A highly selective and sensitive ON–OFF–ON fluorescence chemosensor for cysteine detection in endoplasmic reticulum

The first ER-targeting flavone-based fluorescent probe for Cys: Applications in real-time tracking in an epilepsy model and food analysis

Epilepsy is one of the most commonly-seen neurological disorders, and both endoplasmic reticulum stress (ERS) and oxidative stress (OS) have been demonstrated to be associated with epileptic seizures. As one of the three endogenous thiol-containing amino acids, cysteine (Cys) is recognized not only as an important biomarker of various biological processes but also widely used as a significant additive in the food industry. However, the exact role that Cys plays in ERS has not been well answered up to now. In this paper, we reported the first flavone-based fluorescent probe (namely BFC) with nice endoplasmic reticulum (ER)-targeting ability, which was capable of monitoring Cys in a fast response (3.0 min), large stokes shift (130 nm) and low detection limit (10.4 nM). The recognition mechanism of Cys could be attributed to the addition-cyclization reaction involving a Cys residue and an acrylate group, resulting in the release of the strong excited-state intramolecular proton transfer (ESIPT) emission molecule of benzoflavonol (BF). The low cytotoxicity and good biocompatibility of the probe BFC allowed for monitoring the fluctuation of endogenous Cys levels under both ERS and OS processes, as well as in zebrafish models of epilepsy. Quantitative determination of Cys with the probe BFC was also achieved in three different food samples. Additionally, a probe-immersed test strips integrated with a smartphone device was successfully constructed for on-site colorimetric detection of Cys. Undoubtedly, our work provided a valuable tool for tracking Cys levels in both an epilepsy model and real food samples.

2-hydroxy-1- Naphthaldehyde Based Colorimetric Probe for the Simultaneous Detection of Bivalent Copper and Nickel with High Sensitivity and Selectivity

A neoteric colorimetric probe based on 2-hydroxy-1-naphthaldehyde (PMB3) was designed and synthesized for the real-time as well as on-site naked-eye detection of Cu2+/Ni2+ ions. Various physicochemical methods were employed to characterize the probe, and its colorimetric response to different metal ions was meticulously investigated. The probe, PMB3, exhibited a sensitive colorimetric response to Cu2+/Ni2+ ions among other competing metal ions, culminating in a prominent colour change from colourless to yellow. The stoichiometry of the ligand metal complexes was ascertained to be in a 1:1 ratio using Job's plot analysis, which was further corroborated by ESI-MS data. With detection limits of 4.56 µM for Cu2+ and 2.68 µM for Ni2+, the method was effectively extended to real sample analysis, ensuring propitious results that closely aligned with the actual values.

High-pressure study of a 3d-4f heterometallic CuEu-organic skeleton

We prepared a 3d-4f heterobimetallic CuEu-organic framework NBU-8 with a density of 1921 kg m-3 belonging to the family of dense packing materials (dense metal-organic frameworks or MOFs). This MOF material was prepared from 4-(pyrimidin-5-yl)benzoic acid (HPBA) with a bifunctional ligand site as a tripodal ligand and Cu2+ and Eu3+ as the metal centres; the molecular formula is Cu3Eu2(PBA)6(NO3)6·H2O. This material is a very promising dimethylformamide (DMF) molecular chemical sensor. Systematic high-pressure studies of NBU-8 were carried out by powder X-ray diffraction, high-pressure X-ray diffraction and molecular dynamics simulation. The high-pressure experiment shows that the (006) diffraction peak of the crystal structure moves toward a low angle with increasing pressure, accompanied by the phenomenon that the d-spacing increases, and as the pressure increases, the (10-2) diffraction peak moves to a higher angle, the amplitude of the d-spacing is significantly reduced and finally merges with the (006) diffraction peak into one peak. The amplitude of the d-spacing is significantly reduced, indicating that NBU-8 compresses and deforms along the a-axis direction when subjected to uniform pressure. This is caused by tilting of the ligands to become more vertical along the c direction, leading to its expansion. This allows greater contraction along the a direction. We also carried out a Rietveld structure refinement and a Birch-Murnaghan solid-state equation fitting for the high-pressure experimental results. We calculated the bulk modulus of the material to be 45.68 GPa, which is consistent with the calculated results. The framework is among the most rigid MOFs reported to date, exceeding that of Cu-BTC. Molecular dynamics simulations estimated that the mechanical energy absorbed by the system when pressurized to 5.128 GPa was 249.261 kcal mol-1. The present work will provide fresh ideas for the study of mechanical energy in other materials.

An aqueous mediated ultrasensitive facile probe incorporated with acrylate moiety to monitor cysteine in food samples and live cells

A colorimetric probe TQA ((E)-4-(((8-(sec-butoxy)-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-9-yl)methylene)amino)benzylacrylate) possessing greater potent towards the sensing of cysteine was successfully synthesized and characterized. The aqueous soluble probe TQA detects Cys based on "ON-OFF" effect with excellent absorbance and emission properties. The probe TQA detects Cys up to its ultra-low level concentration of 1.5 nM and also quantifies the Cys up to 5.05 nM with the quicker response time of 140 s (2.3 min). In addition, the color change produced by the probe TQA on integrated with Cys was also identified easily via paper strip, cotton wool buds and RGB color picker app in smart mobiles. Further, the admirable selectivity and sensitivity of the probe TQA towards Cys extends its utility towards food samples and imaging of live HeLa cells.

Single Organic Ligands Act as a Bifunctional Sensor for Subsequent Detection of Metal and Cyanide Ions, a Statistical Approach toward Coordination and Sensitivity

The detection of key ions in environmental samples has garnered significant attention in recent years in the pursuit of a cleaner environment for living organisms. Bifunctional and multifunctional sensors, as opposed to single-species sensors, have emerged as a rapidly developing field. Many reports in the literature have documented the use of bifunctional sensors for the subsequent detection of metal and cyanide ions. These sensors, consisting of simple organic ligands, form coordination compounds with transition metal ions, resulting in clear visible or fluorescent changes that facilitate detection. In some cases, a single polymeric material can act as a ligand and coordinate with metal ions, forming a complex that serves as a sensor for cyanide ion detection in biological and environmental samples through various mechanisms. Nitrogen is the most dominant coordinating site in these bifunctional sensors, with the sensitivity of the sensors being directly proportional to the denticities of ligands for metal ions, while for cyanide ions the sensitivity was found independent of the denticity of the ligands. This review covers the progress made in the field over the past fifteen years (2007-2022), with most ligands detecting copper (II) and cyanide ions, but with the capability to detect other metals such as iron, mercury, and cobalt as well.

Triphenylamine-embedded copper(II) complex as a "turn-on" fluorescent probe for the detection of nitric oxide in living animals

Nitric oxide (NO) is one of three major signaling molecules, which is involved in a large amount of physiological and pathological processes in biological systems. Furthermore, more and more evidence indicates that NO levels are closely associated with several aspects of human health. Accordingly, it is of great significance to develop a convenient and reliable detection method for NO in biological systems. In this work, a novel triphenylamine-embedded copper(II) complex (NZ-Cu²⁺) has been developed to be used as a fluorescence probe for the detection of NO in living animals. The proposed sensing mechanism of NZ-Cu²⁺ towards NO has been confirmed by high-resolution mass spectrometry, spectroscopic titration and density functional theory calculation. NO induced the conversion of paramagnetic Cu²⁺ to diamagnetic Cu⁺, which blocked the photoinduced electron transfer process of NZ-Cu²⁺, resulting in a remarkable enhancement of the emission spectra. The NZ-Cu²⁺ probe possesses several advantages including high selectivity, low detection limit (12.9 nM), long emission wavelength (640 nm), large Stokes shift (201 nm), fast response time (60 s) and low cytotoxicity. More importantly, NZ-Cu²⁺ has been successfully applied to detect NO in vivo by fluorescence imaging.

A phenothiazine-based turn-on fluorescent probe for the selective detection of hydrogen sulfide in food, live cells and animals

In this work, a phenothiazine-based fluorescent probe (PR) has been developed for the selective detection of hydrogen sulfide (H₂S) in biosystems and monitoring H₂S produced in the food spoilage process. The nucleophilic attack of H₂S on the CC double bond of PRvia a Michael addition interdicted the ICT process to trigger 34-fold enhancement of the fluorescence emission. PR featured high selectivity and sensitivity (1.8 μM), low cytotoxicity and reliability at physiological pH. "Naked-eye" monitoring of H₂S produced in the food spoilage process using PR was successfully accomplished. The preliminary fluorescence imaging studies showed that PR is suitable for the visualization of exogenous and endogenous H₂S in living cells and live animals. Moreover, PR has been successfully applied to the visualization of H₂S generation in an inflammation model. The results indicated that PR is an effective tool to monitor H₂S production in the fields of biomedicine and food safety.

A Mitochondrial-Targeting Near-Infrared Fluorescent Probe for Revealing the Effects of Hydrogen Peroxide And Heavy Metal Ions on Viscosity

As an important cell organelle, the mitochondrion has special viscosities, while abnormal mitochondrial viscosity is closely related to many diseases. Hydrogen peroxide (H₂O₂) is an active molecule related to the cell microenvironment, and its influence on mitochondrial viscosity is still not clear, so further investigation is needed. In addition, since excessive accumulation of heavy metal ions would lead to cells' dysfunction, the study of effect of excessive heavy metal ions on mitochondrial viscosity has not been reported. Herein, we designed and synthesized a mitochondrial-targeting near-infrared fluorescent probe (Mito-NV) for real-time in situ imaging and analysis of mitochondrial viscosity. Furthermore, the probe revealed that H₂O₂ can raise mitochondrial viscosity, while heavy metal ions reduce the viscosity. This work is of great significance for understanding the execution of mitochondrial functions and the occurrence and development of related diseases.

Toward Food Freshness Monitoring: Coordination Binding-Based Colorimetric Sensor Array for Sulfur-Containing Amino Acids

Herein, a self-assembled colorimetric chemosensor array composed of off-the-shelf catechol dyes and a metal ion (i.e., Zn2+) has been used for the sulfur-containing amino acids (SCAAs; i.e., glutathione, glutathione disulfide, L-cysteine, DL-homocysteine, and L-cystine). The coordination binding-based chemosensor array (CBSA) fabricated by a competitive assay among SCAAs, Zn2+ ions, and catechol dyes [i.e., pyrocatechol violet (PV), bromopyrogallol red (BPR), pyrogallol red (PR), and alizarin red S (ARS)] yielded fingerprint-like colorimetric changes. We succeeded in the qualification of SCAAs based on pattern recognition [i.e., a linear discrimination analysis (LDA)] with 100% correct classification accuracy. The semiquantification of reduced/oxidized forms of SCAAs was also performed based on LDA. Furthermore, we carried out a spike test of glutathione in food samples using the proposed chemosensor array with regression analysis. It is worth mentioning that we achieved a 91-110% recovery rate in real sample tests, which confirmed the accuracy of the constructed model. Thus, this study represents a step forward in assessing food freshness based on supramolecular analytical methods.

An endoplasmic reticulum-targeting fluorescent probe for discriminatory detection of Cys, Hcy and GSH in living cells

Endoplasmic reticulum, known to us as the ER, is the largest organelle in many kinds of eukaryotic cells and plays vital roles in maintaining the normal function of cells. Biothiols (Cys, Hcy, GSH) in secretory proteins will be modified as they enter the ER and are of great importance in balancing redox state of ER environments. In this article, we have developed the first endoplasmic reticulum-targeting fluorescent probe, ER-CP, for concurrent distinguishment of Cys, Hcy and GSH with favorable sensitivity and selectivity. ER-CP was successfully used in fluorescence imaging of Cys, Hcy and GSH in HeLa cells. In addition, ER-CP exhibited a good ER-targeting property (Pearson's correlation coefficient = 0.90).

A rapid “on–off–on” mitochondria-targeted phosphorescent probe for selective and consecutive detection of Cu2+ and cysteine in live cells and zebrafish

The detection of mitochondrial Cu²⁺ and cysteine is very important for investigating cellular functions or dysfunctions. In this study, we designed a novel cyclometalated iridium(iii) luminescence chemosensor Ir bearing a bidentate chelating pyrazolyl-pyridine ligand as a copper-specific receptor. The biocompatible and photostable Ir complex exhibited not only mitochondria-targeting properties but also an “on–off–on” type phosphorescence change for the reversible dual detection of Cu²⁺ and cysteine. Ir had a highly sensitive (detection limit = 20 nM) and selective sensor performance for Cu²⁺ in aqueous solution due to the formation of a non-phosphorescent Ir–Cu(ii) ensemble through 1 : 1 binding. According to the displacement approach, Ir was released from the Ir–Cu(ii) ensemble accompanied with “turn-on” phosphorescence in the presence of 0–10 μM cysteine, with a low detection limit of 54 nM. This “on–off–on” process could be accomplished within 30 s and repeated at least five times without significant loss of signal strength. Moreover, benefiting from its good permeability, low cytotoxicity, high efficiency, and anti-interference properties, Ir was found to be suitable for imaging and detecting mitochondrial Cu²⁺ and cysteine in living cells and zebrafish.

An iridium(iii) complex-based mitochondria targeting phosphorescent probe for selectively detecting Cu²⁺ and Cys in aqueous solution, living cells and zebrafish has been developed.

A novel iron quantum cluster confined in hemoglobin as fluorescent sensor for rapid detection of Escherichia coli

A new method based on fluorescent probe of iron quantum cluster has been proposed for rapid detection of Escherichia coli (E. coli). The iron quantum cluster was synthesized using hemoglobin as both a source of iron and a protective agent (Hb-FeQCs). The investigation of the sensitivity of Hb-FeQCs towards metal ions showed a highly selective turn off fluorescence for Cu²⁺. It suggests that Cu²⁺ can induce fluorescence quenching by binding to amino acids of Hb. The ability of E. coli bacteria to capture and reduce of Cu ions caused to efficient recovery of the fluorescence of Hb-FeQCs from Cu²⁺-caused quenching. This probe has a satisfactorily linear range of 0.35-35 μM for Cu²⁺ under the optimal iron quantum cluster concentration (500 μg/mL) with an 85 nM detection limit. Rapid and facile detection of E.coli bacteria with the limit of detection around 8.3 × 10³ CFU/mL was successfully achieved in the artificially contaminated urine, tap water, and DMEM samples within 30 min. The fluorescence recovery was investigated by different types of bacteria and only E. coli revealed 56% recovery which related to its capability to Cu²⁺ reduction and the great potential of the fluorescent probe for rapid detection of pathogenic E. coli bacteria. Furthermore, the Hb-FeQCs can detect E. coli bacteria in an infected urine sample by retrieving up to 74% of its fluorescence which is helpful to accelerate the diagnosis and treatment of urinary tract infection (UTI).

A New Endoplasmic Reticulum (ER)-Targeting Fluorescent Probe for the Imaging of Cysteine in Living Cells

Cysteine (Cys) is an important endogenous amino acid and plays critical physiological roles in living systems. Herein, an endoplasmic reticulum (ER)-targeting fluorescent probe (FER-Cys) was designed and prepared for imaging of Cys in living cells. The probe FER-Cys consists of a fluorescein framework as the fluorescent platform, acrylate group as the response site for the selective recognition of Cys, and ER-specific p-toluenesulfonamide fragment. After the response of probe FER-Cys to Cys, a turn-on fluorescence signal at 546 nm could be detected obviously. The probe FER-Cys further shows desirable selectivity to Cys. Finally, the probe FER-Cys was proven to selectively detect Cys in live cells and successfully image the changes of Cys level in the cell models of H₂O₂-induced redox imbalance.

Luminescent probes for hypochlorous acid in vitro and in vivo

HClO/ClO^- is the most effective antibacterial active oxygen in neutrophils. However, its excessive existence often leads to the destruction of human physiological mechanisms. In recent years, the developed luminescent probes for the detection of HClO/ClO^- are not only conducive to improve the sensitivity and selectivity of HClO/ClO^- detection, but also play a crucial role in understanding the biological functions of HClO/ClO^-. In addition, luminescent probe-based biological imaging for HClO/ClO^- at sub-cellular resolution has become a powerful tool for biopathology and medical diagnostic research. This article reviews a variety of luminescent probes for the detection of HClO/ClO^-in vitro and in vivo with different design principles and mechanisms, including fluorescence, phosphorescence, and chemiluminescence. The photophysical/chemical properties and biological applications of these luminescent probes were outlined. Finally, we summarized the merits and demerits of the developed luminescent probes and discussed their challenges and future development trends. It is hoped that this review can provide some inspiration for the development of luminescent probe-based strategies and to promote the further research of biomedical luminescent probes for HClO/ClO^-.

A Copper (II) Ensemble-Based Fluorescence Chemosensor and Its Application in the 'Naked-Eye' Detection of Biothiols in Human Urine

Quick and effective detection of biothiols in biological fluids has gained increasing attention due to its vital biological functions. In this paper, a novel reversible fluorescence chemosensor (L-Cu2+) based on a benzocoumarin-Cu2+ ensemble has been developed for the detection of biothiols (Cys, Hcy and GSH) in human urine. The chemosensing ensemble (L-Cu2+) contains a 2:1 stoichiometry structure between fluorescent ligand L and paramagnetic Cu2+. L was found to exclusively bond with Cu2+ ions accompanied with a dramatic fluorescence quenching maximum at 443 nm and an increase of an absorbance band centered at 378 nm. Then, the in situ generated fluorescence sluggish ensemble, L-Cu2+, was successfully used as a chemosensor for the detection of biothiols with a fluorescence "OFF-ON" response modality. Upon the addition of biothiols, the decomplexation of L-Cu2+ led to the liberation of the fluorescent ligand, L, resulting in the recovery of fluorescence and absorbance spectra. Studies revealed that L-Cu2+ possesses simple synthesis, excellent stability, high sensitivity, reliability at a broad pH range and desired renewability (at least 5 times). The practical application of L-Cu2+ was then demonstrated by the detection of biothiols in human urine sample.

High peroxidase-mimicking activity of gold@platinum bimetallic nanoparticle-supported molybdenum disulfide nanohybrids for the selective colorimetric analysis of cysteine

A sensitive and selective colorimetric sensor was designed for cysteine detection based on a high activity peroxidase-mimicking gold@platinum bimetallic nanoparticle-supported molybdenum disulfide nanohybrid.

Nanomolar detection of biothiols via turn-ON fluorescent indicator displacement

A simple, visual colour and turn-ON fluorescent method for the detection of biothiols under physiological conditions is reported. The chemosensing is achieved on the basis of the displacement of BODIPY dyes from the surface of gold nanoparticles.

Switch on fluorescence mode for determination of l-cysteine with carbon quantum dots and Au nanoparticles as a probe

Citric acid and urea were used as precursors for the preparation of carbon quantum dots (CQDs) which exhibited a maximum emission wavelength at 515 nm when excited at 410 nm. Upon addition of citrate-stabilized Au nanoparticles (AuNPs) with the maximum absorption wavelength at 520 nm, the fluorescence of the CQDs could be efficiently quenched, attributed to the energy transfer between CQDs and AuNPs. However, the further introduction of l-cysteine (Cys) could cause the aggregation of AuNPs along with a drop in absorption at 520 nm, resulting in the fluorescence recovery of the CQDs–AuNPs system. Therefore, a simple and reliable switch on fluorescence sensing platform for determination of Cys was constructed. The significant factors, such as pH and incubation time, that affected the detection of Cys were optimized with the AuNP concentration set as 2.50 nM at room temperature. Under the optimized conditions, the fluorescence recoveries (ΔF) were strongly correlated with Cys concentration in the 0.20 to 4.0 μM range, and the detection limit is 0.012 μM. More importantly, our CQD-based sensing platform was successfully used for the detection of Cys in milk samples with high precision and accuracy, indicating the potential of the probe in practical applications.

We demonstrated a fluorescence probe composed of CQDs and AuNPs for switch on detection of Cys, where CQDs as fluorescence reporters and AuNPs as fluorescence quenchers were chosen.

Coumarin-Based Small-Molecule Fluorescent Chemosensors

Coumarins are a very large family of compounds containing the unique 2H-chromen-2-one motif, as it is known according to IUPAC nomenclature. Coumarin derivatives are widely found in nature, especially in plants and are constituents of several essential oils. Up to now, thousands of coumarin derivatives have been isolated from nature or produced by chemists. More recently, the coumarin platform has been widely adopted in the design of small-molecule fluorescent chemosensors because of its excellent biocompatibility, strong and stable fluorescence emission, and good structural flexibility. This scaffold has found wide applications in the development of fluorescent chemosensors in the fields of molecular recognition, molecular imaging, bioorganic chemistry, analytical chemistry, materials chemistry, as well as in the biology and medical science communities. This review focuses on the important progress of coumarin-based small-molecule fluorescent chemosensors during the period of 2012-2018. This comprehensive and critical review may facilitate the development of more powerful fluorescent chemosensors for broad and exciting applications in the future.

A highly sensitive two-photon fluorescent probe for glutathione with near-infrared emission at 719 nm and intracellular glutathione imaging

A near-infrared turn-on two-photon fluorescent probe ST-BODIPY for glutathione-specific detection was designed and synthesized by attaching triphenylamine to BODIPY skeleton through the Knoevenagel condensation to prolong the maximum emission wavelength to the NIR region. And 2,4-dinitrobenzenesulfonyl group (DNBS), as the fluorescence quencher and thiol recognition moiety, was modified in 8 position of BODIPY. In the presence of GSH, the probe afforded an "off-on" signal response with a significant NIR fluorescence enhancement centered at 719 nm accompanying by quantum yield increased to 0.44, which was ascribed to the glutathione-induced S_NAr (aromatic substitution) reaction. Surprisingly, we found that the probe could discriminate GSH from other biothiols including Cys and Hcy upon the addition of intracellular concentrations of them. Time-dependence also demonstrated that the probe could distinguish GSH from Cys and Hcy under physiological environment. The limit of detection (LOD) for GSH was calculated as 25.46 nM from the titration experiments, which is lower than most previously reported GSH-selective probes. Under the Ti:sapphire pulsed laser's 800 nm irradiation, ST-BODIPY toward GSH generated an "off-on" signal response with a significant enhancement of fluorescence emission at 719 nm after treatment with GSH. Besides, the 2PA cross section value (σ₂) was calculated to be 410 GM, suggesting that it could not only function well as an excellent two-photon fluorescent probe for the detection of intracellular GSH, but also be applied for two-photon imaging with high sensitivity in living cells. Moreover, ST-BODIPY probe has been successfully employed for monitoring exogenous and endogenous GSH in MCF-7 cells with satisfying results, perhaps it was feasible for detecting abnormal contents of GSH in a biological system and accomplishing the goal of maintaining normal human activities.

A far-red FRET fluorescent probe for ratiometric detection of l-cysteine based on carbon dots and N-acetyl-l-cysteine-capped gold nanoparticles

A novel far-red fluorescence resonance energy transfer (FRET) fluorescent probe for ratiometric detection of l-cysteine (l-Cys) has been designed. The system was established a FRET assembly by positively charged carbon dots (CDs) and negatively charged N-acetyl-l-cysteine capped gold nanoparticles (NAC-AuNPs). The fluorescence of CDs at 539 nm could be effectively quenched in the presence of NAC-AuNPs owing to FRET process, while the emission of NAC-AuNPs at 630 nm was appeared. Subsequently, the interactions between l-Cys and NAC-AuNPs resulted in the decreased emission intensity of NAC-AuNPs, but the emission intensity of CDs kept almost constant due to the continuous FRET efficiency. The ratio of emission intensities at 539 and 630 nm (I₅₃₉/I₆₃₀) exhibited a linear correlation to the l-Cys concentration in the range of 1.0-110 μM with the detection limit of 0.16 μM. Moreover, this far-red ratiometric sensor also revealed excellent selectivity toward l-Cys over other amino acids, which showed very high potential in the practical application for diagnosing of cysteine-related disease.

Turn-On Fluorescence Probe for Nitric Oxide Detection and Bioimaging in Live Cells and Zebrafish

An effective bioanalytical method for rapid, sensitive, specific, and in situ sensing of nitric oxide (NO) is the key for further unveiling the biological functions of this gasotransmitter molecule in vitro and in vivo. In this contribution, a new fluorescence probe for sensing and imaging of NO in live systems was developed. The probe, FP-NO, was designed by exploring a novel sensing mechanism, i.e., the rotation of the N-N single bond of a coumarin derivative. FP-NO was prepared by incorporating a recognition unit, thiosemicarbazide moiety into a coumarin fluorophore. The weakly fluorescent FP-NO quickly and selectively reacts with NO to form a highly fluorescent product, FP-P. Such an enhancement of fluorescence emission allows NO detection with high sensitivity. The detection limit was 47.6 nM. The reaction mechanism was validated by HRMS titration analysis and the "OFF-ON" fluorescence response mechanism was rationalized by theoretical computation. FP-NO is biocompatible and live cell membrane permeable. The feasibility of FP-NO as the fluorescence probe for imaging and flow cytometry analysis of exogenous NO in MCF-7 cells and exogenous NO production in inflamed J774A.1 macrophage cells was then evaluated. Visualization of exogenous and endogenous NO production in live zebrafish was then achieved, implying the potential application of FP-NO in the studies of the NO roles in live organisms.

A specific fluorescent probe for fast detection and cellular imaging of cysteine based on a water-soluble conjugated polymer combined with copper(II)

In pure water system, the specific and rapid detection of cysteine (Cys) is very important and challenging. Herein, a new optical probe was developed for the purpose based on the complex of cupric ion (Cu²⁺) with a water-soluble conjugated polymer, poly[3-(3-N,N-diacetateaminopropoxy)-4-methyl thiophene disodium salts] (PTCO₂). The fluorescence of PTCO₂ in 100% aqueous solution can almost completely extinguished by Cu²⁺ ions due to its intrinsic paramagnetic properties. Among various amino acids, only Cys causes immediately the efficient recovery of the Cu²⁺-quenched fluorescence of PTCO₂ with ~31-folds fluorescence enhancement because of the stronger affinity of Cys to Cu²⁺ leading to the formation of Cu²⁺-Cys complex through Cu-S bond and separation of Cu²⁺ from weak-fluorescent PTCO₂-Cu(II) ensemble and thereby restoring the free PTCO₂ fluorescence. In tris-HCl buffer solution (2 mM, pH 7.4), the intensity of the restored fluorescence is linear with the concentration of Cys, ranging from 0 to 120 μM and the estimated detection limit of Cys is 3.3 × 10^-7 M with the correlation coefficient R = 0.9981. In addition, the PTCO₂-Cu(II) ensemble probe exhibits low cytotoxicity and good membrane penetration, and its application in living cell imaging of Cys has also been explored.

A coumarin based highly sensitive fluorescent chemosensor for selective detection of zinc ion

A very effective and highly sensitive fluorescent chemosensor, based on 4-hydroxycoumarin skeleton substituted by benzothiazole moiety was synthesized and investigated for the detection of zinc ion. This chemosensor displays highly selective and sensitive fluorescence enhancement to Zn²⁺ over other metal ions examined in solution and in biological systems. The detection limit for the fluorescent chemosensor 1 toward Zn²⁺ was 3.58 × 10^-8 M. A simple and efficient approach was improved for the synthesis of chemosensor 1 starting from 4-hydroxycoumarin.

Rational Design of a Hepatoma-Specific Fluorescent Probe for HOCl and Its Bioimaging Applications in Living HepG2 Cells

Liver cancer is a kind of high mortality cancer due to the difficulty of early diagnosis. And according to the reports, the concentration of reactive oxygen species (ROS) was higher in cancer cells than normal cells. Therefore, developing an effective fluorescent probe for hepatoma-selective imaging of hypochlorous acid (HOCl) which is one of the vital ROS is of great importance for understanding the role of HOCl in liver cancer pathogenesis. However, the cell-selective fluorescent probe still remains a difficult task among current reports. Herein, a galactose-appended naphthalimide (Gal-NPA) with p-aminophenylether as a new receptor and galactose moiety as hepatoma targeting unit was synthesized and employed to detect endogenous HOCl in living HepG2 cells. This probe was proved to possess good water solubility and could respond specifically to HOCl. In addition, probe Gal-NPA could completely react to HOCl within 3 s meanwhile accompanied by tremendous fluorescence enhancement. The quantitative linear range between fluorescence intensities and the HOCl concentrations was 0 to 1 μM (detection limit = 0.46 nM). More importantly, fluorescence confocal imaging experiments showed that probe Gal-NPA could discriminate hepatoma cells over other cancer cells and simultaneously trace endogenous HOCl levels in living HepG2 cells. And we thus anticipate that probe Gal-NPA has the potential application for revealing the functions of HOCl in hepatoma cells.

A highly specific fluorescent probe for rapid detection of hypochlorous acidin vivoand in water samples

We report the development of a new chromogenic and fluorogenic probe for the detection of HOCl in zebrafish, mice with arthritis and environmental water samples.

Rapid Response Fluorescence Probe Enabled In Vivo Diagnosis and Assessing Treatment Response of Hypochlorous Acid-Mediated Rheumatoid Arthritis

Diagnosis and early assessment of the treatment response of rheumatoid arthritis (RA) necessitates a reliable bioanalytical method for rapid, sensitive, and specific detection of the hypochlorous acid (HOCl) biomarker in inflammatory diseases. Herein, two fluorescence probes, Probe-1 and Probe-2 are developed for quantitative monitoring and visualization of inflammatory response-related HOCl levels in vitro and in vivo. In the presence of HOCl, fluorescence "OFF-ON" response is obtained for both the probes as a result of specific HOCl-triggered C=N bond cleavage reaction. Probe-1 and Probe-2 feature rapid response (<4 s), a high degree of sensitivity and selectivity toward HOCl, which allow them to be used for quantification of HOCl in a simulated physiological condition. Using Probe-2 as the probe, fluorescence imaging and flow cytometry analysis of HOCl levels in lysosome of inflammatory mimic cells, visualization of HOCl generation in endotoxin-induced inflammation of adult zebrafish and RA of mice are possible. Probe-2 exhibits high effectiveness for early assessment of the treatment response of HOCl-mediated RA in mice with an antiarthritic drug, methotrexate (MTX). The results demonstrate that Probe-2 is a powerful tool for future studies on diagnosis and monitoring treatment efficiency in a broad range of inflammatory diseases, including RA.

Nitroolefin-based BODIPY as a novel water-soluble ratiometric fluorescent probe for detection of endogenous thiols

Small molecule biothiols, including cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), play many crucial roles in physiological processes. In this work, we have prepared a nitroolefin-based BODIPY fluorescent probe with excellent water solubility for detection thiols, which displayed ratiometric fluorescent signal for thiols. Incorporation of a nitroolefin unit to the BODIPY dye would transform it into a strong Michael acceptor, which would be highly susceptible to sulfhydryl nucleophiles. This probe shows an obvious ratio change upon response with thiols, an increase of the emission at 517 nm along with a concomitant decrease of fluorescence peak at 573 nm. Moreover, these successes of intracellular imaging experiments in A549 cells indicated that this probe is suitable for imaging of ex-/endogenous thiols in living cells.

Selective and sensitive detection of cysteine in water and live cells using a coumarin–Cu2+ fluorescent ensemble

A coumarin–Cu²⁺ ensemble based fluorescent chemosensor was developed for the selective detection of cysteine in aqueous media and live cells.

A heterobimetallic metal–organic framework as a “turn-on” sensor toward DMF

It is for the first time that a non-luminescent 3d–4f heterobimetallic CuEu organic framework (NBU-8) realized specific selective light recovery of Eu³⁺ ions toward N,N′-dimethylformamide (DMF) even in the presence of other amide molecules with similar functions.

A fast response fluorescence probe specific for hypochlorous acid detection and its applications in bioimaging

The features ofDNPH-NA, including its high sensitivity, selectivity, and reliability at physiological pH, together with a rapid response, enable its successful application in the detection of endogenous HOClin vitroandin vivo.

A colorimetric sensor of cysteine based on self-assembly nanostructures of Fe3+-H2O2/Tetramethylbenzidine system with "On-Off" switching function

Many strategies have been explored for selectively and sensitively detecting cysteine in different samples. Here, a novel colorimetric sensor based on self-assembly nanostructures of Fe³⁺-H₂O₂/Tetramethylbenzidine system with dual-level logic gate function and colorimetric determination of cysteine were firstly explored. The proposed Fe³⁺-H₂O₂-TMB system provides a sensitive optical signal due to the selectively reductive ability of cysteine to the oxidized TMB and thus could be successfully applied to the construction of instant on-site visual detection method with a paper based test strip for cysteine determination in a sample solution as well as for a dual-level logic gate fabrication.