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An electrochemical sensor based upon a poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT-PSS) co-polymer film with gold nanoparticles (AuNPs) modified microelectrode is reported for the determination of Fe(III). Scanning electron microscopy images showed that the AuNPs were immobilized on gold (Au) microelectrode by formation of a nanofilm with PEDOT-PSS. The individual particles and their cluster-like aggregates provide a larger active electrochemical area and higher conductivity, which facilitates the determination of Fe(III). Electrochemical impedance spectroscopy (EIS) shows the AuNPs/PEDOT-PSS/Au microelectrode possesses high conductivity. A low detection limit of 0.01 µM Fe(III) was obtained using the modified microelectrode by differential pulse voltammetry (DPV) due to its large specific surface area, high conductivity, and the presence of more active sites. The optimized pH of the supporting acetate buffer was 2.0. The AuNPs/PEDOT-PSS/Au provided a linear range from 0.0119 μM to 7.14 μM. The modified electrode was successfully employed for the the determination of total dissolved iron in river water from Three Gorges with satisfactory results. [ABSTRACT FROM AUTHOR]

A sensitive and precise method for copper (Cu) speciation [electroactive Cu (II), acid-dissolved Cu (0, II), and inert Cu (0)] in coastal waters was developed using flow-injection analysis and electrochemical detection. The reaction is based on a simple redox reaction using a gold nanoparticle modified electrode. The effects of experimental parameters were investigated and optimized. The presence of iron, lead, zinc, cadmium, and aluminum did not interfere with the determination of copper. For total copper, the method detection limit was 1.3 nM, and the quantification range was from 5 to 1000 nM (R2 equal to 0.995), which is sufficiently sensitive for coastal water analysis. A certified reference material was used to characterize the accuracy and good agreement was obtained. The developed method was applied to analyze coastal water samples collected from the Guangdang River, Shandong, China. The Cu species present are reported and discussed. [ABSTRACT FROM AUTHOR]

Contrast-based photoacoustic imaging is an emerging imaging technology that gold nanoparticles (a kind of photoacoustic contrast agent with a size of 100 nm) are injected into blood vessels for photoacoustic imaging. Image reconstruction is a critical step in photoacoustic imaging, due to the fact that limitations and incompleteness of photoacoustic imaging data of image reconstruction are equivalent to the linear inverse problems. The photoacoustic data is transferred to IOT based on the platform of MATLAB and is quickly processed through the regularization method of Krylov space (the widely used method is LSQR). In order to solve the problem of Krylov space uncertainty, Krylov space dimension selection, and the minimum mismatch of the LSQR objective function (the limitation of LSQR algorithm) of LSQR algorithm, a KRLODPLSMR-GCV3DC algorithm is proposed to solve the above problems in this paper.In this study, the raw photoacoustic data was obtained by injecting gold nanoparticles into capillaries and subcutaneous veins of the palm, and the KRLODPLSMR-GCV3DC algorithm was verified to solve the limitations of LSQR algorithm through four groups of experiments. [ABSTRACT FROM AUTHOR]

In this paper, reduced graphene oxide/gold nanoparticle/Nafion (rGO/AuNP/Nafion) modified electrode was fabricated through in-situ synthesis and used for determination of copper ions in strong salt electrolyte (0.5 M NaCl) by differential pulse anodic stripping voltammetry (DPASV). This in-situ synthesis procedure was based on the ion-exchange and electrochemical reduction. The use of rGO provided a larger electrode surface and the presence of more active sites, while electron transfer was accelerated by incorporating AuNPs. Nafion was utilized as a cation exchange polymer in which rGO and AuNPs could be tightly attached to the electrode surface. The physical and electrochemical characterizations of the as-prepared modified electrode were studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and cyclic voltammetry. AuNPs with diameter of 5–10 nm on rGO decorated in the gold electrode surface were observed. Under the optimal conditions, the rGO/AuNP/Nafion electrode had a linear response to copper ions in the concentrations range from 20 nM to 1 μM (R 2 = 0.998), with the lowest detectable concentration of 8 nM and the detection limit of 4 nM (S/N = 3). Additionally, this electrode was successfully applied to the speciation analysis of copper (free, dissolved and total) in seawater. [ABSTRACT FROM AUTHOR]

An electrochemical sensor based on reduced graphene oxide (rGO) and gold nanoparticles (AuNPs) modified electrode was utilized for determination of trace iron in coastal waters with the aid of the iron complexing ligand 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP). 5-Br-PADAP reacted with iron in short chelating reaction time (<3 min). rGO as a support provided large specific surface area for AuNPs, which would facilitate the electrochemical reduction of Fe(III)-5-Br-PADAP. Under the optimized conditions, the response of Fe(III) at this resulting sensor was linear in the range of 30 nM to 3 μM with a detection limit of 3.5 nM. This sensor also had excellent reproducibility and repeatability. Additionally, the modified electrode had been successfully applied to the determination of Fe(III) in real coastal waters. [ABSTRACT FROM AUTHOR]

Nanomaterial-functionalized voltammetric microsensors are promising tools for detecting trace metals at low concentrations in the complex environment of natural seawater. However, the sensitivity reduction caused by the loss of modified nanomaterials in the detection process has always been a major problem. Herein, to fabricate a highly stable sensing platform, a microneedle electrode with a hierarchical porous tip was prepared through electrochemical etching technology to firmly embed nanoparticles. Using copper (Cu) as a model trace metal, a micro-cluster needle sensor based on a gold nanoparticle (AuNP)-embedded tip-porous microneedle electrode (P-MNE) was fabricated for the direct voltammetric determination of labile Cu in natural seawater. The porous structure of P-MNE not only provided a larger specific surface area and active sites for AuNPs which had excellent electrocatalytic performance for Cu2+ determination, but also protected from their loss during the detection process in seawater. Therefore, this novel micro-cluster needle sensor exhibited significantly improved stability with a relative standard deviation (RSD) of 1.5% for 30 detections. The linear range of Cu2+ on this micro-cluster needle sensor was from 0.1 to 1000 nM with a detection limit of 0.03 nM. More importantly, this micro-cluster needle sensor was successfully used for directly detecting labile Cu in natural seawater samples without any preaccumulation treatment or reagent addition to obtain the contribution proportions of the labile fraction in total dissolved Cu. Furthermore, this sensing platform might also be extended to the reliable determination of other labile metals in seawater by changing the functional nanoparticles embedded in the nanopores. A highly stable sensing platform based on nanoparticle-embedded tip-porous microneedle sensor was developed for the direct determination of labile trace metal in natural seawater. [Display omitted] • The nanoparticle-embedded tip-porous microneedle electrode has been fabricated. • The micro-cluster needle sensor has a superior stability for metals detection. • The sensor has achieved the direct determination of labile copper in seawater. • The sensor has obtained the contribution of labile copper in total dissolved ones. • The sensor-based highly stable sensing platform has been developed for trace metals. [ABSTRACT FROM AUTHOR]

An effective and sensitive method for electrochemical determination of iron was reported, based on the ionic liquid-reduced graphene oxide (IL-rGO) supported gold nanodendrites (AuNDs). IL-rGO as a soft support could provide large specific surface area for AuNDs and make them smaller sizes and unique forms, which would benefit to the electrochemical reduction of iron. Nafion is employed as a cation exchange polymer in which IL-rGO and AuNDs can be tightly attached to the electrode surface. The proposed sandwich structured IL-rGO/AuNDs/Nafion modified electrode shows excellent electrochemical properties. The IL-rGO/AuNDs/Nafion modified electrode combined individual advantages as a whole and showed good responses for iron ions. Under the optimized conditions, the reduction peak currents of iron have a good linear relation with its concentrations ranging from 0.30 to 100 μmol L −1 with the detection limit of 35 nmol L −1 . More importantly, this sandwich structured modified electrode had a good anti-interference ability and successfully applied in the determination of the total dissolved iron in coastal waters. [ABSTRACT FROM AUTHOR]

A nanocomposite, prepared from reduced graphene oxide (rGO), Methylene Blue (MB) and gold nanoparticles (AuNPs), was used to modify a glassy carbon electrode for the determination of total dissolved iron by differential pulse voltammetry. The use of rGO warrants a larger electrode surface and the presence of more active sites, while electron transfer is accelerated by incorporating AuNPs. MB acts as an electron mediator, as an anchor for the AuNPs (which were grown in situ), and also prevents the aggregation of rGO. The modified electrode displayed a remarkably improved sensitivity and selectivity for Fe(III). The kinetics of the electrode reaction is adsorption-controlled, and the reversible process involves one proton and one electron. The response to Fe(III) is linear in the 0.3 to 100 μM concentration range, and the detection limit is 15 nM. Possible interferences by other ions were studied. The electrode was successfully applied to the determination of total dissolved iron in real coastal waters. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

• The micro-needle sensor based on PEDOT-PSS/AuNCs has been successfully fabricated. • The micro-needle sensor has a superior performance for Fe3+ determination. • The determination of Fe3+ in coastal river water has been conducted with this sensor. • This work provides a promising sensor for the analysis of Fe3+ in coastal waters. A novel micro-needle sensor based on gold nanoclusters (AuNCs) immobilized with conducting polymer film poly(3,4-ethylenedioxythiophene)-poly(sodium 4-styrenesulfonate) (PEDOT-PSS) was fabricated for determination of iron in coastal waters. The unique aciform structure of the micro-needle electrode (MNE) provided larger specific surface area than common electrodes. The surface modification of MNE with PEDOT-PSS improved the conductivity of the electrode and increased the active sites for combination and immobilization of AuNCs. The cluster-like structure of AuNCs was formed as a result of the regulation of PEDOT-PSS, which showed excellent electrocatalytic activity for the reduction of Fe3+. The so-fabricated AuNCs/PEDOT-PSS/MNE showed excellent sensitivity, selectivity, reproducibility, and repeatability for iron determination with the linear range of 0.01–5 μM and detection limit of 3.1 nM, respectively. Furthermore, the micro-needle sensor was successfully used for the determination of acidified dissolved iron in a coastal river from the source to the estuary with satisfactory results. [ABSTRACT FROM AUTHOR]

Wehave proposed a Fenton-like reaction-mediated etching of goldnanorods and applied it to the sensitive visual detection of Co2+ions. With the presence of bicarbonate (HCO3–) and hydrogen peroxide(H2O2),Co2+ions trigger a Fenton-like reaction, resulting inthe generation of superoxide radical (O2•–). As a result, the gold nanorods are gradually etched by O2•–in the presence of SCN–, accompanied by an obvious color change from green to red. The goldnanorods etching process preferentially occurs along the longitudinaldirection, which is observed by transmission electron microscope.The etching mechanism is carefully proved by investigating the effectsof different radical scavengers (e.g., dimethyl sulfoxide). The auto-oxidationof hydroxylamine assay further confirms the mechanism. Then, the mainfactors, including reactants concentrations, temperature, and incubationtime, are specifically investigated. Under optimized conditions, weget an excellent sensing performance for Co2+with a lowerdetection limit of 1.0 nM via a spectrophotometer and a visual detectionlimit of 40 nM. In addition, this principle may provide a new conceptof “intermediate-mediated etching of nanoparticles”for sensing. [ABSTRACT FROM AUTHOR]

A honeycomb-like micro-needle sensor with gold nanoparticles embedded for the determination of hexavalent chromium in seawater. [Display omitted] • A stainless steel micro-needle sensor with honeycomb-like structure was fabricated. • The honeycomb-like holes were embedded with gold nanoparticles. • The sensor showed high sensitivity and stability for the determination of Cr (VI). • The sensor was adopted for the determination of Cr (VI) in real seawater samples. As one of the most toxic heavy metals, hexavalent chromium (Cr(VI)) is a typical environmental pollutant that directly affects human health. In this work, a novel micro-needle sensor with honeycomb-like structure and embedded gold nanoparticles was proposed for the stable and sensitive determination of Cr(VI). The honeycomb-like structure provided larger specific surface area to support more gold nanoparticles which exhibited excellent catalytic activity towards the electrochemical reduction of Cr(VI) to Cr(Ⅲ). In addition, gold nanoparticles were embedded into the holes of the honeycomb-like structure, which can effectively prevent them from falling off from the electrode surface due to the protection of the holes. Combining the honeycomb-like structure of micro-needle electrode with the excellent catalytic activity of gold nanoparticles, the fabricated sensor exhibited outstanding stability and sensitivity for the cathodic stripping determination of Cr(VI). A linear range of Cr(VI) from 0.5 to 300 μmol/L was obtained, with the detection limit of 0.15 μmol/L. The recovery of the sensor for the determination of hexavalent chromium in seawater samples was also investigated. Moreover, the sensor might be further adapted for the determination of other heavy metals with different nanoparticles embedded. [ABSTRACT FROM AUTHOR]

Abstract Noble metals supported on substrates have been proven as highly efficient catalysts for the reduction of nitro-compounds. However, their large-scale applications are still limited by the problems of fouling and transport during the mass production process. Herein, we first fabricated a spherical montmorillonite (Mt) substrate via spray drying technique, followed by the deposition of Au NPs through polydopamine chemistry to synthesize spherical Au nanoparticles supported Mt (Au@Mt) microspheres. The Au loading is 14.5 wt%, whereas the specific surface area of the Au@Mt microspheres is 47.3 m2 g−1, endowing the prepared Au@Mt microspheres with excellent catalytic activity to the reduction of 4-nitrophenol (4-NP) in the presence of NaBH 4 with the optimized apparent reduction rate constant higher than 1.05 min−1. Furthermore, the microspheres can be easily recycled with self-sedimentation without any devices involved and showed excellent stability and recyclability for at least 20 cycles without almost unchanged spherical morphology and catalytic performance. Our straightforward strategy to solve the issue of the mass production process through granulation of amorphous nanomaterial substrate facilitates the practical application of these catalysts in the reduction of nitro-compounds. Graphical abstract Unlabelled Image Highlights • Spherical Au nanoparticles supported montmorillonite (Au@Mt) microspheres were fabricated. • Au@Mt microspheres exhibited highly efficient catalytic ability for reduction of 4-nitrophenol. • Au@Mt microspheres can be easily recycled with self-sedimentation. • Au@Mt microspheres showed excellent stability and recyclability for at least 20 cycles. [ABSTRACT FROM AUTHOR]

Abstract Here, a needle-shaped electrode based on commercial acupuncture needle was fabricated and functionalized with dendritic gold nanostructures (AuNDs) and ion-exchange polymer (Nafion) for voltammetric speciation analysis of copper (Cu) in seawater. To achieve the enhanced performance for voltammetric determination of Cu in seawater, the acupuncture needle electrode (ANE) was functionalized with AuNDs via electrochemical deposition and covered with Nafion. AuNDs facilitate the electrochemical responses of Cu due to their excellent catalytic and electroconductive properties, whereas Nafion can stabilize the AuNDs deposited on the surface of the needle tip and enhance the voltammetric responses through its specific cation-exchange ability with Cu2+. The so-designed AuNDs/Nafion/ANE showed excellent performance for the determination of Cu in complex matrix like seawater. Under the optimal conditions, the response of Cu at this functional needle-shaped electrode was linear in the concentration range from 0.05 to 1 nmol L−1 with an ultralow detection limit of 15.4 pmol L−1. Additionally, the functional needle-shaped electrode has been successfully used for the direct determination of different Cu species in seawater via anodic stripping voltammetry. Graphical abstract Dendritic gold nanostructures/ion-exchange polymer based needle-shaped electrode was fabricated for the ultrasensitive determination of copper in seawater. Image 1 Highlights • The AuNDs/Nafion functionalized electrode has been successfully fabricated. • Ultralow detection limit of Cu2+ can be obtained at this functional needle-shaped electrode. • The different speciation of Cu in seawater has been analyzed by this electrode. • This needle-shaped electrode as a platform has a great potential in marine electrochemistry. [ABSTRACT FROM AUTHOR]

Gold nanoparticles (Au NPs) supported by a covalent organic framework (COF) exhibited a remarkably catalytic performance towards organic pollutants, while the application is limited by the recovery and reuse from the mixture due to the size of Au NPs@COF at the nanoscale. Herein, Au NPs were in situ reduced on the surface of sulfhydryl groups functionalized new COF with NaBH 4 , followed by the deposition on polydopamine modified micron-sized porous spherical montmorillonite (SMt) to construct a spherical SMt@COF@Au NPs heterostructure. SMt was used here due to its excellent adsorption ability towards methylene blue (MB), increasing the concentration of MB near COF@Au NPs, thus accelerating the catalytic reaction. Hence, the optimized apparent reduction rate constant (K app) and turnover frequency (TOF) in our experiment could reach 8.32 min−1 and 3.2 × 105 h−1, respectively, at 40 °C and pH values of 10, which is much better than the reported. Furthermore, micro-sized SMt with self-sedimentary property could be easily recovered from the mixture without any devices involved. More importantly, the granular micro-sized morphology of the SMt-based heterostructure could facile transport on the product line and reduce the fouling, facilitating mass production COF@Au NPs based catalyst for application. [Display omitted] • A spherical montmorillonite-based heterostructure was fabricated. • The prepared heterostructure showed an efficient catalytic activity towards methylene blue. • The prepared heterostructure could be easily recycled with self-sedimentation. [ABSTRACT FROM AUTHOR]