Modification of Au electrode (upper row) using carboxybetaine aryldiazonium derivative (CB) and lectin (SNA-I). In the first step, carboxybetaine-bearing SAM layer was formed using cyclic voltammetry, and subsequently served for the covalent immobilization of a lectin. Lower row shows MP@silica@Au composite spontaneously modified with CB-derivative and subsequently with an antibody (Ab, anti-fPSA, chemically treated). After enrichment of fPSA from human sample using MP@silica@Au/CB/Ab by a permanent magnet, a sandwich was prepared and the signal was evaluated electrochemically.