The immobilization of alcohol dehydrogenase (ADH) on Au-colloid modified gold electrodes has been investigated. Colloidal Au was first self-assembled onto gold electrodes through the thiol groups of an 1,6-hexanedithiol monolayer. Piezoelectric quartz crystal sensor, cyclic voltammetry, and electrochemical impedance techniques were used to investigate the immobilization of ADH on Au colloids. The cyclic voltammogram tends to be more irreversible with increased ADH concentration. In the impedance spectroscopic study, an obvious difference of the electron transfer resistance between the Au-colloid modified electrode and the bare gold electrode was observed. Using the piezoelectric quartz crystal sensor, the Michaelis constant, K-m, and the maximum initial rate, V-max, of the immobilized ADH were estimated as 6.03 x 10(-4) M and 0.63 Hz s(-1), respectively. The binding constant of ADH with nicotinamide adenine dinucleotide (NAD) was also determined as 1.87 x 10(4) M-1. Experimental results showed that colloidal An can be used as a biocompatible matrix for enzyme immobilization. (C) 2003 Elsevier Science (USA). All rights reserved.