A Unique "Integration" Strategy for the Rational Design of Optically Tunable Near-Infrared Fluorophores

Analysis of optical properties and response mechanism of H2S fluorescent probe based on rhodamine derivatives

H2S plays a crucial role in numerous physiological and pathological processes. In this project, a new fluorescent probe, SG-H2S, for the detection of H2S, was developed by introducing the recognition group 2,4-dinitrophenyl ether. The combination of rhodamine derivatives can produce both colorimetric reactions and fluorescence reactions. Compared with the current H2S probes, the main advantages of SG-H2S are its wide pH range (5-9), fast response (30 min), and high selectivity in competitive species (including biological mercaptan). The probe SG-H2S has low cytotoxicity and has been successfully applied to imaging in MCF-7 cells, HeLa cells, and BALB/c nude mice. We hope that SG-H2S will provide a vital method for the field of biology.

Tailoring obeticholic acid activity by iridium(III) complex conjugation to develop a farnesoid X receptor probe

INTRODUCTION

The farnesoid X receptor (FXR) is a crucial regulator in the intestine, maintaining bile acid homeostasis. Inhibiting intestinal FXR shows promise in managing inflammatory bowel and liver diseases by reducing bile acid accumulation. Additionally, changes in FXR expression could serve as a potential biomarker for intestinal diseases. Therefore, developing an imaging probe for FXR holds significant potential for the early detection, simultaneous treatment, and monitoring of FXR-related diseases.

OBJECTIVES

The study aimed to develop a bioimaging probe for FXR by conjugating obeticholic acid (OCA), an FXR agonist, to an iridium(III) complex, and to investigate its application for targeting FXR in intestinal cells.

METHODS

OCA was conjugated to an iridium(III) complex to generate the novel complex 1. The effect of complex 1 on FXR activity, nuclear translocation, and downstream targets was investigated in intestinal epithelial cells using various biochemical and cellular assays. Additionally, the photophysical properties of complex 1 were assessed for FXR imaging.

RESULTS

Complex 1 retained the desirable photophysical properties for monitoring FXR in intestinal cells while reversing OCA's activity from agonistic to antagonistic. It disrupted FXR-RXR heterodimerization, inhibited FXR nuclear translocation, and downregulated downstream targets responsible for bile acid absorption, transport, and metabolism in intestinal epithelial cells.

CONCLUSION

The study successfully developed an imaging probe and modulator of FXR by conjugating OCA to an iridium(III) complex. Complex 1 retained the favorable photophysical properties of the iridium(III) complex, while reversing OCA's activity from agonistic to antagonistic. The findings highlight the exciting application of using metals to tailor the activity of nuclear receptor modulators in living systems.

Julolidinyl aza-BODIPYs as NIR-II fluorophores for the bioimaging of nanocarriers

The aggregation-caused quenching (ACQ) rationale has been employed to improve the fluorescence imaging accuracy of nanocarriers by precluding free probe-derived interferences. However, its usefulness is undermined by limited penetration and low spatiotemporal resolution of NIR-I (700-900 nm) bioimaging owing to absorption and diffraction by biological tissues and tissue-derived autofluorescence. This study aimed to develop ACQ-based NIR-II (1000-1700 nm) probes to further improve the imaging resolution and accuracy. The strategy employed is to install highly planar and electron-rich julolidine into the 3,5-position of aza-BODIPY based on the larger substituent effects. The newly developed probes displayed remarkable photophysical properties, with intense absorption centered at approximately 850 nm and bright emission in the 950-1300 nm region. Compared with the NIR-I counterpart P2, the NIR-II probes demonstrated superior water sensitivity and quenching stability. ACQ1 and ACQ6 exhibited more promising ACQ effects with absolute fluorescence quenching at water fractions above 40% and higher quenching stability with less than 2.0% fluorescence reillumination in plasma after 24 h of incubation. Theoretical calculations verified that molecular planarity is more important than hydrophobicity for ACQ properties. Additionally, in vivo and ex vivo reillumination studies revealed less than 2.5% signal interference from prequenched ACQ1, in contrast to 15% for P2.

Tetraanionic Oligo-Dioxaborines: Strongly Absorbing Near-Infrared Dyes

Polymethine dyes of tetraanionic nature comprising 1,3,2-dioxaborine rings in the polymethine chain and end-groups of different electron-accepting abilities have been synthesized. They can be considered as oligomeric polymethines, where a linear conjugated π-system passes through three 1,3,2-dioxaborine units and a number of tri- and dimethine π-bridges between two end-groups. The obtained dyes exhibit near-infrared absorption and fluorescence, with molar absorption coefficients reaching as high as 564000 M-1 cm-1 in DMF, rendering them among the strongest absorbers known. The novel compounds are bright NIR fluorophores, with fluorescence quantum yields up to 0.13 in DMF. A comparative analysis of the electronic structure of the obtained dyes with respective dianionic and trianionic oligomers was conducted through quantum chemical calculations.

Ratiometric Near-Infrared Fluorescent Probe Monitors Ferroptosis in HCC Cells by Imaging HClO in Mitochondria

Hypochlorous acid (HClO) is a typical endogenous ROS produced mainly in mitochondria, and it has strong oxidative properties. Abnormal HClO levels lead to mitochondrial dysfunction, strongly associated with various diseases. It has been shown that HClO shows traces of overexpression in cells of both ferroptosis and hepatocellular carcinoma (HCC). Therefore, visualization of HClO levels during ferroptosis of HCC is important to explore its physiological and pathological roles. So far, there has been no report on the visualization of HClO in ferroptosis of HCC. Thus, we present a ratiometric near-infrared (NIR) fluorescent probe Mito-Rh-S which visualized for the first time the fluctuation of HClO in mitochondria during ferroptosis of HCC. Mito-Rh-S has an ultrafast response rate (2 s) and large emission shift (115 nm). Mito-Rh-S was constructed based on the PET sensing mechanism and thus has a high signal-to-noise ratio. The cell experiments of Mito-Rh-S demonstrated that Fe2+- and erastin-induced ferroptosis in HepG2 cells resulted in elevated levels of mitochondrial HClO and that high concentration levels of Fe2+ and erastin cause severe mitochondrial damage and oxidative stress and had the potential to kill HepG2 cells. By regulating the erastin concentration, erastin induction time, and treatment of the ferroptosis model, Mito-Rh-S can accurately detect the fluctuation of mitochondrial HClO levels during ferroptosis in HCC.

Rational Design and Biological Application of Hybrid Fluorophores

Fluorophores are considered powerful tools for not only enabling the visualization of cell structures, substructures, and biological processes, but also making for the quantitative and qualitative measurement of various analytes in living systems. However, most fluorophores do not meet the diverse requirements for biological applications in terms of their photophysical and biological properties. Hybridization is an important strategy in molecular engineering that provides fluorophores with complementarity and multifunctionality. This review summarizes the basic strategies of hybridization with four classes of fluorophores, including xanthene, cyanine, coumarin, and BODIPY with a focus on their structure-property relationship (SPR) and biological applications. This review aims to provide rational hybrid ideas for expanding the reservoir of knowledge regarding fluorophores and promoting the development of newly produced fluorophores for applications in the field of life sciences.

Enzyme-Activatable Near-Infrared Photosensitizer with High Enrichment in Tumor Cells Based on a Multi-Effect Design

Enzyme-activatable near-infrared (NIR) fluorescent probes and photosensitizers (PSs) have emerged as promising tools for molecular imaging and photodynamic therapy (PDT). However, in living organisms selective retention or even enrichment of these reagents after enzymatic activation at or near sites of interest remains a challenging task. Herein, we integrate non-covalent and covalent retention approaches to introduce a novel "1-to-3" multi-effect strategy-one enzymatic stimulus leads to three types of effects-for the design of an enzyme-activatable NIR probe or PS. Using this strategy, we have constructed an alkaline phosphatase (ALP)-activatable NIR fluorogenic probe and a NIR PS, which proved to be selectively activated by ALP to switch on NIR fluorescence or photosensitizing ability, respectively. Additionally, these reagents showed significant enrichment (over 2000-fold) in ALP-overexpressed tumor cells compared to the culture medium, accompanied by massive depletion of intracellular thiols, the major antioxidants in cells. The investigation of this ALP-activatable NIR PS in an in vivo PDT model resulted in complete suppression of HeLa tumors and full recovery of all tested mice. Encouragingly, even a single administration of this NIR PS was sufficient to completely suppress tumors in mice, demonstrating the high potential of this strategy in biomedical applications.

Revealing the elevation of Zn2+ in the brain of depressed mice by a ratiometric fluorescent probe with dual near-infrared emissions

A mitochondria-targeted ratiometric fluorescent probe (Mito-Zn) was first designed and synthesized with dual emissions both located in the near-infrared region, for Zn2+ detection with high sensitivity and selectivity. By using the developed Mito-Zn, a high level of Zn2+ in the depressed mouse brain was discovered for the first time.

A novel colorimetric fluorescent probe for sensing bisulfite detection in plant and zebrafish

Sulfur dioxide (SO2) and its derivatives (SO32- and HSO3-), are important active sulfur species that play significant roles in physiological processes. Fluorescence probe imaging technology, due to its high temporal and spatial resolution, real-time non-invasive and non-destructive detection, has emerged as a valuable tool for studying SO2 in biological systems. In this study, we presented a colorimetric fluorescent probe for the detection of HSO3-. The structure of probe TPN-BP consists of a triphenylamine group and a benzopyrylium group that are connected by a vinyl double bond. The benzopyrylium group in probe TPN-BP, which carries a positive charge, serves two important functions: enhancing water solubility, allowing for its effective use in fully aqueous environments, and acting as a fluorescence quencher for the triphenylamine group. Upon interaction with HSO3-, probe TPN-BP exhibited significantly increase in fluorescence at 480 nm, causing the solution to change from blue to colorless. Spectral experiments showed that probe TPN-BP showed quick response time (10 s), high sensitivity (12.7 nM), and excellent selectivity towards HSO3-. It is worth noting that probe TPN-BP has been successfully used for fluorescence imaging and detection of HSO3- in plants and zebrafish. The results of this study indicated that probe TPN-BP can be used as a promising tool for the research and monitoring of SO2 in living organisms.

Visualizing Dipeptidyl Peptidase-IV with an Advanced Non-π-Conjugated Fluorescent Probe for Early Thyroid Disease Diagnosis

Early detection and effective treatment of thyroid cancer are vital due to the aggressiveness and high mortality rate of the cancer. Nevertheless, the exploration of dipeptidyl peptidase-IV (DPP-IV) as a biomarker for thyroid diseases has not been widely conducted. In this study, we developed a novel non-π-conjugated near-infrared fluorescent probe, MB-DPP4, specifically designed to visualize and detect endogenous DPP-IV. Traditional DPP-IV-specific fluorescent probes rely primarily on the intramolecular charge transfer mechanism. For this reason, these probes are often hampered by high background levels that can inhibit their ability to achieve a fluorescence turn-on effect. MB-DPP4 successfully surmounts several drawbacks of traditional DPP-IV probes, boasting unique features such as exceptional selectivity, ultrahigh sensitivity (0.29 ng/mL), innovative structure, low background, and long-wavelength fluorescence. MB-DPP4 is an "off-on" chemosensor that exhibits strong fluorescence at 715 nm and releases a methylene blue (MB) fluorophore upon interacting with DPP-IV, resulting in a visible color change from colorless to blue. Given these remarkable attributes, MB-DPP4 shows great promise as a versatile tool for advancing research on biological processes and for evaluating the physiological roles of DPP-IV in living systems. Finally, we conducted a comprehensive investigation of DPP-IV expression in human serum, urine, thyroid cells, and mouse thyroid tumor models. Our findings could potentially establish a foundation for the early diagnosis and treatment of thyroid diseases.

Engineering a near-infrared LAP fluorescent probe with high sensitivity and selectivity for surgical resection of liver cancer

Hepatocellular carcinoma (HCC) is a type of cancer associated with a high rate of mortality and morbidity. In order to achieve precise HCC theranostics, it is important to develop excellent fluorescent probes. However, the existing probes are not sensitive or specific enough to accurately identify HCC margins and contours. For diagnosing HCC and identifying tumors during surgery, it is urgent to engineer highly sensitive and selective fluorescent probes. Liver tumor progression is closely associated with leucine aminopeptidase (LAP) overexpression, a biomarker of liver cancer. Herein, we have rationally designed a NIR fluorescent probe, NLAP, which is specially activated by LAP. The probe exhibited high sensitivity (detection limit = 6.8 mU L-1) and superior affinity (Km = 2.98 μM) for LAP. With this probe, we distinguished cancer cells overexpressing LAP from normal cells and applied it intraoperatively to guide liver tumor excisions. Furthermore, NLAP was employed to successfully detect the LAP of intestinal and splenic metastatic tumors in orthotopic liver tumor mice by "in situ spraying" and good performances were demonstrated.

Strategies to convert organic fluorophores into red/near-infrared emitting analogues and their utilization in bioimaging probes

Organic fluorophores aided by current microscopy imaging modalities are essential for studying biological systems. Recently, red/near-infrared emitting fluorophores have attracted great research efforts, as they enable bioimaging applications with reduced autofluorescence interference and light scattering, two significant obstacles for deep-tissue imaging, as well as reduced photodamage and photobleaching. Herein, we analyzed the current strategies to convert key organic fluorophores bearing xanthene, coumarin, and naphthalene cores into longer wavelength-emitting derivatives by focussing on their effectiveness and limitations. Together, we introduced typical examples of how such fluorophores can be used to develop molecular probes for biological analytes, along with key sensing features. Finally, we listed several critical issues to be considered in developing new fluorophores.

Conformationally confined three-armed supramolecular folding for boosting near-infrared biological imaging

Herein, a triphenylamine derivative (TP-3PY) possessing 4-(4-bromophenyl)pyridine (PY) as an electron-accepting group and tris[p-(4-pyridylvinyl)phenyl]amine (TPA) with large two-photon absorption cross-sections as an electron-donating group was obtained, and showed intense absorption in the visible light region (λmax = 509 nm) and weak near-infrared (NIR) fluorescence emission at 750 nm. After complexation with cucurbit[8]uril (CB[8]), TP-3PY showed bright NIR fluorescence emission at 727 nm and phosphorescence emission at 800 nm. When the supramolecular assembly (TP-3PY⊂CB[8]) further interacted with dodecyl-modified sulfonatocalix[4]arene (SC4AD), the fluorescence and phosphorescence emissions were further enhanced at 710 and 734 nm, respectively. However, only the fluorescence emission of TP-3PY was enhanced in the presence of cucurbit[7]uril (CB[7]) and SC4AD. More interestingly, the photoluminescence of TP-3PY⊂CB[8]@SC4AD and TP-3PY⊂CB[7]@SC4AD assemblies could be excited by both visible (510 nm) and NIR light (930 nm). Finally, these ternary supramolecular assemblies with bright NIR light emission were applied to lysosome imaging of tumor cells and real-time biological imaging of mice.

Near-Infrared Persistent Luminescence Nanoprobe for Ultrasensitive Image-Guided Tumor Resection

Near-infrared (NIR) fluorescence imaging poses significant superiority over traditional medical imaging for tumor resection, thus having attracted widely attention. However, for tiny tumor residues, it requires relative high sensitivity to determine. Here, based on persistent luminescence nanoparticles (PLNPs), an ultrasensitive nanoprobe with extraordinary tumor imaging result is developed to guide surgical removal. Persistent luminescence (PersL) is quenched in normal tissue by the outer layer of MnO2 , and is recovered due to the degradation of MnO2 in tumor microenvironment, significantly improving the sensitivity of tumor imaging. Combined with the absence of background fluorescence in imaging of PLNPs, ultrahigh sensitivity is achieved. In orthotopic breast cancer model, the intraoperative tumor-to-normal tissue (T/NT) signal ratio of the nanoprobe is 58.8, about 9 times that of downconversion nanoparticles. The T/NT ratio of residual tumor (<2 mm) remains 12.4, considerably high to distinguish tumor tissue from normal tissue. Besides, multiple-microtumor, 4T1 liver-implanted tumor and lung metastasis models are built to prove that this ultrasensitive nanoprobe is feasible to recognize tumor residues. Notably, PersL imaging takes only 1.5 min, appropriate to be applied for intraoperative imaging. Overall, an ultrasensitive and convenient imaging for recognizing residual tumor tissue is introduced, holding promise for complete surgical removal.

Rational Design of MMP-Independent Near-Infrared Fluorescent Probes for Accurately Monitoring Mitochondrial Viscosity

Mitochondrial viscosity affects metabolite diffusion and mitochondrial metabolism and is associated with many diseases. However, the accuracy of mitochondria-targeting fluorescent probes in measuring viscosity is unsatisfactory because these probes can diffuse from mitochondria during mitophagy with a decreased mitochondrial membrane potential (MMP). To avoid this problem, by incorporating different alkyl side chains into dihydroxanthene fluorophores (denoted as DHX), we developed six near-infrared (NIR) probes for the accurate detection of mitochondrial viscosity, and the sensitivity to viscosity and the mitochondrial targeting and anchoring capability of these probes increased by increasing the alkyl chain length. Among them, DHX-V-C₁₂ had a highly selective response to viscosity variations with minimum interference from polarity, pH, and other biologically relevant species. Furthermore, DHX-V-C₁₂ was used to monitor the mitochondrial viscosity changes of HeLa cells treated by ionophores (nystatin, monensin) or under starvation conditions. We hope that this mitochondrial targeting and anchoring strategy based on increasing the alkyl chain length will be a general strategy for the accurate detection of mitochondrial analytes, enabling the accurate study of mitochondrial functions.

A novel near-infrared fluorescent probe with hemicyanine scaffold for sensitive mitochondrial pH detection and mitophagy study

Mitochondria, as an energy-producing powerhouse in live cells, is considered to be directly linked to cellular health. However, dysfunctional mitochondria and abnormal mitochondria pH would possibly activate mitophagy, cell apoptosis and intercellular acidification process. In this work, we synthesized a novel near infrared fluorescent probe (FNIR-pH) for measurement of mitochondrial pH based on the hemicyanine skeleton as a fluorophore. The FNIR-pH probe functioned as a mitochondrial pH substrate and exhibited quick and sensitive turn-on fluorescence responses to mitochondrial pH in basic solution due to the deprotonation of hydroxy group in the structure. From pH 3.0 to 10.0, the FNIR-pH exhibited almost 100-fold increase in fluorescence intensity at 766 nm wavelength. The FNIR-pH also displayed superior selectivity to various metal ions, excellent photostability, and low cytotoxicity, which facilitated further biological application. Owing to the proper pKa value of 7.2, the FNIR-pH paved the way for real-time monitoring of mitochondria pH changes in live cells and sensitive sensing of mitophagy. Moreover, the FNIR-pH probe was also implemented for fluorescent imaging of tumor-bearing mice to validate its potential application for in vivo imaging of bioanalytes and biomarkers.

Dihydroxanthene-Based Near-infrared Fluorescent Probes for Monitoring Mitochondrial Viscosity in Living Cells and Mice

Aberrant mitochondrial viscosity is closely associated with many diseases and cellular malfunctions. Thus, the development of reliable methods for monitoring mitochondrial viscosity variations has attracted considerable attention. Herein, through stepwise structural modulation of the dihydroxanthene fluorophore (DHX), we developed three NIR fluorescent probes, named DHX-V-1-3, for detecting mitochondrial viscosity. Among them, DHX-V-3 displayed the highest signal-to-noise ratio (67-fold) for viscosity with outstanding selectivity and showed excellent mitochondria targeting and immobilization ability. At the cellular level, the DHX-V-3 probe was successfully applied to image the mitochondrial viscosity in live cells upon treatment with lipopolysaccharide (LPS) or nystatin. Moreover, benefiting from its NIR emission and the increased depth of tissue imaging, DHX-V-3 demonstrated the ability to visualize the increased viscosity in LPS-treated mice.

An oral ratiometric NIR-II fluorescent probe for reliable monitoring of gastrointestinal diseases in vivo

Early monitoring of gastrointestinal diseases via orally delivered NIR-II ratiometric fluorescent probes represents a promising noninvasive diagnostic modality, but is challenging due to the limitation of harsh digestive environment. Here, we report a single-component NIR-II ratiometric molecular nanoprobe (LC-1250 NP) to monitor gastrointestinal disease with high specificity to its biomarker H₂O₂ via oral administration. LC-1250 NP displays stable fluorescence in the channel of 1250 long-pass (F_1250LP) before and after the gastrointestinal disease detection as the reference, while it presents significantly enhanced fluorescence signal in the response channel of 1150 nm short-pass (F_1150SP) in diseased gastrointestinal environment due to the intramolecular cyclization of LC-1250 molecules activated by H₂O₂. The fluorescence ratio (F_1150SP/F_1250LP) increases linearly with the concentration of H₂O₂ with a low detection limit of 20 nM. Therefore, when delivered orally, LC-1250 NP can accurately map the diseased areas and surmount the false-positive interference from biological heterogeneity by NIR-II ratiometric fluorescence imaging, providing sensitive and reliable evaluation for the progress of gastroenteritis.

γ-Glutamyltransferase-Activatable Fluoro-Photoacoustic Reporter for Highly Sensitive Diagnosis of Acute Liver Injury and Tumor

γ-Glutamyltransferase (GGT) has been recognized as an important clinical biomarker that is closely related to many diseases. Visualizing the GGT fluctuation facilitates early disease-related diagnosis and therapy. Herein, an activated probe (NIR-GGT) for the imaging of GGT activity was prepared. The probe consists of a stable NIR fluorophore with the tunable amino group decorated with the γ-glutamate group as a GGT-sensing unit linked by a self-elimination group. NIR-GGT can sensitively recognize GGT and cause a strong turn-on fluorescent and photoacoustic signal. The up-regulation of the GGT expression in acetaminophen-induced acute liver injury was imaged using NIR-GGT. The probe can track changes in the GGT level in the early stages of drug-induced acute liver injury (DIALI) and its remedy process by fluorescent and photoacoustic dual-modality imaging with a high temporal-spatial resolution. NIR-GGT can also be used to differentiate between tumor and para-carcinowa tissues in vivo. The probe may be a potential tool for the diagnosis of early-stage DIALI and accurate tumor resection in the clinical field.

Activity-Based Fluorescent Probes Based on Hemicyanine for Biomedical Sensing

In recent years, fluorescent probes, as an analytical tool that can target and rapidly detect analytes, have been increasingly used for applications related to medical treatment, detection, and bioimaging. Researchers are interested in hemicyanine-based fluorescent probes because of their high quantum yield, tunable spectrum characteristics, absorption and emission in the near-infrared (NIR) region, and good photo-stability. The development of these dyes and their derivatives as NIR fluorescent probes for biological applications has advanced significantly in the last ten years. This review introduces processes for making hemicyanine dyes and the methodology for creating functional activity-based fluorescent probes. A variety of hemicyanine-based probes have been systematically developed for the detection of small biomolecules in various illnesses. Finally, the potential drawbacks of hemicyanine-based functional probes, and the prospects for future research and translation into clinical medicine, are also discussed. This study is intended to provide strategies for the development and design of novel fluorescence probes.

Reversible Near-Infrared Fluorescent Probe for Rapid Sensing Sulfur Dioxide and Formaldehyde: Recognition and Photoactivation Mechanism and Applications in Bioimaging and Encryption Ink

A novel near-infrared (NIR) fluorescent Probe 1 was successfully developed for the reversible detection of sulfur dioxide derivatives and formaldehyde. The purple solution of Probe 1 faded to colorless in 1.8 s with the addition of HSO₃^-. Meanwhile, its fluorescence signal disappeared instantaneously with a 39 nM detection limit. The probe exhibited excellent selectivity toward HSO₃^- over other potential interfering agents. Then, its absorption and fluorescence bands were able to effectively recover in response to formaldehyde. Remarkably, this reverse process was able to accelerate 84 times under UV light in 122 s and achieved a recovery rate of 98% by UV light, the photoactivation mechanism was fully determined by HRMS and theoretical calculation. Furthermore, we demonstrated that Probe 1 was successfully applied for the detection of sulfur dioxide derivatives and formaldehyde in living cells and data encryption.

Rational Design of a Near-Infrared Ratiometric Probe with a Large Stokes Shift: Visualization of Polarity Abnormalities in Non-Alcoholic Fatty Liver Model Mice

Tracking liver polarity with noninvasive and dynamic imaging techniques is helpful to better understand the non-alcoholic fatty liver (NAFL). Herein, a novel near-infrared (NIR) fluorescent probe Cy-Mp is constructed using a "symmetry collapse" strategy. The structure modification leads to the conversion of locally excited state fluorescence to charge transfer state fluorescence. Cy-Mp emits at near-infrared (NIR) wavelengths with high photostability as well as a large Stokes shift. Cy-Mp exhibits a ratiometric response to polarity, providing more accurate analysis of intracellular polarity via the built-in internal reference correction. Most importantly, the in vivo studies indicate that Cy-Mp can accumulate in the liver and the decreased polarity in the liver of mice with NAFL is verified by the ratiometric imaging, implying the great potential of Cy-Mp in the diagnosis of NAFL.

An ultrasensitive lipid droplet-targeted NIR emission fluorescent probe for polarity detection and its application in liver disease diagnosis

Compared to normal cells, cancer cells require more energy supply during proliferation and metabolism. In living cells, in addition to mitochondria, lipid droplets are also an important organelle for providing energy. Studies have shown that the number and distribution of lipid droplets change significantly during the production of lesions in cells. At this stage, the predisposing factors for the development of cellular lesions are not clear, thus leading to limitations in the early diagnosis and treatment of diseases such as liver injury, fatty liver, and hepatitis. To meet the urgent challenge, we used a near-infrared emission fluorescent probe SSR-LDs based on the intramolecular charge transfer effect (ICT) to detect polarity changes within intracellular lipid droplets. The probe SSR-LDs has ultra-sensitive polarity sensitivity, excellent chemical stability and photo-stability. In addition, by comparing normal and cancer cells through cell imaging experiments, we found that the robust probe has the ability to sensitively monitor the changes in lipid droplet polarity in the living cells. More importantly, using the constructed fluorescent probe, we have achieved an in vitro fluorescence detection of liver injury and fatty liver, and the detection of hepatitis at the in vivo level. The unique fluorescent probe SSR-LDs is expected to serve as a powerful tool for the medical diagnosis of diseases related to lipid droplet polarity.

Bioinspired large Stokes shift small molecular dyes for biomedical fluorescence imaging

Long Stokes shift dyes that minimize cross-talk between the excitation source and fluorescent emission to improve the signal-to-background ratio are highly desired for fluorescence imaging. However, simple small molecular dyes with large Stokes shift (more than 120 nanometers) and near-infrared (NIR) emissions have been rarely reported so far. Here, inspired by the chromophore chemical structure of fluorescent proteins, we designed and synthesized a series of styrene oxazolone dyes (SODs) with simple synthetic methods, which show NIR emissions (>650 nanometers) with long Stokes shift (ranged from 136 to 198 nanometers) and small molecular weight (<450 daltons). The most promising SOD9 shows rapid renal excretion and blood-brain barrier passing properties. After functioning with the mitochondrial-targeted triphenylphosphonium (TPP) group, the resulting SOD9-TPP can be engineered for head-neck tumor imaging, fluorescence image-guided surgery, brain neuroimaging, and on-site pathologic analysis. In summary, our findings add an essential small molecular dye category to the classical dyes.

Assessment of mitochondrial dysfunction and implications in cardiovascular disorders

Mitochondria play a pivotal role in cellular function, not only acting as the powerhouse of the cell, but also regulating ATP synthesis, reactive oxygen species (ROS) production, intracellular Ca²⁺ cycling, and apoptosis. During the past decade, extensive progress has been made in the technology to assess mitochondrial functions and accumulating evidences have shown that mitochondrial dysfunction is a key pathophysiological mechanism for many diseases including cardiovascular disorders, such as ischemic heart disease, cardiomyopathy, hypertension, atherosclerosis, and hemorrhagic shock. The advances in methodology have been accelerating our understanding of mitochondrial molecular structure and function, biogenesis and ROS and energy production, which facilitates new drug target identification and therapeutic strategy development for mitochondrial dysfunction-related disorders. This review will focus on the assessment of methodologies currently used for mitochondrial research and discuss their advantages, limitations and the implications of mitochondrial dysfunction in cardiovascular disorders.

Natural flavylium-inspired far-red to NIR-II dyes and their applications as fluorescent probes for biomedical sensing

Fluorescent probes that emit in the far-red (600-700 nm), first near-infrared (NIR-I, 700-900 nm), and second NIR (NIR-II, 900-1700 nm) regions possess unique advantages, including low photodamage and deep penetration into biological samples. Notably, NIR-II optical imaging can achieve tissue penetration as deep as 5-20 mm, which is critical for biomedical sensing and clinical applications. Much research has focused on developing far-red to NIR-II dyes to meet the needs of modern biomedicine. Flavylium compounds are natural colorants found in many flowers and fruits. Flavylium-inspired dyes are ideal platforms for constructing fluorescent probes because of their far-red to NIR emissions, high quantum yields, high molar extinction coefficients, and good water solubilities. The synthetic and structural diversities of flavylium dyes also enable NIR-II probe development, which markedly advance the field of NIR-II in vivo imaging. In the last decade, there have been huge developments in flavylium-inspired dyes and their applications as far-red to NIR fluorescent probes for biomedical applications. In this review, we highlight the optical properties of representative flavylium dyes, design strategies, sensing mechanisms, and applications as fluorescent probes for detecting and visualizing important biomedical species and events. This review will prompt further research not only on flavylium dyes, but also into all far-red to NIR fluorophores and fluorescent probes. Moreover, this interest will hopefully spillover into applications related to complex biological systems and clinical treatments, ranging in focus from the sub-organelle to whole-animal levels.

A novel long excitation/emission wavelength fluorophore as platform utilized to construct NIR probes for bioimaging and biosensing

Near-infrared (NIR) fluorophores, especially dicyano-based fluorophores and xanthene-based hemicyanines, have beenput high expectation in bioimaging application due to their excellent optical properties. However, they suffer from inherentshortagessuch as short excitation/emission wavelength (less than 700 nm) or small Stokes shift (20-50 nm). Herein, we constructed a novel NIR dicyano-based fluorophore (DCO-HBTN). Toourknowledge, it is the first reported dicyano-based fluorophore of which the excitation/emission wavelength is more than 650 nm and Stokes shift is more than 100 nm. To demonstrate the feasibility of our efforts, we developed two NIR fluorescent probes (Probe-Cys and Probe-H₂S) based on the fluorophore, Probe-Cys displayed good selective and highly sensitive (LOD = 0.28 μM) recognition of Cys over Hcy and GSH, which was used to visualize endogenous Cys in tumor tissue. Probe-H₂S exhibited an. excellent specific and sensitive (LOD = 0.11 μM) response to H₂S, which was applied in monitoring H₂S releasing from the prodrug in vitro and in vivo.

Activatable molecular rotor based on bithiophene quinolinium toward viscosity detection in liquids

The development of non-invasive and effective viscosity inspection methods during the liquid deterioration process is urgently needed since viscosity is one of the most important physical parameters of liquids. Methods featuring rapid detection, high sensitivity, cheap equipment, and fast result output are greatly desired. In this study, a viscosity-sensitive molecular rotor (BTPEQ) with a large Stokes shift (187 nm), and long emission wavelength (648 nm) has been developed. The rotor is comprised of a bithiophene donor and quinolinium acceptor, and displays a typical twisted intramolecular-charge transfer (TICT) feature, with good photostability, selectivity, and universality in various commercial liquids. With the aid of BTPEQ, the thickening effects of liquid thickeners can be determined. More importantly, BTPEQ was explored to visualize the viscosity variations in liquids at different metamorphic stages, and it was found that the viscosity level in microenvironments is highly dependent on the liquid food metamorphic period. It is worth noting that this approach can facilitate the continued perfection of fluorescent analytical methods for food quality and safety inspection.

Encoding, transmission, decoding, and specificity of calcium signals in plants

Calcium acts as a signal and transmits information in all eukaryotes. Encoding machinery consisting of calcium channels, stores, buffers, and pumps can generate a variety of calcium transients in response to external stimuli, thus shaping the calcium signature. Mechanisms for the transmission of calcium signals have been described, and a large repertoire of calcium binding proteins exist that can decode calcium signatures into specific responses. Whilst straightforward as a concept, mysteries remain as to exactly how such information processing is biochemically implemented. Novel developments in imaging technology and genetically encoded sensors (such as calcium indicators), in particular for multi-signal detection, are delivering exciting new insights into intra- and intercellular calcium signaling. Here, we review recent advances in characterizing the encoding, transmission, and decoding mechanisms, with a focus on long-distance calcium signaling. We present technological advances and computational frameworks for studying the specificity of calcium signaling, highlight current gaps in our understanding and propose techniques and approaches for unravelling the underlying mechanisms.

A Facile, Protein-Derived Supramolecular Theranostic Strategy for Multimodal-Imaging-Guided Photodynamic and Photothermal Immunotherapy In Vivo

Theranostic systems that permit both diagnosis and treatment in vivo are highly appealing means by which to meet the demands of precision medicine. However, most such systems remain subject to issues related to complex molecular design and synthesis, potential toxicity, and possible photoactivity changes. Herein, a novel supramolecular theranostic strategy involving biomarker protein activation (BPA) and a host-guest strategy is proposed. To exemplify BPA, a facile "one-for-all" nanotheranostic agent for both albumin detection and cancer treatment is demonstrated, which utilizes a nanoparticulate heavy-atom-free BODIPY dye derivative (B4 NPs). The fluorescence and photoactivity of BODIPY dyes are completely suppressed by aggregation-induced self-quenching in the nanoparticulate state. However, a Balb/c nude mouse model is used to confirm that following the disassembly of injected B4 NPs, BODIPY specifically binds albumin in vivo, accompanied by significantly enhanced biocompatibility and photothermal conversion efficiency. More importantly, this supramolecular host-guest BPA strategy enables the resultant nanoplatform to act as a facile and efficient strategy for photodynamic and photothermal immunotherapy.

Synthesis of sialic acid conjugates of the clinical near-infrared dye as next-generation theranostics for cancer phototherapy

Cancer is a multifaceted global health problem that requires continuous action to develop next-generation cancer theranostics. Inspired by the emerging use of indocyanine green (ICG), the only clinically approved near-infrared (NIR) dye for cancer phototherapy, here we synthesized two ICG conjugate theranostics by coupling ICG to sialic acid (Sia) through the C2 and C9 positions of Sia, respectively, referred to as Sia-C2-ICG and Sia-C9-ICG. Encouragingly, Sia-C2/C9-ICGs show superior in vitro properties, including enhanced stability, reduced non-specific binding to serum proteins, and improved blood compatibility, highlighting the benefits of Sia coupling. Notably, in vivo NIR imaging shows that Sia-C9-ICG significantly promotes tumor targeting and effectively prolongs the circulation time in the body, while Sia-C2-ICG is superior to ICG but inferior to Sia-C9-ICG in targeting tumors. Furthermore, Sia-C9-ICG combined with NIR laser irradiation can lead to excellent photothermal and photodynamic therapies for cancer cells, resulting in superior solid tumor ablation. To our knowledge, this is the first report of Sia-NIR conjugates achieving significant tumor reduction in vivo. Together, these advances render Sia-C9-ICG an attractive lead as next-generation cancer theranostics that can be translated clinically to treat human patients.

Revealing the Phase Separation in ER Membranes of Living Cells and Tissues by In Situ NIR Ratiometric Imaging

Biomembranes in the endoplasmic reticulum (ER) play indispensable roles in various bioactivities, and therefore, visualizing the phase separation in ER membranes is crucial for the studies on the fundamental biology of the ER. However, near-infrared (NIR) ratiometric imaging of the phase behaviors of the ER in living cells with different statuses and in diverse tissues has not been investigated. Herein, we developed a polarity-responsive NIR fluorescent probe (DCA) for the visualization of the phase behavior in ER membranes. The probe displayed a large Stokes shift and was highly sensitive to polarity. By direct and native fluorescence imaging at room temperature, the ER_o and ER_d biomembranes in the ER could be clearly distinguished by dual NIR emission colors. Oxidative damage by H₂O₂ and homocystein (Hcy)-induced ER stress can efficiently induce the formation of large-scale ER_o domains in ER membranes. Moreover, we have also revealed that different tissues exhibited diverse phase behaviors in the ER membranes. The ER membranes in cardiac and skeletal muscle tissues showed no evident phase separation, while large-scale ER_o domains existed in the ER of liver tissues and formed at the ER membranes adjacent to lipid droplets (LDs) in white adipose tissues. We expect that the probe could serve as a powerful molecular tool to promote fundamental research studies on ER membranes and relative biomedical areas.

Synthesis and Properties of V-Shaped Xanthene Dyes with Tunable and Predictable Absorption and Emission Wavelengths

V-shaped xanthene dyes capable of predicting absorption and emission wavelengths are described. These dyes were synthesized by bridging a xanthene ring and an aryl moiety of fluorescein through ether covalent bonds. These dyes showed longer absorption and emission wavelengths than those of the parent fluorescein. Furthermore, substituents introduced on the aryl moiety mainly affected the lowest unoccupied molecular orbital energy level of the molecule. Therefore, the Hammett substituent constants could be used to predict the absorption and emission wavelengths of the compound.

Yb/Er/Ho-engineered rare earth fluoride nanoparticles to unlock multimodal in vivo medical imaging

Fluorescence imaging with advanced multi-channel observation, high sensitivity, and high spatio-temporal resolution holds great promise for biomedical applications. However, the different absorption and scattering spectra of complex tissue structures present...

A mitochondria-targeted fluorescent probe for real-time imaging SO2/H2O2

Studies have shown that changes in the redox state of cells might be closely related to pathological and physiological processes. Sulfur dioxide and hydrogen peroxide, as a significant redox couple in living cells, are endogenously produced by cells. Here, we report a long-wavelength fluorescent probe to reversibly monitor sulfur dioxide and hydrogen peroxide. This probe (NBD) displayed high selectivity and sensitivity, which could be accumulated in mitochondria for real-time imaging of SO₂/H₂O₂. These results indicated that NBD would be an ideal tool for monitoring the redox cycle state in living cells.

Natural and Synthetic Flavylium-Based Dyes: The Chemistry Behind the Color

Flavylium compounds are a well-known family of pigments because they are prevalent in the plant kingdom, contributing to colors over a wide range from shades of yellow-red to blue in fruits, flowers, leaves, and other plant parts. Flavylium compounds include a large variety of natural compound classes, namely, anthocyanins, 3-deoxyanthocyanidins, auronidins, and their respective aglycones as well as anthocyanin-derived pigments (e.g., pyranoanthocyanins, anthocyanin-flavan-3-ol dimers). During the past few decades, there has been increasing interest among chemists in synthesizing different flavylium compounds that mimic natural structures but with different substitution patterns that present a variety of spectroscopic characteristics in view of their applications in different industrial fields. This Review provides an overview of the chemistry of flavylium-based compounds, in particular, the synthetic and enzymatic approaches and mechanisms reported in the literature for obtaining different classes of pigments, their physical-chemical properties in relation to their pH-dependent equilibria network, and their chemical and enzymatic degradation. The development of flavylium-based systems is also described throughout this Review for emergent applications to explore some of the physical-chemical properties of the multistate of species generated by these compounds.

Coumarins to Cyanines: Synthesis of Hemicyanines

Near-infrared (NIR) emitting fluorophores are powerful tools for optical imaging. However, there are only a handful of broadly employed NIR-emitting scaffolds, and the synthetic methods to prepare these molecules are often problematic. Here, we describe a novel, three-step synthesis of chromene-containing hemicyanine probes exhibiting large Stokes shifts and NIR emissions. We develop a pH-activatable probe for visualizing lysosomal trafficking of mAb conjugates. These studies provide a concise approach to hemicyanines with promising properties.

Amino-functionalized Cu metal-organic framework nanosheets as fluorescent probes for detecting TNP

Here, we report a simple and benign method to successfully fabricate amino-functionalized Cu metal-organic framework (NH₂-Cu-MOF) nanosheets. After synthesizing Cu₂O nanocubes, they were mixed with organic ligand 2-aminoterephthalic acid (NH₂BDC) solution at room temperature for 4 hours to form NH₂-Cu-MOF nanosheets. Interestingly, the prepared NH₂-Cu-MOF nanosheets have ultra-thin thickness, directional growth characteristics and excellent crystallinity. Moreover, such nanosheets showed high-intensity and high-stability fluorescence emission under excitation. As TNP in water can quench the fluorescence emission of the fluorescent probe, the NH₂-Cu-MOF nanosheet fluorescent probe was established for detecting TNP in water with high sensitivity and selectivity, which is very useful for assessing the environmental quality and safety of water bodies. Finally, the probe was used to detect TNP in actual samples with good recovery rate.