Graphene oxide-manganese oxide composite as an electrocatalyst for simultaneous detection of manganese- and chromium-contaminated water.

The development of a sensitive and selective electrochemical sensor for simultaneous quantification of manganese (Mn(II)) and chromium (Cr(VI)) using composite of graphene oxide (GO) and manganese oxide modified screen printed carbon electrode (GO-Mn2O3/SPCE) is reported for the first time. The good sensing performance is achieved by mixing GO prepared by modified Hummer's method (GO-H) with proper particle size of Mn2O3 (241 nm). The mechanism of this sensor is based on the formation of Mn-O and Cr-O on the modified electrode with assistance of oxygen moieties provided by both Mn2O3 NPs and GO. The analytical performances were investigated by measuring electrochemical signal of Mn(II) and Cr(VI) by using square-wave cathodic stripping voltammetry (SWCSV). This sensor holds low electrode-to-electrode variation (relative standard deviation (RSD) < 4%) with a good limit of detection (LOD) at about 6.67 and 11.20 µg⋅L-1 for Mn(II) and Cr(VI), respectively. Applicability of this sensor was demonstrated by measuring Mn(II) and Cr(VI) in tap water samples with recovery of 90.77-103.45% and 82.34-103.73% for Mn(II) and Cr(VI) determinations, respectively. With the contribution of both GO and Mn2O3 as electrocatalysts, this developed sensor is capable to be used for water quality monitoring in real samples.

Bimetallic Au-Ag on a Patterned Substrate Derived from Discarded Blu-ray Discs: Simple, Inexpensive, Stable, and Reproducible Surface-Enhanced Raman Scattering Substrates.

A simple and reproducible surface enhanced Raman scattering (SERS) substrate of bimetallic gold-silver (Au-Ag) based on discarded a Blu-ray disc read only memory (BD-ROM) was developed by simply incorporating electrochemical (EC) treatment and chemical reaction. The resurfaced AgBD-ROM substrate (r-AgBD-ROM) was fabricated by EC treatment on a Ag film layer in BD-ROM (AgBD-ROM) to generate silver nanoparticles (AgNPs) on the indented pattern surface. Then, galvanic displacement reaction of Au and Ag was carried out to prepare the bimetallic Au-Ag structure (Au-r-AgBD-ROM). The suitable size and density as well as location of NPs on the surface can be tuned via EC treatment conditions to obtain highly active SERS performance. The SERS enhancement phenomenon on our developed substrate was studied by observing the location of the SERS hot spot obtained by Raman mapping. The developed SERS substrate offers excellent stability (90 days), good uniformity [6.14% relative standard deviation (RSD)], and reproducibility (3.79% of RSD). Moreover, this substrate can be used as a promising sensor for detecting acetaminophen, ibuprofen, and mefenamic acid. This finding suggests a simple and low-priced process, which potentially facilitates fabrication of highly sensitive SERS substrates for practical applications.

Highly branched gold-copper nanostructures for non-enzymatic specific detection of glucose and hydrogen peroxide.

The development of highly sensitive and highly selective sensors for non-enzymatic glucose and hydrogen peroxide (H2O2) detection using gold-copper alloy nanoparticles (AuCu alloy NPs) is reported. The AuCu NPs are nanostructures with branches and can be used as an electrochemical catalyst. Series of AuCu alloy NPs with various metal ratios are synthesized through a coreduction reaction. The morphology of AuCu alloy NPs is altered from highly branched structures (nanourchin, nanobramble, nanostar, nanocrystal) to a spherical shape by increasing Au content in the synthesis reaction. Cu-rich AuCu nanobramble and Au-rich AuCu nanostar exhibit selective electrocatalysis behaviors toward electro-oxidation of glucose and electroreduction of H2O2, respectively. The AuCu nanobramble-based sensor holds great potential in glucose detection with a linear working range of 0.25 to 10 mM. The sensor possesses a sensitivity of 339.35 µA mM-1 cm-2, a limit of detection (LOD) of 16.62 µM, which is an acceptable selectivity and good stability. In addition, the AuCu nanostar-based sensor shows excellent electrochemical responses toward H2O2 reduction with good selectivity, reproducibility, and a short response time of about 2-3 s. The linear range for H2O2 determination is 0.05 to 10 mM, with LOD and sensitivity of 10.93 µM and 133.74 µA mM-1 cm-2, respectively. The good sensing performance is a result of the synergistic surface structure and atomic composition effects, which leads AuCu alloys to be a promising nanocatalyst for sensing both glucose and H2O2. Graphical abstract Schematic illustration presents the construction of gold-copper alloy nanoparticles (AuCu alloy NPs) on the surface of screen-printed carbon electrode (SPCE). The highly branched nanostructures of AuCu alloys with different surface structure and metal ratios give selective electrocatalysis behaviors. Cu-rich AuCu nanobramble-based sensor reveals prominent electrocatalytic activity for glucose detection. Au-rich AuCu nanostar-based sensor provides good electrochemical response for H2O2 detection.

A gold coated polystyrene ring microarray formed by two-step patterning: construction of an advanced microelectrode for voltammetric sensing.

A two-step patterning process was developed based on nanosphere lithography and plasma etching to fabricate an array of electrodes with two different gold ring structures: the arrays of Au micro-ring electrode (Au-MRE) and Au covered with polystyrene micro-ring electrode (Au-PS-MRE). The Au-MRE structure was fabricated by etching a monolayer of polystyrene (PS) spheres on indium tin oxide (ITO) surface to generate PS rings on ITO glass. PS rings served as a mask in secondary etching for blocking an interaction of oxygen plasma and ITO surface to create a ring-patterned ITO surface. Then, the PS residue was removed and gold was deposited. The site-selective electrodeposition of gold was carried out and an array of a gold ring structure was formed on the ITO glass. The Au-PS-MRE structure was fabricated by keeping the PS residue from second etching before deposition of gold. The Au-PS-MRE microelectrode was studied by using hexacyanoferrate as an electrochemical probe where it displayed steady state current in cyclic voltammetry. The respective calibration plots were acquired at a working potential of 0.31 V and 0.12 V (vs. Ag/AgCl) for oxidation and reduction reaction, respectively. The sensitivity is as high as 163.4-220.7 µA·mM-1·mm-2 which is larger by a factor of 95-132 compared to a conventional gold film macroelectrode. The detection limit (at a signal-to-noise ratio of 3) is 2.2 µM. This approach thus yields relatively effective and low-cost fabrication without resorting to high resolution instruments. Conceivably, the technique may be used to produce microelectrode arrays on a large scale. Graphical abstract Schematic presentation of a novel fabrication process of micro-ring electrode arrays. Two-step patterning based on nanosphere lithography leads to electrodes with great electrochemical performance. Direct deposition metal in the presence of polystyrene (PS) mask induces the formation of a new structure with arrays of gold covered with PS microring on the indium tin oxide (ITO) coated glass. The microelectrode-like behavior has been achieved using this fabrication process.

Dually functional polyethylenimine-coated gold nanoparticles: a versatile material for electrode modification and highly sensitive simultaneous determination of four tumor markers.

A novel sandwich-type electrochemical multiplex immunoassay is described for simultaneous detection of the tumor biomarkers alpha fetoprotein (AFP), carcinoembryonic antigen (CEA), prostate-specific antigen (PSA) and interleukin-8 (IL-8). Polyethylenimine-coated gold nanoparticles (PEI-AuNPs) were used for both modification of a screen-printed carbon electrode (SPCE) and as labeling tags. The coated AuNPs can be easily adsorbed on the electrodes which also are loaded with the electroactive metal ions cadmium(II), lead(II) copper(II) and silver(I) and related secondary antibodies (Ab2). These give distinct voltammetric signals at -0.80, -0.55, -0.20 and + 0.05 V, respectively (vs Ag/AgCl). Four corresponding capture antibodies (Ab1) were then conjugated to one of the electrodes. After a sandwich-type structure was formed by binding of the analytes and the labeling AuNPs, the electrochemical signal responses were recorded. Under the optimized testing conditions, there is a linear relationship in range from 0.25-10 ng mL-1 for AFP, CEA and PSA, and from 0.50-100 pg mL-1 for IL-8. The corresponding detection limits are 1.7, 1.6, 0.9 and 1.0 fg mL-1, respectively. Cross reactivity, interferences and stability of the modified electrodes and of the signal nanotags are satisfying in that they can be stored for >4 weeks without significant signal reduction. The method was successfully applied to the determination of the biomarkers in spiked human serum. Graphical abstract Poly(ethylenimine)-coated gold nanoparticles were used in a sandwich-type multiplex electrochemical immunosensor. The coated gold nanoparticles were used for both electrode modification and as electrochemical nanotags. The resultingvmmunosensor exhibits excellent sensitivity for the four analytes studied, and also displays selectivity and long-term stability.