Talanta 77 (2009) 1590–1596 Contents lists available at ScienceDirect Talanta journal homepage: www.elsevier.com/locate/talanta Development of an optical ammonia sensor based on polyaniline/epoxy resin (SU-8) composite A. Airoudj a,b , D. Debarnot a,∗ , B. Bêche c , F. Poncin-Epaillard a a Laboratoire Polymères, Colloïdes, Interfaces, UMR 6120, Université du Maine, Avenue Olivier Messiaen, 72085 Le Mans, France b Laboratoire d’Acoustique de l’Université du Maine, UMR-CNRS 6613, Avenue Olivier Messiaen, 72085 Le Mans, France c Laboratoire PALMS-GMCM, UMR-CNRS 6627-6626, Institut de Physique de Rennes, 35042 Rennes, France article info Article history: Received 3 April 2008 Received in revised form 22 September 2008 Accepted 29 September 2008 Available online 14 October 2008 Keywords: Ammonia sensor Polymer sensitive layer Optical transducer Absorption variation measurement abstract Polyaniline (PANI)/glycidyl ether of bisphenol A (SU-8) composite film is elaborated in order to detect ammonia gas. These composite films are characterized by ultraviolet–visible (UV–vis) spectroscopy, Fourier transformed infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The sensitivity to ammonia is measured by optical absorption changes. The ammonia sensing properties of PANI/SU-8 composite films are studied, and then are compared to pure PANI films elaborated by chemical way. Exper- imental results show that the PANI/SU-8 optical sensor has simultaneously a rapid response to ammonia gas and regenerates easily, that is advantageous compared to pure PANI films. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Electroconducting polymeric materials are of great interest for a large number of applications [1–3] due to their easy processing and relatively low cost compared to other materials such as inor- ganic ones. They can be used as promising materials for different types of chemical sensors (with electrical, optical or piezoelectrical transductions) because of their sensitivity at room temperature and their selectivity for specific chemical agents. The sensing ability of electroconducting polymers is based on modulation of their dop- ing level during redox or acid–base interactions with some gases. This effect results in an immediate alteration of the conductivity and the optical absorbance. Polyaniline (PANI) is one of the most promising conducting polymers because of its easy synthesis either through chemi- cal or electrochemical methods and its selectivity to ammonia [4–6]. PANI shows electrical and optical property variations, when it is in contact with oxidant–reductor chemicals. In particular, the interaction between the conductive form of PANI – emeral- dine salt (ES) – and the ammonia gas results in a decrease of the polaron density inside the band gap of the polymer accord- ing to the mechanism proposed in Fig. 1 [6–8]. Indeed, a lot of ∗ Corresponding author. Tel.: +33 2 43 83 39 82; fax: +33 2 43 83 35 58. E-mail address: Dominique.Debarnot@univ-lemans.fr (D. Debarnot). articles describe electrical and optical sensors for NH 3 detection with PANI as sensitive layer [3,7–21]. Nonetheless, the poor solu- bility and mechanical properties of PANI imply difficulties in its practical use. In order to overcome these disadvantages, several methods have been developed [22–33]. One of them consists to elaborate conductive polymer composites. PANI/polymer compos- ite has attracted considerable attention because even at very low PANI concentration, conducting composites with good mechani- cal properties and chemical stability can be obtained [29–31]. PANI composite can be prepared by chemical or electrochemical poly- merization of aniline in a solution of the polymeric matrix. PANI can also be mixed with other polymers in the melt state. Different polymers can be used, such as polymethyl methacrylate (PMMA) [25,29,30], polyvinyl chloride [30], polystyrene [32], and epoxy resin [33]. For gas detection application, to our knowledge, only one study presents optical sensors based on PANI composite coatings using PMMA as matrix [25]. These gas sensors show slow recov- ery time and regeneration difficulty. On the other hand, the lack of description of optical gas sensors based on the polyaniline compos- ite gives us the opportunity to develop a new optical sensor which will present simultaneously high sensitivity, fast optical response and short recovery time. To improve the characteristics of PANI sensors, we explored an epoxy resin as polymer matrix to elabo- rate conducting PANI composite. The epoxy-based polymer, which commercial name is SU-8, widely used as negative photoresist has also been studied for micro-electro-optical-mechanical sys- 0039-9140/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2008.09.054