Fluorescence Turn-on Response Research Articles

Small Molecule Quinoxaline Fluorescent Probe for AcO- Real-Time Detection in Vivo.

Fluorescent probes to detect biologically important acetate ion (AcO-) are essential for regulating substance metabolism, alleviating inflammatory symptoms, reducing cancer incidence, and diagnosing early diseases. However, the relatively small charge-to-atomic radius ratio in AcO- and its triangular spatial structure pose challenges in recognition and often lead to interference from other anions in detection methods. Herein, we introduce a quinoxaline fluorescent probe, o-(4-(2-(3-oxo-3,4 -dihydroqui-noxalin-2-yl)vinyl)phenyl) dimethylaminothiophene ester (QPDMT), specifically design and synthetic for the accurate detection of AcO-. This probe leverages molecular nucleophilicity and electron transfer to undergo a reaction that releases the fluorophore upon cleavage of the thioformyl ether bond, exhibiting a turn-on fluorescence response at 530nm. QPDMT exhibits an impressively low detection limit of 30 nM, a rapid response time of 20min, a robust linear response in the 1-9 µM range and excellent fluorescence quantum yield, 0.32. Importantly, this probe demonstrates low cytotoxicity, making it an ideal candidate for endogenous AcO- detection in living cells and organisms.

Fluorescence Turn-ON Displacement Assays with Cucurbit[7]uril-Thiophenylpyridinium Complexes as Host-Dye Reporter Pairs.

The N-methyl-4-thiophenylpyridinium cation (ThioPy) is a high affinity (Kd ca. 5 nM), fast-exchanging fluorescent probe for cucurbit[7]uril (CB7). The CB7/ThioPy complex shows a unique fluorescence turn-ON response upon displacement by an analyte in sensing application. This enabled the development of a real-time fluorescence assay with the MRFA peptide for the protease thermolysin, which is also suitable for the cancer biomarker cathepsin B. Moreover, liposome encapsulation of CB7/ThioPy in large unilamellar vesicles (LUVs) provided mechanistic insight into intravesicular dye displacement reactions.

A Bis(Acridino)-Crown Ether for Recognizing Oligoamines in Spermine Biosynthesis.

Oligoamines in cellular metabolism carry extremely diverse biological functions (i.e., regulating Ca2+-influx, neuronal nitric oxide synthase, membrane potential, Na+, K+-ATPase activity in synaptosomes, etc.). Furthermore, they also act as longevity agents and have a determinative role in autophagy, cell growth, proliferation, and death, while oligoamines dysregulation is a key in a variety of cancers. However, many of their mechanisms of actions have just begun to be understood. In addition to the numerous biosensing methods, only a very few simple small molecule-based tests are available for their selective but reversible tracking or fluorescent labeling. Motivated by this, we present herein a new fluorescent bis(acridino)-crown ether as a sensor molecule for biogenic oligoamines. The sensor molecule can selectively distinguish oligoamines from aliphatic mono- and diamino-analogues, while showing a reversible 1:2 (host:guest) complexation with a stepwise binding process accompanied by a turn-on fluorescence response. Both computational simulations on molecular docking and regression methods on titration experiments were carried out to reveal the oligoamine-recognition properties of the sensor molecule. The new fluorescent chemosensor molecule has a high potential for molecular-level functional studies on the oligoamine systems in cell processes (cellular uptake, transport, progression in cancers, etc.).

Thiophene appended schiff base probe for selective ‘turn-on’ response for copper (ii) ion and their applications in live cell imaging Thiophene appended schiff base probe for selective ‘turn-on’ response for copper (ii) ion and their applications in live cell imaging

In this research, we have synthesized a thiophene Schiff base from 5-phenyl thiophene-2-carboxaldehyde and 2-thiophene carboxylic acid hydrazide and characterized by using FT-IR NMR, HRMS and SC-XRD analysis techniques. The probe exhibited a selective turn-on fluorescence response for Cu2+ over 20 other common metal ions in a CH3CN (9:1, v/v) solution. The Job’s plot represents a 1:1 binding complexation mode and further DFT study was carried out to aid in understanding the geometric structure and interaction of the ligand and Cu2+. The detection limit (LOD) and limit of quantification (LOQ) were found to be 20 nM and 69 nM respectively. Furthermore, the probe’s sensing ability was tested in HeLa cells and their fluorescence imaging also supported the effective turn-on response towards Cu2+ ion.

Selective cyanide ion detection using hydrazine carbothioamide probe: A fluorescence turn-on approach

This study reports the synthesis of various hydrazine carbothioamide derivatives through a Schiff base reaction, confirmed by FT-IR, NMR (1H and 13C), and HRMS spectroscopic methods. Among the synthesized derivatives, probe L ((4-fluorobenzylidene)-2-(1-phenylethylidene)hydrazine-1-carbothioamide) was identified as a highly selective fluorometric chemosensor based on its absorbance and emission spectra. Probe L showed a CN− ion-specific turn-on fluorescence response, with very little interference from other anions. Job's method established a 1:1 binding stoichiometry among probe L and the cyanide ion. The detection limits (LOD) and quantification (LOQ) were observed to be 0.639 µM and 2.116 µM, respectively. With the use of FT-IR spectroscopy, 1H NMR titration, 13C NMR and HRMS, the binding mechanism was clarified. Moreover, probe L was employed effectively for detecting CN− ions in water and food samples, highlighting its potential as a practical sensor for cyanide detection.

A Hydrogen Bonded Non-Porous Organic-Inorganic Framework for Measuring Cysteine in Blood Plasma and Endogenous Cancer Cell.

An imbalance in cysteine (Cys) levels in the cells and plasma has been identified as the risk indicator for various human diseases. The structural similarity of cysteine with its congener homocysteine and glutathione offers challenges in its measurement. Herein, we report a hydrogen-bonded organic-inorganic framework of Cu(II) (HOIF) for the selective detection of cysteine over other biothiols. The non-fluorescent HOIF showed 12-fold green emission in the presence of cysteine. The monomeric unit of HOIF is stabilized via intermolecular hydrogen bonds, resulting in a non-porous network structure. Non-interference from homocysteine, glutathione, and other competitive bio-analytes revealed explicit affinity of HOIF for cysteine. Fluorimetric titration showed a wide working concentration window (650 nM-800 μM) for measuring cysteine in an aqueous medium. The mechanistic investigation involving HRMS, EPR, and UV-vis spectroscopic studies revealed the decomplexation of HOIF with Cys, resulting in a fluorescence turn-on response from the luminescent ligand. Validation using a commercial dye, "Cysteine Green", confirmed the prospect of HOIF for early diagnostic purposes. Utilizing the fluorescence turn-on property of HOIF in the presence of cysteine, we measured cysteine quantitatively in the blood plasma samples. Bio-imaging of endogenous cysteine in cancer cells indicated the ability of HOIF to monitor the intracellular cysteine.

Hollow Fiber Sensors with a Turn-On Fluorescence Response, Recycling, and Water Proofing for Monitoring Benzene Series

Hollow Fiber Sensors with a Turn-On Fluorescence Response, Recycling, and Water Proofing for Monitoring Benzene Series

A dual-reaction sites fluorescent probe for accurate detection of benzoyl peroxide in food

Benzoyl peroxide (BPO) is widely used as a whitening agent in flour, but excessive intake of BPO will severely endanger human health. To quickly and accurately detect BPO on-site, we have rationally designed a novel fluorescent probe PTPY-BE with dual-reaction sites. PTPY-BE underwent a specific cascade reaction with BPO to achieve high-contrast fluorescence turn-on response along with significant achromic reaction. The probe has high sensitivity, excellent selectivity, strong anti-interference ability and low detection limit (LOD = 0.83 mg·kg−1) for BPO. Furthermore, a portable detection platform was fabricated, which offers the portability and color visualization of traditional test strips and the color recognition of a smart device, enabling on-site visualization and quantitative detection of BPO. This platform has been successfully used to determine BPO in real food samples with good recoveries (93.59% - 107.13%). Therefore, this platform possessed great prospect and potential application for the determination of BPO in food.

A near infrared fluorescent probe for monitoring peroxynitrite abnormalities in non-alcoholic fatty liver

Peroxynitrite (ONOO−) has emerged as a critical biomarker for detecting pathological alterations in biological stroma. Notably, it has strong correlation with the pathogenesis of conditions like non-alcoholic fatty liver disease (NAFLD), underlining its utility in both identifying and elucidating such diseases. In this work, we report a novel fluorescent probe, TEM-NS, innovatively crafted using an enhanced dicyanoisophorone scaffold, aimed at the precise quantification of ONOO−. Characterized by its turn-on fluorescence response, TEM-NS exhibits an emission profile and a pronounced Stokes shift superior to those of traditional dicyanoisophorone derivatives. Its exceptional specificity and photostability, combined with superior sensitivity in a biological milieu, are noteworthy. Importantly, application of TEM-NS within a NAFLD model substantiated its capability to detect elevated ONOO− levels in liver tissue, thereby affirming its applicability for in-depth analysis of oxidative stress-related disorders.

Fluorescence turn-on detection of arsenite in rice and seawater samples using bisphosphonate-functionalised carbon quantum dots

ABSTRACT In this paper, we illustrate an efficient and simple fluorescence (FL) sensing approach for the specific determination of arsenite (As(III)) in aqueous solution by alendronate-functionalised carbon quantum dots (A-CQDs) as a turn-on fluorescent probe. A-CQDs exhibit linear FL turn-on response towards the increasing concentration of As(III) analyte with a limit of detection of 0.007 µM and a linear range of 0.03–1.87 µM. The selectivity study demonstrates that the A-CQDs are very selective for As(III) detection, even at a higher concentration of other interfering ions. The sensing pathway for the sensitivity of A-CQDs assay to quantify As(III) ions is expected to rely on the chelation-enhanced FL (CHEF) mechanism between A-CQDs and the analyte. This mechanism is verified by the density functional theory methodology. The practical application of this simple and reliable sensor is demonstrated by assaying As(III) in rice and seawater samples, which confirms that A-CQDs have good potential for real sample analysis in food and environmental samples.

Highly selective fluorescence turn-on sensor for·thiol compounds detection

As a kind of commonly-used synthetic materials for many pesticides, thiol compounds, once being leaked, can cause serious harm to the environment and humans. Therefore, the efficient detection of thiol compounds is essential. In this study developed a turn-on fluorescent probe (Cu@Zn-CP) for the highly sensitive fluorescence detection of thiol compounds. The probe was constructed based on a zinc coordination polymer (Zn-CP), whose fluorescence was quenched through the effective doping of Cu2+ ions. After the introduction of methyl thioglycolate (MTC), a rapid fluorescence turn-on response was generated within 90 s with a low detection limit of 23 ppb. Even after being reused for five cycles, the sensor maintains excellent detection performance and demonstrates good recyclability. It can also detect MTC in river water, with a spike recovery rate between 98–103 %. Furthermore, the designed Cu@Zn-CP exhibits good universality for detecting multifarious thiol compounds, including L-cysteine, glutathione, monothioglycerol, and 2-hydroxy-1-ethanethiol. This result provides a potential recyclable fluorescent sensor for thiol compounds.

Fluorescence Turn-on Detection of Perfluorooctanoic Acid (PFOA) by Perylene Diimide-Based Metal-Organic Framework.

A novel, water-stable, perylene diimide (PDI) based metal-organic framework (MOF), namely, U-1, has been synthesized for selective and sensitive detection of perfluorooctanoic acid (PFOA) in mixed aqueous solutions. The MOF shows highly selective fluorescence turn-on detection via the formation of a PFOA-MOF complex. This PFOA-MOF complex formation was confirmed by various spectroscopic techniques. The detection limit of the MOF for PFOA was found to be 1.68 μM in an aqueous suspension. Upon coating onto cellulose paper, the MOF demonstrated a significantly lower detection limit, down to 3.1 nM, which is mainly due to the concentrative effect of solid phase extraction (SPE). This detection limit is lower than the fluorescence sensors based on MOFs previously reported for PFAS detection. The MOF sensor is regenerable and capable of detecting PFOA in drinking and tap water samples. The PDI-MOF-based sensor reported herein represents a novel approach, relying on fluorescence turn-on response, that has not yet been thoroughly investigated for detecting per- and polyfluoroalkyl substances (PFAS) until now.

An Expanded Palette of Fluorescent COS/H2S-Releasing Donors for H2S Delivery, Detection, and In Vivo Application.

Hydrogen sulfide (H2S) is an important reactive sulfur species that is involved in many biological functions, and H2S imbalances have been indicated as a potential biomarker for various diseases. Different H2S donors have been developed to deliver H2S directly to biological systems, but few reports include donors with optical responses that allow for tracking of H2S release. Moreover, donor systems that use the same chemistry to deliver H2S across a palette of fluorescent responses remain lacking. Here we report five thiol-activated fluorescence turn-on COS/H2S donors that utilize blue, yellow, orange, red, and near infrared-emitting dyes functionalized with an H2S-releasing sulfenyl thiocarbonate scaffold. Upon treatment with thiols, each donor provides a fluorescence turn-on response (3-310-fold) and high H2S release efficiencies (>60 %). Using combined electrode and fluorescence experiments, we directly correlate the measured H2S release with the fluorescence response. All donors are biocompatible and release H2S in live cell environments. In addition, we demonstrate that the NIR donor allows for imaging H2S release in live rats via subcutaneous injection of the donor loaded into an alginate gel, which to the best of our knowledge is the first in vivo tracking of H2S release from a fluorogenic donor in non-transparent organisms.

Rapid detection of hypobromous acid by a tetraphenylethylene-based turn-on fluorescent AIE probe and its applications

BackgroundSimilar to hypochlorous acid (HClO), hypobromous acid (HBrO) is one of the most notable reactive oxygen species (ROS). Overexpression of HBrO is linked to various diseases causing organ and tissue loss. Due to HBrO's role in the oxidation of micropollutants, real-time monitoring of HBrO in water-based systems is essential. Tetraphenylethylene (TPE)-based organic aggregation-induced emission luminophores (AIEgens) are an emerging category of fluorescent probe materials that have attracted considerable attentions. However, AIE probes are rarely applied to detect HBrO. Developing faster, more precise, and more sensitive AIE probes is thus crucial for detecting biological and environmental HBrO. ResultsA small molecule fluorescent probe 4-(1,2,2-triphenylvinyl)benzamidoxime (SWJT-21) was synthesized for the sensitive and selective detection of hypobromous acid (HBrO) based on aggregation-induced emission (AIE). The amidoxime unit of SWJT-21 would undergo an oxidation reaction with HBrO, leading to a structure differentiation between the probe and the product, and therefore the turn-on fluorescence by the AIE effect. The probe could recognize hypobromous acid rapidly (less than 3 s) in high aqueous phase (99 % water) with a turn-on fluorescence response. It was determined that the limit of detection for HBrO was 5.47 nM. Moreover, SWJT-21 demonstrates potential as a test strip for the detection of HBrO. SWJT-21 was also successfully used for the monitoring of HBrO in water samples and for the detection of endogenous/exogenous HBrO in living cells and zebrafish. SignificanceA special AIE fluorescence turn-on probe SWJT-21 based on tetraphenylethylene was designed for detecting HBrO in the environmental and biological systems. This probe has an extremely low detection limit of 5.47 nM and is able to detect HBrO in 99 % aqueous phase in less than 3 s.

A novel coumarin-linked tetraphenylethene fluorescent probe for simultaneous sensing of ATP and GSH

Adenosine triphosphate (ATP) as the intracellular energy currency, and glutathione (GSH) as the regulator of redox homeostasis in the cell microenvironment, are all closely associated with numerous important physiological processes in living organisms. However, the fluorescent probes that can simultaneously detect ATP and GSH are rarely reported. Herein, a bifunctional coumarin-linked tetraphenylethene (TPE) probe P1 was successfully developed, which exhibits a red emission at 633 nm owing to the fluorescence resonance energy transfer (FRET) from energy donor coumarin to energy acceptor TPE. P1 can detect ATP with a fluorescence turn-on response at 633 nm in the red channel by complexation-enhanced aggregation mechanism, and showed a ratiometric detection toward GSH through the disruption of the FRET process, accompanied by an increase in the blue channel at 467 nm and a decrease in the red channel at 633 nm. P1 also displays a superior sensitivity and high selectivity to ATP and GSH, with a detection limit of 20.80 nM for ATP and 3.47 µM for GSH. Significantly, P1 can discriminate GSH from ATP and other analytes due to the different response times. Furthermore, P1 can localize mitochondria and has been discovered to be capable of imaging ATP and GSH in living cells and zebrafish.

Water bridges as the trigger in an amino functionalized Zn-MOF for highly selective and sensitive fluorescent sensing of water

Water is a fundamental element for life. The highly selective and sensitive sensing of water is always attractive for mankind in activities such as physiological processes study and extraterrestrial life exploration. Fluorescent MOFs with precise channels and functional groups might specifically recognize water molecules with hydrogen-bond interaction or coordination effects and work as water sensors. As a proof of concept, herein, an amino functionalized Zn-MOF (named as complex 1) with pores that just right for water molecules to form hydrogen bond bridges is revealed for highly selective and sensitive fluorescent sensing of water. The single-crystal X-ray diffraction analysis indicates that the 3D framework of complex 1 is functionalized with free amino groups in the channels. Hydrogen bonds formed in the channel along b-axis as water bridges to connect two adjacent NH2bdc ligands and result in the restriction of intramolecular motions (RIM) which could responsible for the selective turn-on fluorescence response to water. Complex 1 exhibits high sensitive to trace amount of water in organic solvents and could be used for water detection in a wide range water contents. Take advantages of complex 1, portable sensors (complex 1@PMMA) were prepared and used in the highly sensitive water sensing.

D-A-D type based NIR fluorescence probe for monitoring the cysteine levels in pancreatic cancer cell during ferroptosis

Cysteine (Cys) as a crucial precursor for intracellular glutathione (GSH) synthesis, plays an important role in the redox regulation in ferroptosis, Therefore, evaluating intracellular Cys levels is worthy to better understand ferroptosis-related physiological process. In this work, we constructed a novel NIR coumarin-derived fluorescent probe (NCDFP-Cys) based on a dual-ICT system, the NCDFP-Cys can show fluorescence turn-on response at 717 nm toward Cys over other amino acids, and possess large Stokes shift (Δλ = 167 nm), low detection limit, hypotoxicity. More significantly, NCDFP-Cys has been utilized to monitor the intracellular Cys fluctuation in pancreatic cancer cells during ferroptosis induced by Erastin and RSL3 respectively, and revealing the difference of Cys levels changes in different activator-triggered ferroptosis pathways.

A difunctional fluorescent probe to detect hypochlorite and hydrogen sulfide ions in ferroptosis and oxidative stress induced by Aspirin

HOCl and H2S frequently coexist in living cells and work in concert to maintain the redox dynamic balance in vivo. It is challenging to precisely and simultaneously trace both HOCl and H2S using a single recognition-type fluorescence probe. Here, a novel fluorescent probe (MB-HS) for the selective detection of hydrogen sulphide (H2S) and hypochlorous acid (HOCl) has been established based on the coupling of the methylene blue fraction and the indolium fraction. For HOCl, the dual-signal probe MB-HS displays quick turn-on fluorescence responses. However, for H2S, it exhibits turn-off fluorescence at 586 nm and turn-on at 513 nm, respectively. MB-HS showed many advantages such as quick response, strong selectivity, and high sensitivity. It was effectively used to detect endogenous HOCl/H2S in ferroptosis and oxidative stress induced by Aspirin in HepG-2 cells.

Aggregation-induced emission activity of sensor TBM-C1 hybrid of methoxy-triphenylamine (OMe-TPA) and dicyanovinyl for cyanide detection in aqueous THF: Mechanistic insights and potential applications

A series fluorescent probes (TBM-Cx (x = 1, 4, 8)) were designed based on embedding various alkoxy chains on the electron donor of triphenylamine (TPA)-based dicyanovinyl (MT) compound with an electron-deficient benzothiadiazole (BTD) for sensitive, selective, and visualizing detection of cyanide in aqueous solution. Due to the nucleophilic addition of CN−, the intramolecular charge transfer (ICT) of these probes was inhibited by the destroyed conjugated structure, exhibiting excellent “turn-on” fluorescence response toward cyanide anion (CN−) in tetrahydrofuran (THF). However, the alkoxy chains with different lengths embedded in TPA not only enhance the sensitivity and solubility, but also regulate the emission behavior from ICT to aggregation-induced emission (AIE) characteristics. The binding mechanism and AIE sensing performances between the probes and CN− have been investigated and compared in THF/water mixture by spectral tools and theoretical calculations. The results showed that the ICT-based TBM-C1 probe with methoxy chain showed significantly turn-on fluorescence response to CN− as low as 0.077 μM in THF/water solution at high water fraction (90 %). Due to the AIE sensing process, TBM-C1 was successfully employed to determine CN− in food and water samples, image CN− in living cells and BALB/c mice, and prepare test kits for visualizing cyanide.

A chromogenic anthraimidazoldione probe for ratiometric analysis of Hg2+ exclusively at mesoscopic interface: Screening of real-life biological samples

In the present work, we have synthesized amphiphilic anthraimidazoldione derivative that can form nanoassembly in the aqueous medium. The π-conjugated backbone with facile intramolecular charge transfer from the substituted aryl residue to anthraquinone unit attributed to the profound orange color. Despite having the metal ion chelating aminoethyl acetamide unit, the compound showed no interaction with metal ions in the aqueous medium. However, a highly selective color-changing response, from orange to yellow (Δλ ∼52 nm), was observed upon addition of Hg2+ ion at micellar interface. Also, a turn-on fluorescence response (∼5.2-fold) was witnessed with Hg2+. It was observed that in addition to hydrophobic microenviroment, the orientation of molecules at water-surfactant interface also responsible for the chromogenic response towards Hg2+ ion. The mechanistic investigation indicated that Hg2+ ion coordinates with the aminoethyl acetamide unit, resulting restriction in the extent of intramolecular charge transfer. Considering such highly ratiometric response, the present system has been employed for analysis of Hg2+ ion in diluted urine and blood serum samples. The high recovery values (95.4 % to 104.3 %) with relatively low standard deviations (< 4.2 %) indicated that the present system is fairly successful in screening of complex real-life samples. Finally, we have designed low-cost, reusable, chemically modified paper strips for on-location, rapid analysis of mercury ions.