ORIGINAL PAPER Development of electrochemical DNA biosensor for Trichoderma harzianum based on ionic liquid/ZnO nanoparticles/chitosan/gold electrode Shafiquzzaman Siddiquee & Nor Azah Yusof & Abu Bakar Salleh & Soon Guan Tan & Fatimah Abu Bakar Received: 26 September 2010 / Revised: 22 December 2010 / Accepted: 23 January 2011 / Published online: 8 February 2011 # Springer-Verlag 2011 Abstract Electrochemical DNA biosensor was successfully developed by depositing the ionic liquid (e.g., 1-ethyl-3- methylimidazolium trifluoromethanesulfonate ([EMIM] [Otf])), ZnO nanoparticles, and chitosan (CHIT) nanocompo- site membrane on a modified gold electrode (AuE). The electrochemical properties of the [EMIM][Otf]/ZnO/CHIT/ AuE for detection of DNA hybridization were studied. Under optimal conditions using cyclic voltammetry, the target DNA sequences could be detected in the concentration range of 1.0×10 -18 to 1.82×10 -4 mol L -1 , and with the detection limit of 1.0×10 -19 mol L -1 . This DNA biosensor detection approaches provide a quick, sensitive, and convenient method to be used in the identification of Trichoderma harzianum. Keywords DNA electrochemical biosensor . DNA hybridization . ZnO nanopaticles . Ionic liquid . Chitosan Introduction Trichoderma harzianum is a ubiquitous soil species and is used as a biological control to protect plants against root, seed, and foliar diseases, and storage rots [1, 2]. Results from field trials showed that the isolates are well adapted to different environmental conditions, protecting several crops, as well as controlling various plant pathogens [3]. Therefore, numerous number of T. harzianum strains could be selected for their activity against the casual pathogens on different crops and specific environmental factors [4]. Thus, rapid and sensitive detection methods are required to meet the challenge for the detection of T. harzianum strains. Practical challenges for timely and effective viability detection include speed and portability. DNA is a fundamental biomolecule which stores genetic information as it plays a vital role in determination of hereditary characteristics. From this approach, DNA is considered as the major target interacting with various molecules [5]. The inherent stability of a biomolecule is an important issue in the development of the DNA-based biosensor that influenced directly on the sensor response [6]. Many types of nano- particles (NPs) of different sizes and compositions are available to support the electrochemical-related applications S. Siddiquee (*) Biotechnology Research Institute, Universiti Malaysia Sabah, Kota Kinabalu, Sabah 88400, Malaysia e-mail: shafiq.siddiquee@gmail.com e-mail: shafiqpab@ums.edu.my S. Siddiquee : N. A. Yusof (*) Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, Serdang, Selangor 43400 UPM, Malaysia e-mail: azah@science.upm.edu.my N. A. Yusof : A. B. Salleh : F. Abu Bakar Institute of Bioscience, Universiti Putra Malaysia, Serdang, Selangor 43400 UPM, Malaysia A. B. Salleh : S. G. Tan Faculty of Biotechnology and Biomolecular Science, Universiti Putra Malaysia, Serdang, Selangor 43400 UPM, Malaysia F. Abu Bakar Department of Food Science, Faculty of Food Science and Technology, Universiti Putra Malaysia, Serdang, Selangor 43400 UPM, Malaysia J Solid State Electrochem (2012) 16:273–282 DOI 10.1007/s10008-011-1322-y