Two novel functionalized polythiophenes, poly[3-(6-hydroxyhexyl)thiophene] and poly(3-octanethio-2,2＇-bithiophene), were used as selective coating materials for quartz crystal microbalance (QCM) sensors. These conductive polymers on admixture with stearyl alcohol were deposited on QCM devices by the Langmuir-Blodgett (LB) technique. These LB films exhibited a selective adsorption for the first-row transitions ions in the Irving-Williams order due to the complexation of metal ions with sulfur atoms in the polymers. These LB film coated QCM sensors were found applicable in detecting heavy metal ions in aqueous solution, which are major pollutants in wastewater. The coated QCM sensors can selectively adsorb heavy metal ions (Hg2+) from solution over a wide range from 0.1 to 100 ppm concentration by complexation with sulfur atoms in the polymers. The bound mercury could be removed by ethylenediaminetetraacetic acid (EDTA) solution. The presence of ferrous, lead, cobalt, and chromium cations in the solution did not interfere with the detection of mercury ions.