A new approach to design ratiometric fluorescent probe for mercury(II) based on the Hg(2+)-promoted deprotection of thioacetals

Development of a new series of thioacetal based fluorescence chemosensors for highly sensitive determination of Hg2+ in environmental samples and cell imaging

Mercury ion is one of the most harmful metal ions with significant hazards to the environment and human health. Thus, the development of innovative, sensitive, and selective sensors to help address the detrimental impacts of heavy metal contamination is necessary. In this work, we present three new chemosensors based on the deprotection reaction of the thioacetal group for distinguishing Hg2+ in environmental samples. These chemosensors show good photophysical properties with high quantum yield in aqueous medium. These prepared chemosensors were employed as fluorometric sensors for the determination of Hg2+ through the quenching of fluorescence emission due to the Hg2+-induced hydrolysis of the thioacetal to the aldehyde group. In the presence of Hg2+, chemosensors showed an emissive color transformation from blue fluorescence to non-fluorescence under UV light, which was readily seen by the visual eye. These chemosensors also exhibited highly distinctive selectivity toward Hg2+ over other interfering metal ions, with detection limits of 1.1 ppb, 13.4 ppb, and 12.7 ppb. Moreover, the practical applicability of chemosensor was successfully demonstrated in real water samples and herb extract samples.

Turn-on Coumarin Precursor: From Hydrazine Sensor to Covalent Inhibition and Fluorescence Detection of Rabbit Muscle Aldolase

Hydrazine, a highly toxic compound, demands sensitive and selective detection methods. Building upon our previous studies with pre-coumarin OFF-ON sensors for fluoride anions, we extended our strategy to hydrazine sensing by adapting phenol protecting groups (propionate, levulinate, and γ-bromobutanoate) to our pre-coumarin scaffold. These probes reacted with hydrazine, yielding a fluorescent signal with low micromolar limits of detection. Mechanistic studies revealed that hydrazine deprotection may be outperformed by a retro-Knoevenagel reaction, where hydrazine acts as a nucleophile and a base yielding a fluorescent diimide compound (6,6'-((1E,1'E)-hydrazine-1,2diylidenebis(methaneylylidene))bis(3(diethylamino)phenol, 7). Additionally, our pre-coumarins unexpectedly reacted with primary amines, generating a fluorescent signal corresponding to phenol deprotection followed by cyclization and coumarin formation. The potential of compound 3 as a theranostic Turn-On coumarin precursor was also explored. We propose that its reaction with ALDOA produced a γ-lactam, blocking the catalytic nucleophilic amine in the enzyme's binding site. The cleavage of the ester group in compound 3 induced the formation of fluorescent coumarin 4. This fluorescent signal was proportional to ALDOA concentration, demonstrating the potential of compound 3 for future theranostic studies in vivo.

Triphenylamine-Based Polythioacetal for Selective Sensing of Mercury(II) with High Specificity and Sensitivity

Utilizing the mercury (Hg2+)-triggered deprotection of thioacetals to aldehyde groups, we constructed a water-soluble triphenylamine (TPA)-based polythioacetal PTA-TPA with thioacetal groups in the backbones for efficient sensing of Hg2+ in aqueous solutions. PTA-TPA is conveniently prepared by polycondensation of 3, 6-dioxa-1,8-octanedithiol (DODT) with 4-(N,N-diphenylamino) benzaldehyde (TPA-CHO) using thiol-terminated mPEG2k-SH as a capping agent. The interaction of Hg2+ with PTA-TPA activates the aggregation-induced emission (AIE) process of TPA-CHO molecules, which makes the emission enhanced, and the emission color changes to sky blue, while other metal ions do not interfere with the sensing process. PTA-TPA can be used as a highly selective and ultrafast detection system for Hg2+ with a low detection limit (LOD) of 9.88 nM and a fast response of less than 1 min. In addition, the prepared test strips report the presence of Hg2+ with an LOD as low as 1 × 10-5 M. Intracellular imaging applications have demonstrated that PTA-TPA acts as a biocompatible fluorescent probe for efficient Hg2+ sensing in HeLa cells. Overall, the PTA-TPA fluorescence probes have the characteristics of easy synthesis, cost-effective, ultrafast detection speed, high selectivity, and high sensitivity, which can be used in practical applications.

Dual colorimetric and near-infrared fluorescence probe for Hg2+ detection and cell imaging

Hg²⁺ in the environment endangers human health, and a convenient monitoring method is needed for the detection of Hg²⁺. In this study, we constructed a dual colorimetric near-infrared fluorescent probe (E)-2-(3-(3-(1,3-dithian-2-yl)-4-hydroxystyryl)-5,5-dimethylcyclohex-2-en-1-ylidene)malononitrile (YF-Hg), based on the malononitrile isophorone. YF-Hg can detect Hg²⁺ rapidly and sensitively, with fluorescence emission in the near-infrared region (659 nm) with an obvious color change from violet to red in the visible light range. In addition, the low toxicity and large Stokes shift (191 nm) of YF-Hg also suggest that it is a potential tool for live-cell fluorescence imaging.

Cu Nanoparticle-Based Solution and Paper Strips for Colorimetric and Visual Detection of Heavy Metal Ions

The intrinsic toxicity of heavy metal ions to human health or other species calls for the need to develop an analytical tool for the easy and rapid detection of these ions based on inexpensive and stable nanomaterials. This article describes the potential utility of stable Cu nanoparticles (CuNPs) in the detection of toxic metal ions by solution and paper strip-based methods. For this, first, a dodecyl sulfate ion-stabilized CuNP (DS-CuNP) colloid was synthesized by a chemical reduction method. This was followed by treating the dispersion with heavy metal ions and monitoring the spectral change by spectrophotometric and colorimetric techniques. Among a host of metal ions, Hg²⁺, Cd²⁺, and Pb²⁺ have been found to significantly affect the surface plasmon resonance band of CuNPs by concomitantly altering the color of its solution. Notably, the brownish color of CuNP solution changed readily to milky white in the presence of Hg²⁺. Furthermore, the fabricated brownish-yellow test paper strips containing DS-CuNPs transformed to a prominent white color in the presence of a few drops of Hg²⁺ solution. This change in color of the paper strips could be visually detected by the naked eye. The experiments involving the detection of the various ions were carried out by optimizing the experimental conditions qualitatively as well as quantitatively. The limit of detection of the analytes (metal ions) has been found to be 10 μM. Routine analytical techniques like UV-vis spectroscopy, dynamic light scattering, transmission electron microscopy, and Fourier transform infrared spectroscopy formed part of the experiments.

New NIR spectroscopic probe with a large Stokes shift for Hg2+ and Ag+ detection and living cells imaging

A new near-infrared (NIR) probe based on a coumarinyl ligand (CL) was designed and synthesized. The probe CL can be used for simultaneous fluorescent turn-on and colorimetric detection of Hg²⁺ and Ag⁺ in ethanol/water medium. Colorless solution of probe CL changed to light yellow or dark yellow after addition of Hg²⁺ or Ag⁺ ions. Meanwhile the maximum absorption band shifted from 379 nm to 404 nm and the intensity increased enormously (for Hg²⁺) or moderately (for Ag⁺). Probe CL displayed an extraordinarily large Stokes shift of 316 nm and addition of Hg²⁺ or Ag⁺ to probe CL induced enhancement in the intensity of fluorescence emission at 695 nm by 15 or 8 fold. The detection limit of CL for Hg²⁺ and Ag⁺ ions is 0.83 and 8.8 μM, respectively. The applicable pH for sensing Hg²⁺ by probe CL is in a broad range of 2-12. Application of probe CL for in vitro U87MG cell imaging to detect Hg²⁺ ions was confirmed.

Tb3+ luminescence cholate hydrogel-based multi-functionalized platform for Hg2+ and NO2 detection

In this paper, Tb3+ luminescence cholate hydrogel (Tb3+/hydrogel) was selected as a multi-functionalized platform, and PS-BD@Tb3+/hydrogel or PS-BS@Tb3+/hydrogel systems were fabricated respectively for selective detecting of Hg2+ in water and...

An ethyl thioglycolate-based chemosensor: Spectrophotometric detection of Fe3+ and fluorometric detection of Hg2+ with high selectivity

A novel symmetric bianthracene derivative (D2) containing one benzene ring and two ethyl thioglycolates connecting to the benzene ring on both sides of the bianthracene unit was designed and synthesized. D2 can detect Fe³⁺ and Hg²⁺ in acetonitrile/water (6:4, v/v) solution via different changes of absorbance and fluorescence in the pH range from 3 to 10. D2 exhibits high colorimetric sensitivity for Fe³⁺ with low detection limit (1.87 × 10^-5 mol/L). The absorbance intensity of D2 in acetonitrile/water solution show a linear response to Fe³⁺ in the wide concentration range of 0 -1000 μM, which is beneficial for quantitative analysis. D2 also displays highly selective fluorescent sensing for Hg²⁺ with a low detection limit of 1.07 µM over other metal ions and can accurately detect the existence of Hg²⁺ in water samples.

An ultrasensitive ratiometric fluorescent probe for the detection of Hg2+ and its application in cell and zebrafish

Mercury is a highly toxic metal element, and the accumulation of mercury in the human body can cause great harm, including but not limited to brain damage, kidney damage and behavioral disorders. Therefore, an effective way to detect mercury ions in the environment is urgently needed. In this study, a novel fluorescent probe (CP-Hg) was synthesized with coumarin as the fluorophore and propanethiol as the recognition receptor. The probe was characterized with high sensitivity (detection limit is approximately 0.5 nM) and selectivity. Note that the probe can react with mercury ions with a distinct color change. In addition, it has been proved to have low toxicity and successfully applied to detect mercury in water samples, macrophages and zebrafish model.

In-situ synthesis of carbon dots-embedded europium metal-organic frameworks for ratiometric fluorescence detection of Hg2+ in aqueous environment

A novel dual-emission ratiometric fluorescent sensor (CDs@Eu-MOFs) has been synthesized successfully by encapsulating water-soluble fluorescent CDs into the chambers of Eu-MOFs via a simple one-pot hydrothermal method, which can be used for the detection of Hg²⁺ in environmental water samples. The synthesized CDs@Eu-MOFs inherited simultaneously the excellent luminescence performance of Eu³⁺ and CDs and exhibited good structural and fluorescence stability in aqueous solution. The presence of Hg²⁺ changed the fluorescence intensity of CDs, while the fluorescence intensity of Eu-MOFs hardly changed, which could be used as the recognition part and the reference part respectively to construct the ratiometric fluorescence sensor. The obtained Hg²⁺ fluorescent probe showed a wide linear range (0-300 μM) and a low detection limit (0.12 nM). The developed method can be used as a multi-functional fluorescent sensor with high sensitivity and good selectivity for the determination of Hg²⁺ in actual water samples.

Bithiophene-based fluorescent sensor for highly sensitive and ultrarapid detection of Hg2+ in water, seafood, urine and live cells

Using Hg²⁺-promoted deprotection reaction, we have developed a new fluorescent turn-on sensor 2TS based on bithiophene fluorophore for Hg²⁺ detection. The sensing mechanism of 2TS towards Hg²⁺ was strongly proved by ¹H NMR, FTIR, HRMS, UV-vis and fluorescence spectra. Remarkly, 2TS towards Hg²⁺ in 100% aqueous solution shows high sensitivity with a low detection limit of 19 nM, superior selectivity and ultra-rapid response of 20 s during a wide sensing pH range from 4 to 10. Taking advantage of the excellent properties, the low-cost sensor 2TS-based filter paper/TLC test strips were fabricated for visual, immediate and quantitative detection of Hg²⁺ in water, proving its applicability towards sensitive in-situ and on-site detection. Meanwhile, 2TS showed high analytical performance for Hg²⁺ detection in water, seafood as well as human urine samples. Moreover, thanks to the good water solubility, negligible cytotoxicity, good biocompatibility and cell-membrane permeability, 2TS was further applied to effectively image Hg²⁺ in live cells. Furthermore, the developed sensor 2TS acted as good fluorescent display material for Hg²⁺ with obvious color change.

A new 3-hydroxyphthalimide-based turn-on fluorescent probe for Hg2+ detection in aqueous solution

A new 3-hydroxyphthalimide-based turn-on fluorescent probe is designed and synthesized. This probe can be used to determine the presence of Hg2+ ions by fluorescence spectroscope with high selectivity over other metal ions in aqueous solution. The analytical detection limit for Hg2+ is as low as 6.5 × 10−7 M. The recognition mechanism is attributed to Hg2+-promoted carbonothioate group cleavage and a subsequent excited-state intramolecular proton transfer mechanisms.

A novel coumarin-derived dithioacetal chemosensor for trace detection of Hg2+ in real water samples

A novel coumarin-derived dithioacetal chemosensor, 8-(1,3-dithian-2-yl)-7-hydroxy-4-methylcoumarin (LS), has been designed and synthesized. The sensor LS showed highly selective fluorescent sensing for Hg2+ with a low detection limit of 0.81 nM in the pH range from 6.15 to 9.96 in ethanol/water (1:1, v/v) solution. The sensing mechanism of LS toward Hg2+ was proposed and verified by 1H nuclear magnetic resonance spectroscopy studies. Under an ultraviolet lamp, the fluorescence color changes could be easily detected by the naked eye. In addition, the sensor LS has been applied in the trace detection of Hg2+ in real water samples.

Carbon dots-based fluorescent turn off/on sensor for highly selective and sensitive detection of Hg2+ and biothiols

In this work, sodium salicylate and ethylenediamine (EDA) are used as the precursors to synthesize green fluorescent carbon dots (CDs). The CDs have some attractive properties, including better oxidation resistance, good water solubility, and excellent stability in high ionic strength solutions in a pH range of 6.0-10.0. Compared to other metal ions, only Hg²⁺ can quench the fluorescence of CDs, and with the introduction of biothiols, the fluorescence of the CDs/Hg²⁺ system can be recovered. Therefore, a turn off/on fluorescent sensor is constructed using CDs as a fluorescent probe, and the sensor is applied to the detection of Hg²⁺ and biothiols (glutathione, homocysteine and cysteine). In addition, the fluorescent sensor exhibits excellent selectivity and sensitivity. The linear range of Hg²⁺ is 0.05-10 μM with the detection limit of 44 nM. Glutathione, homocysteine, and cysteine have a linear response in the range of 0.5-10 μM with the limit of detection of 80, 76, and 69 nM, respectively. Furthermore, the fluorescence method is successfully used to detect Hg²⁺ in actual water samples and biothiols in human plasma.

A new thiosemicarbazone fluorescent probe based on 9,9'-bianthracene for Hg2+ and Ag. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2019;215:34-40. [PMID: 30825868 DOI: 10.1016/j.saa.2019.02.036]

A new 9,9'-bianthracene-based thiosemicarbazone (D1) has been successfully synthesized and utilized for chemosensors. The properties of D1 were systematically investigated by UV-Vis, fluorescence titration and theoretical calculations. As a result, D1 exhibits a characteristic fluorescence quenching phenomenon in the presence of Hg²⁺ or Ag⁺ compared to other metal cations (Na⁺, K⁺, Mg²⁺, Ba²⁺, Al³⁺, Zn²⁺, Fe²⁺, Pb²⁺, Cu²⁺, Co²⁺, Cd²⁺, Ni²⁺ and Mn²⁺). The detection limits of Hg²⁺ and Ag⁺ reach 6.62×10^-7M and 1.99×10^-5M, respectively. This is mainly attributed to the Hg²⁺ (or Ag⁺) forms a stable five-membered ring with the N atom in Schiff base CN and the S atom in thiourea. The results suggest that the probe D1 is a promising candidate for chemosensors in aqueous media due to its highly selectivity for Hg²⁺ and Ag⁺.

Sensitive Water-Soluble Fluorescent Probe Based on Umpolung and Aggregation-Induced Emission Strategies for Selective Detection of Hg2+ in Living Cells and Zebrafish

Using Hg²⁺-induced umpolung reaction and aggregation induced emission (AIE), we have rationally developed a water-soluble fluorescent probe 2,2'-(((4-(4,5-bis(4-methoxyphenyl)-1-phenyl-1H-imidazol-2-yl)phenyl)methylene)bis(sulfanediyl))diethanol (MPIPBS) for Hg²⁺ detection. MPIPBS was found to have high selectivity and sensitivity toward Hg²⁺ detection. The mechanism of MPIPBS response to Hg²⁺ was verified by ¹H NMR titration, HPLC, and HRMS spectroscopy. The detection limit was examined to be 1.45 nM, which is lower than most reported probes for Hg²⁺. Taking advantage of excellent optical properties of AIEgen, a paper based sensor for Hg²⁺ detection was fabricated by immobilizing the MPIPBS on Waterman test paper. Meanwhile, MPIPBS showed satisfactory analytical performance in real water and urine samples. Further, thanks to the high water solubility, cell membrane permeability and low cytotoxicity, MPIPBS was further used to detect Hg²⁺ both in living cells and zebrafish. We anticipate that the prepared probe was available to detect Hg²⁺ in environment and biosamples.

Hg2+-Promoted Spirolactam Hydrolysis Reaction: A Design Strategy for the Highly Selective Sensing of Hg2+ over other Metal Ions in Aqueous Media

A mercury sensor (N-(rhodamine-6G)lactam-ethylenediamine-4-dimethylamino-cinnamaldehyde—RLED) based on the Hg²⁺-promoted hydrolysis reaction has been designed and developed with a combination of theoretical calculations and experimental investigations. The interaction between RLED and Hg²⁺ goes through a fast-initial stage with formation of a 1:1 complex, followed by a slow hydrolysis process. The formation of durable intermediate complexes is due to quite a long hydrolysis reaction time. As a result, RLED can selectively detect Hg²⁺ in the presence of other metal ions, with a detection limit of 0.08 μM for the colorimetric method, and of 0.008 μM with the fluorescent method. In addition, the RLED sensor can work in a solution with a small amount of organic solvent, with a wide pH range from 5 to 10. The time-dependent density functional theory has been used for investigations of the excitation and de-excitation processes in RLED, intermediate complexes, and reaction products, thereby clarifying the changes in the fluorescence intensity before and after the RLED interacts with Hg²⁺ ions.

A highly selective and sensitive ESIPT-based coumarin–triazole polymer for the ratiometric detection of Hg2+

A reversible ESIPT based system for the detection of Hg²⁺ was developed. The system exhibited better properties compared to that of recently developed ratiometric fluorescent systems.

Naked-eye Detection of Hg2+ in Practical Applications Using a Highly Selective and Sensitive Fluorescent Probe

A highly selective and sensitive probe, DAC-Hg, has been designed and synthesized for the naked-eye detection of Hg²⁺ in practical applications. DAC-Hg showed applicative "turn-off" sensing for Hg²⁺ over other ions. The detection limit was determined to be 5.0 nM, the same as the strictest standard of Hg²⁺ measurements. A naked-eye evaluation with test strips demonstrated the potential of DAC-Hg for conveniently handled in-situ detection. The application of this established method for analyzing environmental and seafood samples supplied satisfactory results. Therefore, DAC-Hg offered a promising approach for Hg²⁺ detection as well as hints for sensing other heavy and transition metal ions.

A highly selective colorimetric and ratiometric fluorescent probe for instantaneous sensing of Hg2+ in water, soil and seafood and its application on test strips

A new simple and efficient oligothiophene-based colorimetric and ratiometric fluorescent probe has been developed for highly sensitive and fast detection of Hg2+ in water, soil and seafood. The probe 5-(1,3-dithiolan-2-yl)-2,2':5',2″-terthiophene 3 TS can selectively detect Hg2+ via the Hg2+-promoted deprotection reaction of thioacetals, which caused a remarkable color change from colorless to yellow and a strong fluorescence enhancement with emission color varying from blue to yellow, enabling naked-eye detection of Hg2+. The probe shows high sensitivity with the detection limit down to 1.03 × 10-8 M. Visual color changes of 3 TS were observed on filter paper and TLC testing strips when they were impregnated on testing strips and immersed in Hg2+ solution. Moreover, the probe 3 TS has been successfully used to rapidly detect trace amounts of hazardous Hg2+ ions in tap, distilled, river and lake water, cropland soil, fish, shrimp and kelp samples with acceptable results and good recoveries.

Reaction-based conjugated polymer fluorescent probe for mercury(ii): good sensing performance with “turn-on” signal output

Based on a Hg²⁺-promoted deprotection reaction of dithioacetal, the conjugated polymer PDT showed high sensitivity with the detection limit of 1.0 × 10⁻⁶ mol L⁻¹ and 1 × 10⁻⁵ mol L⁻¹ in solution and as test strips, respectively.

A novel histidine-functionalized 1,8-naphthalimide-based fluorescent chemosensor for the selective and sensitive detection of Hg2+ in water

A novel water soluble fluorescent sensor was synthesized by employing the carboxyl and imidazolyl moiety as the hydrophilic group site and Hg²⁺ binding site, whereas a naphthalimide moiety was used as the signal group.

An Ionic 1,4-Bis(styryl)benzene-Based Fluorescent Probe for Mercury(II) Detection in Water via Deprotection of the Thioacetal Group

Highly sensitive and selective mercury detection in aqueous media is urgently needed because mercury poisoning usually results from exposure to water-soluble forms of mercury by inhalation and/or ingesting. An ionic conjugated oligoelectrolye (M1Q) based on 1,4-bis(styryl)benzene was synthesized as a fluorescent mercury(II) probe. The thioacetal moiety and quaternized ammonium group were incorporated for Hg²⁺ recognition and water solubility. A neutral Hg²⁺ probe (M1) was also prepared based on the same molecular backbone, and their sensor characteristics were investigated in a mixture of acetonitrile/water and in water. In the presence of Hg²⁺, the thioacetal group was converted to aldehyde functionality, and the resulting photoluminescence intensity decreased. In water, M1Q successfully demonstrated highly sensitive detection, showing a binding toward Hg²⁺ that was ~15 times stronger and a signal on/off ratio twice as high, compared to M1 in acetonitrile/water. The thioacetal deprotection by Hg²⁺ ions was substantially facilitated in water without an organic cosolvent. The limit of detection was measured to be 7 nM with a detection range of 10–180 nM in 100% aqueous medium.

An AIE-based bioprobe for differentiating the early and late stages of apoptosis mediated by H2O2

A bioprobe, TPE-Zn₂BDPA, with aggregation-induced emission characteristics was designed and synthesized to differentiate the early and late stages of apoptosis mediated by H₂O₂. TPE-Zn₂BDPA does not respond to healthy cells, but it selectively lights up the membrane of apopotic cells in both stages with brighter fluorescence in the late apoptotic stage.

A PET-based fluorometric chemosensor for the determination of mercury(II) and pH, and hydrolysis reaction-based colorimetric detection of hydrogen sulfide

A simple fluorescent chemosensor 1 for the detection of Hg(2+) and pH was developed by a combination of 2-aminoethyl piperazine and 4-chloro-7-nitrobenz-2-oxa-1,3-diazole. The sensor 1 showed OFF-ON behavior for different colors of fluorescence in the presence of Hg(2+) and under acidic conditions, respectively, in a near-perfect aqueous solution. The turn-on fluorescence caused by inhibition of photoinduced electron transfer was explained by theoretical calculations. 1 could be used to quantify Hg(2+) in water samples, and its in vitro studies with HeLa cells showed fluorescence in the presence of Hg(2+). In addition, 1 could selectively detect S(2-) by changing its color from orange to pink in a near-perfect aqueous solution. Moreover, 1 could be used as a practical, visible test kit for S(2-).

A through bond energy transfer based ratiometric probe for fluorescent imaging of Sn2+ ions in living cells

A 4-(naphthalen-1-ylethynyl) aniline appended rhodamine based fluorescent chemosensor ‘NAP-RD’ is synthesized which undergoes through bond energy transfer in the presence of Sn²⁺ ions in mixed aqueous media.

A colorimetric chemosensor for sulfide in a near-perfect aqueous solution: practical application using a test kit

A selective chemosensor with practical applications was developed for the colorimetric detection of S²⁻ in a near-perfect aqueous solution.

Controlled synthesis of a dual-emission hierarchical quantum dot hybrid nanostructure as a robust ratiometric fluorescent sensor

A highly stable and biocompatible CdTe@SiO₂@CdTe@SiO₂ dual-emission hierarchical hybrid nanostructure was synthesized and used as a robust ratiometric fluorescent sensor.