Carbon nanotube (CNT) gel, which is composed of a mixture of single-wall CNT, an ionic liquid, and a thermostable d-proline dehydrogenase (d-Pro dH) immobilized electrode was utilized for the determination of d-amino acids (dAAs) in food samples. When a critical comparison with CNT, Ketjen Black (KB), and carbon powder (CP) was also carried out, the CNT/d-Pro dH immobilized electrode showed the highest sensitivity and the lowest detection limit of d-proline. In addition, the CNT/d-Pro dH immobilized electrode was applied to detection of dAAs in rice wine and vinegar samples. The concentrations of dAAs in rice wine and vinegar samples were 0.0210 ± 0.0001 and 0.55 ± 0.05 mmol L -1 , respectively.

Direct oxidation of tryptophan on multi-wall carbon nanotubes modified glassy carbon electrode was examined. Surface poisoning, which was suppression of oxidative current caused from adsorption of oxidized compounds of amino acids through multiple redox scan, was observed on carbon material electrodes (multi-wall carbon nano tube(CNT), carbon powder(CP), Ketjen Black (KB) and glassy carbon(GC). It was found that CNT showed a highly inhibitory effect on the surface poisoning and high current value in the direct oxidation of tryptophan because of a π-π interaction between CNT and indole ring of tryptophan results from orbital mixing. This CNT modified GC electrode was applied to an anode in a fuel cell used with amino acids as fuel. As a result, the maximum of the power density showed 0.36 mW cm -2 at 2.5 mA cm -2 of the current density and 140 mV of the cell voltage.

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