Near-Infrared Fluorescent Probe with High Quantum Yield and Its Application in the Selective Detection of Glutathione in Living Cells and Tissues

Near-infrared fluorescent probe for the imaging of viscosity in fatty liver mice and valuation of drug efficacy

Fatty liver disease affects at least 25 percent of the population worldwide and is a severe metabolic syndrome. Viscosity is closely related to fatty liver disease, so it is urgent to develop an effective tool for monitoring viscosity. Herein, a NIR fluorescent probe called MBC-V is developed for imaging viscosity, consisting of dimethylaniline and malonitrile-benzopyran. MBC-V is non-fluorescent in low viscosity solutions due to intramolecular rotation. In high viscosity solution, the intramolecular rotation of MBC-V is suppressed and the fluorescence is triggered. MBC-V has long emission wavelength at 720 nm and large Stokes shift about 160 nm. Moreover, MBC-V can detect changes in cell viscosity in fatty liver cells, and can image the therapeutic effects of drug in fatty liver cells. By taking advantage of NIR emission, MBC-V can be used as an imaging tool for fatty liver disease and a way to evaluate the therapeutic effect of drug for fatty liver disease.

Recent progress and outlooks in rhodamine-based fluorescent probes for detection and imaging of reactive oxygen, nitrogen, and sulfur species

Reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulfur species (RSS) serve as vital mediators essential for preserving intracellular redox homeostasis within the human body, thereby possessing significant implications across physiological and pathological domains. Nevertheless, deviations from normal levels of ROS, RNS, and RSS disturb redox homeostasis, leading to detrimental consequences that compromise bodily integrity. This disruption is closely linked to the onset of various human diseases, thereby posing a substantial threat to human health and survival. Small-molecule fluorescent probes exhibit considerable potential as analytical instruments for the monitoring of ROS, RNS, and RSS due to their exceptional sensitivity and selectivity, operational simplicity, non-invasiveness, localization capabilities, and ability to facilitate in situ optical signal generation for real-time dynamic analyte monitoring. Due to their distinctive transition from their spirocyclic form (non-fluorescent) to their ring-opened form (fluorescent), along with their exceptional light stability, broad wavelength range, high fluorescence quantum yield, and high extinction coefficient, rhodamine fluorophores have been extensively employed in the development of fluorescent probes. This review primarily concentrates on the investigation of fluorescent probes utilizing rhodamine dyes for ROS, RNS, and RSS detection from the perspective of different response groups since 2016. The scope of this review encompasses the design of probe structures, elucidation of response mechanisms, and exploration of biological applications.

D-π-A-π-D-Configured Imidazole-Tethered Benzothiadiazole-Based Sensor for the Ratiometric Discrimination of Picric Acid: Applications in Latent Fingerprint Imaging

A tetraphenyl imidazole-appended benzothiadiazole-based fluorogenic probe (4,7-bis(4-(1,4,5-triphenyl-1H-imidazol-2-yl)phenyl)benzo[c][1,2,5]thiadiazole (BIPT)) has been successfully synthesized and characterized by NMR and high-resolution mass spectrometry (HRMS) spectral analyses. A low limit of detection (LOD) can be achieved to detect picric acid (PA; 7.89 nM). When benzothiadiazole acceptors are incorporated in the D-A-D probe, it can produce a large Stokes shift (206 nm) as a result. Fascinatingly, the fluorescence signals of BIPT were ratiometrically induced by the interaction with PA and exhibited an apparent emission shift from pink to green. The detection process of BIPT is triggered by an intermolecular charge transfer process, as the charge transfer takes place from the electron-rich imidazole to the electron-deficient PA. Moreover, fluorescence detection of PA has been employed in paper strips. Advantageously, sensor BIPT can potentially be applied to contact mode and real-time detection of PA in environmental water samples. Additionally, the BIPT sensor has been successfully employed for latent fingerprint imaging. The study provides clear insights into the rational design of chemosensors for sensing and real-time applications.

Sequence-Defined Tertiary Amine-Based Oligomer Employing a Scalable, Support-Free, and Protection/Deprotection-Free Iterative Strategy

Sequence-defined oligomers (SDOs) with their unique monomeric sequence and customizable nature are attracting the attention of researchers globally. The structural and functional diversity attainable in SDOs makes this platform promising, albeit with challenges in the synthesis. Herein, we report the design and synthesis of a novel class of SDO by incorporating tertiary amines into the backbone from commercially available inexpensive materials. Tertiary amines were selected due to their various material and biomedical applications. Even though the synthesis and purification of amine compounds are challenging, their various significant applications, such as pharmaceuticals, catalysts, surfactants, corrosion inhibitors, dye intermediates, polymer additives, rubber accelerators, gas treating agents, agriculture, and analytical chemistry, make them fascinating. The synthetic strategy that is designed here is extremely efficient and economical for the scalable synthesis of the SDO and is support-free, protection-deprotection chemistry-free, and catalyst/template-free. Most importantly, no extra design and synthesis of the monomer is required here. The key reactions employed for the SDO synthesis are (i) transformation of the hydroxy group to a halide and (ii) substitution of the halide by the secondary amine units. Including the purifying processes, the multigram synthesis of 4-mer was completed in 12-14 h. The synthetic strategy was established by synthesizing two different sequences of SDOs. The SDOs are characterized by 1H NMR and LC-MS. The tandem MS (MS/MS) experiment was conducted in order to validate the sequences over the SDO chain. Furthermore, the SDO platform was advanced in two ways: (i) by increasing the chain length via attaching a linker, which provides a rapid method for increasing the tertiary amine over the SDO chain, and (ii) postsynthetic modification of SDO with other functional groups, including guanidine for biological importance and a well-known fluorophore dansyl group for material significance.

A novel sensitive fluorescent probe with double channels for highly effective recognition of biothiols

Biothiols play a crucial role in maintaining redox balance in organisms, and anomalous levels of biothiols in human organs can lead to various sicknesses and biological disorders. This work developed a novel sensitive fluorescent probe TZ-NBD with double channels for highly efficient recognition of biothiols. TZ-NBD adopts 4-Chloro-7-nitrobenzofurazan (NBD-Cl) as the recognition moiety with simultaneous fluorescence output. By incorporating NBD-Cl with the other fluorophore, benzothiazole dihydrocyclopentachromene derivative (TZ-OH), the dual-channel sensitive fluorescence probe TZ-NBD was built. The existence of Cys/ Hcy could significantly trigger both the green and red fluorescent emissions, which were derived from fluorophores amine-substituted NBD and TZ-OH, respectively. While exposing to GSH, only the red-channel fluorescence signal could be detected, indicating the release of TZ-OH. The phenomena was mainly attributed to the fact that sulfur-substituted NBD has nearly no fluorescence, while amine-substituted NBD shows obvious green fluorescence. In our study, TZ-NBD exhibited dual-channel sensitivity, fast response, and excellent selectivity to biothiols in vitro. Moreover, TZ-NBD was favorably utilized for recognition of biothiols in vivo. We believe that the sensitive fluorescence probe with double channels can afford an alternate approach for monitoring biothiols in organisms and would be useful for studying diseases associated with biothiols.

Carbon Monoxide: A Second Biomarker to Couple with Viscosity for the Construction of "Dual-Locked" Near-Infrared Fluorescent Probes for Accurately Diagnosing Non-Alcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) can progress to cirrhosis and liver cancer if left untreated. Therefore, it is of great importance to develop useful tools for the noninvasive and accurate diagnosis of NAFLD. Increased microenvironmental viscosity was considered as a biomarker of NAFLD, but the occurrence of increased viscosity in other liver diseases highly reduces the diagnosis accuracy of NAFLD by a single detection of viscosity. Hence, it is very necessary to seek a second biomarker of NAFLD. It has been innovatively proposed that the overexpressed heme oxygenase-1 enzyme in NAFLD would produce abnormally high concentrations of CO in hepatocytes and that CO could serve as a potential biomarker. In this work, we screened nine lactam Changsha dyes (HCO-1-HCO-9) with delicate structures to obtain near-infrared (NIR), metal-free, and "dual-locked" fluorescent probes for the simultaneous detection of CO and viscosity. Changsha dyes with a 2-pyridinyl hydrazone substituent could sense CO, and the 5-position substituents on the 2-pyridinyl moiety had a great electron effect on the reaction rate. The double bond in these dyes served as the sensing group for viscosity. Probe HCO-9 was utilized for precise diagnosis of NAFLD by simultaneous detection of CO and viscosity. Upon reacting with CO in a high-viscosity microenvironment, strong fluorescence at 745 nm of probe HCO-9 was turned on with NIR excitation at 700 nm. Probe HCO-9 was proven to be an effective tool for imaging CO and viscosity. Due to the advantages of NIR absorption and low toxicity, probe HCO-9 was successfully applied to image NAFLD in a mouse model.

A simple indanone-based red emission fluorescent probe for the rapid detection of cysteine in vitro and in vivo

Cysteine is a vital biothiols that plays an important role in numerous physiological and pathological processes. The development of simple molecule tools for detection and analysis Cys in subcellar environment is significant for further exploring their pathophysiological. In this work, a simple but activated fluorescent probe AMIA was constructed with a donor-π-accepter (D- π -A) structure, which using an indanone as the electron-withdrawing unit acting as the fluorophore, dimethylamino group attached to the position 4 of the benzene ring as the electron-donating, two double bonds as the linker group, and the acryloyl ester group as the trigger and response unit. This probe AMIA was exhibited highly selective and sensitive response to Cys over other amino acids and ions under physiological conditions. It was found that AMIA showed a red turn-on fluorescence response at 630 nm towards Cys with a large stroke shift of 170 nm and a very low detection limit of 26.3 nM. HRMS, 1H NMR and TD-DFT calculation further confirmed that the response mechanism is the Cys triggered the addition-cyclization reaction between AMIA' acryloyl group and Cys' sulfhydryl and amino unit, leading to the release of a red fluorescent dye AMIA-OH, which can be identified by naked eyes. Furthermore, AMIA was successfully applied for simultaneous determination of Cys in living cells and zebrafish with lower cytotoxicity and good cell permeability. We hope that this novel indanone-based probe AMIA will provide a new reference for visualized Cys in other complex biological system.

Noninvasive Imaging of Tumor Glycolysis and Chemotherapeutic Resistance via De Novo Design of Molecular Afterglow Scaffold

Chemotherapeutic resistance poses a significant challenge in cancer treatment, resulting in the reduced efficacy of standard chemotherapeutic agents. Abnormal metabolism, particularly increased anaerobic glycolysis, has been identified as a major contributing factor to chemotherapeutic resistance. To address this issue, noninvasive imaging techniques capable of visualizing tumor glycolysis are crucial. However, the currently available methods (such as PET, MRI, and fluorescence) possess limitations in terms of sensitivity, safety, dynamic imaging capability, and autofluorescence. Here, we present the de novo design of a unique afterglow molecular scaffold based on hemicyanine and rhodamine dyes, which holds promise for low-background optical imaging. In contrast to previous designs, this scaffold exhibits responsive "OFF-ON" afterglow signals through spirocyclization, thus enabling simultaneous control of photodynamic effects and luminescence efficacy. This leads to a larger dynamic range, broader detection range, higher signal enhancement ratio, and higher sensitivity. Furthermore, the integration of multiple functionalities simplifies probe design, eliminates the need for spectral overlap, and enhances reliability. Moreover, we have expanded the applications of this afterglow molecular scaffold by developing various probes for different molecular targets. Notably, we developed a water-soluble pH-responsive afterglow nanoprobe for visualizing glycolysis in living mice. This nanoprobe monitors the effects of glycolytic inhibitors or oxidative phosphorylation inhibitors on tumor glycolysis, providing a valuable tool for evaluating the tumor cell sensitivity to these inhibitors. Therefore, the new afterglow molecular scaffold presents a promising approach for understanding tumor metabolism, monitoring chemotherapeutic resistance, and guiding precision medicine in the future.

Targeted theranostics: Near-infrared triterpenoic acid-rhodamine conjugates as prerequisites for precise cancer diagnosis and therapy

Pentacyclic triterpenoic acids have shown excellent potential as starting materials for the synthesis of highly cytotoxic agents with significantly reduced toxicity for non-malignant cells. This study focuses on the development of triterpenoic acid-rhodamine conjugates with fluorescence shifted to the near-infrared (NIR) region for theranostic applications in cancer research. Spectral analysis revealed emission wavelengths around λ = 760 nm, enabling stronger signals and deeper tissue penetration. The conjugates were evaluated using SRB assays on tumor cell lines and non-malignant fibroblasts, demonstrating low nanomolar activity and high selectivity, similarly to their known rhodamine B counterparts. Additional staining experiments proved their mode of action as mitocans.

A novel colorimetric/fluorescent dual-signal probe based on silver nanoparticles functionalized with L-cysteine and rhodamine 6G derivatives for copper ion detection and cell imaging

The dual-signal probe utilizing functionalized silver nanoparticles (AgNPs) is a promising sensing tool. Herein, a novel colorimetric/fluorescent dual-signal probe (AgNPs-L-Cys-Rh6G2) was fabricated for copper ion (Cu2+) detection and cell imaging by using L-cysteine as a "bridge" to connect AgNPs and rhodamine 6G derivatives. The AgNPs-L-Cys-Rh6G2 probe exhibits a dual-signal response to Cu2+ due to Rh6G2 hydrolysis, resulting in a high fluorescence response and a significant change in color from light yellow to pink under sunlight. The linear detection ranges of the AgNPs-L-Cys-Rh6G2 probe for Cu2+ were 100-450 μM and 150-650 μM using fluorescent and colorimetry methods, respectively. The detection limits were as low as 0.169 μM and 1.36 μM, respectively. Meanwhile, the proposed probe was applied to detect Cu2+ in the actual sediment with satisfactory recovery and low relative standard deviation. Furthermore, the probe was further employed for fluorescence imaging in HeLa cells. In brief, the developed AgNPs-L-Cys-Rh6G2 sensing platform can be used for simultaneous Cu2+ determination and cell imaging.

Metal-free auxiliary pyrophosphate detection based on near-infrared carbon dots

The excessive use of pyrophosphate (PPi) anions as additives poses a serious threat to human health and the environment. Considering the current status of PPi probes, the development of metal-free auxiliary PPi probes has important applications. In this study, a novel near-infrared nitrogen and sulfur co-doped carbon dots (N,S-CDs) were prepared. The average particle size of N,S-CDs was 2.25 ± 0.32 nm with average height was 3.05 nm. The probe N,S-CDs showed a special response to PPi, and a good linear relationship was obtained with PPi concentrations ranging from 0 to 1 μM, with the limit of detection being 0.22 nM. Tap water and milk were used for practical inspection, and ideal experimental results were acquired. In addition, the probe N,S-CDs also showed good results in biological systems, such as cell and zebrafish experiments.

A methionine biomolecule-modified chromenylium-cyanine fluorescent probe for the analysis of Hg2+ in the environment and living cells

The objective of the study is, for the first time, to construct a new near infrared (NIR) fluorophore, spectrophotometric, colorimetric, ratiometric, and turn-on probe (CSME) based on chromenylium cyanine platform decorated with methionine biomolecule to provide an efficient solution for critical shortcoming to be encountered for analysis of hazardous Hg²⁺ in environment and living cell. The CSME structure and its interaction with Hg²⁺ ion were evaluated by NMR, FTIR, MS, UV-Vis and fluorescence methods as well as Density Functional Theory (DFT) calculations. The none fluorescence CSME having spirolactam ring only interacted with Hg²⁺ in aqueous solution including competing ions. This interaction caused the fluorescence CSME with opened spirolactam form which exhibited spectral and colorimetric changes in the NIR region. The probe based on UV-Vis and fluorescence techniques respond in 90 s, has wide linear ranges (for UV-Vis: 6.29 × 10^-8 - 1.86 × 10^-4 M; for fluorescence: 9.49 × 10^-9 - 1.13 × 10^-5 M), and has a lower Limit of Detection (LOD) value (for fluorescence: 4.93 × 10^-9 M, 0.99 ng/mL) than the value predicted by the US Environmental Protection Agency (EPA) organization. Hg²⁺ analysis was performed in drinking and tap water with low Relative Standard Deviation (RSD) values and high recovery. Smartphone and living cell applications were successfully performed for colorimetric sensing Hg²⁺ in real samples and 3T3 cells, respectively.

Colorimetric and near-infrared spectrophotometric monitoring of bisulfite using glyoxal modified chromenylium-cyanine chemosensor: Smartphone and paper strip applications for on-site food and beverages control

Detection of bisulfite (HSO₃^-) in food and beverages has vital importance because the excessive amount leads to ill effects on the human body. Colorimetric and fluorometric chromenylium-cyanine-based chemosensor CyR was synthesized and applied for high selective and sensitive analysis of HSO₃^- in red wine, rose wine and, granulated sugar with high recovery ranges and very fast response time without any interference from other competitive species. The limits of detection (LOD) for the UV-Vis and fluorescence titrations were found as 11.5 μM and 3.77 μM, respectively. The on-site and very rapid methods based on paper strips and smartphone which depend on the color changes from yellow to green have been successfully developed to analyze HSO₃^- concentration (10^-5-10^-1 M for paper strip and 163-1205 μM for smartphone). CyR and the bisulfite-adduct formed in the nucleophilic addition reaction with HSO₃^- were verified by FT-IR, ¹H NMR, and MALDI-TOF results as well as Single-Crystal X-Ray Crystallography for CyR.

An ESIPT-Based Fluorescent Probe for Aqueous Cu+ Detection through Strip, Nanofiber and Living Cells

Constructed on the benzothiazole-oxanthracene structure, a fluorescent probe RBg for Cu⁺ was designed under the ESIPT mechanism and synthesized by incorporating amide bonds as the connecting group and glyoxal as the identifying group. Optical properties revealed a good sensitivity and a good linear relationship of the probe RBg with Cu⁺ in the concentration range of [Cu⁺] = 0-5.0 μmol L^-1. Ion competition and fluorescence-pH/time stability experiments offered further possibilities for dynamic Cu⁺ detection in an aqueous environment. HRMS analysis revealed a possible 1:1 combination of RBg and Cu⁺. In addition, colorimetric Cu⁺ detection and lysosome-targeted properties of the probe RBg were analyzed through RBg-doped PVDF nanofiber/test strips and RBg-Mito/Lyso trackers that were co-stained in living HeLa cells, enabling the probe's future applications as real-time detection methods for dynamic Cu⁺ tracking in the lysosomes and Cu⁺ detection under diversified conditions.

A PET Fluorescent Probe for Dynamic Pd2+ Tracking with Imaging Applications in the Nanofiber and Living Cells

Constructed on the moiety of a lactam screw ring, a near-infrared fluorescent probe RCya for Pd²⁺ was designed under the PET mechanism and synthesized by incorporating 2,4-dihydroxybenzaldehyde as the recognition group. Dynamic detection of aqueous Pd²⁺ by the probe RCya could be accomplished through ion competition, linear response, fluorescence-pH/time stabilities, and other optical tests. Moreover, the high selectivity, low cytotoxicity, cell permeability, and lysosome accumulation properties of RCya enabled the imaging applications on solid-state RCya-PAN composite nanofibers and in living cells. The recognition mechanism of probe RCya toward Pd²⁺ was further studied through simulation calculation and MS analysis.

Development of carbazole-based fluorescent probe for highly sensitive application in fluoride ion detection

Fluorine is a necessary element for human, which is closely related to life activities, such as metabolism of teeth and bone tissue. A small amount of fluoride ions can promote the strengthen of our body. However, a large amount of fluoride ions will damage the human immune system to produce organ diseases. Sensitive and rapid detection of fluoride ions has attracted great interests for researchers. In this work, a reactive fluorescent probe SCP for detection of fluoride ions with high quantum yield was designed and synthesized based on the carbazole ring. Subsequently, the photophysical properties of the probe SCP were carefully studied. At last, SCP performed 62.8% quantum yield in physiological condition, excellent ability of quantitative analysis, well selectivity, and distinguishing features for HepG2 cell imaging.

Near-Infrared Probes for Biothiols (Cysteine, Homocysteine, and Glutathione): A Comprehensive Review

Biothiols (cysteine, homocysteine, and glutathione) are an important class of compounds with a free thiol group. These biothiols plays an important role in several metabolic processes in living bodies when present in optimum concentration. Researchers have developed several probes for the detection and quantification of biothiols that can absorb in UV, visible, and near-infrared (NIR) regions of the electromagnetic spectrum. Among them, NIR organic probes have attracted significant attention due to their application in in vivo and in vitro imaging. In this review, we have summarized probes for these biothiols, which could work in the NIR region, and discussed their sensing mechanism and potential applications. Along with focusing on the pros and cons of the reported probes we have classified them according to the fluorophore used and summarized their photophysical and sensing properties (emission, response time, limit of detection).

A biotin-guided near-infrared fluorescent probe for imaging hydrogen sulfide and differentiating cancer cells

Imaging cancer specific biomarkers with near-infrared (NIR) fluorescent probes can help inaccurate diagnosis. Hydrogen sulfide (H₂S) has been reported to be involved in many physiological and pathological processes and is considered as one of the key gasotransmitters during the development of cancer. To achieve specific H₂S detection in cancer cells, we reported a biotin-guided NIR fluorescent sensor P1 targeting a cancer cell surface biomarker, based on the H₂S-specific thiolysis of the NBD-amine-hemicyanine conjugate. The probe showed a fast turn-on signal at 754 nm upon H₂S activation and good selectivity towards H₂S over millimolar levels of other biothiols. We successfully employed P1 to image endogenous H₂S and demonstrated its tumor-targeting ability in live cells. P1 could differentiate multiple cancer cells with various levels of H₂S from normal cells, indicating its potential for cancer imaging.

Synergistic Modulation by Halogens and Pyridine Crossing the Blood-Brain Barrier for In Situ Visualization of Thiol Flux in the Epileptic Brain

Epilepsy is a nervous system disease, and seizures are closely related to oxidative stress. Thiols, as the main antioxidant in an organism, play a key role in regulating the redox balance and defending from oxidative stress. As a result of the complexity of the brain structure, there is still a lack of suitable in situ detection methods of thiols to reveal the relationship between epilepsy and thiol level fluctuations. Therefore, by combining picolinate as the new recognition site for thiols, parallel synthesis, and the fluorescence rapid screening method, DCI-Br-3 was developed as a rapid, highly sensitive, and selective probe to monitor thiols in vitro and in vivo. It is worth noting that DCI-Br-3 effectively crossed the blood-brain barrier (BBB) to reveal the negative relationship between the level of thiols and the occurrence of epilepsy and may further provide important information for the prevention and treatment of thiol-related neurological diseases.

Fully Reversible Ratiometric Nanosensors for Continuously Quantifying Mitochondrial Glutathione Concentration in Living Cells

Mitochondrial glutathione (mGSH) is both the cause of the oxidative damage and a mechanism for maintaining the redox homeostasis in mitochondria. To effectively measure mGSH dynamics in living cells, we have developed a new FRET-based nanosensor by immobilizing rhodamine B into dendritic mesoporous silica nanoparticles and installing GSH probes and mitochondria-targeting motifs onto the surface of nanoparticles. The result shows that these nanosensors show efficient FRET and a full reversibility and rapid response (<10 s) to GSH in the range of 0.5-20 mM, due to their unique nanostructure and well-overlapped spectra. The excellent photostability and low cytotoxicity make them an effective means for monitoring mGSH concentration in real time. When the mGSH nanosensors are used for quantitatively measuring mGSH variations under glucose deprivation stimulation in HeLa cells, they successfully prove themselves a useful tool for mitochondrial redox activity studies.

An activatable and tumor-targeting NIR fluorescent probe for imaging of histone deacetylase 6 in cancer cells and in vivo

An activatable and tumor-targeting near-infrared (NIR) fluorescent probe CyAc-RGD was synthesized for the imaging of histone deacetylase 6 (HDAC6). The probe exhibited higher sensitivity and specificity for HDAC6 detection in cancer cells. Moreover, CyAc-RGD demonstrated good tumor-targeting ability and realized HDAC6 imaging in vivo.

Near-infrared (NIR) fluorescence-emitting small organic molecules for cancer imaging and therapy

We discuss recent advances made in the development of NIR fluorescence-emitting small organic molecules for tumor imaging and therapy.

An activatable near-infrared hemicyanine-based probe for selective detection and imaging of Hg2+ in living cells and animals

A near-infrared hemicyanine-based probe (CyP) was designed for selective detection and imaging of Hg2+ in living cells and animals.

Activatable NIR-II Fluorescence Probe for Highly Sensitive and Selective Visualization of Glutathione In Vivo

Visualization of glutathione (GSH) enables us to understand GSH-related pathophysiological processes in living subjects. Currently, in vivo visualization methods of GSH are based on visible or first near-infrared (NIR-I) window fluorescence (FL) probes, which possess limitations due to their low tissue penetration depth and strong tissue autofluorescence. Herein, we developed a GSH-activatable second near-infrared (NIR-II) window FL probe (denoted as LET-7) for highly sensitive and selective visualization of GSH in vivo. LET-7, composed of an anionic polymethylcyanide skeleton linked with a FL quenching group of 3,5-bis(trifluoromethyl)benzenethiol, can be specifically activated by GSH, thus triggering a significant NIR-II FL emission enhancement with excellent photostability, which enables us to efficiently distinguish GSH from closely related low-molecular-weight biothiols. The limit of detection of LET-7 for GSH was determined to be as low as 85 nM. Most intriguingly, the in vivo studies demonstrated that LET-7 showed high sensitivity and good selectivity toward GSH. Therefore, our study provides a solution to design activatable NIR-II FL probes for in vivo imaging of GSH and other disease-related biomarkers.

Crystal structure of (4′E)-6′-(diethylamino)-2-[(E)-[(pyren-1-yl)methylidene]amino]-4′-{2-[(2E)-1,3,3-trimethyl-2,3-dihydro-1H-indol-2-ylidene]ethylidene}-1′,2,2′,3,3′,4′-hexahydrospiro[isoindole-1,9′-xanthene]-3-one, C54H48N4O2

C54H48N4O2, triclinic, P 1 ‾ $P\overline{1}$ (no. 2), a = 11.1883(5) Å, b = 13.5364(5) Å, c = 14.3412(5) Å, α = 105.885(3)°, β = 97.710(3)°, γ = 94.126(3)°, Z = 2, V = 2056.64(14) Å3, R gt (F) = 0.0685, wR ref (F 2) = 0.1606, T = 293(2) K.

Crystal structure of (4′E)-6′-(diethylamino)-2-[(E)-[(6-methylpyridin-2-yl)methylidene]amino]-4′-{2-[(2E)-1,3,3-trimethyl-2,3-dihydro-1H-indol-2-ylidene]ethylidene}-1′,2,2′,3,3′,4′-hexahydrospiro[isoindole-1,9′-xanthene]-3-one, C44H45N5O2

C44H45N5O2, triclinic P 1 ‾ $P\overline{1}$ (no. 2), a = 11.2140(4) Å, b = 11.9932(5) Å, c = 14.2703(5) Å, α = 98.879(3)°, β = 102.025(3)°, γ = 91.122(3)°, Z = 2, V = 1851.98(12) Å3, R gt (F) = 0.0549, wR ref(F 2) = 0.1616, T = 293(2) K.

Molecular-Dimension-Dependent ESIPT Break for Specific Reversible Response to GSH and Its Real-Time Bioimaging

Glutathione (GSH) plays many important roles in maintaining intracellular redox homeostasis, and determining its real-time levels in the biological system is essential for the diagnosis, treatment, and pathological research of related diseases. Fluorescence imaging has been regarded as a powerful tool for tracking biomarkers in vivo, for which specificity, reversibility, and fast response are the main issues to ensure the real-time effective detection of analytes. The determination of GSH is often interfered with by other active sulfur species. However, in addition to the common features of nucleophilic addition, GSH is unique in its large molecular scale. 2-(2-Hydroxyphenyl) benzothiazole (HBT) was often formed in the ESIPT process. In this study, HBT was installed with α,β-unsaturated ketone conjugated coumarin derivates or nitrobenzene, which were used to adjust the reactivity of α,β-unsaturated ketone. Experimental and theoretical calculations found ESIPT to be favorable in HBT-COU but not HBT-COU-NEt₂ or HBT-BEN-NO₂ due to the higher electronic energies in the keto form. Thus, for HBT-COU, in the presence of GSH, the hydrogen-bonding interaction between C═N of the HBT unit and carboxyl of GSH would inhibit the process, simultaneously promoting the Michel addition reaction between α,β-unsaturated ketone and GSH. As a consequence, probe HBT-COU could exhibit a rapid reversible ratiometric response to GSH. Small structures of Hcy and Cys are passivated for such reactions. Cell imaging demonstrated the specific response of the probe to GSH, and the probe was successfully used to monitor fluctuations in GSH concentration during cells apoptosis in real-time.

Hemicyanine-Based Near-Infrared Activatable Probes for Imaging and Diagnosis of Diseases

Molecular activatable probes with near-infrared (NIR) fluorescence play a critical role in in vivo imaging of biomarkers for drug screening and disease diagnosis. With structural diversity and high fluorescence quantum yields, hemicyanine dyes have emerged as a versatile scaffold for the construction of activatable optical probes. This Review presents a survey of hemicyanine-based NIR activatable probes (HNAPs) for in vivo imaging and early diagnosis of diseases. The molecular design principles of HNAPs towards activatable optical signaling against various biomarkers are discussed with a focus on their broad applications in the detection of diseases including inflammation, acute organ failure, skin diseases, intestinal diseases, and cancer. This progress not only proves the unique value of HNAPs in preclinical research but also highlights their high translational potential in clinical diagnosis.

A turn-on fluorescence strategy for cellular glutathione determination based on the aggregation-induced emission enhancement of self-assembled copper nanoclusters

As a class of ideal fluorescent nanomaterials, self-assembled copper nanoclusters (CuNCs) have attracted increasing interest. Unfortunately, most of these CuNCs only possessed bright luminescence in acidic solution, which limited their practical applications in a physiological environment. Retaining the strong fluorescence of these CuNCs in neutral or alkaline solution is still a challenging task. In this strategy, self-assembled CuNCs were prepared by using 4-methylthiophenol as the protecting ligand. The self-assembled CuNCs display stable and bright luminescence with excitation/emission maxima at 330/605 nm even in neutral and alkaline environments. Interestingly, with the addition of glutathione (GSH), the fluorescence intensity of CuNCs is enhanced strongly through the GSH-controlled aggregation-induced emission enhancement of self-assembled CuNCs. The turn-on fluorescence strategy can determine the GSH concentration in the range from 1 to 100 μM with a limit of detection of 300 nM. In addition, the method is employed for the determination of GSH levels in cells. Therefore, the turn-on fluorescence strategy is reliable, sensitive and suitable for the determination of cellular GSH levels.

Ultrasensitive and selective fluorescent sensor for cysteine and application to drug analysis and bioimaging

A fluorescent sensor based on coumarin-maleimide conjugate was developed for efficient discrimination of Cys from Hcy and GSH in both organic and aqueous solution. Addition of Cys to the non-fluorescent sensor solution in DMF induced bright blue fluorescence and enhanced the fluorescence intensity by 320-fold while other amino acids and biothiols (Gly, Hcy, GSH, Glu, Val, Tyr, Arg, Trp, Lys, His, Leu, Phe, Asp and Met) did not bring about remarked change. The sensor responds to Cys extremely rapidly. If Cys was added to the sensor solution, the fluorescence intensity increased by 170-fold immediately and attained the maximum value in 5 min. A linear relationship was observed between Cys concentration within 2-20 μM and the fluorescence intensity of the sensor solution. The detection limit of the sensor toward Cys is as low as 4.7 nM. The sensor is also effective for specific detection of Cys in aqueous (DMF/H₂O = 9:1, v/v) solution. Practical application of the sensor to drug analysis and bioimaging of living Hela cells has been verified. Possible sensing mechanism of the sensor toward Cys has been proposed.

An aniline trimer-based multifunctional sensor for colorimetric Fe3+, Cu2+ and Ag+ detection, and its complex for fluorescent sensing of L-tryptophan

The detection of metal ions and amino acids by the aniline oligomer-based receptor has not been reported yet, to the best of our knowledge. In this study, an efficient multifunctional cation-amino acid sensor (CAS) with aniline moiety and chiral thiourea binding site was synthesized by the reaction of aniline trimer and (S)-(+)-1-phenyl ethyl isothiocyanate. CAS can sense Fe³⁺, Cu²⁺, Ag⁺ ions, and L-tryptophan. These results can be recognized by the naked eye. The appropriate pH range for the quantitative analysis of Fe³⁺, Cu^2+, and Ag⁺ by CAS in DMSO/water (30 vol% water) was evaluated. The interaction between CCS and metal ions was analyzed by ¹H NMR titration. The detection limits of CAS for the Cu²⁺, Ag^+, and Fe³⁺ were 0.214, 0.099, and 0.147 μM, respectively. Moreover, the CASCu²⁺ complex can act as a turn-on fluorescence sensor for L-tryptophan. On the contrary, there is no response upon the addition of other amino acids, such as L-histidine, L-proline, L-phenylalanine, L-threonine, L-methionine, L-tyrosine, and L-cystine to CASCu²⁺ complex.

Dual modulation sites for a reversible fluorescent probe for GSH over Cys/Hcy

An abnormal concentration of glutathione (GSH) is a health-associated risk factor, and it is an important signal for diseases such as Parkinson's disease, liver injury and cancer.

A turn-on fluorescence strategy for biothiols determination by blocking Hg(II)-mediated fluorescence quenching of adenine-rich DNA-templated gold nanoclusters

Fluorescent adenine (A)-rich DNA-templated gold nanoclusters were demonstrated to be a novel probe for determination of biothiols (including cysteine, glutathione, and homocysteine). Fluorescence intensity of adenine-rich DNA-templated gold nanoclusters could be greatly quenched by Hg(II) ions through the formation of a gold nanoclusters-Hg(II) system. When biothiols (cysteine as the model) were introduced into the system, the fluorescence intensity recovered due to the formation of a more stable Hg(II)-thiol coordination complex using Hg-S metal-ligand bonds, which inhibited the Hg(II)-mediated fluorescence quenching of adenine-rich DNA-templated gold nanoclusters. Based on this fluorescence phenomenon, an on-off-on fluorescence strategy was designed for the sensitive determination of biothiols. The method allowed sensitive detection of cysteine with a linear detection range from 100 nM to 5 μM and a limit of detection of 30 nM. Additionally, the assay can be applied for detection of biothiol levels in human plasma samples. Therefore, it can provide a simple and rapid fluorescent platform for biothiol detection.

Efficient β-Carboline Alkaloid-Based Probe for Highly Sensitive Imaging of Endogenous Glutathione in Wheat Germ Tissues

Discriminative detection of GSH is achieved by employing a highly sensitive and selective fluorescent probe (KL-DN) that bears β-carboline alkaloid as a potential fluorophore and an azide group as the recognition unit. A rapid fluorescence off-on change is caused by special redox reaction; KL-DN has the capability of monitoring endogenous GSH in wheat germ tissues, indicating that this probe holds great potential for biological applications in plant tissues.

Activatable Nanocomposite Probe for Preoperative Location and Intraoperative Navigation for Orthotopic Hepatic Tumor Resection via MSOT and Aggregation-Induced Near-IR-I/II Fluorescence Imaging

The precise location of tumor and completeness of surgical resection are critical to successful tumor surgery; thus, the method capable of preoperatively locating a tumor site and intraoperatively determining tumor margins would be highly ideal. Herein, an activatable nanocomposite probe was developed for preoperatively locating orthotopic hepatic tumor via multispectral optoacoustic tomography imaging and for intraoperative navigation via near-IR-1 (NIR-I) and NIR-II fluorescence imaging. The molecular probe comprises an electronic donor, an acceptor, and a recognition moiety and forms the nanocomposite probe with bovine serum albumin. The probe specifically responds to nitroreductase overexpressed in tumor cells, which transforms the aromatic nitro group into an electron-donating amino group and thus activates the probe. The activated probe with the aggregation-induced emission feature generates strong NIR-I/NIR-II fluorescence and optoacoustic signals for dual-mode imaging. Owing to the in situ response toward nitroreductase in tumor cells in the hepatic region, the probe is found capable of detecting early stage orthotopic liver tumors. Furthermore, with the nanocomposite probe, we can obtain the 3D MSOT images to accurately locate orthotopic liver tumors preoperatively and the NIR-I/NIR-II fluorescence images to provide intraoperative guidance for tumor resection surgery.

Development of a fast-responsive and turn on fluorescent probe with large Stokes shift for specific detection of cysteine in vivo

Cysteine has a great effect on the physiological and pathological processes, which could bring out various diseases such as skin lesions, edema, hair depigmentation, Alzheimer's, Parkinson's, and liver damage due to the abnormal concentrations of cysteine. Therefore, it is of great impoatance to develop a method for imaging Cys. Herein, a novel fluorescent probe was developed for imaging Cys in vivo specially. This turn-on probe exhibited favorable advantages including large Stokes shift (90 nm), fast response (10 min), good selectivity, low cytotoxicity and so on. Furthermore, the probe could be applied to monitoring cysteine in living HeLa cells, which indicates that this turn-on probe could penetrate viable cell membranes and image Cys over other analystes especially HCy and GSH.

Quinolone-based fluorescent probes for distinguished detection of Cys and GSH through different fluorescence channels

Dual-channel discrimination of Cys and GSH using a red fluorescent probe.

Simultaneous imaging of mitochondrial viscosity and hydrogen peroxide in Alzheimer's disease by a single near-infrared fluorescent probe with a large Stokes shift

Simultaneous imaging of mitochondrial viscosity and hydrogen peroxide in Alzheimer's disease by a single near-infrared fluorescent probe with a large Stokes shift.

A near-infrared biothiol-specific fluorescent probe for cancer cell recognition

Cancer is a global health issue and a leading cause of death. The discrimination of cancer cells from normal cells is of significant importance for the early diagnosis of cancers. As one of the useful biomarkers for developing cancer diagnosis and chemotherapy resistance systems, biothiols not only play an essential role in physiological and pathological processes but also exhibit cytoprotective effects in the susceptibility to carcinogenesis. It would be highly desirable to explore near-infrared biothiol-specific fluorescent probes for cancer diagnosis with outstanding specificity. In this study, a novel near-infrared fluorescent probe BPO-THAZ decorated with thiazole as a recognition site was presented for sensitive and selective detection of endogenous biothiols. BPO-THAZ can be used to not only evaluate the biothiol level in living HeLa cells upon treatment with H2O2 or anti-cancer drugs but also assess endogenous biothiols in stem cells. Furthermore, BPO-THAZ was successfully utilized to discriminate cancer cells from normal cells showing great promise for cancer diagnosis.

A redox-responsive hyaluronic acid-based hydrogel for chronic wound management

Polymer-based hydrogels have been widely applied for chronic wound therapeutics, due to their well-acclaimed wound exudate management capability. At the same time, there is still an unmet clinical need for simple wound diagnostic tools to assist clinical decision-making at the point of care and deliver on the vision of patient-personalised wound management. To explore this challenge, we present a one-step synthetic strategy to realise a redox-responsive, hyaluronic acid (HA)-based hydrogel that is sensitive to wound environment-related variations in glutathione (GSH) concentration. By selecting aminoethyl disulfide (AED) as a GSH-sensitive crosslinker and considering GSH concentration variations in active and non-self-healing wounds, we investigated the impact of GSH-induced AED cleavage on hydrogel dimensions, aiming to build GSH-size relationships for potential point-of-care wound diagnosis. The hydrogel was also found to be non-cytotoxic and aided L929 fibroblast growth and proliferation over seven days in vitro. Such a material offers a very low-cost tool for the visual detection of a target analyte that varies dependent on the status of the cells and tissues (wound detection), and may be further exploited as an implant for fibroblast growth and tissue regeneration (wound repair).

Fluorescence quantum yield of natural dye extracted from Tradescantia pallida purpurea as a function of the seasons: Preliminary bioapplication as a fungicide probe for necrotrophic fungi

In this work, over the course of four seasons (12 months), we have monitored the fluorescence quantum efficiency (η) from two sets (S1 and S2) of fresh natural dye extracts from the leaves of Tradescantia pallida purpurea. The natural dye was extracted in aqueous solutions from leaves collected from regions with a predominance of shade (S1) and sun (S2) during the day. The thermo-optical parameter fractional thermal load (φ) was measured using conical diffraction (CD) patterns caused by thermally driven self-phase modulation, for η determination in both sets of solutions. Fluorescence measurements corroborate the CD results, and the η values are, on average, slightly higher (~ 11%) in the summer than in the other seasons for both sets of samples (S1 and S2). In addition, the experimental results are presented using natural dye extracted from Tradescantia pallida purpurea as a fungicide probe in Fusarium solani, Sclerotinia sclerotiorum, and Colletotrichum gloeosporioides fungi. The promising fungicide results obtained for the aqueous natural dye extract were compared with those obtained for other natural dyes and fungi. The fungi tested are of the necrotrophic group and constitute important pathosystems in Brazil, causing diseases in several crops that synthetic fungicides often cannot control or do so with low efficiency.