Modified Polyaniline Nanofibres for Ascorbic Acid Detection
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Modified Polyaniline Nanofibres for Ascorbic Acid Detection Larisa Florea1, Emer Lahiff1 and Dermot Diamond1 1 CLARITY: The Centre for Sensor Web Technologies, Dublin City University, Dublin 9, Ireland. ABSTRACT Polyaniline nanofibres (PAni) can be surface modified to improve electroactivity over a broader pH range. The technique we describe here can be used to attach carboxylic acid terminated substituents. Modified nanofibres maintain their high surface area, and ability to switch between different redox states. These properties make the material suitable for sensing applications. Unlike unmodified PAni, the functionalised material is self-doping and hence more stable in higher pH solutions. Here we demonstrate how modified PAni fibres can be used for the detection of ascorbic acid. INTRODUCTION Ascorbic acid (AA) is an effective reducing agent, and a powerful antioxidant in food. Various methods have been reported for the determination of ascorbic acid, such as spectrophotometry [1], fluorimetry [2], chromatography [3] and electrochemical detection [4]. Modified electrodes have been applied for the determination of AA electrochemically [5,6], and using conducting polymer electrodes specifically has advantages such as three-dimensional mediator distribution, broad potential window and good electrode stability [7-9]. Polyaniline (PAni) is an example of a stable conducting polymer whose properties (optical, electrical and electrochemical) change in response to the immediate molecular environment of the material. PAni can be cheaply and conveniently synthesized, and thus has huge potential for sensor applications. The nanofibre form of PAni can be synthesised directly by chemical means, such as interfacial polymerisation. Synthesis by this method is scalable, whereby increasing the amount of reactant results in a greater yield of the nanofibre product. By using PAni nanofibres (versus bulk) the surface area exposed to the target molecules can be dramatically increased, resulting in a sensor material with enhanced sensitivity and improved response times [10-14]. Our focus in this paper is on the covalent modification of these nanostructures post-polymerisation [15]. We functionalise the nanofibres with carboxylic acid terminated side-chains, resulting in self-doped PAni. Using the technique described, control over the extent of functionalisation can be achieved [16] and, the modified fibres can be used for the successful detection of ascorbic acid. EXPERIMENT Aniline (BDH), HCl (Fisher Scientific), ammonium peroxydisulfate (Aldrich), ascorbic acid (Aldrich), mercaptopropanoic acid (Aldrich), mercaptohexadecanoic acid (Aldrich) and
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Phosphate Buffered Saline (Aldrich) were used. The aniline monomer was purified by vacuum distillation before use. Other chemicals were used as received. Polyaniline nanofibres were synthesised by interfacial polymerisation between an aqueous and an organic layer, as reported previously [10]. The product was purified by centrifugation (4000 rpm/5 min/3 cycles) and suspended as a collo
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