29th July 2009

Poly-phenothiazine derivative-modified glassy carbon electrode for NADH electrocatalytic oxidation

Delia Gligor, Yusuf Dilgin, Ionel Catalin Popescu and Lo Gorton

• The amperometric detection of NADH, at +200 mV vs. SCE, is described by the following electroanalytical parameters: a sensitivity of 1.82 mA M⁻¹, a detection limit of 2 μM and a linear domain up to 0.1 mM NADH.
• Bis-phenothiazin-3-yl methane (BPhM):

• The GC electrode was mechanically polished with alumina (Al₂O₃, 1 μm) to a mirror finish and then cleaned by sonication in Millipore water
• The peak potential separation (ΔE_p 67 mV, at 20 mV s⁻¹) and the high value of the peak width at half peak height (100 mV) in comparison with their theoretical values (0 and 45.3 mV, respectively) confirm the quasi-reversible character of the surface-confined redox process, generating the voltammetric response of the GC/poly-BPhM modified electrode. REF 35 = R.W. Murray In: W.H. Saunders Jr., Editor, Techniques of Chemistry vol. 22, Wiley, New York (1992)

Materials list

Mediators: DCPIP

Electrode materials: Graphite paste, PMMA

Electrochemiscal cell for GC electrode (CHI instruments)

Enzyme + Bile Acid

July 20th 2009

A highly performing electrochemical sensor for NADH based on graphite/poly(methylmethacrylate) composite electrode

Hong Dai, Huifeng Xu, Yanyu Lin, Xiaoping Wu and Guonan Chen

• NADH direct detection at Graphite/PMMA electrode
• Ep = 437 mV, and also a 2.4 fold current increase in comparison to Carbon Paste electrode (Ep = 710 mV).
• In addition, the CVs with different sweep rates in NADH solution were carried out. It yielded linear i_p versus v^1/2 plot (r = 0.9930) for potential scan rates from 1 mV s⁻¹ to 200 mV s⁻¹ (not shown), suggesting the oxidation current was diffusion-controlled under these conditions.
• The electrode surface fouled by oxidation of NADH at ordinary electrode is a notorious problem associated with the accumulation of reaction product. The graphite/PMMA electrode could be regenerated by simply rinsing with ultra-pure water to get a full fresh surface. The standard deviation of the peak currents for six successive rinsing was less than 5% by using the same electrode in 2 mM NADH solution. It was found that the oxidation currents remained constant over six months, and this showed the excellent stability of the composite electrode. By using the same process for preparation of the composite electrode, the reproducibility for 6 different composite electrodes was quite good, the electrochemical signal responsed to 2 mM NADH could be achieved within a mean value of about ⁺15%.
• Need to check method for graphite/PMMA electrode fabrication in: D. Hong, W. Xiaoping, W. Youmei, Z. Weichao and C. Guonan, Electrochimica Acta 53 (2008), p. 5113.