A turn-on fluorescent probe for selective and sensitive detection of hydrogen sulfide

An imidazolethione based turn-on fluorescent probe was synthesized for the detection of hydrogen sulfide, a biologically relevant molecule and an important air pollutant. The probe rapidly and selectively reacted with hydrogen sulfide to produce a strongly fluorescent product, resulting in the fluorescence enhancement of the system. The detection limit was determined to be 30 nM at the probe concentration of 1.0 μM. An indicating paper for visual detection of hydrogen sulfide gas has been fabricated by immobilizing the probe on a piece of appropriate paper substrate, and the detection limit of the visual method reached as low as 0.7 ppm. Moreover, the fluorescence turn-on/off of the system showed good reversibility when exposed alternately to hydrogen sulfide and mercuric ion, which was utilized to make an INHIBIT logic circuit for the presence of the two species.     

Trace analysis of uranyl ion (UO2) in aqueous solution by fluorescence turn-on detection via aggregation induced emission enhancement effect

A sensitive fluorescence turn-on method for trace amounts of uranyl ion (UO₂²⁺) in solution has been developed in this study, based on aggregation induced emission enhancement (AIEE) characteristics of 4-pethoxycarboxyl salicylaldehyde azine (PCSA) induced by complex interaction between UO₂²⁺ and PCSA. Under optimized conditions, a fluorescence enhancement at 540 nm could be observed, which was linearly related to the concentration of UO₂²⁺ in the range of 1–25 ppb (part per billion). Analytical data showed that a detection limit of 0.2 ppb was achieved with the relative standard deviation (R.S.D.) 1.3% (n = 5). The proposed method was successfully utilized in quantifying UO₂²⁺ in fuel processing wastewaters.     

Sensitive and selective fluorescence determination of trace hydrazine in aqueous solution utilizing 5-chlorosalicylaldehyde

A facile fluorescent method for the determination of hydrazine in aqueous solution with excellent sensitivity was developed. 5-Chlorosalicylaldehyde (CS), a readily commercially available compound, was applied as the derivatization reagent in this work. Under the addition of CS to hydrazine aqueous solution (ethanol/water/acetic acid = 30/66/4), an intense fluorescence enhancement was observed at 570 nm with a large stokes shift of ∼170 nm. Upon the optimal condition, the fluorescence intensity linearly increased with the concentration of hydrazine in the range of 0.2 and 9.3 μM with a correlation coefficient of R² = 0.9995 (n = 10) and a detection limit of 0.08 μM. The R.S.D. was 2.0% (n = 5). Determination of hydrazine in river and drinking water samples was successfully performed. Hydrazine vapor sensing by the proposed method was also reported.     

Ultrasensitive fluorescence detection of glutaraldehyde in water samples with bovine serum albumin-Au nanoclusters

Based on the cross-linking nature of BSA in the presence of glutaraldehyde (GA), the fluorescence of BSA-stabilized Au nanoclusters was effectively quenched by GA. A new method for ultrasensitive GA detection in water samples was thus developed with fluorescent BSA-stabilized Au nanoclusters. The fluorescence quenching of BSA-stabilized Au nanoclusters in the presence of GA fitted to Stern-Volmer equation. In the GA concentration range of 0.8–6 μM, a linear relationship of F₀/F versus GA concentration was obtained with a limit of detection (LOD) of 0.2 μM. The relative standard deviation of 5 replicate measurements of 4 μM GA is 1.3%. This method shows good selectivity over other organics in water samples. The feasibility of the new sensor for GA in different water samples was demonstrated.     

A nonionic surfactant-decorated liquid crystal sensor for sensitive and selective detection of proteins

Proteins are responsible for most biochemical events in human body. It is essential to develop sensitive and selective methods for the detection of proteins. In this study, liquid crystal (LC)-based sensor for highly selective and sensitive detection of lysozyme, concanavalin A (Con A), and bovine serum albumin (BSA) was constructed by utilizing the LC interface decorated with a nonionic surfactant, dodecyl β-d-glucopyranoside. A change of the LC optical images from bright to dark appearance was observed after transferring dodecyl β-d-glucopyranoside onto the aqueous/LC interface due to the formation of stable self-assembled surfactant monolayer, regardless of pH and ion concentrations studied in a wide range. The optical images turned back from dark to bright appearance after addition of lysozyme, Con A and BSA, respectively. Noteworthy is that these proteins can be further distinguished by adding enzyme inhibitors and controlling incubation temperature of the protein solutions based on three different interaction mechanisms between proteins and dodecyl β-d-glucopyranoside, viz. enzymatic hydrolysis, specific saccharide binding, and physical absorption. The LC-based sensor decorated with dodecyl β-d-glucopyranoside shows high sensitivity for protein detection. The limit of detection (LOD) for lysozyme, Con A and BSA reaches around 0.1 μg/mL, 0.01 μg/mL and 0.001 μg/mL, respectively. These results might provide new insights into increasing selectivity and sensitivity of LC-based sensors for the detection of proteins.     

A fluorescence turn-on probe for the detection of thiol-containing amino acids in aqueous solution and bioimaging in cells

A turn-on fluorescent probe, based on a water-soluble terphenyl derivative, for the detection of cysteine and homocysteine is reported. The aldehyde groups in the probe play crucial roles in providing reaction with thiol groups in the amino acids, leading to a formation of thiazolidine (from cysteine) or thiazinane ring (from homocysteine). As a result, the new formation of such rings alters the electronic property of the conjugated system in the probe and results in emission enhancement. The probe in aqueous solution exhibits a remarkable increase in its quantum yield upon exposure to cysteine (up to 20-fold) and to homocysteine (up to 700-fold), while slight quenching is observed in the presence of glutathione. Moreover, an investigation on time-resolved fluorescence spectra of the probe in the presence of cysteine and homocysteine reveals potential discriminatory detection of cysteine and homocysteine. Bioimaging of the thiols in live HeLa cells was successfully applied.     

Binding equilibrium study of phosphotungstic acid and HSA or BSA with UV spectrum, fluorescence spectrum and equilibrium dialysis

The binding equilibrium between phosphotungstic acid (H7[P(W2O7)6] · XH2O;PTA) and human serum albumin (HSA) or bovine serum albumin (BSA) has been studied by UV-Vis, fluorescence spectroscopies and equilibrium dialysis. It has been observed that UV absorption enhanced and the fluorescence quenched as the PTA binding to HSA or BSA at physiological pH 7.43(?.02). The Scatchard analysis indicated that there exists a strong binding site of PTA in both HSA and BSA, and the successive stability constants of these two systems are obtained by nonlinear least-squares methods fitting Bjerrum formula.     

Highly sensitive fluorescence detection of chloride ion in aqueous solution with Ag-modified porous g-C3N4 nanosheets

The porous g-C₃N₄ (PCN) nanosheets are successfully synthesized and further modified with nano-sized Ag by a simple wet-chemical process. Interestingly, the Ag-modified porous g-C₃N₄ (Ag-PCN) nanosheets exhibit competitive fluorescence detection performance of chloride ion (Cl⁻) in aqueous solution. Under the optimized conditions, the concentration of Cl⁻ could be quantitative analyzed with the Ag-PCN in a wide detection range from 0.5 mmol/L to 0.1 mol/L, with a low detection limitation of 0.06 mmol/L. It is confirmed that the fluorescence of PCN could be effectively decayed by the photoinduced charge transfer via the adsorbed Cl⁻ for trapping holes, mainly by means of the time-resolved fluorescence and surface photovoltage spectra. The porous structure and modified Ag promote the adsorption of Cl⁻ on resulting Ag-PCN, leading to excellent fluorescence detection for Cl⁻. This work provides a feasible route to develop a fluorescence detection of Cl⁻ with g-C₃N₄ nanosheets in environment water.     

A novel and synthetically facile coumarin-thiophene-derived Schiff base for selective fluorescent detection of cyanide anions in aqueous solution: Synthesis,anion interactions,theoretical study and DNA-binding properties

A colorimetric and fluorescent chemosensor (chemosensor 2) for the detection of cyanide anions in aqueous solution has been designed and synthesized in high yield. The sensing mechanism of the chemosensor was verified via UV–vis, fluorimetric, and NMR titrations, and was theoretically explained using DFT and TD-DFT calculations. The chemosensor could optically discriminate the presence of fluoride ions over other anions by a color change from yellow to red with an enhancement of pink fluorescence in DMSO. However, it showed strong green fluorescence when CN^? was added to a mixture of DMSO/water (6:4 v/v). Thus, the chemosensor can be employed in selective detecting of CN^? besides other interference anions (F^?, AcO^? and H₂PO₄^?) in aqueous solution. Moreover, 2 can be used to detect CN^? at a concentration as low as 0.32?μM, which is lower than the WHO guideline (2.7?μM) for cyanide. A low quantity of CN^? (1.08?μM) can be detected and quantified using the prepared chemosensor. Moreover, the UV–vis and fluorescence spectroscopy studies of the interactions between 2 and dublex DNA revealed intercalative binding of calf thymus DNA to the chemosensor.     

A novel water-soluble AIE-based fluorescence probe with red emission for the sensitive detection of heparin in aqueous solution and human serum samples

Heparin is widely used to anticoagulation treatment in clinic, while the overdoses of heparin can cause potentially catastrophic complications. Thus, the selective and sensitive detection of heparin is of great importance. Herein, a novel water-soluble AIE-based fluorescent probe (TIBI) with red emission (650 nm) has been rationally developed to detect heparin by the electrostatic-interaction and ion replacing strategy. TIBI exhibited excellent selectivity and low detection limit (0.08 μM) for detection of heparin. Moreover, TIBI was successfully applied to detect heparin in complicated serum samples with satisfactory results. This study holds great promise for real time monitoring heparin in clinical application.     

BSA mediated Ag@Bi2S3 composites: synthesis,characterization, photodegradation of mixed dyes via metal-semiconductor interface,antimicrobial and antioxidant activities

Nowadays, the development of metal-metal sulfide interface semiconductors using green approach is best material for the photocatalytic and biological applications. Here, we provided for the first time, an environmentally friendly route to fabricate bovine serum albumin (BSA) assisted Ag@Bi₂S₃ composites through a metal-metal sulphide interface via a simple hydrothermal method for the evaluation of photochemical and biological applications. The synthesized composites were characterized by UV–vis DRS, PL, XRD, TEM, and N₂ adsorption-desorption isotherms. The UV–vis DRS and PL spectra show that the obtained nano-sized Ag@Bi₂S₃ composite displays enhanced visible-light absorption and a decreased fluorescence emission compared to that of Bi₂S₃ nanorods (NRs). The photocatalytic performances of the synthesized composites were evaluated by the degradation of the single (RhB and MB) and mixed dye (RhB+MB) under sunlight irradiation. The results indicated that the Ag@Bi₂S₃ composite exhibits superior photocatalytic activity (98.38%) than that of individual Ag NPs and Bi₂S₃ NRs due to the synergistic effect of Ag and Bi₂S₃ nanophases in the Ag@Bi₂S₃ composite, which results in an effective charge separation, fast electron transfer from Ag to Bi₂S₃, and a low recombination of photo-induced electron-hole pairs. The Ag@Bi₂S₃ composite also has good recycling stability up to 5 cycles and its mechanism also investigated. The evaluation of reactive species during the photocatalytic reaction was also carried out. Further, the effects of Bi₂S₃ and Ag NPs on the antimicrobial and antioxidant activity of the resultant Ag@Bi₂S₃ composite were also systematically investigated.     

A tetraphenylethene based polarity dependent turn-on fluorescence strategy for selective and sensitive detection of Hg in aqueous medium and in living cells

A turn-on fluorescent chemosensor strategy based on the change in the polarity of aggregation induced emission active tetraphenylethene is presented for the detection of Hg²⁺ in aqueous medium and in living cells. The sensing mechanism involves the formation of nonpolar fluorescent aggregates of tetraphenylethene molecules by elimination of polar moieties of TPE with Hg²⁺ interaction.     

Highly sensitive and selective optical chemosensor for determination of Cu2+ in aqueous solution

A highly selective and sensitive rhodamine-based colorimetric chemosensor (1) for quantification of divalent copper in aqueous solution has been investigated in this work. It was designed using salicylaldehyde hydrazone and rhodamine 6G as copper-chelating and signal-reporting groups, respectively. In environmentally friendly media (50% (v/v) water/ethanol and 10 mM NaAc–HAc neutral buffer (pH 7.0)), the sensor exhibited selective absorbance enhancement to Cu²⁺ over other metal ions at 529 nm, with a dynamic working range of 0.05–5.00 μM and a detection limit of 10 nM Cu²⁺, respectively. To achieve fluorometric determination of Cu²⁺, the Cu²⁺-induced absorbance enhancement of 1 was efficiently converted to fluorescence quenching by fluorescence inner filter effects using rhodamine B (RB) as a fluorophore. The selectivity and sensitivity of fluorescence analysis were similar to those of absorptiometric measurement. Both absorptiometric and fluorometric methods were successfully applied to the detection of Cu²⁺ in three water samples.     

A fluorescein-based fluorogenic and chromogenic chemodosimeter for the sensitive detection of sulfide anion in aqueous solution

A highly sensitive chromo- and fluorogenic chemodosimeter for sulfide anion was developed based on its nucleophilicity. 2,4-Dinitrobenzenesulfonyl-fluorescein (I) is a weakly fluorescent compound. Upon mixing with sulfide anion in aqueous acetone solution, the 2,4-dinitrobenzenesulfonyl group of I was efficiently removed and highly fluorescent fluorescein was released, hence leading to the dramatic increases in both fluorescence and absorbance of the reaction solution. The fluorescence increment is linear with sulfide anion concentration in the range 50-1000 nmol L⁻¹ with a detection limit of 4.3 nmol L⁻¹ (3σ). The proposed chemodosimeter showed excellent selectivity toward sulfide anion and was successfully applied to the determination of sulfide anion in synthetic wastewater samples.     

Highly selective and sensitive fluorescence turn-on probe for a catalytic amount of Cu(I) ions in water through the click reaction

A simple azide-functionalized coumarin (1) was utilized as a fluorescence turn-on probe for a catalytic amount of Cu(I) ions in HEPES buffer. The probe has shown a selective and sensitive response to the cuprous ions over other various cations through a Cu(I)-mediated click reaction of 1 to an alkyne. When a catalytic amount of copper sulfates was added in the presence of ascorbate, the prominent fluorescence ‘Off-On’ change of 1 was observed so that submicromolar concentration of copper ions was detectable by the naked eye.     

A highly selective and ratiometric fluorescence probe for the detection of Hg and pH change based on coumarin in aqueous solution

A simple but highly selective coumarin-based fluorescence probe 1, 8-(1,3-dithiane)-7-hydroxycoumarin was designed and synthesized for both the ratiometric detection of Hg²⁺ and the on–off response to pH change in aqueous solution. The sensor detected Hg²⁺ selectively via Hg²⁺-promoted thioacetal deprotection reaction within five minutes and reflected pH in the range from 7.8 to 11.9 as a result of the equilibrium between weak-fluorescent acid form and strong-fluorescent base form. In addition, the probe has an excellent selectivity towards Hg²⁺ over other competitive metal ions for biomedical and environmental applications. The sensing behavior of our probe was studied by UV–visible absorption spectra and fluorescence spectra.     

Photosensitizing properties of octacarboxy metallophthalocyanines in aqueous medium and their interaction with bovine serum albumin

Photosensitizing properties of aluminium, silicon, zinc and germanium octacarboxy phthalocyanines ((OH)AlOCPc, (OH)₂SiOCPc, ZnOCPc and (OH)₂GeOCPc) were studied in aqueous medium and in the presence of bovine serum albumin (BSA). Triplet quantum yields increased with increasing atomic number of the central metals of the metallophthalocyanine. The efficiency of singlet oxygen generation via energy transfer from the excited triplet state of the octacarboxy metallophthalocyanines (MOCPcs) to ground state oxygen increased markedly in the presence of BSA. The triplet state lifetimes of the MOCPc complexes in the presence of BSA were found to be longer than in the absence of BSA, ranging from 110 to 580 μs. These complexes bind readily to BSA. Stern–Volmer quenching constant K_SV as well as the binding constant k_b values were calculated. The probable mechanism of quenching of BSA fluorescence by the MOCPc complexes is by static quenching.     

Crystal structure and interaction with bovine serum albumin of the Cu(I/II) complex [C20H32Cu2I3N4] n

[C₂₀H₃₂Cu₂I₃N₄] _n was synthesized and characterized by elemental analysis, ESI-MS spectrometry, and IR spectra. The crystal structure was determined by X-ray single-crystal diffraction. The binding of the complex with bovine serum albumin (BSA) was studied by fluorescence spectroscopy under simulated physiological conditions. The binding constant (K _b), the number of binding sites (n), and the corresponding thermodynamic parameters ΔH, ΔS, ΔG were calculated based on the van’t Hoff equation. The complex had strong ability to quench the fluorescence from BSA, and the quenching mechanism of this complex to BSA was static quenching. Hydrogen bonds and van der Waals forces are the interactions between the Cu(I/II) complex and BSA. According to the Förster non-radiation energy transfer theory, the binding average distance between the donor (BSA) and the acceptor (Cu(I/II) complex) was obtained. The effect of the complex on the BSA conformation was also studied by using synchronous fluorescence spectroscopy.     

A new ESIPT-based fluorescent probe for highly selective and sensitive detection of HClO in aqueous solution

A new ESIPT-based fluorescent probe, PHC2, for the detection of hypochlorous acid has been rationally designed and developed. Endowed by the specific reaction between hypochlorous acid and phenyl azo group, PHC2 features high degree of selectivity and sensitivity for HClO with a low detection limit (13.2 nM) under physiological conditions in neutral aqueous solution.     

Fluorescence turn-on chemodosimeter for rapid detection of mercury (II) ions in aqueous solution and blood from mice with toxicosis

The heavy metal mercury (Hg) is a threat to the health of people and wildlife in many environments. Among various chemical forms, Hg²⁺ salts are usually more toxic than their counterparts because of their greater solubility in water; thus, they are more readily absorbed from the gastrointestinal tract into circulation. Therefore, new chemical receptors for detecting Hg²⁺ ions in circulation are needed. In this study, we developed a rhodamine-based turn-on fluorescence probe to monitor Hg²⁺ in aqueous solution and in blood of mice with toxicosis. The chemodosimeter responds to Hg²⁺ ions stoichiometrically, rapidly, and irreversibly at room temperature as a result of a chemical reaction that produces strongly fluorescent oxadiazole. The new fluorescent probe shows good fluorescence response, with high sensitivity and selectivity, toward Hg²⁺ ions in aqueous solution and in blood from mice with toxicosis and facilitates the naked-eye detection of Hg²⁺ ions.