A conductive polymer based electronic nose for early detection of Penicillium digitatum in post-harvest oranges Jonas Gruber a, ⁎, Henry M. Nascimento b , Elaine Y. Yamauchi a , Rosamaria W.C. Li c , Carlos H.A. Esteves a , Gustavo P. Rehder d , Christine C. Gaylarde e , Márcia A. Shirakawa d a Instituto de Química, Universidade de São Paulo, Av. Prof. Lineu Prestes, 748, CEP 05508-000 São Paulo, SP, Brazil b Sociedade Brasileira de Microbiologia, São Paulo, SP, Brazil c Centro Universitário Estácio Radial São Paulo, São Paulo, SP, Brazil d Escola Politécnica, Universidade de São Paulo, São Paulo, SP, Brazil e University of Portsmouth, Portsmouth, UK abstract article info Article history: Received 5 July 2012 Received in revised form 28 January 2013 Accepted 23 February 2013 Available online 1 March 2013 Keywords: Electronic nose Gas sensor Conductive polymer Oranges Penicillium digitatum Biodeterioration We describe the construction of an electronic nose, comprising four chemiresistive sensors formed by the deposi- tion of thin conductive polymer films onto interdigitated electrodes, attached to a personal computer via a data ac- quisition board. This e-nose was used to detect biodeterioration of oranges colonized by Penicillium digitatum. Significant responses were obtained after only 24 h of incubation i.e. at an early stage of biodeterioration, enabling remedial measures to be taken in storage facilities and efficiently distinguishing between good and poor quality fruits. The instrument has a very low analysis time of 40 s. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Microbiological contamination of food presents health risks and entails human and economic losses due to biodeterioration. Microbi- ological quality control is of fundamental importance to avoid such problems [1,2]. Brazil is the world's largest producer and exporter of oranges. According to the US Foreign Agricultural Service [3] the production of oranges in Brazil in 2010/11 reached 20.2 billion tons. It is estimated that 85% of the harvest is used for juice and the rest sold as fresh fruit. For both purposes, the quality of the oranges may be compromised by post-harvest fungal attack. Penicillium digitatum, Elsinoe australis and Guignardia citricarpa are important pests in all citrus producing coun- tries [4]. An electronic nose (e-nose) is an analytical tool that mimics the human nose [5–7] and can detect volatile compounds at low concentra- tions, sometimes not noticeable by the human nose [8]. Since microor- ganisms produce a large variety of volatile chemical compounds [9,10] they can be detected and even identified by an e-nose [11]. Some reported examples are: spoilage detection in stored cereal grains [12], and detec- tion of microbial contamination in various fruits such as blueberries [13] and kiwi [14]. There are several types of e-noses commercially available and they all share the same basic principle. It is an integrated system, with an array of sensors with partial specificity, through which volatile compounds pass and cause changes in a physical property, e.g., electrical conductance. The response of the sensors is digitized and treated by a pattern-recognition software, which produces an output of results [5]. The cost of many of these instruments, however, is too high for routine use in many industries. Low-cost gas sensors and e-noses based on chemiresistive conduc- tive polymer films were described in 2005 [15] and have since been used for a wide range of applications e.g. detection of organic solvents [16], low-molecular-weight alcohols [17], volatile halogenated organic compounds [18], carbonyl compounds in indoor air [19], automotive fuel analysis [20], wood analysis [21], and detection of methanol in alco- holic beverages [22]. The key to effective utilization of an e-nose is the ability to detect fungal activity rapidly at an early stage in biodeterioration, enabling remedial measures to be taken in storage facilities and efficiently distinguishing between good and poor quality fruits. Before beginning the industrial production of orange juice, physical characteristics perceived by touch and vision are used to differentiate Materials Science and Engineering C 33 (2013) 2766–2769 ⁎ Corresponding author. Tel.: +55 11 3091 1103; fax: +55 11 3815 5579. E-mail address: jogruber@iq.usp.br (J. Gruber). 0928-4931/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.msec.2013.02.043 Contents lists available at SciVerse ScienceDirect Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec