Various electrochemical chemo/bio-sensors and optical sensors are facilely explored for the sensitive determination of biomolecules, drug molecules, environmental pollutants, and metal ions using a carboxylic-functionalized poly(3,4-ethylenedioxythiophene) derivative (PC4), which is easily obtained by the direct electropolymerization of a water-soluble 4-((2,3-dihydrothieno[3,4-b][1,4] dioxin-2-yl) methoxy)-4-oxobutanoic acid (C4-EDOT-COOH) monomer in a microemulsion system. The effect of different pH values on the electropolymerization of C4-EDOT-COOH monomer is investigated, and the as-prepared PC4 film is characterized by electrochemical method, infrared spectrum, and scanning electron microscope. The resulting high-quality PC4 film as a sensing material not only can combine with various biologically active species via covalent linkage and inorganic materials via layer-by-layer self-assembly for the construction of electrochemical chemo/bio-sensors, but also excellent optical performance of PC4 can be employed for the fabrication of optical sensors. These as-prepared chemo/bio-sensors can be applied to the simple, fast and sensitive detection of environmental pollutants, pharmaceuticals, hazardous substances, and biological active substance and nutrients present in food by means of electrochemistry, ultraviolet and fluorescence spectroscopy. Satisfactory results indicate that chemo/biosensors based on PC4 possess excellent chemo/bio sensing performance and enhanced optical response, and its carboxylic group can realize the immobilization of biologically active species, self-assembly of inorganic nanomaterials. (C) 2013 Elsevier Ltd. All rights reserved.