Communication: Zeolite-modified quartz crystal microbalances are demonstrated to have excellent characteristics as chemical sensors. The Figure illustrates the synthetic strategy used to form the zeolite film on the electrode: the gold electrode (left) is covered with a partially crosslinked surface of siloxy groups, to which a cationic polymer is attached, The colloidal silicalite-1 crystals (blocks) act as seeds for the growth of an oriented silicalite layer.