Jen-Lin Chang

Activated Nickel Platform for Electrochemical Sensing of Phosphate

We report here a highly selective enzymeless approach for the determination of phosphate (PO(4)(3-)) by flow injection analysis (FIA). In this system, the activation of barrel plated nickel electrode (Ni-BPE) in alkaline media to form a Ni(OH)(2)/NiO(OH) film was found to trigger the adsorption of phosphate at the electrode surface. Based on the suppressed current of the electrocatalytic oxidation of glucose at the activated Ni-BPE in 0.1 M NaOH solution caused by adsorption of phosphate, we develop an FIA detection scheme for the determination of phosphate. Under the optimized conditions of flow rate = 300 microL/min and detection potential = 0.55 V vs Ag/AgCl with 25 microM glucose in 0.1 M NaOH as carrier solution, the calibration curve showed a linear range up to 1 mM. Possible interferences from the coexisting ions were also investigated. The results demonstrated that sensor could be used for the determination of phosphate in the presence of nitrate, chloride, sulfate, acetate, oxalate, carbonate, and some anionic species of toxicological and environmental interest, such as chlorate, chromate, and arsenate ions. The electrode can be effectively regenerated without extra treatment under the hydrodynamic condition. For eight continuous injections of 40 microM PO(4)(3-), a relative standard deviation of 0.28% was obtained, indicating good reproducibility of the proposed method. The detection limit (S/N = 3) was calculated as 0.3 microM.

Single-run electrochemical determination of melamine in dairy products and pet foods.

A simple electrochemical approach, which does not require any expensive and complex instruments, is established for the selective and quantitative recognition of melamine in diary products and pet foods. During a preconcentration step (at 1.8 V versus Ag/AgCl), the formation of a polymer film from melamine on a preanodized screen-printed carbon electrode was identified by SEM and XPS. The as-formed polymer was found to be electroactive with a reversible redox peak, and hence square-wave voltammetry was applied to further increase the detection sensitivity to meet the detection limit for application in real sample analysis. Simply with a medium exchange procedure, melamine was selectively detected with a detection limit (S/N=3) of 0.8 μM (i.e., 98.3 ppb) by square-wave voltammetry. Lower than 1 ppm of melamine in real samples can be easily detected with good recoveries of 98.7-100.9% by the proposed approach. The recovery tests established for external calibration and standard addition techniques verified that the analysis can be done in a single-run measurement.

Bismuth oxide nanoparticles as a nanoscale guide to form a silver–polydopamine hybrid electrocatalyst with enhanced activity and stability for the oxygen reduction reaction

Highly dispersed Ag nanoparticles (Ag NPs) were successfully synthesized on functionalized polydopamine (PDA)@Bi2O3 NPs for use as an electrocatalyst. In the proposed method, a uniform layer of PDA was first coated on Bi2O3 NPs. The surface of the PDA@Bi2O3 can then be used as a nanoscale guide to deposit Ag NPs and hence for the formation of Ag–PDA@Bi2O3 hybrid nanocatalysts. It was found that Ag NPs enhanced the electrocatalytic ability on PDA@Bi2O3 by a synergetic effect for direct 4e− transfer in the oxygen reduction reaction (ORR) with a low overpotential. The surface morphology and lattice fringes of Ag NPs of crystalline nature of the obtained Ag–PDA@Bi2O3 hybrid nanocatalysts were examined through HR-TEM and SAED patterns. The materials purity and chemical functional groups were identified by FT-IR analysis. This strategy provides new opportunities to design and optimize heterogeneous nanocatalysts with tailored size, morphology, chemical configuration and supporting substrates for metal-catalyzed reactions.

Sensitive and selective detection of iron-catalysed hydroxyl radical formation in water without chemical probes

We report here a highly selective hydroxyl radical assay through the depletion of H2O2 as an indicator for iron-catalysed hydroxyl radical formation without any separation process and chemical probe. By purging with N2 gas under suitable humidity, H2O2 can be carried out with water and detected in the gas media using a disposable sensor made of a screen-printed edge band carbon ultramicroelectrode deposited with Pt nanoparticles and coated with Nafion as the solid polymer electrolyte. This H2O2 detection scheme is highly selective and thus can monitor the hydroxyl radical without any separation process and chemical probe. Based on Fenton chemistry, the quantitation of the hydroxyl radical is achieved through the suppressed peak current of hydrogen peroxide with a linear dependence on [Fe2+] in the range of 25 μM to 1 mM and a detection limit of 4.48 μM (S/N = 3). The proposed method has been applied to evaluate the antioxidative activity of phenolic compounds and catechins.

Biomolecule-Free, Selective Detection of o -Diphenol and Its Derivatives with a Screen-Printed Electrochemical Sensor

AbstractWe report here biomolecule-free, selective detection of o-diphenol and its derivatives with a screen-printed electrochemical sensor. It is based on the preparation of a highly stable slurry made of 2,2-diphenyl-1-picrylhydrazyl (DPPH) dissolved in 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) room temperature ionic liquid for use as screen-printed ink in fabricating the proposed sensor. A detailed investigation by scanning electron microscope (SEM) along with UV-visible and FT-IR spectroscopic studies indicates that DPPH is well dispersed and stabilized by BMIMPF6 ionic liquid. Enhanced current response is observed using the as-printed electrode (designated as SP-DPILE) in electrochemical measurements of o-diphenols with good sensitivity and selectivity. Its selectivity is proved through the discrimination of catechol signal from resorcinol and hydroquinone in the absence of biomolecule auxiliary. This is valuable in real sample analysis, and the feasibility of the SP-DPILE is demonstrated for the detection of gallic acid in green tea by flow injection analysis. A highly stable slurry made of 2,2-diphenyl-1-picrylhydrazyl (DPPH) distributed within room temperature ionic liquid ([BMIM] [PF6]) was developed for use as screen-printing ink in fabricating disposable sensors.Graphical Abstract

Electrochemical Hydroxylation of C 3 –C 12 n -Alkanes by Recombinant Alkane Hydroxylase (AlkB) and Rubredoxin-2 (AlkG) from Pseudomonas putida GPo1

An unprecedented method for the efficient conversion of C3–C12 linear alkanes to their corresponding primary alcohols mediated by the membrane-bound alkane hydroxylase (AlkB) from Pseudomonas putida GPo1 is demonstrated. The X-ray absorption spectroscopy (XAS) studies support that electrons can be transferred from the reduced AlkG (rubredoxin-2, the redox partner of AlkB) to AlkB in a two-phase manner. Based on this observation, an approach for the electrocatalytic conversion from alkanes to alcohols mediated by AlkB using an AlkG immobilized screen-printed carbon electrode (SPCE) is developed. The framework distortion of AlkB–AlkG adduct on SPCE surface might create promiscuity toward gaseous substrates. Hence, small alkanes including propane and n-butane can be accommodated in the hydrophobic pocket of AlkB for C–H bond activation. The proof of concept herein advances the development of artificial C–H bond activation catalysts.