Carbon nanotube-thermally reduced graphite oxide (CNT-TRGO) was modified by ambient plasma. beta-cyclodextrin (beta CD) was then functionalized over the composite surface and used for electrochemical detection of ascorbic acid. The ambient plasma increased the electrochemical surface area, adsorption capacity, and electric conductivity, so that more functionalization of beta CD was found on the surface of CNT-TRGO. Final sensitivity of 2.5 mu AmM-1 was obtained in the range from 0.05 to 30 mM of ascorbic acid. The ambient plasma method for the modification of the surface showed very efficient, easy, and economic.