Two chemodosimeters for fluorescence recognition of biothiols in aqueous solution and their bioimaging application

Two fluorescein derivatives containing 2,4-dinitrobenzenesulfonyl group have been developed as fluorescent probes to detect the biothiols (Cys, Hcy and GSH) in aqueous solution. Probes 1 and 2 can distinguish these biothiols in the presence of other amino acids. While probe 1 can recognize the biothiols in PBS/DMSO (v:v = 95:5, pH = 7.40) solution, notably probe 2 could be used in PBS buffer solution (pH = 7.40). The detection limit of Cys for probe 2 reached at 0.021 μM in aqueous solution, which was lower than the intracellular concentration of Cys. In the recognition process, a reaction between the probes and the biothiols occurred, in which the S–O bond was cleaved to remove 2, 4-dinitrobenzenesulfonyl group. The data of ¹H NMR, MS and DFT/TD-DFT calculation further confirmed the detection mechanism. Moreover, two probes were successfully applied to the HeLa cell imaging.     

Development of [(2E,6E)-2,6-bis(4-(dimethylamino)benzylidene)cyclohexanone] as fluorescence-on probe for Hg2+ ion detection: Computational aided experimental studies

Selective metal ion detection is highly desired in fluorometric analysis. In the current study a curcumin-based fluorescence-on probe/[(2E,6E)-2,6-bis(4-(dimethylamino) benzylidene) cyclohexanone]/probe was designed for the removal of one of the most toxic heavy metal ion i.e. Hg²⁺. The structure of the probe was confirmed by FTIR and ¹H NMR spectroscopic analysis displaying distinctive peaks. The complex formation between probe and Hg²⁺ ion was also studied by density functional theory to support the experimental results. Chelation enhanced fluorescence was observed upon interaction with Hg²⁺ ion. Different parameters like pH, effect of mercury ion concentration, contact time, interference study and effect of probe concentration on the fluorescence enhancement were also investigated. A rapid response was detected for Hg²⁺ ion with limit of detection and quantification as 2.7 nM and 3 nM respectively with association constant of 1 × 10¹¹ M^?2. The probe displayed maximum fluorescence intensity at physiological pH. The results showed that the synthesized probe can be employed as an excellent probe for the detection and quantification of Hg²⁺ ions in aqueous samples with high selectivity and sensitivity due to its higher binding energy and larger charge transferring ability.     

Facile synthesis of an optical sensor for CO32− and HCO3− detection

A novel fluorogenic signalling probe (E)-3-(4-methoxyphenyl)-4-[(4-nitrobenzylidene)amino]-1H-1,2,4-triazole-5(4H)-thione (6) for the carbonate and bicarbonate ions has been developed through microwave assisted Schiff base formation reaction. The anion recognition occurs through hydrogen bonding assessed by ¹H NMR titration experiments. The photophysical results of probe 6 corroborates its applicability as an optical sensing platform for carbonate as well as bicarbonate ions in mixed aqueous organic media depending on pH of reaction solution. The fluorescence emission signal enhancement at 424 nm and considerable shift in the signal position as well as molar absorptivity to the probe absorption bands upon CO₃^2? and HCO₃^? addition suggest the affinity of probe 6 towards these ions in comparison to a variety of competitive ions in aqueous/ethanol (7:3, v/v) at neutral pH and ambient temperature. From the fluorescence titration experiment, the limit of detection was calculated to be 1.91 μM.     

A highly selective naked-eye probe for hypochlorite with the p-methoxyphenol-substituted aniline compound

A highly selective naked-eye detection of ClO⁻ is successfully established with probe 1 by taking advantage of the oxidation transformation of p-methoxyphenol into benzoquinone with ClO⁻ and the ICT absorption within the electron donor-acceptor compound. The color of the solution of probe 1 was changed, obviously upon addition of ClO⁻ and ClO⁻ with concentration as low as 1.74 μM can be analyzed in aqueous solution with probe 1. Moreover, the interferences of other anions can be neglected.     

Polythiophene–Chitosan Magnetic Nanocomposite as a Novel Sorbent for Disperse Magnetic Solid Phase Extraction of Triazine Herbicides in Aquatic Media

In this paper, polythiophene/chitosan magnetic nanocomposite as a novel adsorbent is proposed for the preconcentration of triazines in aqueous samples prior to gas chromatography. The synthesized nanoparticles, magnetic chitosan and polythiophene–chitosan magnetic nanocomposite were characterized by scanning electron microscopy. The magnetic polythiophene–chitosan nanocomposite containing analytes could be removed from the sample solution by applying a permanent magnet. The major factors influencing the extraction efficiency including desorption conditions, nanocomposite components ratio, sorbent amount, extraction time, ionic strength and sample pH were optimized. The developed method proved to be rather convenient and offers sufficient sensitivity and good reproducibility. The limit of detection (S/N = 3) and limit of quantification (S/N = 10) of the method under optimized conditions were 10–30 and 100 ng L⁻¹, respectively. Under the optimum conditions, good linearity was obtained within the range of 100–5000 ng L⁻¹ for all triazines with correlation coefficients >0.9994. The relative standard deviation at a concentration level of 150 ng L⁻¹ was 7–12 %. Furthermore, the method was successfully applied to the determination of triazines in real samples, where relative recovery percentages of 96–102 % were obtained. Compared with other methods, the current method is characterized by easy, fast separation and low detection limits.

     

A high-efficiency and low-cost AEE polyurethane chemo-sensor for Fe3+ and explosives detection

An aggregation enhanced emission (AEE) polyurethane named STMPU-211 containing 0.13% mole concentration of 4,4′-((1Z,3Z)-1,4-diphenylbuta-1,3-diene-1,4-diyl) dibenzaldehyde (TABDAA) in the soft segments was synthesized and proved to be sensitive to Fe³⁺ and nitroaromatic explosives. The fluorescence of the AEE polyurethane was reduced in the presence of Fe³⁺, and almost quenched when 5000?μM Fe³⁺ was added. Meanwhile, the fluorescence intensity of STMPU-211 solution in DMF/water mixture was decreased when explosives like 2,4,6-trinitrophenol (PA) and 3-nitro-1,2,4-triazol-5-one (NTO) were applied. Especially, the quenching coefficient K_SV value of PA was 5.7?×?10⁶?M^?1, confirming that the polyurethane STMPU-211 could be a highly sensitive sensor for the detection of PA. Therefore, AEE polyurethanes with low concentration of TABDAA have promising applications in biological probe, environment monitoring and antiterrorism fields.     

A facile route of polythiophene nanoparticles via Fe3+‐catalyzed oxidative polymerization in aqueous medium

We have demonstrated that unsubstituted thiophene can be polymerized by Fe³⁺‐catalyzed oxidative polymerization inside nanosized thiophene monomer droplets, that is, nanoreactors, dispersed in aqueous medium, which can be performed under acidic solution conditions with anionic surfactant. Besides, we proposed a synthetic mechanism for the formation of the unsubstituted polythiophene nanoparticles in aqueous medium. This facile method includes a FeCl₃/H₂O₂ (catalyst/oxidant) combination system, which guarantees a high conversion (ca. 99%) of thiophene monomers with only a trace of FeCl₃. The average particle size was about 30 nm, within a narrow particle‐size distribution (PDI = 1.15), which resulted in a good dispersion state of the unsubstituted polythiophene nanoparticles. Hansen solubility parameters were introduced to interpret the dispersion state of the polythiophene nanoparticles with various organic solvents. The UV–Visible absorption and photoluminescence (PL) spectrum were measured to investigate the light emitting properties of the prepared unsubstituted polythiophene nanoparticle emulsions. According to non‐normalized PL analysis, the reduced total PL intensity of the polythiophene nanoparticle emulsions can be rationalized by self‐absorption in a wavelength range less than 500 nm. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2097–2107, 2008     

Characterization and properties of a polythiophene with a malonic acid dimethyl ester side group

A new polythiophene derivative bearing a malonic acid dimethyl ester substituent attached to the 3-position of the repeat unit has been prepared by chemical oxidative-coupling polymerization. The chemical structure of poly(2-thiophen-3-yl-malonic acid dimethyl ester) has been analyzed by FTIR and ¹H NMR spectroscopy and, additionally, the distribution of the head-to-tail and head-to-head diads arising from polymerization was found to be a 75-25%. The glass transition temperature identified for this polymer was 17.6 °C lower than that recently determined for a closely related polythiophene derivative, in which the ester substituent arose from acrylic acid rather than from malonic acid. On the other hand, the electrical conductivity of the new material, which was soluble in polar solvents but not in water, was higher than that typically found for poly(3-alkylthiophene) derivatives. Ab initio quantum mechanical calculations on simple model compounds were used to predict the regiochemistry of the polymer chain, which was in excellent agreement with the experimental observation, and the conformational preferences of both the inter-ring dihedral angle and the bulky side group. Interestingly, calculations predict that the inter-ring dihedral angles adopt a syn-gauche conformation rather than the anti-gauche arrangement typically found in substituted polythiophenes. Thus, in this case the former conformation reduces the strong repulsive interactions induced by the bulky substituent. The lowest π-π^∗ transition energy derived from calculations on an idealized molecular model is in agreement with the experimental estimation determined using UV-vis spectroscopy. This electronic property is significantly higher for poly(2-thiophen-3-yl-malonic acid dimethyl ester) than for other substituted polythiophene derivatives, which is consequence of the geometrical distortions induced by bulky side group.     

A rapid responsive and highly selective probe for cyanide in the aqueous environment

A colorimetric and fluorescent cyanide probe based on 7-(trifluoroacetamino)coumarin has been prepared. This structurally simple probe displays rapid response and high selectivity for cyanide over other common anions in the aqueous solution. The sensing of cyanide was performed via the nucleophilic attack of cyanide anion to carbonyl of the probe with a 1:1 binding stoichiometry, which could be confirmed by Job’s plot, ¹H NMR, and MS studies. DFT/TDDFT calculations support that the fluorescence enhancement of the probe is mainly due to the ICT process improvement. The detection limit of the fluorescent assay for cyanide is as low as 0.3 μM in a rapid response of less than 30 s. Thus, the present probe should be applicable as a practical system for the monitoring of cyanide concentrations in aqueous samples.     

A New Fluorescence Turn-On Probe for Aluminum(III) with High Selectivity and Sensitivity,and its Application to Bioimaging

The development of novel selective probes with high sensitivity for the detection of Al³⁺ is widely considered an important research goal due to the importance of such probes in medicine, living systems and the environment. Here, we describe a new fluorescent probe, N′-(4-diethylamino-2-hydroxybenzylidene)-2-hydroxybenzohydrazide (1), for Al³⁺. Probe 1 was evaluated in a solution of acetonitrile/water (1:1 v/v). Compared with previously reported probes for Al³⁺, probe 1 can be synthesized easily and in high yield. A Job plot confirmed that probe 1 is able to complex Al³⁺ in a 1:1 ratio, and the binding constant was determined to be 4.25×10⁸ m⁻¹. Moreover, the detection limit was as low as 6.7×10⁻⁹ m, suggesting that probe 1 has a high sensitivity. Common coexistent metal ions, such as K⁺, Co²⁺, Ca²⁺, Ba²⁺, Ni²⁺, Pb²⁺, Hg²⁺, Ce²⁺, Zn²⁺, Cd²⁺, Fe³⁺, showed little or no interference in the detection of Al³⁺ in solution, demonstrating the high selectivity of the probe. Finally, the ability of probe 1 to act as a fluorescent probe for Al³⁺ in living systems was evaluated in Gram-negative bacteria, Escherichia coli, and confocal laser scanning microscopy confirmed its utility. The results of this study suggest that 1 has appropriate properties to be developed for application as a fluorescent probe of Al³⁺ for use in biological studies.     

A ratiometric fluorescent probe for fluoride ion employing the excited-state intramolecular proton transfer

A ratiometric fluorescent probe 1 for fluoride ion was developed based on modulation of the excited-state intramolecular proton transfer (ESIPT) process of 2-(2′-hydroxyphenyl)benzimidazole (HPBI) through the hydroxyl group protection/deprotection reaction. The probe 1 was readily prepared by the reaction of HPBI with tert-butyldimethylsilyl chloride (TBS-Cl) and shows only fluorescence emission maximum at 360 nm. Upon treatment with fluoride in aqueous DMF solution, the TBS protective group of probe 1 was removed readily and ESIPT of the probe was switched on, which resulted in a decrease of the emission band at 360 nm and an increase of a new fluorescence peak around 454 nm. The fluorescent intensity ratio at 454 and 360 nm (I₄₅₄/I₃₆₀) increases linearly with fluoride ion concentration in the range 0.3-8.0 μmol L⁻¹ and the detection limit is 0.19 μmol L⁻¹. The proposed probe shows excellent selectivity toward fluoride ion over other common anions. The method has been successfully applied to the fluoride determination in toothpaste and tap water samples.     

A switch-on near-infrared fluorescence-ready probe for Cu(I): live cell imaging

A reaction-based strategy exploiting metal ion mediated oxidative C–O bond cleavage affords selective ‘switch-on’ near-infrared (NIR) emitting cyanine probe for Cu⁺ in aqueous media and live cells. Near-infrared fluorescence-ready probe TPACy readily reacts with Cu⁺ to release the quinone embedded heptamethine cyanine (Cy-quinone) with extended π-electron conjugation responsible for the switch-on NIR fluorescence in aqueous buffer solution (50 mM HEPES, pH 7.2). This probe can be conveniently used for monitoring Cu⁺ without the interference from pH dependent effects of physiological media. Utility of the probe has been demonstrated by its application in the detection of unbound copper species (Cu⁺) in live cells.     

Silver nanoparticles embedded temperature-sensitive nanofibrous membrane as a smart free-standing SERS substrate

To develop a smart free-standing surface enhanced Raman scattering(SERS) substrate,silver nanoparticles(AgNPs) embedded temperature-sensitive nanofibrous membrane was fabricated by electrospinning their aqueous solution containing the copolymer poly(N-isopropylacrylamide-co-Nhydroxymethylacrylamide),followed by heat treatment to form crosslinking structure within its constituent nanofibers.To avoid negative effect of the additive like stabilizer and the reactant like reductant on their SERS efficiency,the AgNPs were in-situ synthesized through reducing Ag~+ions dissolved in the polymer solution by ultraviolet irradiation.The prepared hybrid nanofibrous membrane with high stability in aqueous medium can reach its swelling or deswelling equilibrium state within 15 seconds with the medium temperature changing between 25℃and 50℃alternately.When it was used as a free-standing SERS substrate,10~(-12) mol/L of 4-nitrothiophenol in aqueous solution can be detected at room temperature,and elevating detection temperature can further lower its low detection limit.Since its generated SERS signal has desirable reproducibility,it can be used as SERS substrate for quantitative analysis.Moreover,the hybrid membrane as SERS substrate is capable of real-time monitoring the reduction of 4-nitrothiophenol into 4-aminothiophenol catalyzed by its embedded AgNPs,and the detected intermediate indicates that the reaction proceeds via a condensation route.     

Molecularly imprinted polymers prepared in aqueous solution selective for [Sar,Ala]angiotensin II

Conventional molecular imprinting technology allows the synthesis in organic solvents of molecularly imprinted polymers (MIPs) selective toward relatively low molecular weight compounds. However, synthesis in aqueous media of chemically and mechanically stable MIPs that can recognize biomolecules such as peptides and proteins still is a great challenge. In this article, we report the successful synthesis of peptide-selective MIPs in aqueous solution. HPLC evaluation of these polymers with a water-based mobile phase showed their selectivity for the peptide, [Sar¹,Ala⁸]angiotensin II (SA), that had been used as the template, but not for its parent peptide angiotensin II (AII). The binding capacity and selectivity of our MIPs depended on the ratio of template to functional monomer in the polymerization mixture, as well as on the ionic strength and pH of the chromatographic mobile phase. These MIPs can be used for chromatographic detection of the octapeptide [Sar¹,Ala⁸]angiotensin II in aqueous solution, with a detection limit of 8 pmol and a response that is linear (r²>0.99) over the concentration range 0.4-20 μM.     

Aza-BODIPY based probe for photoacoustic imaging of ONOO− in vivo

The effective detecting ONOO⁻ variations in vivo is of great importance to well understand the complex pathophysiological processes. We reported here a photoacoustic (PA) probe AZB-1 for imaging ONOO⁻ in vivo. AZB-1 showed an originally strong photoacoustic signal at 660 nm. And its PA signal can be turned off by shutting the ICT effect caused by the conjugated electron withdrawing group at 2-position of the aza-BODIPY core. Moreover, the probe was successfully employed to imaging ONOO⁻ variations in inflammatory mice models. Wisely utilized this strategy may serve as powerful platforms for the preparation of novel PA chemosensors.     

Electrogenerated chemiluminescence induced by sequential hot electron and hole injection into aqueous electrolyte solution

Hole injection into aqueous electrolyte solution is proposed to occur when oxide-coated aluminum electrode is anodically pulse-polarized by a voltage pulse train containing sufficiently high-voltage anodic pulses. The effects of anodic pulses are studied by using an aromatic Tb(III) chelate as a probe known to produce intensive hot electron-induced electrochemiluminescence (HECL) with plain cathodic pulses and preoxidized electrodes. The presently studied system allows injection of hot electrons and holes successively into aqueous electrolyte solutions and can be utilized in detecting electrochemiluminescent labels in fully aqueous solutions, and actually, the system is suggested to be quite close to a pulse radiolysis system providing hydrated electrons and hydroxyl radicals as the primary radicals in aqueous solution without the problems and hazards of ionizing radiation. The analytical power of the present excitation waveforms are that they allow detection of electrochemiluminescent labels at very low detection limits in bioaffinity assays such as in immunoassays or DNA probe assays. The two important properties of the present waveforms are: (i) they provide in situ oxidation of the electrode surface resulting in the desired oxide film thickness and (ii) they can provide one-electron oxidants for the system by hole injection either via F- and F⁺-center band of the oxide or by direct hole injection to valence band of water at highly anodic pulse amplitudes.     

Direct electrochemical behavior of cytochrome c, and its determination on phytic acid modified electrode

Phytic acid (PA) with its unique structure was attached to a glassy carbon electrode (GCE) to form PA/GCE modified electrode which was characterized by electrochemical impedance. The electrochemical behavior of cytochrome c (Cyt c) on the PA/GCE modified electrode was explored by cyclic voltammetry and differential pulse voltammetry. The Cyt c displayed a quasi-reversible redox process on PA modified electrode pH 7.0 phosphate buffer solution with a formal potential (E ^0′) of 57 mV (versus Ag/AgCl). The peak currents were linearly related to the square root of the scan rate in the range of 20–120 mV·s^?1. The electron transfer rate constant was determined to be 12.5 s^?1. The PA/GCE modified electrode was applied to the determination of Cyt c, in the range of 5?×?10^?6 to 3?×?10^?4 M, the currents increase linearly to the Cyt c concentration with a correlation coefficient 0.9981. The detection limit was 1?×?10^?6 M (signal/noise?=?3).     

Saturation ESR spectroscopy of PA12 polyamide

This work presents the results of our EPR study of polyamide 12 (PA12) -[NH-(CH₂)₁₁-CO]_n-NH-(CH₂)₁₁-CO-. In this study the spin probe method with “conventional” or “continuous saturation” at low temperatures (4-260 K) was used. The aim of our investigation was to determine if it possible to obtain the saturation effects and establish experimental conditions by using commercial ESR spectrometers. We also wanted to know what information about the relaxation processes in polymeric materials could be obtained. We have found that the information about the relaxation processes (below frequency ≈10⁴ Hz) at low-temperatures in polymers could be obtained. The process, which could be associated with mobility of the spin probe is probably connected with the process called γ (in PA12 as yet unrecorded by using others methods). This process in other systems is usually connected with mobility of the methylene sequences and could be used to study the amorphous regions of PA12.     

An ESIPT-based fluorescent probe for Hg2+ in aqueous solution and its application in live-cell imaging

A new Excited-State Intramolecular Proton Transfer (ESIPT) based fluorescent probe for the detection of Hg²⁺ has been rationally designed and developed. Based on the specific reactivity of mercury-promoted hydrolysis, the probe exhibits high selectivity and sensitivity for mercury ions in almost pure aqueous solution (containing only 1% DMSO) with a low detection limit of 1.9?ppb. Furthermore, the probe was also successfully used for fluorescence imaging of Hg²⁺ in live cells.     

Azobenzene–Hemicyanine Conjugated Polymeric Chemosensor for the Rapid and Selective Detection of Cyanide in Pure Aqueous Media

A water-soluble polymeric probe was designed and synthesized that can be used for the colorimetric selective detection of cyanide ions in pure aqueous media. In particular, P1, a water-soluble random terpolymer (P1) of N,N′-dimethylacrylamide, 2-((E)-4-((E)-(4-((2-(acryloyloxy)ethyl)(methyl)amino)phenyl)diazenyl)styryl)-1,3,3-trimethyl-3H-indol-1-ium (M1), and N-(4-benzoylphenyl)acrylamide was synthesized via traditional free-radical polymerization. Upon the addition of CN⁻ ions to a P1 solution, a macroscopically detectable color change of the solution from brick red to light yellow took place, which was associated with a low limit of analyte detection (1.23 μM). Notably, P1 exhibited excellent selectivity toward CN⁻ over other anions and biothiols, which may be present in the medium. Such highly selective colorimetric response to CN⁻ by P1 originated from the nucleophilic attack of CN⁻ anions onto the electron-deficient polarized CN bonds of P1's indolium moieties, resulting in the perturbation of the intramolecular charge transfer process occurring within the probe via destruction of the polymer's extended π-conjugation. P1 was also immobilized on a quartz slide by spin coating and then exposed to ultraviolet light. The resulting polymeric film displayed a rapid response to CN⁻ consisting in a distinct color change, extending the scope of the usefulness of P1 as a cyanide-ion probe beyond the solution phase. © 2019 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 124–131