Sensors and Actuators B 228 (2016) 278–286 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical jo u r nal homep age: www.elsevier.com/locate/snb An effective surface design based on a conjugated polymer and silver nanowires for the detection of paraoxon in tap water and milk Janset Turan a , Melis Kesik a , Saniye Soylemez a,1 , Seza Goker a , Sahin Coskun c , Husnu Emrah Unalan c,e , Levent Toppare a,b,d,e,∗ a Department of Chemistry, Middle East Technical University, Ankara 06800, Turkey b Department of Biotechnology, Middle East Technical University, Ankara 06800, Turkey c Department of Metallurgical and Materials Engineering, Middle East Technical University, Ankara 06800, Turkey d Department of Polymer Science and Technology, Middle East Technical University, Ankara 06800, Turkey e The Center for Solar Energy Research and Application (GUNAM), Middle East Technical University, Ankara 06800, Turkey a r t i c l e i n f o Article history: Received 3 November 2015 Received in revised form 22 December 2015 Accepted 9 January 2016 Available online 13 January 2016 Keywords: Amperometric biosensor Conducting polymer Silver nanowire Pesticide biosensor Butyrylcholinesterase a b s t r a c t In this study, a novel approach for the fabrication of a biosensor utilizing a conducting polymer and silver nanowires is reported. To obtain immobilization platform for butyrylcholinesterase (BChE), a graphite electrode was modified with the poly(5,6-bis(octyloxy)-4,7-di(thieno[3][3,2-b]thiophen-2- yl)benzo[c][1,2,5]oxoadiazole) (PTTBO) which has a hydrophobic alkyl chain as the pendant group providing hydrophobic nature to the matrix. Since biomolecules contain both hydrophobic and hydrophilic parts in their structure, alkyl chains interact with the proteins which provide an enhanced stability. Biosensor performance was improved through the deposition of silver nanowires on the polymer coated surfaces which enhances the charge transfer rate. This enabled the development of rapid, highly sensitive and stable amperometric sensors for the quantitative determination of organophosphorus pes- ticide; paraoxon. Fabricated biosensor showed two linear ranges between 0.5–8 M and 10–120 M with a low detection limit of 0.212 M when butyryl thiocholine iodide is used as the substrate. Surface modifications were monitored by scanning electron microscope (SEM) and cyclic voltammetry (CV) tech- niques. Under optimal operational parameters, fabricated sensors were tested for paraoxon detection in milk and tap water based on the inhibition of the enzyme molecules, where recovery tests proved the applicability of the designed system. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Environmental monitoring and food control are the two main concerns in many research fields due to the excessive use of pes- ticides in agriculture, industry and chemical warfare [1]. Among the pesticides, organophosphates and carbamic pesticides are the most commonly used ones in agriculture as insecticides in order to fight pests and to increase the yield. Unfortunately, toxicity of these compounds causes serious health defects on mammalians due to their inhibitory effect on cholinesterase enzyme (ChE) [2]. ∗ Corresponding author at: Middle East Technical University, Department of Chemistry, Ankara 06800, Turkey. Fax: +90 3122103200. E-mail addresses: janset.trn@gmail.com (J. Turan), kesik.melis@gmail.com (M. Kesik), saniyesoylemez@gmail.com (S. Soylemez), sezagoker@gmail.com (S. Goker), sacoskun@metu.edu.tr (S. Coskun), unalan@metu.edu.tr (H.E. Unalan), toppare@metu.edu.tr (L. Toppare). 1 On leave from Ordu University. Blockage of the active sides of ChE by pesticides can result in distur- bance of normal neuronal function, which leads to immunological diseases, nerve disorders and eventually death [3]. Since contam- ination of agricultural products and aquatic systems cause these lethal effects, the need for pesticide detection gains high priority. Chromatographic methods, such as high performance liquid chro- matography (HPLC), gas chromatography (GC), mass-spectrometry (MS) among others have been employed for monitoring pesticides in contaminated water and food products [4–6]. Such analytical methods provide very sensitive and selective detection. Never- theless, they have also several drawbacks as they require long analysis time, complicated pretreatment methods, qualified opera- tors and intricate equipments [7]. To minimize these complications, cholinesterase enzymes based bioanalytical systems integrated with amperometric, potentiometric and optical methods have been employed over the last few years [8–13]. These analytical systems not only provide fast and highly sensitive detection but also are potentially applicable for use in field. Recently, enzyme inhibi- http://dx.doi.org/10.1016/j.snb.2016.01.034 0925-4005/© 2016 Elsevier B.V. All rights reserved.