To evaluate lectin-sugar interactions, a sugar/thionine-modified Au electrode was constructed. In this study, concanavalin A(Con A)-mannose binding at a mannose/thionine-modified electrode was investigated with voltammetry. Thionine with two active amino groups was selected as an electroactive compound. One amino group combines with 3,3'-dithiobis (sulfosuccinimidyl propionate), and the other amino group combines with sugar. Because the prepared reagent has a disulfide group, the Au electrode is modified with a self-assembled multilayer. When Con A-mannose binding at the electrode occurred, the thionine moiety was held at the binding site of Con A to mannose. Therefore, the binding was monitored through the decrease of the electrode response of the thionine moiety. On the other hand, measurements to several lectins not having binding sites to mannose were carried out. In the presence of Con A, measurement at a galactose/thionine-modified electrode was also attempted. As a result, almost no decrease of the peak current was observed. Consequently, it is concluded that the mannose/thionine-modified Au electrode responds selectively to Con A. (C) 2003 Elsevier B.V. All rights reserved.