Sensor For Heavy Metal Ions Research Articles

Catalytic Deposition of Pb on Regenerated Gold Nanofilm Surface and Its Application in Selective Determination of Pb2+

We report a simple method of catalytic deposition of Pb on a gold nanofilm substrate, which was in situ prepared and used as nanocrystal seeds. Due to the unique properties of gold nanocrystal seeds, Pb could be catalytically deposited on the surface of the gold nanofilm. Compared with the deposition of Pb on bare gold electrode, a larger amount of Pb was deposited on the gold nanofilm and the electrical response was amplified significantly. The catalytic deposition of Pb on the gold nanofilm was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and electrochemical methods. A stable and quasi-reversible redox couple was obtained in neutral solution and studied in detail. The surface of the gold nanofilm could be easily regenerated in 0.1 mol L(-1) nitric acid solution. Since the redox peaks of Pb could be effectively separated from those of other metals such as Cu, Cd, and Zn, a selective determination of Pb2+ was achieved. Linear sweep voltammetry (LSV) was used for the determination of Pb2+. The peak currents of Pb varies linearly with the concentration of Pb2+ in aqueous solution ranging from 1.0 to 10.0 micromol L(-1) (R=0.999), with a detection limit of 0.1 micromol L(-1). It is expected that the gold nanofilm will facilitate the appearance of heavy metal ion sensors with good performance.

Picogram detection of metal ions by melanin-sensitized piezoelectric sensor

A heavy metal ion sensor was constructed by cross-linking melanin onto the gold electrode of quartz crystal microbalance (QCM). A mercury ion sensitivity of 518±37Hz/ppm was observed, a substantial increase in sensitivity compared to previous reports of 10–50Hz/ppm with the limit of detection at 5ppb. Detection of other metal ions including Sn2+, Ge4+, Li+, Zn2+, Cu2+, Bi3+, Co2+, Al3+, Ni2+, Ag+, and Fe3+ were also performed. Unexpectedly, binding of Mn7+, Pb2+, Cd2+, and Cr3+ increased resonant frequencies. The surface profile of melanin thin film upon binding to metal ions was investigated by atomic force microscopy (AFM). Structural change of melanin upon binding to metal ions was characterized by circular dichroism and by infrared spectroscopy. The current study provides the first example of melanin-coated piezoelectric sensor showing high sensitivity and selectivity to metal ions.

Heavy Metal Ion Sensing by N-(4-Styrylphenyl)iminodiacetic Acid Probe/Cyclodextrin Complexes in Water

A N- (4-styrylphenyl) iminodiacetic acid probe 1 with a simple structure, which can be incorporated into the cyclodextrin (CyD) cavities, has been synthesized as a sensor for heavy metal ions. The UV-Vis and fluorescence analyses revealed that the probe 1 was essentially selective for Cu2+. The α- and β-CyDs formed stable 1: 1 complexes with 1. However, no influence was noted for the response selectivity of 1 as α- and β-CyD complexes. In contrast, although γ- CyD showed a weak binding ability for 1 without metal ions, the 2: 1 binding of 1 for heavy metal ions was evidently enhanced inside the γ- CyD cavity, resulting in the increased recognition ability for Cu2+, Co2+, Zn2+, and Ni2+. For NH2-β-CyD possessing an additional NH2 coordination site at the CyD rim, the 1/NH2-β-CyD complex was found to exhibit the response selectivity for both Cu2+ and Ni2+.

Chemical sensors using peptide-functionalized conducting polymer nanojunction arrays

We demonstrate a heavy metal-ion sensor for drinking water analysis using a conducting polymer nanojunction array. Each nanojunction is formed by bridging a pair of nanoelectrodes separated with a small gap (<60nm) with electrodeposited peptide-modified polyanilines. The signal transduction mechanism of the sensor is based on the change in the nanojunction conductance as a result of polymer conformational changes induced by the metal-ion chelating peptide. The nanojunction sensor allows real-time detection of Cu2+ and Ni2+ at ppt range.

Antibody-based sensors for heavy metal ions

Competitive immunoassays for Cd(II), Co(II), Pb(II) and U(VI) were developed using identical reagents in two different assay formats, a competitive microwell format and an immunosensor format with the KinExA™ 3000. Four different monoclonal antibodies specific for complexes of EDTA–Cd(II), DTPA–Co(II), 2,9-dicarboxyl-1,10-phenanthroline–U(VI), or cyclohexyl–DTPA–Pb(II) were incubated with the appropriate soluble metal–chelate complex. In the microwell assay format, the immobilized version of the metal–chelate complex was present simultaneously in the assay mixture. In the KinExA format, the antibody was allowed to pre-equilibrate with the soluble metal-chelate complex, then the incubation mixture was rapidly passed through a microcolumn containing the immobilized metal-chelate complex. In all four assays, the KinExA format yielded an assay with 10–1000-fold greater sensitivity. The enhanced sensitivity of the KinExA format is most likely due to the differences in the affinity of the monoclonal antibodies for the soluble versus the immobilized metal–chelate complex. The KinExA 3000 instrument and the Cd(II)-specific antibody were used to construct a prototype assay that could correctly assess the concentration of cadmium spiked into a groundwater sample. Mean analytical recovery of added Cd(II) was 114.25±11.37%. The precision of the assay was satisfactory; coefficients of variation were 0.81–7.77% and 3.62–14.16% for within run and between run precision, respectively.

Transfer of heavy metal ions across the water∣nitrobenzene microinterface facilitated by the cadmium selective ionophore ETH1062

Abstract Selective neutral ionophores play an important role for the development of selective and sensitive chemical sensors. In this paper, the facilitating effect of the cadmium selective ionophore N,N,N′,N′-tetrabutyl-3,6-dioxaoctane-dithioamide (ETH1062) on the transfer of heavy metal ions across a water ∣ nitrobenzene microinterface has been studied by steady-state cyclic voltammetry. Complexes of the general composition MLz+ were found for the ions Zn2+, Ag+ and Tl+. The formation of ML2z+ complexes was deduced for Cd2+, Cu2+ and Pb2+. The standard potentials (in mV) of the facilitated ion transfer and, in parentheses, the estimated logarithms of the over-all stability constants (molar scale) for Cd2+, Pb2+, Cu2+, Zn2+, Tl+ and Ag+ in nitrobenzene are −234 (19.6), −207 (17.9), −157 (17.2), +95 (8.7), −170 (6.3) and −797 (17.9), respectively. The ionophore ETH1062 appears suitable for the design of a voltammetric or amperometric screening sensor for heavy metal ions.

Immobilised reagents for optical heavy metal ions sensing

Many ligands such as 1-nitroso-2-naphthol (NN), 4-(2-pyridylazo)resorcinol (PAR), 2,4-dinitrosoresorcinol (DNR) and 1-(2-pyridylazo)-2-naphthol (PAN) have been investigated in the development of optical sensors for heavy metal ions found in aquatic environments which include Co 2+, Cu 2+, Ni 2+, Fe 3+, Cd 2+, Zn 2+, Pb 2+ and Hg 2+. The reagents were immobilised by physical adsorption on to polymeric materials such as XAD-4, XAD-7 and Dowex ion-exchange resins, and were found to exhibit chromic characteristics in the absence and presence of metal ions in solution. Reflectance measurements are used here. Parameters such as pH, measurement wavelength and reagent concentration have been optimised for a given metal ion, and the reversibility/regenerability characteristics of the sensing reagent have been studied together with the limit of detection and the concentration range producing linear response for the metal ion.

Stability improvement of an optochemical heavy metal ion sensor by covalent receptor binding

An optochemical sensor for the detection of mercury(II) and cadmium(II) is presented. The sensing layer consists of a thin film of a polymeric matrix (hydrogel) which contains a metal complexing porphyrin derivative as optical transducer. The spectral responses that occur when metal ions are complexed by the porphyrin receptor are used as sensor signal. In order to enhance the stability of the sensor which is terminated by leaching of the receptor dye a monofunctionalized porphyrin derivative (5-(4′-aminophenyl)-10,15-20-tris(4′-sulfonatophenyl) porphyrin, ATPPS) was covalently bound to poly(2-hydroxyethylmethacrylate) (PolyHEMA). The sensor was prepared by layering PolyHEMA coupled prophyrin as a thin film (thickness 2.5 μm) onto a poly(methycrylate) (PMMA) substrate. The procedure developed for sensor fabrication results in sensitive layers with a good chemical and mechanical stability. After an initial decrease a constant sensor signal is obtained at ca. 85% of the starting value over a period of 4 weeks of continuous operation. Within a measuring time of 10 min detection limits of 1 × 10 −7 mol l −1 (20 μg l −1) and 6 × 10 −7 mol l −1 (63 μg l −1 for Hg(II) and Cd(II), respectively, are obtained. The spectral differences of porphyrin-Hg(II)- and -Cd(II) complexes would allow simultaneous detection using appropriate procedures for spectral deconvolution (e.g. PLS algorithm).

A fiber optical sensor for heavy metal ions based on immobilized xylenol orange

A new fiber optical reflectance sensor for determination of heavy metal ions is described. It is based on xylenol orange which is electrostatically immobilized on an anion-exchange resin. The sensor was tested for lead ions. It is sensitive to Pb2+ ions in a concentration range from 3 × 10−6 − 3 × 10−5M. A response time of 1.5–2 min was observed. The optrode is not fully reversible, but can be regenerated in acidic solution (pH 1).

HEAVY METAL ION SENSORS PREPARED FROM QUINONOID POLYMER ELECTRODES MODIFIED WITH MERCAPTIDES

Abstract Quinonoid polymer electrode, prepared by the electrochemical oxidation of mercaptohydroquinone, was modified with mercaptide of heavy metal ions of interest, such as Ag+ ion, Hg2+, ion, Cd2+ ion, Cu2+ ion, and Pb2+ ion. The quinonoid polymer electrodes modified with mercaptides showed a function as selective ion sensors for heavy metal ions in solution.