Ratiometric Fluorescent Chemosensor Research Articles

Pyrene‐based ratiometric fluorescent chemosensor for sensitive detection of hypochlorite in a perfect aqueous solution

AbstractWe synthesized a pyrene‐based sensitive fluorescent chemosensor, TPA‐Cl ((E)‐N,N,N‐trimethyl‐2‐oxo‐2‐(2‐(pyren‐1‐ylmethylene)hydrazinyl)ethan‐1‐aminium chloride), to detect hypochlorite in a perfect aqueous solution. TPA‐Cl showed high selectivity for hypochlorite through fluorescence color change from sky blue to blue. The detection limit for hypochlorite was calculated as 0.27 μM, which is a quite low value. Moreover, the presence of other anions or ROS hardly hindered the sensing of hypochlorite by TPA‐Cl. Furthermore, TPA‐Cl could be applied successfully as a test kit for the simple recognition of hypochlorite. Surprisingly, TPA‐Cl is the first pyrene‐based fluorescent chemosensor that can detect ClO− by using the TPA‐Cl‐coated test kit. Moreover, TPA‐Cl could achieve the quantification of ClO− in various environmental water samples. The hydrolytic cleavage and oxidation mechanism of TPA‐Cl by hypochlorite was elucidated through UV–vis and fluorescent spectroscopy, 1H NMR titration, ESI‐MS analysis and DFT calculation.

Comprehensive investigations of four ratiometric fluorescent chemosensors based on 4-(1H-imidazol-2-yl)benzaldehyde skeleton for malononitrile detection

Malononitrile is a very important chemical material and has wide application fields in production of medicines, pesticides, and extraction of gold. However, its nonnegligible hypertoxicity inspired researchers to develop more efficient analysis techniques to sensitively and selectively detect malononitrile. Nopinone derivatives initiated by our research group have been developed as a class of organic fluorescent chemosensors for identifying multiple analytes in recent years. Different heterocyclic compounds based on nopinone were designed and synthesized to be applied in the fields of environmental analysis, food detection and bioimaging. Nevertheless, the comparison research on the optical properties of fluorescent compounds containing the nopinyl matrix with other structural analogs including alkyl, cyclohexyl and phenyl groups was deficient. Herein, four 4-(1H-imidazol-2-yl)benzaldehyde-based ratiometric fluorescent chemosensors based on o-dimethyl cyclohexyl, phenyl and nopinyl units for recognizing malononitrile were designed and developed, and their differences in the optical properties and detection performances were investigated by using spectral analysis combined with theoretical calculations. Moreover, the nopinone-based 4-(1H-imidazol-2-yl)benzaldehyde fluorescent chemosensor NMZQ was successfully applied in the dual channel fluorescence bioimaging of malononitrile in living HeLa cells and zebrafish, which attributed to its outstanding spectral property and detection performance.

Highly selective Cu2+ detection with a naphthalimide-functionalised pillar[5]arene fluorescent chemosensor.

Ligand 1, a rim-differentiated pillar[5]arene macrocycle modified with five naphthalimide groups through click chemistry, serves as an effective ratiometric fluorescent chemosensor for Cu2+. In contrast to the monomeric naphthalimide control compound 2, which shows only monomer emission, ligand 1 demonstrates dual emission characteristics encompassing both the monomer and excimer of the naphthalimide moieties. The binding properties of ligand 1 toward 15 different metal ions were systematically investigated in CH2Cl2/CH3CN (v/v, 1 : 1) by UV-vis and fluorescence spectroscopy. Remarkably, ligand 1 exhibits exceptional selectivity for Cu2+ ions. Upon complexation with Cu2+, the excimer emission of ligand 1 diminishes, concomitant with an enhancement of its monomer emission. The binding ratio for 1·Cu2+ was determined to be 1 : 1, with an association constant of (3.39 ± 0.40) × 105 M-1 calculated using a nonlinear least-squares curve-fitting method. Furthermore, the limit of detection (LOD) was found to be 185 ± 7 nM. Our results from 1H NMR titration, high-resolution mass spectrometry analysis and density functional theory calculations of 1·Cu2+ suggest synergistic coordination between Cu2+ and the triazole groups on ligand 1.

An aggregation-induced emission-based ratiometric fluorescent chemosensor for Hg(II) and its application in Caenorhabditis elegans imaging

A chromone-based ratiometric fluorescent probe L2 was developed for the selective detection of Hg(II) in a semi-aqueous solution based on aggregation-induced emission (AIE) and chelation-enhanced fluorescence (CHEF) effect. The probe L2 fluoresced significantly at 498 nm in its aggregated state, and when chelated with Hg(II), the soluble state fluoresced 1-fold higher. In addition, Job’s plot reveals that the probe forms a 1:1 stoichiometry complex with Hg(II) with an association constant of 9.10 × 103M−1 estimated by the BH plot. The probe L2 detects Hg(II) down to 22.47 nM without interference from other interfering ions. The FTIR, ESI mass, and DFT-based computational studies investigated the binding mechanism of probe L2 with Hg(II). Taking advantage of its AIE characteristics, the probe L2 was successfully applied for bio-capability analysis in Caenorhabditis elegans (a nematode worm) imaging of Hg(II) in a living model.

A combined theoretical and experimental study of ratiometric fluorescent Schiff base chemosensor for detection of Fe3+ ion and its anticancer activity

Schiff-base fluorescent chemosensor (E)-N-(4-(dimethylamino)benzylidene)quinolone-3-amine (DBQA) was synthesized and characterized by FT-IR,1H NMR,13C NMR, ESI-MS spectrometry and Single X-ray crystallographic studies. The synthesized chemosensor (DBQA) was used for the detection of Fe3+ successfully. UV-visible and fluorescence spectra of (DBQA) exhibits a ratiometric behaviour along with a bathochromic shift upon the successive addition of Fe3+. The fluorescence spectra of chemosensor (DBQA) were recorded followed by addition of concentrations of different metal ions and NH3. The chemosensor (DBQA) showed a favourable linear relationship between the fluorescence intensity and concentration of Fe3+ ion. DBQA exhibits a ratiometric response and illustrates high sensitivity (with a detection limit of 0.4 ​μM) and good selectivity for the Fe3+ ion over other transition metal ions. DBQA shows 0.6 ​μM detection limit for NH3 along with ratiometric behaviour also. The association constant (Ka) of chemosensor (DBQA) was found to be 1.455×102 ​M-1/2 for Fe3+. The mechanism of sensing of the present ratiometric fluorescent chemosensor (DBQA) was explained by ICT (Intra-molecular charge transfer) using DFT calculations. The interaction model of chemosensor (DBQA) with Fe3+ was determined to be 2:1 stoichiometry using Job's plot analysis and ESI-MS spectra which further confirms DFT studies. Moreover, tested DBQA ​+ ​Fe3+ was showed that remarkable anticancer activity against the HCT116 colon cancer cells by MTT assay. Novelty and importance of DBQA as it can be investigate, test or analyse of detect Fe3+ rapidly as compared to other tested ions. Lastly, DBQA can be investigate, test or analyse of Fe3+ in environmental and biological samples.

High-Throughput Analysis of Bacterial Toxic Lipopolysaccharide in Water by Dual-Wavelength Monitoring Using a Ratiometric Fluorescent Chemosensor.

Lipopolysaccharide (LPS) is a bacterial toxin that causes fever in humans. Our small-molecule chemosensor named Zn-dpa-C2OPy shows rapid ratiometric fluorescence response to LPS in water with a detection limit of 11 pM, which is lower than that of our previously reported sensor. Spectroscopic measurements (fluorescence, absorbance, 1H NMR, and fluorescence lifetime), dynamic light scattering measurements, and transmission electron microscopy observations revealed that the fluorescence response was induced by the changes in the aggregation state via multi-point recognition of LPS through hydrophobic and electrostatic interactions, in addition to the coordination between the zinc(II)-dipicolylamine moiety of the chemosensor and the phosphate group of LPS. The proposed Zn-dpa-C2OPy chemosensor was applied to an original flow injection analysis (FIA) system with a self-developed dual-wavelength fluorophotometer, and a high throughput of 36 samples per hour was achieved. These results demonstrate the feasibility of this unique methodology combining a ratiometric fluorescent chemosensor and FIA for continuous online monitoring of LPS in water.

A colorimetric/ratiometric chemosensor based on an aggregation-induced emission strategy for tracing hypochlorite in vitro and in vivo

Excessive levels of hypochlorite (ClO−) negatively affect environmental and biological systems. Thus, it is essential to develop sensors that can identify ClO− in various systems such as the environment and living organisms. In this study, we report the development and evaluation of a novel aggregation-induced emission (AIE) strategy-based colorimetric and ratiometric fluorescent chemosensor 2,2′-(((1E,1′E)-[2,2′-bithiophene]− 5,5′-diylbis(methanylylidene))bis(hydrazin-1-yl-2-ylidene))bis(N,N,N-trimethyl-2-oxoethan-1-aminium) chloride (BMH-2∙Cl) for detecting ClO−. BMH-2∙Cl enabled highly selective ClO− detection through a color change from yellow to colorless and a fluorescence color change from turquoise to blue in a perfect aqueous solution. BMH-2∙Cl exhibited low limits of detection (2.4 ×10−6 M for colorimetry and 2.9 ×10−7 M for ratiometric fluorescence) for detecting ClO− with a rapid response within 5 s. The detection mechanism for ClO− and an AIE property change of BMH-2∙Cl were demonstrated by 1H NMR titration, ESI-MS, variation of water fraction (fw) and theoretical calculations. In particular, we confirmed not only the practicality of BMH-2∙Cl by using test strips, but also demonstrated the potential for efficient ClO− detection in biological and environmental systems such as real water samples, living zebrafish and bean sprouts.

Biocompatible ratiometric fluorescent chemosensor for ultrasensitive detection of endogenous aminopeptidase N In Vitro and In Vivo

Aminopeptidase N (APN) plays an important role in promoting the circulation of amino acids and influences many important physiological functions of organisms. Monitoring of APN level is of great value for the early clinical diagnosis and prognosis of diseases and certain cancers. In this study, we designed a ratiometric APN fluorescent chemosensor NB-APN by using Nile blue derivative as a fluorophore and alanyl as a recognition unit. After APN was recognized by alanyl of NB-APN, the NB previously blocked by the alanyl group was released, causing the inverse evolution trend of fluorescence intensitis of signal peaks at 675 nm and 610 nm. The ratiometric signal sensitively responded to the concentration of APN, and the detection limit was as low as 15 pg/mL. This chemosensor was successfuly applied for quantitative detection of APN in urine samples. Moreover, the chemosensor realized ratiometric fluorescence imaging of APN in in vitro and in vivo, and demonstrated the potential value of APN in the diagnosis and treatment of liver diseases in a drug-induced liver injury model. Therefore, the proposed chemosensor can potentially be applied in diagnosis of APN-related diseases.

A sensitive ratiometric fluorescent chemosensor for visual and wearable mercury (II) recognition in river prawn and water samples

A novel ratiometric fluorescent probe p-RPT was prepared with triphenylamine and a rhodamine derivative. The probe displays high sensitivity and selectivity for Hg2+, which was applied in real water sample detection and biologic cell imaging. Hydrogel-coated paper sensors were fabricated with p-RPT, which displayed fluorescent colour change upon Hg2+ ion contact with a detection limit of 1.2 × 10-8 M (∼10 ppb). In addition, flexible fluorescent p-RPT gloves were developed for visible and wearable Hg2+ detection and applied to detect mercury (II) in river prawn samples. In summary, the p-RPT probe not only shows great potential in mercury (II) detection for food and water, but also provides a new perspective for wearable sensing apparatus.

Fluorescent RET-Based Chemosensor Bearing 1,8-Naphthalimide and Styrylpyridine Chromophores for Ratiometric Detection of Hg2+ and Its Bio-Application.

Dyad compound NI-SP bearing 1,8-naphthalimide (NI) and styrylpyridine (SP) photoactive units, in which the N-phenylazadithia-15-crown-5 ether receptor is linked with the energy donor naphthalimide chromophore, has been evaluated as a ratiometric fluorescent chemosensor for mercury (II) ions in living cells. In an aqueous solution, NI-SP selectively responds to the presence of Hg2+ via the enhancement in the emission intensity of NI due to the inhibition of the photoinduced electron transfer from the receptor to the NI fragment. At the same time, the long wavelength fluorescence band of SP, arising as a result of resonance energy transfer from the excited NI unit, appears to be virtually unchanged upon Hg2+ binding. This allows self-calibration of the optical response. The observed spectral behavior is consistent with the formation of the (NI-SP)·Hg2+ complex (dissociation constant 0.13 ± 0.04 µM). Bio-imaging studies showed that the ratio of fluorescence intensity in the 440–510 nm spectral region to that in the 590–650 nm region increases from 1.1 to 2.8 when cells are exposed to an increasing concentration of mercury (II) ions, thus enabling the detection of intracellular Hg2+ ions and their quantitative analysis in the 0.04–1.65 μM concentration range.

Two-Photon Photodynamic Therapy Targeting Cancers with Low Carboxylesterase 2 Activity Guided by Ratiometric Fluorescence.

Human carboxylesterase 2 (hCES2) converts anticancer prodrugs, such as irinotecan, into their active metabolites via phase I drug metabolism. Owing to interindividual variability, hCES2 serves as a predictive marker of patient response to hCES2-activated prodrug-based therapy, whereby a low intratumoral hCES2 activity leads to therapeutic resistance. Despite the ability to identify nonresponders, effective treatments for resistant patients are needed. Clinically approved photodynamic therapy is an attractive alternative for irinotecan-resistant patients. Here, we describe the application of our hCES2-selective small-molecule ratiometric fluorescent chemosensor, Benz-AP, as a single theranostic agent given its discovered functionality as a photosensitizer. Benz-AP produces singlet oxygen and induces photocytotoxicity in cancer cells in a strong negative correlation with hCES2 activity. Two-photon excitation of Benz-AP produces fluorescence, singlet oxygen, and photocytotoxicity in tumor spheroids. Overall, Benz-AP serves as a novel theranostic agent with selective photocytotoxicity in hCES2-prodrug resistant cancer cells, making Benz-AP a promising agent for in vivo applications.

An ESIPT-Dependent AIE Fluorophore Based on HBT Derivative: Substituent Positional Impact on Aggregated Luminescence and its Application for Hydrogen Peroxide Detection.

Aiming to develop the facile organic fluorophore possessing excited state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE), we designed and synthesized two isomers with different linkage site between hydroxyl of 2-(2-hydroxyphenyl) benzothiazole (HBT) and a benzothiazole substituent (para position refers to p-BHBT and ortho position refers to o-BHBT). Fluorescence emission properties of p-BHBT and o-BHBT in THF/water mixtures with different water volume fractions indicated an opposite luminescence in aggregates, in which p-BHBT showed an ESIPT-dependent AIE properties while o-BHBT displayed ESIPT effect and aggregation-caused quenching (ACQ) qualities. A possible mechanism for molecular actions to illustrate the aggregating luminescence alteration of these two isomers had been proposed and verified by theoretical and experimental studies. More importantly, Probe-1, generated from dual ESIPT-AIE fluorophore p-BHBT, was successfully used as a ratiometric fluorescent chemosensor for highly selective (above 15-fold over other ROS) and sensitive (69-fold fluorescence enhancement with 0.22 μM of detection limit) detection of hydrogen peroxide in aqueous solution and living cells, respectively.

A Bithiophene‐based Ratiometric Fluorescent Sensor for Sensing Cd2+

AbstractA novel bithiophene‐naphthalene based ratiometric fluorescent chemosensor SS ((2E,2′E)‐2,2′‐([2,2′‐bithiophene]‐5,5′‐diylbis(methanylylidene)) bis(N‐(naphthalen‐1‐yl) hydrazine‐1‐carbothioamide)) for detecting Cd2+ was prepared. SS can detect Cd2+ by a ratiometric fluorescent response with red‐shifted emission from 500 to 540 nm. The binding ratio of SS and Cd2+ was determined to be a 1 : 1 stoichiometry via Job plot. The detection limit was found to be 4.41 μM. The association constant (K) was calculated as 3.00×102 M−1. Sensor SS was successfully applied in real water samples and fluorescent test kits for analysis of Cd2+. The sensing process of SS towards Cd2+ was illustrated by fluorescent, UV‐vis and NMR spectroscopy, ESI‐MS (electrospray ionization‐mass spectrometry), FT‐IR (Fourier transform‐Infrared spectroscopy) and calculations.

An AIRE-active far-red ratiometric fluorescent chemosensor for specifically sensing Zn2+ and resultant Zn2+ complex for subsequent pyrophosphate detection in almost pure aqueous media

A simple Schiff-base fluorescent chemosensor (1) was synthesized by the reaction of 3-amino-pyrazine-2-carbohydrazide and 7-diethylamino-3-formylcoumarin; the sensor 1 displayed a notable green emission at 524 nm in DMSO and an aggregation-induced ratiometric emission (AIRE) at 555 nm in an almost buffered aqueous media (0.5% DMSO content). The AIRE of 1 was quenched following binding to Zn2+ ions, while the fluorescence emission in the far-red region was evidently enhanced at 628 nm. Notably, the ratiometric signal output could be utilized to specifically distinguish Zn2+ among various metal ions. Moreover, the 1-Zn2+ complex was effectively employed as a fluorescent ratiometric chemosensor for pyrophosphate (PPi) detection. The detection limit was 3.52 μM and 2.45 μM for Zn2+ and PPi, respectively. The binding mechanism was evaluated by 1H NMR, ESI-MS, single-crystal X-ray diffraction, TEM, time-resolved fluorescence spectrophotometry, and density functional theory studies. Overall, owing to its sensitive fluorescence behavior, cell imaging studies demonstrated that this sensor is capable of sensing Zn2+ and PPi in living cells.

A novel ratiometric fluorescent chemosensor for detecting malononitrile and application assisted with smartphone

Malononitrile can be transformed into hypertoxic hydrogen cyanide which induces severely jeopardizes to human beings and environment. However, an effective detection technology for malononitrile was still lacking, which means that it is necessary to develop new sensitive analysis technology for malononitrile. Here in, a high sensitive fluorescent probe NQBS for detecting malononitrile was designed and synthesized from the derivative of natural product nopinone. NQBS could selectively recognize malononitrile from 26 kinds of competitive compounds in N, N-dimethylformamide (DMF) solution. The detection limit of NQBS for malononitrile was calculated to be 1.96 μM at the concentration range of 0–25 μM. In addition, the sensing mechanism of NQBS towards malononitrile was proved with high resolution mass spectrometer (HRMS), nuclear magnetic resonance hydrogen spectroscopy (1H NMR), and density functional theory (DFT) calculation analysis as Knoevenagel condensation process and intramolecular cyclization reaction. With the assistance of smartphone and color recognition software, NQBS was well applied in the on-site recognition of malononitrile in real time by analyzing the change trend of the red–greenblue (RGB) value of the NQBS solution.

A dual-channel colorimetric and ratiometric fluorescence chemosensor for detection of Hg2+ ion and its bioimaging applications

A new colorimetric and ratiometric fluorescence chemosensor 4-((3-(octadecylthio)-1,4-dioxo-1,4-dihydronaphthalen-2-yl)amino)benzenesulfonamide (4DBS) was synthesized and investigated for the selective detection of Hg2+ in DMSO-H2O (9:1, v/v) solution. The chemosensor was efficiently synthesized in two steps via Michael-like addition and nucleophilic substitution reactions. The ratiometric fluorescence turn-on response was obtained towards Hg2+, and its fluorescence emission peak was red-shifted by 140 nm with an associated color change from light maroon to pale yellow due to the intramolecular charge transfer effect. The formed coordination metal complex was further evaluated by FT-IR, 1H NMR, and quantum chemical analyses to confirm the binding mechanism. The detection process was sensitive/reversible, and the calculated limit of detection for Hg2+ was 0.451 µM. Furthermore, 4DBS was effectively utilized as a bioimaging agent for detection of Hg2+ in live cells and zebrafish larvae. Additionally, 4DBS showed distinguishing detection of Hg2+ in cancer cells in comparison with normal cells. Thus, 4DBS could be employed as an efficient bioimaging probe for discriminative identification of human cancer cells.

Ratiometric Detection of Mercury (II) Ions in Living Cells Using Fluorescent Probe Based on Bis(styryl) Dye and Azadithia-15-Crown-5 Ether Receptor.

Bis(styryl) dye 1 bearing N-phenylazadithia-15-crown-5 ether receptor has been evaluated as a ratiometric fluorescent chemosensor for mercury (II) ions in living cells. In aqueous solution, probe 1 selectively responds to the presence of Hg2+ via the changes in the emission intensity as well as in the emission band shape, which is a result of formation of the complex with 1:1 metal to ligand ratio (dissociation constant 0.56 ± 0.15 µM). The sensing mechanism is based on the interplay between the RET (resonance energy transfer) and ICT (intramolecular charge transfer) interactions occurring upon the UV/Vis (380 or 405 nm) photoexcitation of both styryl chromophores in probe 1. Bio-imaging studies revealed that the yellow (500–600 nm) to red (600–730 nm) fluorescence intensity ratio decreased from 4.4 ± 0.2 to 1.43 ± 0.10 when cells were exposed to increasing concentration of mercury (II) ions enabling ratiometric quantification of intracellular Hg2+ concentration in the 37 nM–1 μM range.

Rational design of a FRET-based ratiometric fluorescent chemosensor for detecting ClO− with large Stokes based on rhodamine and naphthalimide fluorophores

The design and synthesis of high selective and sensitive fluorescence chemosensor for the determination of ClO− has received great efforts due to its critically important role in the immune system, however, most of chemosensor for detecting ClO− by using single-channel fluorescent signal, which is susceptible to many factors. Herein, a fluorescence resonance energy transfer (FRET)-based ratiometric and colormetric chemosensor containing a 1,8-naphthalimide fluorophore and a rhodamine fluorophore is designed and synthesized for the detection of ClO−, and its structure is characterized by NMR and ESI-MS. The reaction between ClO− and thiosemicarbazide causes the transform of the rhodamine fluorophore from the ring-closed form to the ring-opened form, showing a FRET process with the fluorescence color change from blue to orange. The chemosensor is successfully used for the quantitative detection of ClO− based on the ratio between the fluorescence emission intensities of the two forms, and exhibits a wide linear range of 0–60 μM (R = 0.996) and the detection of limit as low as 4.50 nM. In addition, the detection is highly selective and not significantly affected by various reactive oxygen species (ROS), RNS and other anions in DMSO/PBS buffer (6/4, v/v). The chemosensor can be used for cell staining.

Sensing mechanism of a ratiometric near-infrared fluorescent chemosensor for cysteine hydropersulfide: Intramolecular charge transfer

Previous studies have shown that the cysteine hydropersulfide (Cys-SSH) as the sulfur donor is crucial to sulfur-containing cofactors synthesis. Recently, a selective and sensitive near-infrared ratiometric fluorescent chemosensor Cy-DiSe has been designed and synthesized to detect Cys-SSH spontaneously. Herein, by means of the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) approaches, the sensing mechanism has been thoroughly explored. According to our calculations, the experimental data have been reproduced. The results indicate the intramolecular charge transfer (ICT) is the reason for changes in fluorescence wavelengths. Compared with the chemosensor Cy-DiSe, the larger energy gap of Cy induced by ICT mechanism leads to the blue-shift of the absorption and emission spectra, which guarantees that Cy-DiSe can become a ratiometric fluorescent chemosensor to detect Cys-SSH.

A novel pyrazole bearing imidazole frame as ratiometric fluorescent chemosensor for Al3+/Fe3+ ions and its application in HeLa cell imaging.

New pyrazole bearing imidazole derivative was successfully synthesized and thoroughly characterized by various spectroanalytical techniques. The sensor DIBI shows a highly selective and sensitive fluorescent response with the addition of Al3+/Fe3+ ions in acetonitrile-water mixture. The strong fluorescent molecule exhibits a notable ratiometric emissions at 462nm and 470nm for Al3+ and Fe3+ ions, respectively (λex=280nm). Job's plot studies conclude that the coordination between DIBI with Al3+/Fe3+ was 1:1 binding stoichiometry. The limit of detection of DIBI with Al3+/Fe3+ was calculated as 2.12×10-7M and 1.73×10-6M, respectively. The TD-DFT calculations further supported the photonics performances of the free probe and its complexes. The reversibility and reusability of the sensor molecule are studied using EDTA. The probe was used to track Al3+/Fe3+ in cancer cells via fluorescence microscopy.