Xuan Hung Pham

Simultaneous detection of ultratrace lead and copper with gold nanoparticles patterned on carbon nanotube thin film

Highly sensitive detection of a Pb(2+)-Cu(2+) mixture using gold nanoparticles patterned on single-walled carbon nanotube (AuNP-SWCNT) film is reported. The gold nanoparticles were deposited electrochemically on carbon nanotube film using a cyclic voltammetry technique. The film showed a homogeneous size and density that could be easily controlled by the potential scanning cycle and gold precursor concentration. Square wave stripping voltammetry (SWSV) was applied to the simultaneous detection of Pb(2+) and Cu(2+) under optimized conditions. The AuNP-SWCNT electrode exhibited a high increase in sensitivity with a limit of detection of 0.546 ppb (R(2) = 0.984) and 0.613 ppb (R(2) = 0.991) for Pb(2+) and Cu(2+) ions, respectively, in a mixture of Pb(2+)-Cu(2+) solution (S/N = 3, n = 5), and a good linear response in the range from 3.31 ppb to 22.29 ppb. The electrode exhibited high reproducibility in repetitive measurements with a relative standard deviation as low as 4.2% and 2.6% for Pb(2+) and Cu(2+) ions, respectively. An interference study showed that Sb(3+), As(3+), Zn(2+), Ca(2+), and Na(+) ions did not have a significant effect. This study demonstrated an alternative approach to the rapid and reliable detection of heavy metals of environmental interest.

Electrochemical characterization of a single-walled carbon nanotube electrode for detection of glucose

We developed glucose biosensing electrodes using single-walled carbon nanotube (SWCNT) films on flexible, transparent poly(ethylene terephthalate). The homogeneous SWCNT films were fabricated by a vacuum filtration method, and the averaged resistivity and transparency of the fabricated flexible SWCNT films were 400 Omega sq(-1) and 80%, respectively. The glucose sensing electrodes were constructed by encapsulating glucose oxidase (GOx) by Nafion binder into the SWCNT film, and the variation in current response as a function of enzyme loading amount, Nafion thickness were investigated. 30 mg mL(-1) GOx and 2% Nafion was optimal for the detection of glucose. When ferrocene monocarboxylic acid (FMCA) was introduced as diffusional electron mediator, the current responses toward glucose of the Nafion/GOx/SWCNT electrodes in glucose solution containing FMCA were dramatically improved, and the developed sensor was independent of oxygen. In the application of GOx immobilized SWCNT films for glucose detection, a linear electrical response was observed for concentrations ranging from 0.25 to 3.0 mM, and the detection limit and the sensitivity were assessed to be 97 microM and 9.32 microA mM(-1) cm(-2), respectively. Moreover, according to the Lineweaver-Burk plot, the apparent Michaelis-Menten constant was calculated to be 23.8 mM, and the current responses did not interfere with coexisting electroactive species, indicating that Nafion is an effective permselective polymer barrier.

Electrochemical patterning of gold nanoparticles on transparent single-walled carbon nanotube films

We report a simple, low cost, electrochemical deposition method to pattern gold nanoparticles on flexible, transparent, single-walled carbon nanotube (SWCNT) films, and demonstrate the application of the gold-patterned SWCNT films as surface-enhanced Raman spectroscopy substrates and biosensing electrodes for non-enzymatic glucose detection.

Electrochemical patterning of transparent single-walled carbon nanotube films on plastic substrates.

We report a new patterning method for single-walled carbon nanotubes (SWCNTs) films on flexible, transparent poly(ethylene terephthalate) using electrochemical etching in an aqueous electrolyte solution. Electrochemical etching of the SWCNT films patterned with photoresist polymer was accomplished in a three-electrode system, and the electrochemically patterned SWCNT films were then characterized by scanning electron microscopy (SEM) and Raman spectroscopy. The voltammetry curve showed that SWCNTs underwent drastic oxidation above an applied potential of 1.315 V with the generation of gas bubbles, and the oxidation current became constant above 2.6 V due to the mass transfer limit. SEM images showed that the networks of SWCNTs in the area protected with the photoresist polymer had no damage and vivid connections were obvious, while the connections and shapes of SWCNTs in the area exposed to electrochemical etching were indistinct and slightly damaged. In the Raman spectra of the area protected with the photoresist polymer and the exposed SWCNT area, the intensity ratio of the D-line to the G-line increased from 0.077 to 1.136, which indicated that the ordered carbons of the SWCNT film gradually became amorphous carbons due to electrochemical etching. For optimal patterning, the electrochemical etchings of SWCNT films were performed under various conditions (the applied potential, pH of the electrolyte solution, and electrolyte concentration). An applied potential of 3.0 V in 0.1 M NaCl electrolyte solution (pH 7.0) was optimal for homogeneous electrochemical patterning of SWCNT films. In an electrochemiluminescence reaction, the SWCNT films patterned by this technique could be used successfully as flexible and transparent electrodes.

Hydrazine detection by shape-controlled palladium nanostructures on carbon nanotube thin films

In this article, the electrodeposition of palladium (Pd) nanostructures on flexible and transparent single-walled carbon nanotube (SWCNT) thin films was described. Four different morphologies of Pd nanostructures were synthesized by controlling the potentials. Octahedral-like and flower-like nanostructures were observed at +0.3V and −0.1V, respectively. With a further driving potential decrease, cubic and spherical nanostructures were obtained in turn at 0.0V and −0.5V. The Pd nanostructures were confirmed by XRD data. Subsequently, the fabricated Pd nanostructures on SWCNT thin films were employed as electrodes for hydrazine detection. The electrochemical oxidation of hydrazine by Pd nanostructures was investigated by cyclic voltammetry and amperometry. As results, the specific sensitivities of four Pd nanostructures were 1123 μA mM cm−2 (octahedron), 899 μA mM cm−2 (flower), 827 μA mM cm−2 (cube), and 275 μA mM cm−2 (sphere). The detection limits were 5.90 μM (octahedron), 2.56 μM (flower), 2.85 μM (cube), and 4.83 μM (sphere).The morphology effect of Pd nanostructures on hydrazine oxidation is dependent on the relative fraction of (100), (110), and (111) facets which are associated with the shape. The (111) facet dominant Pd nanostructures exhibited the higher catalytic activities than Pd nanostructures with (100) and (110) facets.