Deposition of EDOT-Decorated Hollow Nanocapsules into PEDOT Films for Optical and Electrochemical Sensing

Hollow nanocapsules (NCs) with ∼1 nm thin porous walls offer unique possibilities for chemical and biosensor design. When used as containers for reagents for optical or electrochemical sensors, e.g., a catalyst, an indicator dye, or a redox mediator, their nanometer-thin porous wall holds and protects the valuable cargo but, at the same time, warrants unhindered bidirectional transport for analyte, substrate, and reaction product molecules. However, the practical utility of such NCs requires an immobilization method that retains the inherent advantages of the reagent loaded NCs. Here, we report an immobilization possibility, namely, the covalent attachment of the reagent loaded NCs to a conductive polymer (PEDOT) film, that overcomes the disadvantages of the incorporation of the NCs in a gel-like supporting matrix which is the most common immobilization method. It required the decoration of the NC surfaces with EDOT moieties that could be copolymerized with free EDOT molecules electrochemically onto electrode surfaces. The EDOT-substituted nanocapsules used in this work were loaded with the indicator dye Nile Blue or an in situ synthesized iron(II) tris(2,2′-bipyridine) complex (Fe(bpy)3) prior to their immobilization. The presence and distribution of the nanocapsules in electrochemically deposited PEDOT films were demonstrated by digital microscopy, SEM, and XPS depth profiling.