Fluorescent Chemosensor Research Articles

Development of Fluorescent Chemosensors for Calcium and Lead Detection.

In the present work, several coumarin-3-carboxamides with different azacrown ether moieties were designed and tested as potential luminescent sensors for metal ions. The derivative containing a 1-aza-15-crown-5 as a metal chelating group was found to yield the strongest response for Ca2+ and Pb2+, exhibiting an eight- and nine-fold emission increase, respectively, while other cations induced no changes in the optical properties of the chemosensor molecule. Job's plots revealed a 1:1 binding stoichiometry, with association constants of 4.8 × 104 and 8.7 × 104 M-1, and limits of detection of 1.21 and 8.04 µM, for Ca2+ and Pb2+, respectively. Computational studies suggest the existence of a PET quenching mechanism, which is inhibited after complexation with each of these two metals. Proton NMR experiments and X-ray crystallography suggest a contribution from the carbonyl groups in the coumarin-3-carboxamide fluorophore in the coordination sphere of the metal ion.

Naphthalimide-based AIE-active receptor: HSO4−/SO42− sensing and detection of Pb2+ by receptor-anion ensemble in aqueous medium

Herein we report a naphthalimide-chromophore based blue light emitting Aggregation-Induced Emission (AIE) active fluorescent chemo-sensor for the selective turn-on fluorescent sensing of HSO4−/SO42− ions in the aqueous medium through in-depth spectroscopic and microscopic analysis. HSO4−/SO42−sensing in aqueous environment is quite challenging due to its high hydration energy, however Nap-1 showed a detection limit down to the micromolar range without any interference from the other tested competitive anions. The sensing mechanism has been discussed thoroughly. Nap-1 was further applied in detection of HSO4−/SO42− ions in real water as well as in fabrication of an economical paper strip model. The receptor-anion ensemble was further used for the sensing of heavy metal ions such as Pb2+ in the micromolar range. Nap-1 was used for the construction of two inputs INHIBIT type molecular logic gate.

Bodipy-based quinoline derivative as a highly Hg2+-selective fluorescent chemosensor and its potential applications

A highly efficient sensor has been successfully developed using quinoline-based BODIPY compounds (8-quinoline-4,4-difluoro-4-boro-3a, 4a-diazaindacene (C1) and 7-hydroxy-8-quinoline-4,4-difluoro-4-boro-3a, 4a-diazindacene (C2) to detect Hg2+ ions. The sensor C1 exhibits remarkable selectivity in detecting Hg2+ with a limit of detection 3.06 × 10-8 mol/L. The developed chemical sensors have shown stability, cost-effectiveness, ease of preparation, and remarkable selectivity towards Hg2+ ions compared to other commonly occurring metal ions. The total recovery of the sensor C1 can be achieved by using a 0.1 mol/L solution of KI. The proposed sensor C1 has been applied to determine Hg2+ in tap and distilled water, yielding excellent results. In addition, the binding mode of C1-Hg2+ and C2-Hg2+ complexes was a 1:1 ratio confirmed by mass spectra, Job’s plot, and DFT study. Moreover, the sensor C1 successfully applied for the biological studies results in negligible cytotoxicity, which demonstrates it can be used to determine Hg2+ in HT22 cells.

Surface-modified gold nanoparticles: A novel chemical probe for precise fluorescent detection of aluminium (Al3+) ions; investigating DFT insights and molecular logic gate behaviour

Trivalent metal cation fluorescence chemosensors are one of the most important areas of research because of their rarity. The necessity for easy-to-synthesize molecular chemosensors and to immobilize them on materials platform are enhancing continually. In this paper, we report the rapid sensing of Al3+ ion recognition by naphthalene derivative (N1) and tethered with gold nanoparticles (N1-AuNps). The cysteine-carrying naphthalene derivative is synthesized (Receptor-N1) and it forms a self-assembled monolayer on gold nanoparticles through the thiol moiety (N1-AuNPs). The structure of the synthesized receptor and the chemosensor assembled with AuNPs are characterized using spectroscopic and imaging techniques. On the gold nanoparticles, the surface-assembled compound highly selectively binds with Al3+ ion in the aqueous medium compared with a free receptor (N1). We present an improved colorimetric method that offers both high sensitivity and rapid detection for transition metal ions, specifically Al3+ ions. The determination of the binding stoichiometry and binding ratio between N1 / N1-AuNPs and Al3+ ion was achieved through the utilization of Jobs' plot and B-H plot which confirmed a 1:1 ratio. The binding phenomenon between N1-AuNPs and Al3+ ion has been ascertained to be predominantly according to the limited PET with CHEF impact technique. The N1-AuNPs chemosensor responds to H+ and Al3+ ions by demonstrating XOR molecular logic gate functionality and operating across a wide pH range. The nanoparticle-tethered chemosensor presents an effective system that can be employed in Al3+ ion sensing. The addition of Na2EDTA to the [N1-AuNPs - Al3+] complex solution caused a quenching of the fluorescence emission, which provides evidence of the reversible nature of the chemosensor. To gain further insights into the binding mode of Al3+ with N1-AuNPs, quantum mechanical investigations using density functional theory (TDDFT) have been conducted. We evaluated the effectiveness of our methodology for quantifying Al3+ ions in the water waste produced by significant industrial reactions.

Exploring the probing capacities of MSA capped CdTe semiconductor quantum dots as optical chemsensors via analytical and isotherms modeling for selective Hg2+ detection

Heavy metal ions bioaccumulation can cause severe damage to environment and human health. Hence, the development of an effective detection assay of trace amounts of these ions is of great importance. Here, CdTe quantum dots (QDs) capped with mercaptosuccinic acid (MSA) ligands have been synthesized in aqueous solution with significant stability and good fluorescence properties. Photophysical characterization was performed using FTIR, XRD, HRTEM and UV–Vis. Absorption, PL and PLRT techniques, seeking their subsequent application as fluorescent probes for metal cations. CdTe-MSA QDs showed selective sensitivity toward Hg2+ ions by monitoring quantitative fluorescence quenching with increasing analyte content. Under optimal conditions, the linear range for the detection was 0.2–6 μM with a detection limit of 0.05 μM. According to the Stern–Volmer model, it can be inferred that a static quenching mechanism via Hg2+ selective binding to MSA carboxylate groups is operating with electron transfer process. Excess of mercuric ions further decreased and red shifted the fluorescence possibly due to competitive cation exchanges. To further explain the corresponding ligation mechanisms, adsorption behavior study was conducted via several isotherms as well as statistical physics models. The pseudo-first-order model can describe the adsorption kinetics of Hg2+ on CdTe-MSA QDs more accurately and the experimental data fitted well the Langmuir isotherm model of monolayer adsorption on homogeneous surface. Furthermore, this spontaneous process conforms to the Hill model as a physisorption with an adsorption energy of 32 kJ.mol−1 associated with the electrostatic interactions and hydrogen bonding. The developed system was assayed in the Hg2+ trace amount detection in real tap water and showed satisfactory accuracy performance meeting analytical requirements. The relevant results demonstrated that CdTe-MSA QDs could be deployed as promising Hg2+ fluorescent chemosensing system with high sensitivity and selectivity over wide linear detection range that have great potential for real water samples analysis.

Synthesis of Di(thiophen-2-yl) Substituted Pyrene-Pyridine Conjugated Scaffold and DFT Insights: A Selective and Sensitive Colorimetric, and Ratiometric Fluorescent Sensor for Fe(III) Ions.

In this context, we used the multicomponent Chichibabin pyridine synthesis reaction to synthesize a novel di(thiophen-2-yl) substituted and pyrene-pyridine fluorescent molecular hybrid. The computational (DFT and TD-DFT) and experimental investigations were performed to understand the photophysical properties of the synthesized new structural scaffold. The synthesized ligand displays highly selective fluorescent sensing properties towards Fe3+ ions when compared to other competitive metal ions (Al3+, Ba2+, Ca2+, Cd2+, Co2+, Cr3+, Cu2+, Fe2+, Hg2+, Na+, Ni2+, Pb2+, Sr2+, Sn2+ and Zn2+). The photophysical properties studies reveal that the synthesized hybrid molecule has a binding constant of 2.30 × 103M-1 with limit of detection (LOD) of 4.56 × 10-5M (absorbance mode) and 5.84 × 10-5M (emission mode) for Fe3+ ions. We believe that the synthesized pyrene-conjugated hybrid ligand can serve as a potential fluorescent chemosensor for the selective and specific detection of Fe3+ ions.

A fluorescence chemo sensor approach for determination of finerenone in pharmaceutical formulation and human plasma: Method development and validation

Finerenone, a non-steroidal mineralocorticoid receptor antagonist, has gained recent approval for treating cardiovascular and kidney-related conditions. Herein, an innovative fluorescence chemo sensor was developed for the determination of finerenone in the pharmaceutical dosage form and the plasma matrix. The method is basically based on chemical transformation of finerenone into a fluorescent product through sequential reactions. This transformation occurs through a sequence of steps involving the interaction of finerenone with trimethylamine, resulting in the formation of a nucleophilic intermediate that subsequently reacts with bromoacetyl bromide to form fluorescent product, (S)-N-(2-bromoacetyl)-4-(4-cyano-2-methoxyphenyl)-5-ethoxy-2,8-dimethyl-1,4-dihydro-1,6-naphthyridine-3-carboxamide. The formed fluorescent product exhibits defined emission peak at 338 nm when excited at 248 nm. Significant concentration-dependent fluorescence enhancement was obtained enabling precise finerenone determination in the pharmaceutical formulation and plasma matrix. The method was optimized and validated providing sensitive determination over linearity range of 1–200 ng/mL with a lower limit of detection at 0.280 ng/mL. This strategy provides an efficient, economical substitute and straightforward, more sensitive analytical method for finerenone assessment in various matrices, in contrast to the previously published method, high-performance liquid chromatography-tandem mass spectrometry, which is expensive and time-consuming.

Fluorescent chemosensors facilitate the visualization of plant health and their living environment in sustainable agriculture.

Globally, 91% of plant production encounters diverse environmental stresses that adversely affect their growth, leading to severe yield losses of 50-60%. In this case, monitoring the connection between the environment and plant health can balance population demands with environmental protection and resource distribution. Fluorescent chemosensors have shown great progress in monitoring the health and environment of plants due to their high sensitivity and biocompatibility. However, to date, no comprehensive analysis and systematic summary of fluorescent chemosensors used in monitoring the correlation between plant health and their environment have been reported. Thus, herein, we summarize the current fluorescent chemosensors ranging from their design strategies to applications in monitoring plant-environment interaction processes. First, we highlight the types of fluorescent chemosensors with design strategies to resolve the bottlenecks encountered in monitoring the health and living environment of plants. In addition, the applications of fluorescent small-molecule, nano and supramolecular chemosensors in the visualization of the health and living environment of plants are discussed. Finally, the major challenges and perspectives in this field are presented. This work will provide guidance for the design of efficient fluorescent chemosensors to monitor plant health, and then promote sustainable agricultural development.

A chloromethyl-triazole fluorescent chemosensor for O6-methylguanine DNA methyltransferase.

Fluorescent chemosensors offer a direct means of measuring enzyme activity for cancer diagnosis, predicting drug resistance, and aiding in the discovery of new anticancer drugs. O6-methylguanine DNA methyltransferase (MGMT) is a predictor of resistance towards anticancer alkylating agents such as temozolomide. Using the fluorescent molecular rotor, 9-(2-carboxy-2-cyanovinyl)julolidine (CCVJ), we synthesized, and evaluated a MGMT fluorescent chemosensor derived from a chloromethyl-triazole covalent inhibitor, AA-CW236, a non-pseudosubstrate of MGMT. Our fluorescence probe covalently labelled the MGMT active site C145, producing a 18-fold increase in fluorescence. Compared to previous fluorescent probes derived from a substrate-based inhibitor, our probe had improved binding and reaction rate. Overall, our chloromethyl triazole-based fluorescence MGMT probe is a promising tool for measuring MGMT activity to predict temozolomide resistance.

Small-molecule fluorogenic probes based on indole scaffold.

Indoles are the most versatile organic N-heterocyclic compounds widely present in bioactive natural products and used in different fields such as coordination chemistry, pharmacy, dyes, and medicine, as well as in the biology and polymer industries. More recently, the indole scaffold has been widely used in analytical chemistry for the design and development of small-molecule fluorescent chemosensors in the fields of molecular recognition and molecular imaging. The indole-based chemosensor derivatives contain heteroatoms like N-, O-, and S-, through which they interact with analytes (cations, anions, and neutral species), producing measurable analytical signals that can be used for the fluorimetric and colorimetric detection of different analytes in biological, agricultural and environmental samples. This review focuses on indole-based small-molecule fluorimetric and colorimetric chemosensors for detecting cations, anions, and neutral species in a comprehensive manner. Furthermore, the recognition mechanisms are discussed in detail, which could help researchers design and develop more powerful and efficient fluorescent chemosensors in the near future.

5-Aminoisophthalate-based kojic acid-appended bis-1,2,3-triazole: a fluorescent chemosensor for Cu2+ sensing and in silico study.

A new, easy-to-prepare, and highly selective fluorescent chemosensor, i.e., 5-aminoisophthalate-based kojic acid-appended bis-1,2,3-triazole, was synthesized from an alkyne of 5-aminoisophthalic acid and azido-kojic acid using Cu(i)-catalyzed click chemistry and then successfully characterized. The alkyne structure of 5-aminoisophthalic acid, 1, was supported by the single-crystal X-ray crystallographic data. The fluorescent probe 3 was found to be highly selective for Cu2+ ions supported by the Job's plot with a stoichiometric ligand : metal ratio of 2 : 1, exhibiting almost a two-fold enhancement in the emission intensity upon the addition of Cu2+ ions (0-25 μM) with a detection limit of 8.82 μM. A comparison with LODs from previously developed chemosensors for Cu2+ ions was also conducted. Reversibility analysis indicated that probe 3 could be used as both a reusable sensor and as a scavenger of copper ions. DFT calculations with the basis sets B3LYP/6-311G(d,p) and LanL2DZ were employed for geometrical optimizations of structures of the alkyne 1, azide 2, probe 3, and complex 3.Cu2+. Hirshfeld surface analysis revealed significant intermolecular interactions in compound 1. Additionally, molecular docking for the antimicrobial activity showed the better antibacterial efficacy of probe 3.

An O-vanillin scaffold as a selective chemosensor of PO43− and the application of neural network based soft computing to predict machine learning outcomes

O-Vanillin derived Schiff base 1-[(E)-(2-hydroxy-3-methoxybenzylidene) amino]-4-methylthiosemicarbazone (VCOH) has been synthesized for colorimetric and fluorescence chemosensors towards PO43− ions.

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.

Nanoarchitectonics of highly dispersed polythiophene on paper for accurate quantitative detection of metal ions

Paper fibers allow the high dispersion of a fluorescent polythiophene chemosensor for the suppression of aggregation-induced quenching, which is applied to the solid-state fluorescent quantitative sensing of metal ions using imaging analysis and pattern recognition techniques.

A simple 'turn-on' fluorescence chemosensor for Al(iii) detection in aqueous solution and solid matrix.

A simple fluorescence chemosensor of FHS-OH based on salicylaldehyde Schiff base was developed via a one-step reaction, which achieved a fast and highly selective response for Al(iii). Mechanism studies showed that when FHS-OH was exposed to Al(iii) with 1 : 2 binding stoichiometry in an aqueous solution at neutral pH, C[double bond, length as m-dash]N isomerization and PET processes were limited, resulting in a 'turn-on' fluorescence response with a low detection limit of 63 nmol L-1 and a satisfying linear range of 0.0-20.0 μmol L-1. Compared to traditional detection methods for Al(iii), fluorometry using FHS-OH has several advantages, including simplicity, quick response, and capability of real-time detection. More importantly, the detection of Al(iii) on a solid matrix (test paper) was successfully achieved. After the addition of Al(iii), a significant emission colour change from green to bright blue was observed by the naked eye owing to the intrinsic aggregation-induced emission (AIE) characteristic of FHS-OH.

Detection of TNP and sulfite ions in an aqueous medium using a pyrazinium-based chemosensor

A pyrazinium-based fluorescent chemosensor exhibited effecient detection of TNP and sulfite ions in aqueous medium. The chemosensor with a visually detectable color change in the presence of sulfite was integrated with a smartphone.

Viscosity-sensitive and AIE-active bimodal fluorescent probe for the selective detection of OCl- and Cu2+: a dual sensing approach via DFT and biological studies using green gram seeds.

A novel dual-mode viscosity-sensitive and AIE-active fluorescent chemosensor based on the naphthalene coupled pyrene (NCP) moiety was designed and synthesized for the selective detection of OCl- and Cu2+. In non-viscous media, NCP exhibited weak fluorescence; however, with an increase in viscosity using various proportions of glycerol, the fluorescence intensity was enhanced to 461 nm with a 6-fold increase in fluorescence quantum yields, which could be utilized for the quantitative determination of viscosity. Interestingly, NCP exhibited novel AIE characteristics in terms of size and growth in H2O-CH3CN mixtures with high water contents and different volume percentage of water, which was investigated using fluorescence, DLS study and SEM analysis. Interestingly, this probe can also be effectively employed as a dual-mode fluorescent probe for light up fluorescent detection of OCl- and Cu2+ at different emission wavelengths of 439 nm and 457 nm via chemodosimetric and chelation pathways, respectively. The fast-sensing ability of NCP towards OCl- was shown by a low detection limit of 0.546 μM and the binding affinity of NCP with Cu2+ was proved by a low detection limit of 3.97 μM and a high binding constant of 1.66 × 103 M-1. The sensing mechanism of NCP towards OCl- and Cu2+ was verified by UV-vis spectroscopy, fluorescence analysis, 1H-NMR analysis, mass spectroscopy, DFT study and Job plot analysis. For practical applications, the binding of NCP with OCl- and Cu2+ was determined using a dipstick method and a cell imaging study in a physiological medium using green gram seeds.

A dual emitting CsPbBr3/Eu-BDC composite as a ratiometric photoluminescent turn-on probe for aliphatic amine sensing.

The impressive photoluminescence properties of all inorganic cesium lead halide perovskite quantum dots (PeQDs) make them highly intriguing for fluorescence chemosensor applications. Herein, a ratiometric dual emitting perovskite-based sensor was designed by synthesizing fluorescent CsPbBr3 PeQDs in situ within a matrix of Eu-BDC (Eu(III) benzene-1,4-dicarboxylate). The results presented here establish the suggested sensor's quick and selective turn-on PL response to volatile primary aliphatic amine derivatives. In the presence of amines, the designed CsPbBr3/Eu-BDC sensor exhibits an enhancement of the PL signal of CsPbBr3 at 518 nm and the Eu-BDC signal at 615 nm served as a standard for constructing the ratiometric sensing system. Thereby, a visual color change from red to green was observed with the incremental addition of methylamine to the probe. A low detection limit of 0.083 ppm was determined for methylamine. In both the solution and vapor phases, this ratiometric sensor responds to a variety of primary aliphatic amines with very quick and strong fluorescence. Moreover, the sensor was effectively used for monitoring meat spoilage owing to the emission of biogenic amine vapor from meat products.

New type of tin(IV) complex based turn-on fluorescent chemosensor for fluoride ion recognition: elucidating the effect of molecular structure on sensing property.

A novel type of chemosensor based on tin(IV) complexes incorporating hydroxyquinoline derivatives has been designed and investigated for selectively detecting fluoride ions. Sn(meq)2Cl2 (meq = 2-methyl-8-quinolinol) (complex 1) exhibits a significant enhancement in luminescence upon the introduction of fluoride ions. This enhancement greatly surpasses that observed with Snq2Cl2 and Sn(dmqo)2Cl2 (q = 8-hydroxyquinnoline; dmqo = 5,7-dimethyl-8-quinolinol). Furthermore, complex 1 displays excellent sensitivity and selectivity for fluoride detection in comparison to halides and other anions. As a result, complex 1 serves as an outstanding turn-on fluorescent chemosensor, effectively sensing fluoride ions. The Benesi-Hilderbrand method and Job's plot confirmed that complex 1 associates with F- in a 1 : 2 binding stoichiometry. Also, complex 1 exhibited a large binding constant (pKb = 10.4 M-2) and a low detection limit (100 nM). To gain a deeper insight into the photophysical properties and the underlying mechanism governing the formation of the tin(IV) fluoride complex via halide exchange, we successfully synthesized partially fluorinated Sn(meq)2F0.67Cl1.33 (2) and fully fluorinated Sn(meq)2F2 (3), all of which were characterized through computational studies, thereby elucidating their photophysical properties. DFT studies reveal that converting Sn(meq)2Cl2 to Sn(meq)2F2, an endergonic process, leads to greater stability due to reducing steric hindrance about the metal center. Furthermore, the fluorinated complex significantly increases dipole moment, resulting in high affinity toward the F- ion.

Reactivity-based amino-1,8-naphthalimide fluorescent chemosensors for the detection and monitoring of phosgene

This review provides an overview of the latest developments using amino-1,8-naphthalimide-based small-molecule fluorescent probes designed for phosgene detection and sensing.