Due to its good electrochemical stability, high conductivity and chemical properties, Poly(3,4-ethylenedioxythiophene) (PEDOT) is one of the most widely used conducting polymers in biosensors field. In this present article a sensor obtained by electroless deposition of gold on top of polymer (PEDOT) viscoelastic layer on quartz crystal microbalance is described. The acoustic impedance of such bi-layer (Au/PEDOT) is different from the one obtained when rigid mass is added directly on quartz surface. Consequently, the Sauerbrey equation overestimates significantly the deposited mass of Au. A procedure to account correctly for viscoelastic properties in estimation of added mass of metal is proposed in this article. (C) 2013 Elsevier Ltd. All rights reserved.