Organic conducting polymers (OCPs) are currently the subject of intense research in the area of biomaterials and bioelectronics. Of the OCPs, poly(3,4-ethylenedioxythiophene) (PEDOT) has attracted significant interest, however there has been little work on investigating the incorporation of biological compounds as the dopant species in the polymer which are aimed at enhancing the biocompatibility and biofunctionality of the material. Here, we incorporate the biological dopants dextran sulphate, chondroitin sulphate, and alginate, into PEDOT polymers and investigate their influence on a suite of physicochemical and electrochemical properties. We employ QCM-D to study the mass of adsorption and the viscoelastic properties of the important extracellular matrix proteins fibronectin and collagen. Furthermore, we use QCM-D to study the adhesion of PC12 neural cells to the PEDOT-biodopant polymers with and without an adsorbed protein conditioning layer. QCM-D was found to be an excellent tool with which to study conducting polymer–biological interactions, with this report the first time that QCM-D has been used to study cell interactions with conducting polymer biomaterials.