A benzothiazole-based chemosensor for significant fluorescent turn-on and ratiometric detection of Al3+ and its application in cell imaging

Luminous Insights: Exploring Organic Fluorescent "Turn-On" Chemosensors for Metal-Ion (Cu+2, Al+3, Zn+2, Fe+3) Detection

There are several metal ions that are vital for the growth of the environmental field as well as for the biological field but only up to the maximum limit. If they are present in excess, it could be hazardous for the human health. With the growing technology, a series of various detection techniques are employed in order to recognize those metal ions, some of them include voltammetry, electrochemical methods, inductively couples, etc. However, these techniques are expensive, time consuming, requires large storage, advanced instrumentation, and a skilled person to operate. So, here comes the need of a sensor and it is defined as a miniature device which detects the substance of interest by giving response in the form of energy change. So, from past few decades, many sensors have been formulated for detecting metal ions with some basic characteristics like selectivity, specificity, sensitivity, high accuracy, lower detection limit, and response time. Detecting various metal ions by employing chemosensors involves different techniques such as fluorescence, phosphorescence, chemiluminescence, electrochemical, and colorimetry. The fluorescence technique has certain advantages over the other techniques. This review mainly focuses on the chemosensors that show a signal in the form of fluorescence to detect Al+3, Zn+2, Cu+2, and Fe+3 ions.

Turn-on detection of Al3+ ions using quinoline-based tripodal probe: mechanistic investigation and live cell imaging applications

In this study, an easily synthesizable Schiff base probe TQSB having a quinoline fluorophore is demonstrated as a fluorescent and colorimetric turn-on sensor for Al3+ ions in a semi-aqueous medium (CH3CN/water; 4 : 1; v/v). Absorption, emission and colorimetric studies clearly indicated that TQSB exhibited a high selectivity toward Al3+, as observed from its excellent binding constant (Kb = 3.8 × 106 M-1) and detection limit (7.0 nM) values. TQSB alone was almost non-fluorescent in nature; however, addition of Al3+ induced intense fluorescence at 414 nm most probably due to combined CHEF (chelation-enhanced fluorescence) and restricted PET effects. The sensing mechanism was established via Job's plot, NMR spectroscopy, ESI-mass spectrometry, and density functional theory (DFT) analyses. Furthermore, to evaluate the applied potential of probe TQSB, its sensing ability was studied in real samples such as soil samples and Al3+-containing Digene gastric tablets as well as on low-cost filter paper strips. Fluorescence microscopy imaging experiments further revealed that TQSB can be used as an effective probe to detect intracellular Al3+ in live cells with no cytotoxicity.

Real samples sensitive dopamine sensor based on poly 1,3-benzothiazol-2-yl((4-carboxlicphenyl)hydrazono)acetonitrile on a glassy carbon electrode

Herein, a novel electrochemical sensor that was used for the first time for sensitive and selective detection of dopamine (DA) was fabricated. The new sensor is based on the decoration of the glassy carbon electrode surface (GC) with a polymer film of 1,3-Benzothiazol-2-yl((4-carboxlicphenyl)hydrazono)) acetonitrile (poly(BTCA). The prepared (poly(BTCA) was examined by using different techniques such as 1H NMR, 13C NMR, FTIR, and UV-visible spectroscopy. The electrochemical investigations of DA were assessed using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results obtained showed that the modifier increased the electrocatalytic efficiency with a noticeable increase in the oxidation peak current of DA in 0.1 M phosphate buffer solution (PBS) at an optimum pH of 7.0 and scan rate of 200 mV/s when compared to unmodified GC. The new sensor displays a good performance for detecting DA with a limit of detection (LOD 3σ), and limit of quantification (LOQ 10σ) are 0.28 nM and 94 nM respectively. The peak current of DA is linearly proportional to the concentration in the range from 0.1 to 10.0 µM. Additionally, the fabricated electrode showed sufficient reproducibility, stability, and selectivity for DA detection in the presence of different interferents. The proposed poly(BTCA)/GCE sensor was effectively applied to detect DA in the biological samples.

Review on Synthesis of 2-(2-Hydroxyaryl) Benzothiazoles (HBT) for Excited-State Intra-molecular Proton Transfer (ESIPT)-Based Detection of Ions and Biomolecules

In this review, we present a systematic and comprehensive summary of the recent developments in the synthetic strategies of 2-(2-hydroxyarylsubstituted)-benzothiazole (HBT) framework along with incorporation of various substituents on phenolic and benzothiazole rings which affect the emission process. The literature, spanning the years 2015-2024, on excited-state intramolecular proton transfer (ESIPT)-based studies of HBT derivatives comprising the effects of solvent polarity, substituents, and extended conjugation on fluorophores has been searched. ESIPT, intramolecular charge transfer, and aggregation-induced emissions enable these fluorescent probes to specifically interact with analytes, thereby altering their luminescence characteristics to achieve analyte detection. These fluorescent probes exhibit large Stokes shifts, high quantum yields, and excellent color transitions. Finally, the applications of HBTs as ESIPT-based fluorescent probes for the detection of cations, anions, and biomolecules have been summarized. We anticipate that this review will provide a comprehensive overview of the current state of research in this field and encourage researchers to develop novel ESIPT-based fluorophores with new applications.

A Review on Small Molecule Based Fluorescence Chemosensors for Bioimaging Applications

This review provides a thorough examination of small molecule-based fluorescence chemosensors tailored for bioimaging applications, showcasing their unique ability to visualize biological processes with exceptional sensitivity and selectivity. It explores recent advancements, methodologies, and applications in this domain, focusing on various designs rooted in anthracene, benzothiazole, naphthalene, quinoline, and Schiff base. Structural modifications and molecular engineering strategies are emphasized for enhancing sensor performance, including heightened sensitivity, selectivity, and biocompatibility. Additionally, the review offers valuable insights into the ongoing development and utilization of these chemosensors, addressing current challenges and charting future directions in this rapidly evolving field.

A quinoline derived Schiff base as highly selective 'turn-on' probe for fluorogenic recognition of Al3+ ion

A quinoline-derived Schiff base QnSb has been synthesized for fluorescent and colorimetric recognition of Al3+ ions in a semi-aqueous medium. The compound QnSb has been characterized by elemental analysis, FT-IR, 1H/13C NMR, UV-Vis and fluorescence spectral techniques. The crystal structure of the QnSb was confirmed by single crystal X-ray diffraction (SC-XRD) analysis. Notably, almost non-fluorescent QnSb served as a 'turn on' responsive probe for Al3+ by inducing a remarkable fluorescence enhancement at 422 nm when excited at 310 nm. The probe QnSb exhibited high selectivity for Al3+ in CH3CN/H2O (4:1, v/v) solution over several competing metal ions (e.g., Mg2+, Pb2+, Zn2+, Cd2+, Co2+, Cu2+, Ca2+, Ni2+, Fe3+/2+, Cr3+, Mn2+, Sn2+, and Hg2+). The limit of detection (LoD) was computed as low as 15.8 nM which is significantly lower than the permissible limit set by WHO for Al3+ ions in drinking water. A 1:1 binding stoichiometry of complex QnSb-Al3+ was established with the help of Job's plot, ESI-MS, NMR and DFT analyses. Based on its remarkable sensing ability, the probe QnSb was utilized to establish molecular logic gates, and the fluorescence detection of Al3+ could clearly be demonstrated on the filter paper test strips.

Fluorescent dyes based on rhodamine derivatives for bioimaging and therapeutics: recent progress, challenges, and prospects

Since their inception, rhodamine dyes have been extensively applied in biotechnology as fluorescent markers or for the detection of biomolecules owing to their good optical physical properties. Accordingly, they have emerged as a powerful tool for the visualization of living systems. In addition to fluorescence bioimaging, the molecular design of rhodamine derivatives with disease therapeutic functions (e.g., cancer and bacterial infection) has recently attracted increased research attention, which is significantly important for the construction of molecular libraries for diagnostic and therapeutic integration. However, reviews focusing on integrated design strategies for rhodamine dye-based diagnosis and treatment and their wide application in disease treatment are extremely rare. In this review, first, a brief history of the development of rhodamine fluorescent dyes, the transformation of rhodamine fluorescent dyes from bioimaging to disease therapy, and the concept of optics-based diagnosis and treatment integration and its significance to human development are presented. Next, a systematic review of several excellent rhodamine-based derivatives for bioimaging, as well as for disease diagnosis and treatment, is presented. Finally, the challenges in practical integration of rhodamine-based diagnostic and treatment dyes and the future outlook of clinical translation are also discussed.

A novel fluorescence probe for the recognition of Cd2+ and its application

A facile fluorescence probe BQBH was synthesized and investigated on its spectrum property. The result showed that the BQBH had high sensitivity and selectivity for Cd²⁺ with lowest detection determined as 0.14 μM by fluorescence response. The 1: 1 binding ratio between BQBH and Cd²⁺ was determined by Job's plot, and the binding details were further confirmed by ¹H NMR titration, FT-IR spectrum and HRMS analysis. The applications including on test paper, smart phone and cell image were all also investigated.

Benzothiazole-based novel fluorescence probe sensing 1, 3-diaminopropane

Amines are extensively present in biological systems and are abundantly used in research, industries and agriculture. Systematic detection and quantification of certain amines can help us in food quality control and diagnosis of many diseases. A Schiff base probe HL was designed and successfully synthesized. It was proposed as a sensor for the exclusive detection of 1, 3- diaminopropane through turn-on fluorescence response in a variety of solvents including water. Micromolar limits of detection was achieved in all these solvents. Mechanism of detection was proposed by investigating mass spectrometric and NMR results. These were corroborated with DFT/TD-DFT calculations. Spiking experiments performed in various real water samples revealed the potential of the sensor to be used in day-to-day applications. Paper strip experiments demonstrated the suitability of the probe for real-life applications.

Control of selectivity in the preparation of 2-substituted benzoazoles by adjusting the surface hydrophobicity in two solid-based sulfonic acid catalysts

A series of metal-free tandem reactions for the synthesis of pharmaceutically important 2-substituted benzoazoles from isothiocyanates and 2-aminothiophenol under catalyst-free conditions in the presence of Et-PMO-Me-PrSO₃H (1a) and SBA-15-PrSO₃H (1b) as solid acids were carried out in a highly selective way under solvent free conditions. A significant selectivity changeover toward either 2-mercaptobenzoxazole or 2-aminobenzoazole derivatives could be achieved by changing the employed catalyst from the relatively hydrophobic material 1a to the more hydrophilic catalyst 1b. This simple experimental procedure with a novel selective approach toward benzoazoles accompanied by green and reusable catalysts could be considered as an alternative to the existing methods for the synthesis of 2-substituted benzoazole derivatives.

A novel dual-function probe for fluorescent turn-on recognition and differentiation of Al3+ and Ga3+ and its application

In this study, a novel dual-function probe BMP based on benzothiazole was easily synthesized and characterized through common optical technique. In the system consisting of DMF/H₂O (v/v, 2/3), probe BMP showed azure and blue-green to Al³⁺ and Ga³⁺, respectively. Besides, the binding ratios of BMP to Al³⁺ and Ga³⁺ were determined as 1:1, which confirmed by Job's plot. Furthermore, for Al³⁺ and Ga³⁺, the limit of detection (LOD) was determined to be 1.51 × 10^-6 M and 4.28 × 10^-6 M, respectively. Moreover, it was worth noting that BMP showed good performances in paper colorimetry, cell phone colorimetric identification and cell imaging.

A ratiometric fluorescent probe based on a dual-ligand lanthanide metal–organic framework (MOF) for sensitive detection of aluminium and fluoride ions in river and tap water

A dual-emission fluorescent probe towards Al3+ and F− using a Ln-MOF material Eu-BDC-NH2/TDA is employed with exceptional sensitivity, high selectivity, low LOD, excellent anti-interference characteristics and direct visual observation.

Synthesis and Characterization of a Carbazole-Based Schiff Base Capable of Detection of Al3+ in Organic/Aqueous Media

A new fluorescence probe (L) selectively detecting Al³⁺ ions was synthesized via the condensation reaction, and characterized using UV-Vis, FT-IR, ¹H-NMR and ¹³C-NMR spectroscopic techniques. The limit of detection for Al³⁺ ions of this synthesized probe was found to be 9.29 × 10^-7 M, while the Ka constant value was determined to be 1.64 × 10⁴ M^-1. The stoichiometric binding ratio of L-Al³⁺ was found to be 2:1 using the Job's plot method, and this ratio was also confirmed by ¹H-NMR titration and mass spectrometry. The recyclability of the chemosensor was found by the fluorescence method through the addition of EDTA to the L-Al³⁺ solution. The obtained data showed that the carbazole-based Schiff base acted as an ideal chemosensor for Al³⁺. Carbazole-based Schiff base as a fluorescent sensor for detection of Al³⁺ was synthesized and characterized. The association constant (K_a) was calculated to be 1.64 × 10⁴ M^-1 and the limit of detection (LOD) value was determined to be 9.29 × 10^-7 M. It was determined that th Schiff base was bound to Al³⁺ ions in 2:1 stoichiometric ratio. In the presence of other competitive metal cations, the selectivity of sensor L to Al³⁺ was not significantly affected.

A Significant Fluorescence Turn-On Probe for the Recognition of Al3+ and Its Application

An easy prepared probe, BHMMP, was designed and synthesized, which displayed a significant fluorescence enhancement (over 38-fold) and obvious color change in the recognition of Al³⁺. The binding ratio of probe BHMMP to Al³⁺ was determined as 1:1, according to Job plot. The binding mechanism was fully clarified by the experiments, such as FT-IR spectrum, ESI-MS analysis, and ¹H NMR titration. A DFT study further confirmed the binding mode of BHMMP to Al³⁺. The limit of detection (LOD) for Al³⁺ was determined as low as 0.70 µM, based on the fluorescence titration of BHMMP. Moreover, the results from real sample experiments, including real water samples, test papers, and cell images, well-demonstrated that BHMMP was capable of sensing Al³⁺ in environmental and biological systems.

New Fluorescent Probes for the Sensitive Determination of Glyphosate in Food and Environmental Samples

In this paper, a dual-functional probe, 2-(benzothiazol)-4-(3-hydroxy-4-methylphenyl) imino phenol (BHMH), was synthesized and characterized for the simultaneous detection of Cu2+ and Fe3+ in dimethyl sulfoxide/4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (DMSO/HEPES) (1:4, v/v, pH = 6.0). The limits of detections (LODs) for Cu2+ and Fe3+ were 9.05 and 48 nM, respectively. Based on the competitive coordination, the complex BHMH-Cu2+/Fe3+ exhibited good sensitivity and selectivity for glyphosate. The LODs of BHMH-Cu2+ and BHMH-Fe3+ for glyphosate were 0.41 and 0.63 μM, respectively. The probe quantitatively detected glyphosate in tap water, Songhua River water, local water and soil, and food samples. The colorimetric on-site glyphosate sensing through the probe BHMH-Cu2+ was also studied based on smartphones. BHMH and BHMH-Cu2+/Fe3+ exhibited outstanding imaging capabilities for Cu2+, Fe3+, and glyphosate in living cells with low cytotoxicity, especially the first time for glyphosate.

A Facile Probe for Fluorescence Turn-on and Simultaneous Naked-Eyes Discrimination of H2S and biothiols (Cys and GSH) and Its Application

Hydrogen sulfide and biothiol molecules such as Cys and GSH acted important roles in many physiological processes. To simultaneously detect and distinguish them was quite necessary by a suitable fluorescent probe. A novel chemosensor 4-(4-(benzo[d]thiazol-2-yl)-2-methoxyphenoxy)-7-nitrobenzo[c][1,2,5]oxadiazole (BMNO) was designed to detect H₂S/Cys/GSH using the combination of nitrobenzofurazan (NBD) and benzothiazole fluorophores linked by a facile ether bond. The probe BMNO was developed for simultaneous identification of H₂S, Cys and GSH. Noticeably, the color changes (from colorless to light purple, light orange and light yellow) of probe BMNO solutions for sensing H₂S, Cys and GSH could be observed by naked eyes, respectively. The probe BMNO exhibited high selectivity and sensitivity for H₂S, Cys and GSH showing distinct optical signal with detection limit as low as 0.15 μM, 0.03 μM and 0.14 μM, respectively. The sensing mechanism was clarified by spectrum analysis and some controlled experiments. In addition, these outstanding properties of probe BMNO enabled its practical applications in detection H₂S in beer, and in cell imaging for Cys and GSH as well.

Development of a fluorescent probe for detecting Al3+ in cooked wheaten food based on phosphonic acid group functionalized polythiophene derivatives

As an unnecessary trace element, the content of aluminium in biological systems should be strictly controlled. Therefore, it was necessary to develop a convenient method for detection of aluminium ions. In this study, a fluorescent probe based on polythiophene derivatives was developed and used to detect Al³⁺ in Chinese traditional pasta. The fluorescence of this probe showed a significant decrease in hexamethylenetetramine-HCl buffer solution (pH 5) when Al³⁺ was present. In addition, the probe exhibited good sensitivity and selectivity to Al³⁺ over other metal ions when EDTA was used as the masking agent. Fluorescence intensity had a good linear relationship with the Al³⁺ concentration in the range 0.1-10 μM and the limit of detection for Al³⁺ was 39 nM. Furthermore, the probe was successfully applied to detect Al³⁺ in food samples and the results were consistent with ICP-AES.

A purine based fluorescent chemosensor for the selective and sole detection of Al3+ and its practical applications in test strips and bio-imaging

A novel purine Schiff base fluorescent probe (WYW), (E)-4-methyl-2-((2-(9-(naphthalen-1-yl)-8-(thiophen-2-yl)-9H-purin-6-yl)hydrazono)methyl)phenol, was designed and prepared as an excellent reversible fluorescent chemosensor for monitoring Al³⁺. The fluorogenic "turn-on" sensor WYW exhibited high selectivity towards Al³⁺ over other coexistent metal ions, accompanying with an obvious visual color change in DMSO/H₂O (9/1, v/v, pH = 7.4) media. The enhancement fluorescence of WYW could be attributed to the inhibition of PET and ESIPT process induced by Al³⁺. Notably, the WYW-Al³⁺ complex exhibited a fluorescence "turn-off" response towards F^- with exceptional selectivity via the displacement approach. The detection limit of WYW for Al³⁺ was calculated to be as low as 82 nM. The formation of complex WYW-Al³⁺ (1:1 stoichiometry) was confirmed by Job's methods and further verified by density functional theory (DFT) calculations. Furthermore, the probe WYW with low cytotoxicity and excellent membrane-permeable property has also been successfully applied for detecting low concertation Al³⁺ in living HeLa cells.

A dual thiourea-appended perylenebisimide "turn-on" fluorescent chemosensor with high selectivity and sensitivity for Hg2+ in living cells

Sensing heavy metal ions particularly for the most toxic Hg²⁺ is a long-term pursuit for chemists because of its obvious and extreme harmfulness to both the environment and human health. Herein, a novel 'turn-on' perylenebisimide-thiourea fluorescent probe PBI-BTB is achieved for rapid detection of Hg²⁺ in a DMSO/H₂O (5/1, v/v) solution through a typical Hg²⁺-promoting desulfurization reaction, which has been investigated through Job's plot titration, FT-IR, ¹H NMR and HRMS analysis. A remarkable fluorescence emission enhancement at 540 and 580 nm is observed in the presence of Hg²⁺, which is visible to the naked eye with high selectivity and sensitivity. Moreover, probe PBI-BTB combined strong anti-interference recognition with short response time (< 1 min). The rapid fluorescence response with low limit of detection (0.35 μM) in a wide pH range of 3.0-11.0 makes PBI-BTB a promising candidate for detection of Hg²⁺ without any buffer system. Furthermore, the practicability of probe PBI-BTB upon the Hg²⁺ recognition in human liver cancer cells (HepG-2) has been studied through fluorescent live cell imaging which reveals the probe's low toxicity to organism as well as the favorable cell permeability of PBI-BTB for detecting Hg²⁺ in biological systems.

Application of real sample analysis and biosensing: Synthesis of new naphthyl derived chemosensor for detection of Al3+ ions

A new chemosensor (NANH) based on naphthyl moiety was synthesized with good selectivity and sensitivity towards Al³⁺ ions via the inhibition by operating through dual mechanisms like photo-induced electron transfer (PET) and excited-state intramolecular proton transfer (ESIPT). The synthesized NANH was validated by various techniques such as ¹H, ¹³C NMR and mass spectrum. While prominent fluorescent enhancement was observed from the NANH upon binding with Al³⁺ ions, however, other metal ions have not responded in the emission spectrum. Detection limit and association constant of NANH for Al³⁺ were calculated as 1.2 × 10^-7 M and 4.09 × 10⁴ M^-1 by using fluorescence titration method. Binding ratio (1:1) of NANH with Al³⁺ ions were proved by Job's plot and DFT studies. Furthermore, aluminium in variety of water samples was determined, and NANH could be used for biosensing of Al³⁺ in living cells.

A dual-response ratiometric fluorescent probe for hypochlorite and hydrazine detection and its imaging in living cells

In this work, a dual-response ratiometric fluorescent probe (E)-3-(5-(2-nitrovinyl)thiophen-2-yl)-9-phenyl-9H-carbazole (NTPC) for high selectivity and sensitivity detection of ClO^- and N₂H₄ was successfully developed. This probe NTPC showed ratiometric fluorescent response to ClO^- and N₂H₄, which induces obvious naked-eye color changes, respectively. In addition, the NTPC for ClO^- and N₂H₄ detection displayed low detection limits of 71.4 nM and 0.6 μM, respectively. And the sensing mechanism of NTPC with ClO^- and N₂H₄ was well confirmed by ¹H NMR and HR-MS spectra. Moreover, this novel probe was applied to monitoring and differentiating ClO^- and N₂H₄ in living cells, and exhibits good biocompatibility and low cytotoxicity.

A dual-functional probe for sensing pH change and ratiometric detection of Cu2

A series of benzothiazole-based compounds were synthesized and characterized. Among them, probe Z showed significant dual-functional performance which was capable of sensing pH change and Cu²⁺. Probe Z displayed fluorescent turn-on under alkaline conditions due to deprotonation of the hydroxyl group along with the obviously color change from colorless to mint green. Interestingly, it further achieved in ratiometric detection of Cu²⁺ through absorbance or fluorescence signals in strong alkaline condition. The limit of detection was calculated correspondingly as 0.37 μM and 1.35 μM, respectively. Especially, the combination of the XNOR and INHIBIT logic gates could be used to confirm that one medium was in neutrality or alkalinity condition. Moreover, Z was successfully used in real water samples and test paper for fast identification of Cu²⁺, respectively.

Biotinylated and fluorophore-incorporated polymeric mixed micelles for tumor cell-specific turn-on fluorescence imaging of Al3

Excessive amounts of Al3+ in the human body can cause adverse effects on immune function and induce several neurodegenerative disorders. So far, most of the reported fluorescent probes for Al3+ present some common drawbacks, such as low sensitivity and poor water solubility. In addition, a number of traditional fluorescent probes failed to image Al3+ in tumor cells due to the lack of tumor cell targeting capacity and cell penetrating abilities. To overcome these shortcomings, we constructed tumor-targeting fluorescent mixed nano-micelles (mPEG-Dye-Biotin) with an average particle size of 21 nm from an amphiphilic polymer containing a Schiff-base fluorescent unit (mPEG-Dye) and another amphiphilic polymer containing a tumor cell recognition ligand (DSPE-PEG-Biotin), through the co-self-assembly of both amphiphilic polymers in water using the film rehydration method. The as-prepared nanoprobe showed a highly sensitive and selective turn-on fluorescence response to Al3+ in aqueous solution with a low detection limit. MTT assay revealed the negligible cytotoxicity of the mPEG-Dye-Biotin nanoprobe to both HeLa cells and COS-7 cells, indicating the safety of mPEG-Dye-Biotin for biological applications. More importantly, the biotinylated nanoprobe showed better ability to enter biotin receptor-positive HeLa cells than that of the non-biotinylated micelle mPEG-Dye, which made it more suitable for imaging Al3+ in biotin receptor-positive tumor cells. This work provides a simple and general strategy to design a highly sensitive and tumor cell-specific metal ion nanoprobe, which can not only be applied in Al3+ imaging, but can also be extended to other ions or biomolecules by changing the incorporated fluorescent unit in the amphiphilic polymer.

A novel fluorescent chemosensor based on coumarin and quinolinyl-benzothiazole for sequential recognition of Cu2+ and PPi and its applicability in live cell imaging

In this study, a highly selective fluorescent sensor (E)-2-((2-(benzo[d]thiazol-2-yl)quinolin-8-yl)oxy)-N'-((7-(diethylamino)-2-oxo-2H-chromen-3-yl)methylene)acetohydrazide (TQC) was synthesized from 2-methylquinolin-8-ol and 4-(diethylamino)-2-hydroxybenzaldehyde and its structure was characterized by ¹H NMR, ¹³C NMR, ESI-HR-MS and density functional theory (DFT) calculation. Sensor TQC showed an obvious "on-off-on" fluorescence response to Cu²⁺ and PPi in a DMSO/HEPES (3:2 v/v, pH = 7.4) buffer system. The detection limits of sensor TQC were 0.06 μM to Cu²⁺ and 0.01 μM to PPi. In addition, sensor TQC showed a 1:1 binding stoichiometry to Cu²⁺ and TQC-Cu²⁺ complex showed a 2:1 binding stoichiometry to PPi. The optimum pH range of sensor TQC and TQC-Cu²⁺ was 3-8. Further studies demonstrated that sensor TQC could be made into test paper strips for the qualitative of Cu²⁺ and PPi and showed sequentially "on-off-on" fluorescent bio-imaging of Cu²⁺ and PPi in HeLa cells.

A novel dual-function probe for recognition of Zn2+ and Al3+ and its application in real samples

A dual-function probe NAHH based on naphthalene was synthesized and characterized. Based on the combination effects derived from the inhabitation of photo-induced electron transfer (PET) and CN isomerization, probe NAHH achieved in the recognition of Zn2+ and Al3+ both through obvious fluorescence enhancement and color changes detected by naked eye, respectively. Probe NAHH showed high sensitivity with the limit of detection as low as 3.02 × 10-7 M for Zn2+ and 7.55 × 10-8 M for Al3+, indicated the capability of probe NAHH in trace detection for Zn2+ and Al3+. The binding ratio of NAHH with Zn2+ and Al3+ were all 1:1 determined by Job plot, and the corresponding association constant was calculated as 8.48 × 104 M-1 and 4.45 × 105 M-1, respectively. The mechanism was further confirmed by FT-IR, 1H NMR titration and ESI-MS analysis. Furthermore, probe NAHH was successfully applied in logic gate construction and the detection of Zn2+ and Al3+ in Songhua River and test stripe. Fluorescence imaging experiments confirmed that NAHH could be used to monitor Zn2+ in plant root.

A Benzothiazole-Based Fluorescent Probe for Ratiometric Detection of Al3+ and Its Application in Water Samples and Cell Imaging

An easily prepared benzothiazole-based probe (BHM) was prepared and characterized by general spectra, including ¹H NMR, ¹³C NMR, HRMS, and single-crystal X-ray diffraction. Based on the synergistic mechanism of the inhabitation of intramolecular charge transfer (ICT), the BHM displayed high selectivity and sensitivity for Al³⁺ in DMF/H₂O (v/v, 1/1) through an obvious blue-shift in the fluorescent spectrum and significant color change detected by the naked eye, respectively. The binding ratio of BHM with Al³⁺ was 1:1, as determined by the Job plot, and the binding details were investigated using FT-IR, ¹H NMR titration, and ESI-MS analysis. Furthermore, the BHM was successfully applied in the detection of Al³⁺ in the Songhua River and on a test stripe. Fluorescence imaging experiments confirmed that the BHM could be used to monitor Al³⁺ in human stromal cells (HSC).

A Naphthalimide-Based Fluorescence "Off-on-Off" Chemosensor for Relay Detection of Al3+ and ClO. Front Chem 2019;7:549. [PMID: 31428604 PMCID: PMC6687763 DOI: 10.3389/fchem.2019.00549]

A novel Al³⁺ chemosensor NPA was designed and synthesized on basis of the mechanism of ICT and CHEF. Upon addition of Al³⁺, the probe NPA displayed a bright green fluorescence under UV radiation and visual color change from yellow to colorless. Spectrum titrations showed that NPA could be recognized as a fluorescent turn-on probe with 10^-8 M detection level. The probe was successfully applied in real water sample and test paper. More important, NPA-Al³⁺ complex were used as a fluorescent turn-off probe for the detection of ClO^- with the detection as low as 2.34 × 10^-8 M. The performance of NPA to Al³⁺ and NPA-Al³⁺ complex to ClO^- demonstrated that NPA could be served as a sensitive probe and exhibit INHIBIT logic gate behavior with Al³⁺ and ClO^- as inputs.