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ABSTRACT: Based on the catalytic etching of gold nanoparticles (AuNPs), a label-free colorimetric probe was developed for the detection of Cu(2+) in aqueous solutions. AuNPs were first stabilized by hexadecyltrimethylammonium bromide in NH3-NH4Cl (0.6M/0.1M) solutions. Then thiosulfate (S2O3(2-)) ions were introduced and AuNPs were gradually dissolved by dissolved oxygen. With the further addition of Cu(2+), Cu(NH3)4(2+) oxidized AuNPs to produce Au(S2O3)2(3-) and Cu(S2O3)3(5-), while the later was oxid-ized to Cu(NH3)4(2+) again by dissolved oxygen. The dissolving rate of AuNPs was thereby remarkably promoted and Cu(2+) acted as the catalyst. The process went on due to the sufficient supply of dissolved oxygen and AuNPs were rapidly etched. Meanwhile, a visible color change from red to colorless was observed. Subsequent tests confirmed such a non-aggregation-based method as a sensitive (LOD=5.0nM or 0.32ppb) and selective (at least 100-fold over other metal ions except for Pb(2+) and Mn(2+)) way for the detection of Cu(2+) (linear range, 10-80nM). Moreover, our results show that the color change induced by 40nM Cu(2+) can be easily observed by naked eyes, which is particularly applicable to fast on-site investigations.
Talanta 08/2013; 112C:37-42. · 3.79 Impact Factor
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ABSTRACT: A fluorescence assay for the highly sensitive and selective detection of Hg(2+) using a gold nanoparticle (AuNP)-based probe was proposed. The assay was based on the formation of Hg-Au alloys, which accelerated the oxidization of o-phenylenediamine by dissolved oxygen to produce 2,3-diaminophenazine, a fluorescent product.
The Analyst 05/2013; · 4.23 Impact Factor
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ABSTRACT: A novel label-free colorimetric strategy was reported for sensitive detection of copper ions (Cu) by using the decelerating etching of gold nanorods (GNRs). HO was employed as the oxidant for corrosion of GNRs, leading to the decrease of the aspect ratio of GNRs. In the absence of Cu, the redox corrosion of GNRs by HO occurred rapidly, causing the distinct color change of GNRs from bluish green to purplish red. By virtue of the strong and specific catalysis by Cu of the decomposition of HO, the rate of redox corrosion can be decelerated. Relevant experimental parameters, including pH value, concentrations of NaSCN and HO, incubation temperature and time were evaluated. Under optimal conditions, our method gave a good linear range of 10-300 nM (R = 0.9985) for Cu and the detection limit with the naked eye is as low as 10 nM. Thus, the proposed colorimetric sensor is simple, sensitive (4.96 nM) and selective, and it has been successfully applied to detect Cu in shellfish samples. Moreover, the potential mechanism was also discussed.
The Analyst 04/2013; 138(7):2080-4. · 4.23 Impact Factor
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ABSTRACT: A simple colorimetric method with high sensitivity and selectivity was developed for sensing of nitrite as low as 4.0 μM by naked eyes, which is based on etching of gold nanorods accompanied by shape changes in aspect ratios (length/width) and a visible color change from bluish green to red and then to colorless with the increase of nitrite.
The Analyst 09/2012; 137(22):5197-200. · 4.23 Impact Factor
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ABSTRACT: Based on inducing the aggregation of gold nanoparticles (AuNPs), a simple colorimetric method with high sensitivity and selectivity was developed for the sensing of thiocyanate (SCN(-)) in aqueous solutions. Citrate-capped AuNPs were prepared following a classic method and Tween 20 was subsequently added as a stabilizer. With the addition of SCN(-), citrate ions on AuNPs surfaces were replaced due to the high affinity between SCN(-) and Au. As a result, Tween 20 molecules adsorbed on the AuNPs surfaces were separated and the AuNPs aggregated. The process was accompanied by a visible color change from red to blue within 5 min. The sensing of SCN(-) can therefore be easily achieved by a UV-vis spectrophotometer or even by the naked eye. The potential effects of relevant experimental conditions, including concentration of Tween 20, pH, incubation temperature and time, were evaluated to optimize the method. Under optimized conditions, this method yields excellent sensitivity (LOD = 0.2 μM or 11.6 ppb) and selectivity toward SCN(-). Our attempt may provide a cost-effective, rapid and simple solution to the inspection of SCN(-) ions in saliva and environmental aqueous samples.
The Analyst 04/2012; 137(11):2682-6. · 4.23 Impact Factor
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ABSTRACT: A novel platform for effective "turn-on" fluorescence sensing of lead ions (Pb(2+)) in aqueous solution was developed based on gold nanoparticle (AuNP)-functionalized graphene. The AuNP-functionalized graphene exhibited minimal background fluorescence because of the extraordinarily high quenching ability of AuNPs. Interestingly, the AuNP-functionalized graphene underwent fluorescence restoration as well as significant enhancement upon adding Pb(2+), which was attributed to the fact that Pb(2+) could accelerate the leaching rate of the AuNPs on graphene surfaces in the presence of both thiosulfate (S(2)O(3)(2-)) and 2-mercaptoethanol (2-ME). Consequently, this could be utilized as the basis for selective detection of Pb(2+). With the optimum conditions chosen, the relative fluorescence intensity showed good linearity versus logarithm concentration of Pb(2+) in the range of 50-1000 nM (R = 0.9982), and a detection limit of 10 nM. High selectivity over common coexistent metal ions was also demonstrated. The practical application had been carried out for determination of Pb(2+) in tap water and mineral water samples. The Pb(2+)-specific "turn-on" fluorescence sensor, based on Pb(2+) accelerated leaching of AuNPs on the surface of graphene, provided new opportunities for highly sensitive and selective Pb(2+) detection in aqueous media.
ACS Applied Materials & Interfaces 02/2012; 4(2):1080-6. · 4.53 Impact Factor
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ABSTRACT: As a sensitive and selective analytical technique, gold nanoparticles-based colorimetric sensing was characterized by its simplicity and cost-effectiveness. Specific methods have been extensively developed for different targets in diverse samples. In this study, a label-free method for sensing Co(2+) in aqueous solutions was described. The target was achieved by the induced aggregation of thiosulfate (S(2)O(3)(2-)) stabilized gold nanoparticles (AuNPs) in the presence of ethylenediamine (en). Co(2+) first reacted with en and formed complexes of Co(en)(3)(2+) in aqueous solutions, which was followed by the oxidation of Co(en)(3)(2+) to Co(en)(3)(3+) by dissolved oxygen. Co(en)(3)(3+) then attacked S(2)O(3)(2-) ligands adsorbed on the AuNPs' surfaces, forming positively charged (en)(2)CoS(2)O(3)(+) on the AuNPs' surfaces, which reduced the surface charges of AuNPs and induced the aggregation of AuNPs. The process was accompanied by a red-shift in the adsorption spectrum and a visible colour change from wine red to blue. Potential effects of relevant experimental conditions, including pH, concentrations of S(2)O(3)(2-) and en, and incubation time were evaluated for optimization of the method. The proposed method is sensitive (LOD = 0.0 4 μM or 2.36 ppb) and selective (by at least 100-fold over other metal ions except for Cu(2+)) toward Co(2+) with a linear range from 0.1 to 0.7 μM. The cost-effective method allows rapid and simple determination of the concentrations of Co(2+) ions in drinking water.
The Analyst 11/2011; 137(2):400-5. · 4.23 Impact Factor
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ABSTRACT: A colorimetric, label-free, and nonaggregation-based silver coated gold nanoparticles (Ag/Au NPs) probe has been developed for detection of trace Cu(2+) in aqueous solution, based on the fact that Cu(2+) can accelerate the leaching rate of Ag/Au NPs by thiosulfate (S(2)O(3)(2-)). The leaching of Ag/Au NPs would lead to dramatic decrease in the surface plasmon resonance (SPR) absorption as the size of Ag/Au NPs decreased. This colorimetric strategy based on size-dependence of nanoparticles during their leaching process provided a highly sensitive (1.0 nM) and selective detection toward Cu(2+), with a wide linear detection range (5-800 nM) over nearly 3 orders of magnitude. The cost-effective probe allows rapid and sensitive detection of trace Cu(2+) ions in water samples, indicating its potential applicability for the determination of copper in real samples.
ACS Applied Materials & Interfaces 11/2011; 3(11):4215-20. · 4.53 Impact Factor
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ABSTRACT: A simple and efficient electrochemical assay based on self-assembled monolayers (SAMs) was developed for the highly sensitive determination of arsenic(III) in water samples. The synergy of glutathione (GSH), dithiothreitol (DTT) and N-acetyl-L-cysteine (NAC) mixed SAMs enhanced the detection specificity and sensitivity of As(III) in water samples, resulting from the immobilization of a large number of As(III) moieties on the gold electrode surface via As-O and As-S linkages. After accumulating As(III), anodic stripping voltammetry (ASV) was performed, and linear sweep voltammetry (LSV) was employed for signal recording. Several main voltammetric parameters were optimized as follows: supporting electrolyte, 1 mol L(-1) HCl; deposition potential, -0.35 V; deposition time, 150 s. A good linear relationship (R = 0.9980) was attained between the concentration of the As(III) standard and peak current, in the range of 3-100 μg L(-1). The limit of detection (LOD) of this sensing system was determined to be 0.5 μg L(-1) at a signal-to-noise ratio of 3. A variety of common coexistent ions in water samples were examined, showing no obvious interferences on the As(III) determination. The amenability of this method to the analyses of water samples was also investigated. High recovery of 90.5% with the precision of 5.1% at spiked 10 μg L(-1), and low LOD of 0.3 μg L(-1) were obtained in seawater. The synergy effect of GSH, DTT and NAC provided the possibility for the rapid and sensitive LSV determination of As(III) in complicated water samples.
The Analyst 09/2011; 136(21):4526-32. · 4.23 Impact Factor
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ABSTRACT: Here we report a "blue-to-red" colorimetric method for determination of mercury ions (Hg²⁺) and silver ions (Ag⁺) based on stabilization of gold nanoparticles (AuNPs) by redox formed metal coating in the presence of ascorbic acid (AA). AuNPs were first stabilized by Tween 20 in phosphate buffer solution with high ionic strength. In a target ion-free system, the addition of N-acetyl-L-cysteine resulted in the aggregation of Tween 20 stabilized AuNPs for mercapto ligand self-assembled on the surface of AuNPs, which induced the AuNPs to be unstable. This would lead to a color change from red to blue. By contrast, in an aqueous solution with Hg²⁺ or Ag⁺, the ions could be reduced with the aid of AA to form Hg-Au alloy or Ag coating on the surface of AuNPs. This metal coating blocked mercapto ligand assembly and AuNPs kept monodispersed after addition of N-acetyl-L-cysteine, exhibiting a red color. Therefore, taking advantage of this mechanism, a "blue-to-red" colorimetric sensing strategy could be established for Hg²⁺ and Ag⁺ detection. Compare with the commonly reported aggregation-based method ('red-to-blue'), the color change from blue to red seems more eye-sensitive, especial in low concentration of target. Moreover, selective analysis of Hg²⁺ and Ag⁺ was simply achieved by the redox nature of target ions and the application of classic ion masking agents, avoiding the design and selection of ion chelating moieties and complicated gold surface modification procedure. This method could selectively detect Hg²⁺ and Ag⁺ as low as 5 nM and 10 nM in pure water with a linear range of 5 × 10⁻⁷ to 1 × 10⁻⁵ M for Hg²⁺ and 1 × 10⁻⁶ to 8 × 10⁻⁶ M for Ag⁺, respectively. It was successfully applied to determination of Hg²⁺ and Ag⁺ in tap water and drinking water.
ACS Applied Materials & Interfaces 04/2011; 3(5):1568-73. · 4.53 Impact Factor
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ABSTRACT: This article describes a nonaggregation-based colorimetric assay of ascorbic acid by tailoring the optical properties of mesoporous silica-coated gold nanorods (MS GNRs) via silver overcoating. The colorimetric measurement of ascorbic acid (AA) concentration strongly relies on the fact that the blue shift effect of localized surface plasmon resonance (LSPR) peak of MS GNRs is gradually enlarged with the increase of AA amount. The limit of detection is determined to be 49 nM, which is comparable to that of quantum dots (QDs)-based fluorimetric methods.
Nanoscale 02/2011; 3(4):1756-9. · 5.91 Impact Factor
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ABSTRACT: The past a few years have witnessed the wide use of metallic nanoparticles as ideal reporters for colorimetric detection, which generally involves an analyte-triggered alteration of aggregation degree of applied nanoparticles, and thus the change of colloidal color. However, these aggregation-based colorimetric probe are associated with a number of drawbacks, including poor stability of nanoaggregates, requirement of complicated functionalization and non-linearity of output signals. To address these problems, we herein employ mesoporous silica-coated gold nanorods (MS AuNRs) as novel nanocomposites for non-aggregation-based label-free colorimetric sensing relying on their chemical redox-modulated surface chemistry. In our sensing system, Hg(2+) ions are reduced to Hg(0) depositing on the surface of MS AuNPs and result in a great color change of MS AuNRs, while the subsequent introduction of S(2-) leads to a reverse process owing to the extraction of Hg(0) by S(2-). The experimental results for colorimetric sensing of Hg(2+) and S(2-) imply considerable sensitivity and specificity, suggesting the high potential of our approach for rapid environmental monitoring and bioanalysis in the future.
The Analyst 09/2010; 136(1):174-8. · 4.23 Impact Factor
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ABSTRACT: A novel nanomaterial/ionophore-modified glassy carbon electrode for anodic stripping analysis of lead (Pb(2+)) is described. Nanosized hydroxyapatite (NHAP) with width of 20-25 nm and length of 50-100 nm has been prepared and used to improve the sensitivity for detection of Pb(2+) because it provides unique three-dimensional network structure and has strong adsorption ability toward Pb(2+). An ionophore, usually used in ion-selective electrodes, is utilized here for its excellent selectivity toward Pb(2+). Nafion, a cation-exchange polymer, is employed as the conductive matrix in which NHAP and the ionophore can be tightly attached to the electrode surface. Such a designed NHAP/ionophore/Nafion-modified electrode shows remarkably improved sensitivity and selectivity to Pb(2+). The electrode has a linear range of 5.0 nM to 0.8 microM with a 10 min accumulation time at open-circuit potential. The sensitivity and detection limit of the proposed sensor are 13 microA/microM and 1.0 nM, respectively. Interference from other heavy metal ions such as Cd(2+), Cu(2+), and Hg(2+) associated with lead analysis can be effectively diminished. The practical application of the proposed sensor has been carried out for determination of trace levels of Pb(2+) in real water samples.
Analytical Chemistry 06/2009; 81(12):5088-94. · 5.86 Impact Factor
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ABSTRACT: A novel chemically modified electrode for stripping determination of cadmium is presented in this paper, based on carbon nanotube-hydroxyapatite (CNT-HAP) nanocomposite, which can be prepared by an easy and effective one-step sonication. The newly synthesized nanocomposite was characterized with FTIR, TEM, and electrochemical methods. Due to the combination of the strong absorption ability of HAP and excellent electroanalytical properties of CNTs, the GC/CNT-HAP electrode has been successfully used for determination of Cd2+ by anodic stripping voltammetry with a linear range of 20 nM–3 μM. The sensitivity and detection limit are 25.6 μA/μM and 4 nM, respectively. The practical application of the proposed electrode has been carried out for the determination of trace levels of Cd2+ in real water samples.
Electroanalysis 02/2009; 21(8):944 - 952. · 2.87 Impact Factor
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ABSTRACT: This study reports a novel, simple and sensitive immunoassay using fluorescence quenching caused by gold nanoparticles coated with antibody. The method is based on a non-competitive heterogeneous immunoassay of human IgG conducted by the typical procedure of sandwich immunocomplex formation. Goat anti-human IgG was first adsorbed on polystyrene microwells, and human IgG analyte was captured by the primary antibody and then sandwiched by antibody labeled with gold nanoparticles. The sandwich-type immunocomplex was subsequently dissociated by the mixed solution of sodium hydroxide and trisodium citrate, the solution obtained, which contains gold nanoparticles coated with antibody, was used to quench fluorescence. The fluorescence intensity of fluorescein at 517 nm was inversely proportional to the logarithm of the concentration of human IgG in the dynamic range of 10-5000 ng mL(-1) with a detection limit of 4.7 ng mL(-1). The electrochemical experiments and the UV-vis measurements were applied to demonstrate whether the immunogold was dissociated completely and whether the gold nanoparticles aggregated after being dissociated, respectively. The proposed system can be extended to detect target molecules such as other kinds of antigen and DNA strands, and has broad potential applications in disease diagnosis.
Analytica chimica acta 02/2007; 583(1):40-4. · 4.31 Impact Factor
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ABSTRACT: Catechins are strong autoxidant to produce steady intermediate in alkali solution. In present work, we, for the first time, developed a electrochemical method based on ruthenium tris (2, 2') bipyridyl (Ru(bpy)(3)(3+)) modified boron-doped diamond (BDD) electrode to investigate the electrochemical reduction of catechin autoxidation intermediate with its existence verified by the electron spin resonance (ESR). The reduction peak potential was observed at -855.5mV, not appearing either in acid solution (pH 2) containing catechins or in oxidized catechin solution (pH 12). Moreover, the effects of pH, ascorbic acid, Cu(2+), Fe(2+) and autoxidation time are investigated, demonstrating the reduction peak being really the reduction of catechin autoxidation intermediate. It is found that the peak current is proportional to scan rate, indicative of a surface confined reduction process. Sensitive amperometric response was obtained covering linear range from 0.3268muM to 0.1591mM. The determination of catechin in commercial preparations using this method shows satisfactory results comparable with those of the traditional methods.
Talanta 02/2005; 65(2):511-7. · 3.79 Impact Factor
