a molecular tool to explore the critical roles of CYP2D6 in the pathogenesis of diseases, high-throughput screening of inhibitors and intensive investigation of CYP2D6-induced MBI in natural systems.

Tuning Tumor Targeting and Ratiometric Photoacoustic Imaging by Fine-Tuning Torsion Angle for Colorectal Liver Metastasis Diagnosis

Photoacoustic (PA) tomography is an emerging biomedical imaging technology for precision cancer medicine. Conventional small-molecule PA probes usually exhibit a single PA signal and poor tumor targeting that lack the imaging reliability. Here, we introduce a series of cyanine/hemicyanine interconversion dyes (denoted Cy-HCy) for PA/fluorescent dual-mode probe development that features optimized ratiometric PA imaging and tunable tumor-targeting ability for precise diagnosis and resection of colorectal cancer (CRC). Importantly, Cy-HCy can be presented in cyanine (inherent tumor targeting and long NIR PA wavelength) and hemicyanine (poor tumor targeting and short NIR PA wavelength) by fine-tuning torsion angle and the ingenious transformation between cyanine and hemicyanine through regulation optically tunable group endows the NIR ratiometric PA and tunable tumor-targeting properties. To demonstrate the applicability of Cy-HCy dyes, we designed the first small-molecule tumor-targeting and NIR ratiometric PA probe Cy-HCy-H2S for precise CRC liver metastasis diagnosis, activated by H2S (a CRC biomarker). Using this probe, we not only visualized the subcutaneous tumor and liver metastatic cancers in CRC mouse models but also realized PA and fluorescence image-guided tumor excision. We expect that Cy-HCy will be generalized for creating a wide variety of inherently tumor-targeting NIR ratiometric PA probes in oncological research and practice.

Recent advances in biomaterials based near-infrared mild photothermal therapy for biomedical application: A review

Mild photothermal therapy (MPTT) generates heat therapeutic effect at the temperature below 45 °C under near-infrared (NIR) irradiation, which has the advantages of controllable treatment efficacy, lower hyperthermia temperatures, reduced dosage, and minimized damage to surrounding tissues. Despite significant progress has been achieved in MPTT, it remains primarily in the stage of basic and clinical research and has not yet seen widespread clinical adoption. Herein, a comprehensive overview of the recent NIR MPTT development was provided, aiming to emphasize the mechanism and obstacles, summarize the used photothermal agents, and introduce various biomedical applications such as anti-tumor, wound healing, and vascular disease treatment. The challenges of MPTT were proposed with potential solutions, and the future development direction in MPTT was outlooked to enhance the prospects for clinical translation.

Dual-locked fluorescent probes for precise diagnosis and targeted treatment of tumors

Cancer continues to pose a significant threat to global health, with its high mortality rates largely attributable to delayed diagnosis and non-specific treatments. Early and accurate diagnosis is crucial, yet it remains challenging due to the subtle and often undetectable early molecular changes. Traditional single-target fluorescent probes often fail to accurately identify cancer cells, relying solely on single biomarkers and consequently leading to high rates of false positives and inadequate specificity. In contrast, dual-locked fluorescent probes represent a breakthrough, designed to enhance diagnostic precision. By requiring the simultaneous presence of two specific tumor-associated biomarkers or microenvironmental conditions, these probes significantly reduce non-specific activations typical of conventional single-analyte probes. This review discusses the structural designs, response mechanisms, and biological applications of dual-locked probes, highlighting their potential in tumor imaging and treatment. Importantly, the review addresses the challenges, and perspectives in this field, offering a comprehensive look at the current state and future potential of dual-locked fluorescent probes in oncology.