Triethanolamine-capped CdSe quantum dots as fluorescent sensors for reciprocal recognition of mercury (II) and iodide in aqueous solution

Water-soluble luminescent CdSe quantum dots surface-modified with triethanolamine (TEA-CdSe-QDs) were prepared with high stability. The fluorescence of the TEA-CdSe-QDs was greatly quenched only when Hg²⁺ and I⁻ coexisted in the solution, whereas addition of either Hg²⁺ or I⁻ individually has no noticeable effect on the fluorescence emission. Such a unique quenching effect could be used for reciprocal recognition of mercury (II) ions and/or iodide anions in aqueous solution with rather high selectivity and sensitivity. The detection limits of Hg²⁺ or I⁻ ion were 1.9 × 10⁻⁷ mol L^-1 or 2.8 × 10⁻⁷ mol L⁻¹, respectively. The adequate experiments showed that iodine (I) anions could bridge between TEA-CdSe-QDs and Hg²⁺ to form a stable complex (QDs-I⁻-Hg²⁺) and the following effective electron transfer from the QDs to the Hg²⁺ could be responsible for the fluorescence quenching of QDs.     

Facile synthesis of N-acetyl-L-cysteine capped ZnS quantum dots as an eco-friendly fluorescence sensor for Hg2+

This paper described an investigation of a novel eco-friendly fluorescence sensor for Hg²⁺ ions based on N-acetyl-l-cysteine (NAC)-capped ZnS quantum dots (QDs) in aqueous solution. By using safe and low-cost materials, ZnS QDs modified by NAC were easily synthesized in aqueous medium via a one-step method. The quantitative detection of Hg²⁺ ions was developed based on fluorescence quenching of ZnS QDs with high sensitivity and selectivity. Under optimal conditions, its response was linearly proportional to the concentration of Hg²⁺ ions in a range from 0 to 2.4 × 10⁻⁶ mol L⁻¹ with a detection limit of 5.0 × 10⁻⁹ mol L⁻¹. Most of common physiologically relevant cations and anions did not interfere with the detection of Hg²⁺. The proposed method was applied to the trace determination of Hg²⁺ ions in water samples. The possible quenching mechanism was also examined by fluorescence and UV-vis absorption spectra.     

Construction of a new Cu2+ coated wire ion selective electrode based on 2-((2-(2-(2-(2-hydroxy-5-methoxybenzylidene amino)phenyl)disufanyl)phenylimino)methyl)-4-methoxyphenol Schiff base

In this article a new coated platinum Cu²⁺ ion selective electrode based on 2-((2-(2-(2-(2-hydroxy-5-methoxybenzylideneamino)phenyl)disufanyl)phenylimino) methyl)-4-methoxyphenol Schiff base (L₁) as a new ionophore is described. This sensor has a wide linear range of concentration (1.2 × 10⁻⁷-1.0 × 10⁻¹ mol L⁻¹) and a low detection limit of 9.8 × 10⁻⁸ mol L⁻¹of Cu(NO₃)₂. It has a Nernstian response with slope of 29.54 ± 1.62 mV decade⁻¹ and it is applicable in the pH range of 4.0-6.0 without any divergence in potentioal. The coated electrode has a short response time of approximately 9 s and is stable at least for 3.5 months. The electrode shows a good selectivity for Cu²⁺ ion toward a wide variety of metal ions. The proposed sensor was successfully applied for the determination of Cu²⁺ ion in different real and environmental samples and as indicator electrode for potentiometric titration of Cu²⁺ ion with EDTA.     

Ultrasensitive Cu sensing by near-infrared-emitting CdSeTe alloyed quantum dots

The near-infrared (NIR)-emitting CdSeTe alloyed quantum dots (AQdots) that capped with l-cysteine were applied for ultrasensitive Cu²⁺ sensing. The sensing approach was based on the fluorescence of the AQdots selectively quenched in the presence of Cu²⁺. Experimental results showed a low interference response towards other metal ions. The possible quenching mechanism was discussed on the basis of the binding between l-cysteine and the metal ions. In addition, biomolecules have low effect on the fluorescence due to the minimized interferences in NIR region. The response of the NIR optical sensor was linearly proportional to the concentration of Cu²⁺ ranging from 2 × 10⁻⁸ to 2 × 10⁻⁶ mol L⁻¹. Furthermore, it has been successfully applied to the detection of Cu²⁺ in vegetable samples.     

A novel colorimetric and fluorescent chemosensor: synthesis and selective detection for Cu and Hg

A novel two-channel metal ion sensor has been synthesized from macrocyclic dioxotetraamine and 1,8-naphthalimide derivative. The metal ion-selective signaling behaviors of the sensor were investigated. The sensor presented the selective coloration for Cu²⁺ and Hg²⁺ that can be detected by the naked-eye, respectively. Besides, the addition of Cu²⁺ and Hg²⁺ quenched the fluorescence of 1 obviously and the detection limit was found to be 3 × 10⁻⁷ M for Cu²⁺ and 7 × 10⁻⁷ M for Hg²⁺. This sensor can be utilized for the visual and spectroscopic detection of Cu²⁺ or Hg²⁺ in the presence of the other competing metal ions.     

Highly sensitive and selective detection of biothiols using graphene oxide-based “molecular beacon”-like fluorescent probe

A fluorometric method for quantity analysis of biothiols was developed using a graphene oxide (GO)-based “molecular beacon”-like probe, which consisted of FITC labeled thymine (T)-rich single-stranded DNA (ssDNA), GO and Hg²⁺ ions. The labeled ssDNA containing T–T mismatches would self-hybridize to duplex in the presence of Hg²⁺, which can avoid its adsorption on GO and the fluorescence of this GO-based probe was recovered. The fluorescence of the probe quenched after the addition of biothiols such as glutathione (GSH) and cysteine (Cys) owing to thiol groups can selectively competitive ligation of Hg²⁺ ions with T–T mismatches. In the present work, the GO-based probe was used for the determination of GSH and Cys. Under the optimal conditions, a linear correlation was established between fluorescence intensity ratio I₀/I and the concentration of GSH in the range of 2.0 × 10⁻⁹–5.0 × 10⁻⁷ mol L⁻¹ with a detection limit of 1.0 × 10⁻⁹ mol L⁻¹. The linear range for Cys is from 5.0 × 10⁻⁹ to 4.5 × 10⁻⁷ mol L⁻¹ with a detection limit of 2.0 × 10⁻⁹ mol L⁻¹. The proposed method was applied to the determination of GSH in human serum and cell extract samples with satisfactory results.     

Langmuir-Blodgett film of p-tert-butylthiacalix[4]arene modified glassy carbon electrode as voltammetric sensor for the determination of Hg(II)

The π-A isotherms and UV-vis spectra of the transferred films suggested that the monolayer of p-tert-butylthiacalix[4]arene can coordinate with Hg²⁺ at the air-water surface. From these observations, a glassy carbon electrode coated with Langmuir-Blodgett film of p-tert-butylthiacalix[4] arene as a new voltammetric sensor is designed for the determination of trace amounts of Hg²⁺. Compared with bare glassy carbon electrode and modified glassy carbon electrode using direct coating method, the Langmuir-Blodgett film-modified electrode can greatly improve the measuring sensitivity of Hg²⁺. Under the selected conditions, the Langmuir-Blodgett film-modified electrode in 0.1 mol L⁻¹ H₂SO₄ + 0.01 mol L⁻¹ KCl solution shows a linear voltammetric response for Hg²⁺ in the range of 5.0 × 10⁻¹⁰ to 1.5 × 10⁻⁷ mol L⁻¹, with a detection limit of 2.0 × 10⁻¹⁰ mol L⁻¹. The proposed method was also applied to determine Hg²⁺ in water samples (tap, lake and river water). In addition, the fabricated electrode exhibited a distinct advantage of simple preparation, non-toxicity, good reproducibility and good stability.     

A highly selective and sensitive fluorescein-based chemodosimeter for Hg2+ ions in aqueous media

A new fluorescein-based chemodosimeter (II) for Hg²⁺ ion was designed and synthesized, and it displayed excellent selective and sensitive toward Hg²⁺ ion over other commonly metal ions in aqueous media. II was a colorless, non-fluorescent compound. Upon addition of Hg²⁺ to the solution of II, the thiosemicarbazide moiety of II would undergo an irreversible desulfurization reaction to form its corresponding oxadiazole (IV), a colorful and fluorescent product. During this process, the spirocyclic ring of II was opened, causing instantaneous development of visible color and strong fluorescence emission in the range of 500-600 nm. Based on the above mechanism, a fluorogenic Hg²⁺-selective chemodosimeter was developed. The fluorescence increase is linearly with Hg²⁺ concentration up to 1.0 μmol L⁻¹ with a detection limit of 8.5 × 10⁻¹⁰ mol L⁻¹ (3σ). Compared with the rhodamine-type chemodosimeter, II is more stable in aqueous media and exhibits higher sensitivity toward Hg²⁺. The findings suggest that II will serve as a practical chemodosimeter for rapid detection of Hg²⁺ concentrations in realistic media.     

Novel potentiometric copper (II) selective membrane sensors based on cyclic tetrapeptide derivatives as neutral ionophores

Two novel membrane sensors sensitive and reasonably selective for Cu²⁺ ions are described. These are based on the use of newly synthesized cyclic tetrapeptide derivatives as neutral ionophores and sodium tetraphenylborate (NaTPB) as an anionic excluder in plasticized PVC membranes. The sensors exhibit fast and stable near-Nernstian response over the concentration range 1.0 × 10⁻⁶ mol l⁻¹ to 1.0 × 10⁻² mol l⁻¹ Cu²⁺ with a cationic slope of 30.2-25.9 mV per decade at pH 4.5-7 with a lower detection limit of 0.05-0.13 μg ml⁻¹. Effects of plasticizers, lipophilic salts and various foreign common ions are tested. The sensors display long life-span, long term stability, high reproducibility, and short response time. Selectivity of both sensors is significantly high for Cu²⁺ over Fe³⁺, Al³⁺, Zn²⁺, Cd²⁺, Hg²⁺, Ni²⁺, Co²⁺, Mn²⁺, alkaline earth and alkali metal ions. The sensors are used for direct measurement of copper content in different rocks and industrial wastewater samples from electroplating factories. The results agree fairly well with data obtained using atomic absorption spectrometry.     

Synchronous determination of mercury (II) and copper (II) based on quantum dots-multilayer film

A sensitive sensor for mercury (II) and copper (II) synchronous detection was established via the changed photoluminescence of CdTe quantum dots (QDs) multilayer films in this work. QDs were deposited on the quartz slides to form QDs-multilayer films by electrostatic interactions with poly(dimethyldiallyl ammonium chloride) (PDDA). Hg²⁺ or Cu²⁺ could quench the photoluminescence of the QDs-multilayer films, and glutathione (GSH) was used to remove Hg²⁺ or Cu²⁺ from QDs-multilayer films due to strong affinity of GSH-metal ions, which resulted in the recovered photoluminescence of QDs-multilayer films. There are good linear relationships between the metal ions concentration and the photoluminescence intensity of QDs in the quenched and recovered process. It was found that the Stern–Volmer constants for Hg²⁺ are higher than that for Cu²⁺. Based on different quenching and recovery constant between Hg²⁺ and Cu²⁺, the synchronous detection of Hg²⁺ and Cu²⁺ can be achieved. The linear ranges of this assay were obtained from 0.005 to 0.5 μM for Hg²⁺ and from 0.01 to 1 μM for Cu²⁺, respectively. And the artificial water samples were determined by this method with satisfactory results, the recoveries for Hg²⁺ and Cu²⁺ ions were found in the range of 90.4–106.4%. To the best of our knowledge, it is the first report about the synchronous detection of Hg²⁺ and Cu²⁺ by using quenched and recovered photoluminescence of quantum dots multilayer films.     

A new Hg-selective fluorescent sensor based on a dansyl amide-armed calix[4]-aza-crown

A new fluorescent chemosensor for Hg²⁺ based on a dansyl amide-armed calix[4]-aza-crown was reported. It exhibits high sensitivity and selectivity toward Hg²⁺ over a wide range of metal ions in MeCN-H₂O (4:1, v/v). The association constant of the 1:1 complex formation for 2-Hg²⁺ was calculated to be 1.31 × 10⁵ M⁻¹, and the detection limit for Hg²⁺ was found to be 4.1 × 10⁻⁶ mol L⁻¹.     

A new method for electrocatalytic oxidation of ascorbic acid at the Cu(II) zeolite-modified electrode

A new method is developed for the catalytic oxidation of ascorbic acid at graphite zeolite-modified electrode, doped with copper(II) (Cu²⁺A/ZCME). Copper(II) exchanged in zeolite type A acts as catalyst to oxidize ascorbic acid. The modified electrode lowered the overpotential of the reaction by ∼400 mV. First, the electrochemical behavior of copper(II), incorporated in the zeolite type A modified electrode, was studied. The results illustrate that diffusion can control the copper(II)/copper(0) redox process at the Cu²⁺A/ZCME. Then, the behavior of electrocatalytic oxidation reaction for ascorbic acid was researched. The electrode was employed to study electrocatalytic oxidation of ascorbic acid, using cyclic voltammetry and chronoamperometry as diagnostic techniques. The diffusion coefficient of ascorbic acid was equal to 1.028 × 10⁻⁵ cm² s⁻¹. A linear calibration graph was obtained over the ascorbic acid with a concentration range of 0.003-6.00 mmol L⁻¹. The detection limit (DL) of ascorbic acid was estimated as 2.76 × 10⁻⁷ mol L⁻¹. The relative standard deviations of 10 replicate measurements (performed on a single electrode at several ascorbic acid concentrations between 3.0 and 200 μmol L⁻¹) were measured between 1.0 and 2.4%.     

A potential visual fluorescence probe for ultratrace arsenic (III) detection by using glutathione-capped CdTe quantum dots

The interaction between mercaptoacetic acid (MA)-capped CdTe QDs, MA-capped CdTe/ZnS QDs or glutathione (GSH)-capped CdTe QDs with As(III) was studied using fluorescence spectrometry. As (III) has a high-affinity to reduced-GSH to form As(SG)₃, and the emission of the GSH-capped CdTe QDs (λ_em. = 612 nm) is quenched effectively. Thus, a novel fluorescence spectrometric method was developed for As (III) determination by using GSH-CdTe QDs. Under optimal conditions, the quenched fluorescence intensity (F₀/F) increased linearly with the concentration of As (III) ranging from 5.0 × 10⁻⁶ to 25 × 10⁻⁵ mol L⁻¹. The limit of detection (3σ) for As (III) was found to be 2 × 10⁻⁸ mol L⁻¹. This method is potentially useful in visual detection of As (III) under irradiation of the ultraviolet light.     

An optical sensor for mercury ion based on the fluorescence quenching of tetra(p-dimethylaminophenyl)porphyrin

An optical sensor for mercury ion (Hg²⁺), based on quenching the fluorescence of the sensing reagent porphyrin immobilized in plasticized poly(vinyl chloride) (PVC) membrane, has been developed. The responses to mercury ion were compared for the sensors modified with three porphyrin compounds including 5,10,15,20-tetraphenylporphyrin (TPP), tetra(p-dimethylaminophenyl)porphyrin (TDMAPP) and tetra(N-phenylpyrazole) porphyrin (TPPP). Among them, TDMAPP showed the most remarkable response to Hg²⁺. The drastic decrease of the TDMAPP fluorescence intensity was attributed to the formation of a complex between TDMAPP and Hg²⁺, which has been utilized as the fabrication basis of a Hg²⁺-sensitive fluorescence sensor. The analytical performance characteristics of the TDMAPP modified sensor was investigated. The response mechanism, especially involving the response difference of three porphyrin compounds, was discussed in detail. The sensor can be applied to the quantification of Hg²⁺ with a linear range covering from 4.0 × 10⁻⁸ mol L⁻¹ to 4.0 × 10⁻⁶ mol L⁻¹. The limit of detection was 8.0 × 10⁻⁹ mol L⁻¹. The sensor exhibited excellent reproducibility, reversibility and selectivity. Also, the TDMAPP-based sensor was successfully used for the determination of Hg²⁺ in environmental water samples.     

Ultrasensitive cysteine sensing using citrate-capped CdS quantum dots

The importance of cysteine (Cys) in biological systems has stimulated a great deal of efforts in the development of analytical methods for the determination of this amino acid. In this work, a novel fluorescent probe for Cys based on citrate (Cit)-capped CdS quantum dots (QDs) is reported. The Cit-capped CdS QDs fluorescent probe offers good sensitivity and selectivity for detecting Cys. A good linear relationship was obtained from 1.0 × 10⁻⁸ mol L⁻¹ to 5.0 × 10⁻⁵ mol L⁻¹ for Cys. The detection limit was calculated as 5.4 × 10⁻⁹ mol L⁻¹. The proposed method was applied to detect Cys in human urine samples, which showed satisfactory results. This assay is based on both the lability of Cit and the strong affinity of thiols to the surface of CdS QDs. The addition of Cys improved the passivation of the surface traps of CdS QDs and enhanced the fluorescence intensity.     

p-Dimethylaminobenzaldehyde thiosemicarbazone: a simple novel selective and sensitive fluorescent sensor for mercury(II) in aqueous solution

A novel and simple fluorophore, p-dimethylaminobenzaldehyde thiosemicarbazone (DMABTS), was prepared in order to find available fluorescent chemosensor for mercuric ion in aquesous solution. DMABTS emitted fluorescence at 448 nm in aqueous solution and its fluorescence intensity was completely quenched upon interaction with Hg²⁺ ions, which should be attributed to the 1:1 complex formation between DMABTS and Hg²⁺. The binding constant of the complex was determined as 7.48 × 10⁶ mol l⁻¹. The linear range of quantitative detection of 0 to 5.77 × 10⁻⁶ mol l⁻¹ and the detection limit of 7.7 × 10⁻⁷ mol l⁻¹ for Hg²⁺ in the 6.3 × 10⁻⁶ mol l⁻¹ DMABTS aqueous solution were obtained from a calibration curve. The coexistence of several transition metal ions and anions did interfere the fluorometric titration of Hg²⁺ ion by less than 4% in the emission change.     

One-step synthesis and applications of fluorescent Cu nanoclusters stabilized by l-cysteine in aqueous solution

Herein, an innovative and simple strategy for synthesizing high fluorescent Cu nanoclusters was successfully established while l-cysteine played a role as the stabilizer. Meaningfully, the current Cu nanoclusters together with a quantum yield of 14.3% were prepared in aqueous solution, indicating their extensive applications. Subsequently, the possible fluorescence mechanism was elucidated by fluorescence, UV–vis, HR-TEM, FTIR, XPS, and MS. Additionally, the CuNCs were employed for assaying Hg²⁺ on the basis of the interactions between Hg²⁺ and l-cysteine; thus facilitating the quenching of their fluorescence. The proposed analytical strategy permitted detections of Hg²⁺ in a linear range of 1.0 × 10⁻⁷ mol L⁻¹ × 10⁻³ mol L⁻¹, with a detection limit of 2.4 × 10⁻⁸ mol L⁻¹ at a signal-to-noise ratio of 3. Significantly, this CuNCs described here were further applied for coding and fluorescent staining, suggesting may broaden avenues toward diverse applications.     

An acyclic,dansyl based colorimetric and fluorescent chemosensor for Hg(II) via twisted intramolecular charge transfer (TICT)

An efficient fluorescent chemosensor for Hg²⁺ ion, based on 5-(dimethylamino)-N-(2-mercaptophenyl)naphthalene-1-sulfonamide, has been developed. It exhibits Hg²⁺-selective on–off fluorescence quenching behavior via twisted intramolecular charge transfer (TICT) mechanism, which is rationalized by time dependent density functional theory (TD-DFT) calculations. The system exhibits visible color change from colorless to gray upon Hg²⁺ binding with very high selectivity and sensitivity (as low as 5.0 × 10⁻¹⁰ mol L⁻¹) over other metal ions such as K⁺, Na⁺, Ag⁺, Mn²⁺, Ca²⁺, Ba²⁺, Fe²⁺, Zn²⁺, Pb²⁺, Cu²⁺, Sn²⁺, Cd²⁺, Ni²⁺ and Co²⁺. The present sensing system is also successfully applied for the detection of Hg²⁺ ion in real samples.     

A novel dual-function molecularly imprinted polymer on CdTe/ZnS quantum dots for highly selective and sensitive determination of ractopamine

A novel dual-function material was synthesized by anchoring a molecularly imprinted polymer (MIP) layer on CdTe/ZnS quantum dots (QDs) using a sol–gel with surface imprinting. The material exhibited highly selective and sensitive determination of ractopamine (RAC) through spectrofluorometry and solid-phase extraction (SPE) coupled with high performance liquid chromatography (HPLC). A series of adsorption experiments revealed that the material showed high selectivity, good adsorption capacity and a fast mass transfer rate. Fluorescence from the MIP-coated QDs was more strongly quenched by RAC than that of the non-imprinted polymer, which indicated that the MIP-coated QDs acted as a fluorescence sensing material could recognize RAC. In addition, the MIP-coated QDs as a sorbent was also shown to be promising for SPE coupled with HPLC for the determination of trace RAC in feeding stuffs and pork samples. Under optimal conditions, the spectrofluorometry and SPE-HPLC methods using the MIP-coated QDs had linear ranges of 5.00 × 10⁻¹⁰–3.55 × 10⁻⁷ and 1.50 × 10⁻¹⁰–8.90 × 10⁻⁸ mol L⁻¹, respectively, with limits of detection of 1.47 × 10⁻¹⁰ and 8.30 × 10⁻¹¹ mol L⁻¹, the relative standard deviations for six repeat experiments of RAC (2.90 × 10⁻⁹ mol L⁻¹) were below 2.83% and 7.11%.