We investigated the effects of amino acid poly-L-tyrosine (PLT) molecule decoration on the surface properties and electron transport of single-walled carbon nanotubes (SWCNTs) compared to the effects of deoxyribonucleic acid (DNA) molecule decoration. Both types of molecules had a similar effect on CNT surfaces; both were applied to tubes as charges, and increased their zeta potential. From the FET characteristics, we found that PLT molecule and DNA molecule decoration have quite different effects on the conduction mechanism of CNTs, which indicates that they are induced by different binding mechanisms. (C) 2010 Elsevier B. V. All rights reserved.