Development of Film Sensors Based on Conjugated Polymers for Copper (II) Ion Detection

A fluorescent film sensor was prepared by chemical modification of a polyfluorene derivative on a glass-plate surface. X-ray photoelectron spectroscopy and ellipsometry measurements demonstrate the covalent attachment of the polyfluorene derivative to the glass-plate surface. The sensor was used to detect Cu2+ ions in aqueous solution by a mechanism exploiting fluorescence quenching of conjugated polymers. Among the tested metal ions, the film sensor presents good selectivity towards Cu2+ ions. Further experiments show that the sensing process is reversible. Moreover, sensory microarrays based on conjugated polymers targeting Cu2+ ions are constructed, which display similar sensing performance to that of the film sensor. The structural motif in which conjugated polymers are covalently confined to a solid substrate surface offers several attractive advantages for sensing applications. First, in comparison with film sensors in which small fluorescent molecules are employed as sensing elements, the sensitivity of our new film sensor is enhanced due to the signal-amplifying effect of the conjugated polymers. Second, the film sensors or microarrays can be used in aqueous environments, which is crucial for their potential use in a wide range of real-world systems. Since the sensing process is reversible, the sensing materials can be reused. Third, unlike physically coated polymer chains, the covalent attachment of the grafted chains onto a material surface precludes desorption and imparts long-term stability of the polymer chains.