高灵敏CdTe量子点探针的构建及与金属离子的作用

采用变性的牛血清白蛋白(dBSA)对水相合成的CdTe量子点进行修饰, 构建了高灵敏金属离子探针, 研究了其对重金属离子的检测性能并对机理进行了探讨. 通过优化反应条件, 合成了具有高量子产率的以巯基乙酸为稳定剂的水溶性CdTe量子点, 并采用变性的牛血清白蛋白分别对不同粒径的CdTe量子点进行修饰, 确定变性的牛血清白蛋白与不同粒径量子点之间的最佳比例. 在纯化变性的牛血清白蛋白修饰的量子点(dBSA-QDs)的基础上, 研究了该量子点与不同金属离子的作用. 结果表明, 量子点经修饰后, 其量子产率、 抗光漂白性及稳定性得到显著提高; 而且dBSA-QDs的荧光可被重金属离子有效猝灭, 与巯基乙酸稳定的量子点(TGA-QDs)相比, 检测灵敏度显著提高.     

Aqueous synthesis of type-II core/shell CdTe/CdSe quantum dots for near-infrared fluorescent sensing of copper(II)

Type-II core/shell CdTe/CdSe quantum dots (QDs) were synthesized in aqueous medium by employing thiol-capped CdTe QDs as core template and CdCl(2) and Na(2)SeSO(3) as shell precursors, respectively. Compared with the original CdTe cores, the core/shell CdTe/CdSe QDs showed an obvious red-shifted emission with the color-tune capability to the near-infrared (NIR) wavelength, because of the formation of an indirect excitation. The prepared QDs exhibited high stability and moderate fluorescence quantum yields (10-20%), and their core/shell heterostructure was characterized by UV-vis absorption, steady-state and time-resolved fluorescence spectra, X-ray powder diffraction, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. The fluorescence of the core/shell QDs could be markedly quenched by Cu(II), and approximate concentrations of other physiologically important cations, such as Zn(II), Ca(II), Na(I) and K(I) etc., had no effect on the fluorescence. Based on this, a simple and rapid method for Cu(II) determination was proposed using the NIR CdTe/CdSe QDs as fluorescent probes. Under optimal conditions, the response was linearly proportional to the concentration of Cu(II) between 0.05 to 50.0 x 10(-6) mol L(-1), the limit of detection was 2.0 x 10(-8) mol L(-1). The developed method was successfully applied to the detection of trace Cu(II) in real samples.     

Luminescent properties of water-soluble denatured bovine serum albumin-coated CdTe quantum dots

Chemically reduced bovine serum albumin (BSA) has been used to modify the surface of water-soluble CdTe quantum dots (QDs). It is demonstrated that the denatured BSA (dBSA) can be conjugated to the surface of CdTe QDs and thereby efficiently improve the chemical stability and the photoluminescence quantum yield (PL QY) of the QDs. It is inferred that a shell-like complex structure CdTe(x)(dBSA)(1-x) will form on the surface of the CdTe "core", resulting in the enhancement of PL intensity and the blue shift of the PL peak. This study of the effects of pH and dBSA concentration on optical properties of dBSA-coated QDs suggests that, at pH 6-9, the solution of dBSA-coated CdTe QDs can keep substantial stability and fluorescent brightness, whereas further increase of pH value leads to a dramatic decrease in PL QY and chemical stability. On the other hand, too high or too low initial dBSA concentration in the QD solution results in a decrease of PL QY for dBSA-coated CdTe QDs. This study provides a new approach of preparing stable water-soluble QDs with high PL QY and controllable luminescent colors for biological labeling applications.     

Purification of denatured bovine serum albumin coated CdTe quantum dots for sensitive detection of silver(I) ions

CdTe quantum dots (QDs) were synthesized in aqueous solution with 3-mercaptopropionic acid as the stabilizer. Chemically reduced bovine serum albumin (BSA) was used to modify the surface of the QDs. Experimental results showed that the denatured BSA (dBSA) could be effectively conjugated to the surface of CdTe QDs. Column chromatography was used to purify the conjugates and determine the optimal ratio of dBSA to QDs. Further experimental results showed that the conjugation of QDs by dBSA efficiently improved the photoluminescence quantum yield, the chemical stability of QDs and their stability against photobleaching. A facile and sensitive method for determination of silver(I) ions was proposed based on the fluorescence quenching of the dBSA–QDs. Under the optimal conditions, the relative fluorescence intensity decreased linearly with the concentration of the silver(I) ions in the range 0.08–10.66 μM. The detection limit was 0.01 μM. This study provides a new method for the detection of metal cations. Figure In this work, denatured BSA was used to modify the surface of CdTe QDs by a simple and rapid method. And the conjugates of dBSA-QDs were purified by column of Sephadex G-100. After the purification of the conjugates, the sensitivity was greatly increased as silver (I) ions probe.     

Functionalized CdSe quantum dots as selective silver ion chemodosimeter

CdSe quantum dots (QDs) have been prepared and modified with mercaptoacetic acid. They are water-soluble and biocompatible. To improve their fluorescence intensity and stability in water solution, bovine serum albumin (BSA) was absorbed onto their surface. Based on the quench of fluorescence signals of the functionalized CdSe QDs in the 543 nm wavelength and enhancement of them in the 570-700 nm wavelength range by Ag(I) ions at pH 5.0, a simple, rapid and specific method for Ag(I) determination was proposed. In comparison with single organic fluorophores, these nanoparticles are brighter, more stable against photobleaching, and do not suffer from blinking. Under the optimum conditions, the response is linearly proportional to the concentration of Ag(I) between 4.0 x 10(-7) and 1.5 x 10(-5) mol L(-1), and the limit of detection is 7.0 x 10(-8) mol L(-1). The mechanism of reaction is also discussed.     

Coated-wire silver ion-selective electrode based on silver complex of cyclam.

A coated-wire ion-selective electrode (ISE) based on cyclam (1,4,8,11-tetraazacyclotetradecane) as a neutral carrier in a polyvinyl chloride (PVC) matrix was fabricated for the determination of Ag(I) ions. The coated-wire ISE exhibited a linear Nernstian response over the range 1 x 10(-1) to 1 x 10(-7) M with a slope of 59 +/- 2 mV per decade change and a detection limit of 5 x 10(-8) M. The ISE shows a greater preference for Ag over other cations with good precision. The electrode was selective towards Ag(I) ions in the presence of 13 different metal ions tested. The selectivity coefficients (K(ij)) were determined for Na(I), K(I), Mg(II), Ca(II), Ba(II), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pb(II) and Hg(II). The selectivity coefficients of these cations are in the range of 10(-4) to 10(-2). This ISE was used for the determination of free silver and total silver in electroplating bath solutions, additives and brighteners.     

Functionalized CdS quantum dots-based luminescence probe for detection of heavy and transition metal ions in aqueous solution

Strong luminescence CdS quantum dots (QDs) have been prepared and modified with l-cysteine by a facile seeds-assistant technique in water. They are water-soluble and highly stable in aqueous solution. CdS QDs evaluated as a luminescence probe for heavy and transition metal (HTM) ions in aqueous solution was systematically studied. Five HTM ions such as silver(I) ion, copper(II) ion, mercury(II) ion, cobalt(II) ion, and nickel(II) ion significantly influence the photophysics of the emission from the functionalized CdS QDs. Experiment results showed that the fluorescence emission from CdS QDs was enhanced significantly by silver ion without any spectral shift, while several other bivalent HTM ions, such as Hg(2+), Cu(2+), Co(2+), and Ni(2+), exhibited effective optical quenching effect on QDs. Moreover, an obvious red-shift of emission band was observed in the quenching of CdS QDs for Hg(2+) and Cu(2+) ions. Under the optimal conditions, the response was linearly proportional to the concentration of Ag(+) ion ranging from 1.25 x 10(-7) to 5.0 x 10(-6)molL(-1) with a detection limit of 2.0 x 10(-8)molL(-1). The concentration dependence of the quenching effect on functionalized QDs for the other four HTM ions could be well described by typical Stern-Volmer equation, with the linear response of CdS QDs emission proportional to the concentration ranging from 1.50 x 10(-8) to 7.50 x 10(-7)molL(-1) for Hg(2+) ion, 3.0 x 10(-7) to 1.0 x 10(-5)molL(-1) for Ni(2+) ion, 4.59 x 10(-8) to 2.295 x 10(-6)molL(-1) for Cu(2+) ion, and 1.20 x 10(-7) to 6.0 x 10(-6)molL(-1) Co(2+) ion, respectively. Based on the distinct optical properties of CdS QDs system with the five HTM ions, and the relatively wide linear range and rapid response to HTM ions, CdS QDs can be developed as a potential identified luminescence probe for familiar HTM ions detection in aqueous solution.     

基于石墨烯和量子点自组装膜的能量转移构筑的高灵敏度DNA界面荧光传感

以QDs作为荧光探针, HIV1病毒序列DNA为研究对象, 设计了Quartz/PDDA/PSS/PDDA/CdTe/ssDNA自组装膜, 利用氧化石墨烯(GO)猝灭自组装膜上CdTe QDs的荧光, 而靶DNA(tDNA)与自组装膜表面ssDNA的互补配对作用使GO与CdTe QDs的距离增加, 导致自组装膜上量子点的荧光恢复, 由此建立了一种基于GO与QDs自组装膜之间荧光共振能量转移的快速灵敏检测DNA的界面分析方法, 检出限为7.26×10^-14 mol/L. 本方法制备的DNA探针操作简单, 自组装膜表面修饰的ssDNA提高了方法的选择性, GO的猝灭作用降低了检测背景, 极大地提高了荧光分析方法的灵敏度.     

Interaction of Ag(I), Hg(II), and Cu(II) with 1,2-ethanedithiol immobilized on chitosan: thermochemical data from isothermal calorimetry

The nature of interactions between metal ions Ag(I), Hg(II), Cu(II) and chitosan derivative of 1,2-ethanedithiol, QTDT, was investigated by isothermal calorimetry using the membrane breaking technique. Simultaneous determination of thermal effects, Q(int), and amount of cation that interacts, n(int), are described. The experimental data have been interpreted in terms of the Langmuir equation to determine the maximum adsorption capacity to form a monolayer, N(mon), and the energy of interaction for a saturated monolayer per gram of QTDT, Q(mon). With N(mon) and Q(mon), the molar enthalpy of interaction for formation of a monolayer of anchored cations per gram of QTDT, Delta(mon)H(m), was determined. The Delta(mon)H(m) values for Ag(I), Hg(II), and Cu(II) were -60.56, -58.05, and -84.36 kJ mol(-1), respectively. Negative values of DeltaG show the spontaneity of the interaction processes. The least entropically favourable processes, i.e., those which present more negative DeltaS values, seem to be compensated by the more favourable enthalpic parameter.     

Solvent control on the selective, nonselective, and absent response of a partially substituted lower rim calix(4)arene derivative for soft metal cations (mercury(II) and silver(I)). Structural and thermodynamic studies

The solvent control on the ability of a partially substituted lower rim calix(4)arene derivative 5,11,17,23,tetra-tert-butyl[25,27-bis(hydroxy)-26,28-bis(ethylthioethoxy)]-calix(4)arene, 1 to host soft metal cations (Hg(II) and Ag(I)) is demonstrated through 1H NMR, electrochemical (conductance measurements), and thermodynamic characterization of the complexation process in a wide variety of solvents. Solvent-ligand interactions were assessed from 1H NMR measurements involving 1 and various solvents in CDCl3. Thus, the formation of a 1:1 1-CH3CN adduct is reported. As far as metal cations are concerned, depending on the medium their complexation with 1 was only observed for Hg(II) and Ag(I). Thus, in acetonitrile, 1 is more selective for Hg(II) relative to Ag(I) by a factor of 2.2 x 10(3). In methanol the selectivity is reversed to an extent that the affinity of 1 for Ag(I) is 1.4 x 10(3) higher than that for Hg(II). However, 1 is unable to recognize selectively these cations in N,N-dimethylformamide while in propylene carbonate the ability of 1 to interact with these cations is lost. An outstanding feature of thermodynamics emerges when an assessment is made of the ligand effect on the complexation of these cations and analogues calix(4)arene derivatives. Thus, in acetonitrile the thermodynamics of cation complexation by the hydrophilic cavity of a calix(4)arene containing mixed pendant groups is built up from thermodynamic data for the same process involving derivatives with common functionalities at the narrow rim. This is a unique example of the additive contribution of pendant arms in the field of thermodynamics of calixarene chemistry.     

Catalytic determination of silver(I) by extractive flow injection analysis

A new catalytic method for the determination of silver(I) was developed based on a metal exchange reaction between ethylenediaminetetraacetatomercury(II) (Hg(II)-EDTA) in the aqueous phase and bis(diethyldithiocarbamato)copper(II) (Cu(II)-DDTC) in the organic phase. This exchange reaction (Cu(II)-DDTC(org)+Hg(II)-EDTA-->Hg(II)-DDTC(org)+Cu(II)-EDTA, where org denotes the organic phase) was observed to proceed slowly and the Cu(II)-DDTC complex transferred quantitatively to Hg(II)-complex in the organic phase in the equilibrium state. In this system, silver(I) acts as the catalyst and can be determined by measuring the decrease in the absorbance of the Cu(II)-DDTC complex (lambda(max)=435 nm). The reaction was applied to the extractive flow injection analysis of silver(I). The present method allows the determination of silver(I) at 10(-7) mol dm(-3) level with the sampling frequency of 30 h(-1). The relative standard deviation of 0.28% (n=10) was obtained at 4.0x10(-7) mol dm(-3) of silver(I).     

Study on the fluorescence resonance energy transfer between CdTe QDs and butyl-rhodamine B in the presence of CTMAB and its application on the detection of Hg(II)

The thioglycolic acid-functionalized CdTe quantum dots (QDs) were synthesized in aqueous solution using safe and low-cost inorganic salts as precursors. Fluorescence resonance energy transfer (FRET) system was constructed between CdTe QDs (donor) and butyl-rhodamine B (BRB) (acceptor) in the presence of cetyltrimethylammonium bromide (CTMAB). CTMAB micelles formed in water reduced the distance between the donor and the acceptor significantly and thus improved the FRET efficiency, which resulted in an obvious fluorescence enhancement of the acceptor. Several factors which impacted the fluorescence spectra of the FRET system were studied. The energy transfer efficiency (E) and the distance (r) between CdTe and BRB were obtained. The feasibility of the prepared FRET system as fluorescence probe for detecting Hg(II) in aqueous solution was demonstrated. At pH 6.60, a linear relationship could be established between the quenched fluorescence intensity of BRB and the concentration of Hg(II) in the range of 0.0625-2.5mumolL(-1). The limit of detection was 20.3nmolL(-1). The developed method was proved to be sensitive and repeatable to detect Hg(II) in a wide range in aqueous solutions.     

Interaction of mixed-donor macrocycles containing the 1,10-phenanthroline subunit with selected transition and post-transition metal ions: metal ion recognition in competitive liquid-liquid solvent extraction of Cu(II), Zn(II), Pb(II), Cd(II), Ag(I), and Hg(II)

Two new mixed aza-thia crowns 5-aza-2,8-dithia[9]-(2,9)-1,10-phenanthrolinophane (L(4)) and 2,8-diaza-5-thia[9]-(2,9)-1,10-phenanthrolinophane (L(7)) have been synthesized and characterized. The coordination behavior of L(4) and L(7) toward the metal ions Cu(II), Zn(II), Pb(II), Cd(II), Hg(II), and Ag(I) was studied in aqueous solution by potentiometric methods, in CD3CN/D2O 4:1 (v/v) by (1)H NMR titrations and in the solid state. The data obtained were compared with those available for the coordination behavior toward the same metal ions of structurally analogous mixed donor macrocyclic ligands L(1)-L(3), L(5), L(6): all these contain a phenanthroline subunit but have only S/O/N(aromatic) donor groups in the remaining portion of the ring and are, therefore, less water-soluble than L(4) and L(7). The complexes [Cd(NO3)2(L(5))], [Pb(L(7))](ClO4)2 x 1/2MeCN, [Pb(L(4))](ClO4)2 x MeCN, and [Cu(L(7))](ClO4)2 x 3/2MeNO2 were characterized by X-ray crystallography. The efficacy of L(1)-L(7) in competitive liquid-liquid metal ion extraction of Cu(II), Zn(II), Cd(II), Pb(II), Ag(I), and Hg(II) was assessed. In the absence of Hg(II), a clear extraction selectivity for Ag(I) was observed in all systems investigated.     

Electrochemiluminescence Enhancement of CdTe Quantum Dots by the Addition of Silver(I) Ions

Water-soluble CdTe quantum dots (QDs) were synthesized by using a 3-mercaptopropionic acid (MPA) capped method. Stable electrochemiluminescence (ECL) was obtained when the CdTe QDs were immobilized onto a glassy carbon electrode (GCE) by Layer-By-Layer (LBL) assembly of CdTe QDs and polydiallyldimethylam-monium chloride (PDDA) by using 2-(dibutylamino)-ethanol (DBAE) as a co-reactant. The ECL enhancement of CdTe QDs by the addition of silver(I) ions was also investigated. The maximum enhancement factor about 4 was obtained on a GCE in the presence and absence of the co-reactant. The enhancement was observed in phosphate-citric acid and phosphate buffer solutions (PBS), but not in borate buffer solution (BBS). This was newly formed Ag nanoparticles or silver(I) complex with large surface area and high catalytic activity in the phosphate-citric acid and phosphate buffer solutions, thus resulting in ECL enhancement.     

A liquid-state copper(II) ion-selective electrode containing a complex of Cu(II) with salicylaniline

A new liquid-state ion-selective electrode based on a complex of Cu(II) with salicylaniline is described. The electrode shows linear dependence of potential on the activity of Cu(2+) in the range from 5 x 10(-6) to 0.1M, with a slope of 28.3 mV/pCu at 18 degrees . The electrode shows a better selectivity relative to Ag(I) and Hg(II) than other copper(II) ion-selective electrodes. The possibilities for using the electrode for determination of copper in the presence of interfering cations are described.     

Complexing Polymer Films in The Preparation of Modified Electrodes for Detection of Metal Ions

Summary: The complexing properties of poly (3-(pyrrol-1-yl)propylmalonic acid) (poly1) and poly(N,N′-ethylenebis[N-[(3-(pyrrole-1-yl)propyl) carbamoyl) methyl]-glycine (poly2) coated electrodes (C|poly1 and C|poly2) towards Cu(II), Pb(II), Hg(II) and Cd(II) cations using the open circuit chemical preconcentration-anodic stripping technique were studied. Sorption process of metal cations onto complexing surfaces was readily investigated through the combination of a chemical pre-concentration-anodic stripping technique with a Langmuir isotherm model. The modified electrodes were used for the voltammetric determination of Cu(II), Pb(II), Hg(II) and Cd(II) ions, giving low detection limits for Cu(II) (5 × 10⁻⁹ mol L⁻¹) and Pb(II) (5 × 10⁻¹⁰ mol L⁻¹). The ability of the modified electrodes to analyze Cu(II) ions in natural sample has been demonstrated by the analysis of a tap water sample. The results of the preconcentration process under competitive conditions clearly shows that the selectivity of complexing molecular electrode materials can be subtly tuned upon playing on the accumulation time, polymer thickness and/or memory effect of the binding polymers, opening up new avenues towards evolutive and efficient smart sensing materials.     

Selective separation of silver(I) and mercury(II) ions in natural water samples using alumina modified thiouracil derivatives as new solid phase extractors

A simple and reliable solid-phase extraction (SPE) method has been developed to synthesise two new sorbents: 6-propyl-2-thiouracil and 5,6-diamino-2-thiouracil physically loaded onto alumina surface, phases I and II, respectively. The synthesis of these new phases has been confirmed by IR-spectroscopy. The surface concentrations of the organic moieties were determined to be 0.182 and 0.562 mmol g^?1 for phases I and II, respectively. The evaluation of the selectivity and metal uptake properties incorporated in these two alumina phases were also studied and discussed for 10 different metal ions: Ca(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hg(II), Pb(II) and Ag(I) under different controlling factors. The data obtained clearly indicated that the new SP-extractors have the highest affinity for retention of Hg(II) ions. Selective separation of Hg(II) from Ag(I) as one of the most interfering ion, in addition to the other eight coexisting metal ions under investigation, was achieved successfully using the new sorbents at pH = 9.0 under static conditions. Therefore, Hg(II) exhibits major retention percentage (100.0%) using phase I or II. However, Ag(I) exhibits minor retention percentage equal to 1.33% using phase I and 0.67% using phase II. On the other hand, the retention percentage of the other eight metal ions ranged (0.0–3.08%) using phase I and (0.0–1.54%) using phase II at the same pH. The new phases were applied for separation and determination of trace amounts of Hg(II) and Ag(I) spiked natural water samples using cold vapour atomic absorption spectroscopy and atomic absorption spectroscopy with no matrix interference. The high recovery values of Hg(II) and Ag(I) obtained using phases I and II were ranged 98.9 ± 0.1–99.2 ± 0.05% along with a good precision (RSD% 0.01–0.502%, N = 3) demonstrate the accuracy and validity of the new sorbents for separation and determination of Hg(II) and Ag(I).     

Influence and role of metal ions in enzymatic catalysis with e.c. 1.2.3.2. xanthine oxidase Application to trace analysis

The effect of metal ions on the reductive half-reaction of xanthine oxidase (XOD) in the catalytic conversion of xanthine into uric acid has been studied spectrophotometrically in Tris-HCl buffer at pH 7.4, 37 +/- 0.1 degrees and ionic strength 0.04M. Some metal ions display inhibitor properties, the sequence of inhibiting efficiency being Ag(I) > Hg(II) > Cu(II) > Cr(VI) > V(V) > Au(III) > Tl(I) and for these the I(50) values were determined. Only Tl(I), V(V) and Cu(II) showed reversible inhibition and therefore for these the mechanisms were assessed [competitive for V(V) and Tl(I); uncompetitive for Cu(II)]. The conditional inhibition constants (K(i)) were also determined. The effect of EDTA for protection of the enzyme against metal inhibition, and for its reactivation after inhibition, was also investigated. Utilization of the linear relationship between relative enzyme activity and inhibitor concentration allowed sensitive and selective (though not specific) determination of Ag(I) and Hg(II) (10(-9)-10(-8)M), and of Cu(II) and Cr(VI) (10(-7)-10(-6)M), the maximum relative error being +/- 4%. For a few metal ions, e.g., Ag(I) and Cr(VI), in the presence of EDTA, a certain specificity is observed.     

Nanoparticles as scaffolds for FRET-based ratiometric detection of mercury ions in water with QDs as donors

The quenching of quantum dots' emission by some analytes (Hg(2+), Pb(2+), etc.) has long been hindering the fabrication of QD-based 'turn-on' or ratiometric fluorescent sensors for these analytes. In this study, we demonstrate a facile solution for constructing a robust FRET-based ratiometric sensor for Hg(2+) detection in water with CdTe QDs as the donor. By using the reverse microemulsion approach, CdTe QDs were first embedded into nanosized silica particles, forming the QDs/silica cores, a positively charged ultrathin spacer layer was then deposited on each QDs/silica core, followed by the coating of a mercury ion probe on the particle surfaces. The resultant multilayered QDs/silica composite nanoparticles are dispersible in HEPES buffered water; and in the presence of mercury ions, the QDs inside the nanoparticles will not be quenched by mercury ions due to the existence of the positively charged spacer layer, but can transfer their excited energy to the acceptors (probe/Hg(2+) complex), thus achieving the FRET-based ratiometric sensing for mercury ions in totally aqueous media. With its detection limit of 260 nM, this QD-based sensor exhibits high selectivity toward mercury ion and can be used in a wide pH range. This strategy may be used to construct QDs-based ratiometric assays for other ions which quench the emission of QDs.     

Highly selectively monitoring heavy and transition metal ions by a fluorescent sensor based on dipeptide

Fluorescent sensor (DMH) based on dipeptide was efficiently synthesized in solid phase synthesis. The dipeptide sensor shows sensitive response to Ag(I), Hg(II), and Cu(II) among 14 metal ions in 100% aqueous solution. The fluorescent sensor differentiates three heavy metal ions by response type; turn on response to Ag(I), ratiometric response to Hg(II), and turn off detection of Cu(II). The detection limits of the sensor for Ag(I) and Cu(II) were much lower than the EPA's drinking water maximum contaminant levels (MCL). Specially, DMH penetrated live cells and detected intracellular Ag⁺ by turn on response. We described the fluorescent change, binding affinity, detection limit for the metal ions. The study of a heavy metal-responsive sensor based on dipeptide demonstrates its potential utility in the environment field.