Spectral features of Raman scattering of isolated single-walled carbon nanotubes (SWNT) on gold surface in aqueous solution was investigated under electrochemical potential control. Spectrum of the radial breathing mode of SWNT was dependent upon the electrode potential. Change in the intensity of the spectrum was reversible. Distinct difference in the potential dependence was observed at SWNT with different diameter. Absolute potential of the Fermi level of individual tubes was estimated from the potential dependence. Observations suggest that the work function of the tube becomes larger in a manner inversely proportional to the diameter of SWNT. Linewidth of the spectrum also showed potential dependence at the metallic tubes. Characteristics of the spectral changes induced by electrochemical doping were correlated to the difference in electronic density of individual SWNT with distinct diameter and chirality. (c) 2005 Elsevier Ltd. All rights reserved.