Coating the surface with carbon nanotubes to improve amperometric biosensors

Much effort is put into creating electrodes that can detect the voltage during nicotinamide adenine dinucleotide (NADH) enzyme reactions. Normal electrodes often fail either because the voltage on these enzymes is above the upper design limits of the curcuits, or because chemicals react on the surface and leave behind fouling byproducts.

Musameh et al point to an intriguing of improving these electrodes. They solvated carbon nanotubes (either single-walled or multi-walled) in concentrated sulfuric acid, cast the solution on the glassy carbon electrode surface, and subsequently dried the coated product. The researchers then compared the sensing capabilities of each both the modified and unmodified electrodes.

The carbon nanotube coated electrodes, as expected, promoted the electron-transfer reactions of the NADH, leading to a number of improved conditions:

1) Over a 60 minute period and operating at a potential of 0.60 mV, the multi walled carbon nanotube (MWCNT) coated electrode produced a much more consistent response to a concentration of 0.005 M NADH. While the control exhibited a 86% current decay at the end of the time period, the current of the MWCNT electrode had only decayed by 10%.

2) The researchers measured the catalytic activity of the CNT coated electrodes by using hydrodynamic voltammograms 0.0001 M NADH solution. In the control, there is no response (ie, current) at electrode potentials lower than 6 V. However when the solution was placed with CNT coated electrodes the response was visible even when there was no potential. When the voltage was at the max (10 V), the response in the CNT modified electrode was six fold greater than that of the control electrode. The researchers also confirmed the catalytic activity of the electrodes using standard cyclic voltammetry.

3) The CNT modified electrodes are rapidly responsive to small changes in concentrations of NADH (0.0001 M) while the control surface cannot detect such changes.

4) A decrease in detrimental overvoltage and a decrease in surface fouling.

The electron promotion of NADH is a biologically important compound and the ability of carbon nanotubes to catalyze its reaction is important not only for its potential as coating for an electrode but also as an engineered in vivo stimulant of other such redox reactions.

Reference

Musameh M, Wang J, Merkoci A, Lin Y. 2002 Low-potential stable NADH detection at carbon-nanotube-modified glassy carbon electrode. Electrochemistry Communications 4: 743-746. doi: doi:10.1016/S1388-2481(02)00451-4.