Single-Use Sensor Platforms Based on Carbon Nanotubes for Electrochemical Detection of DNA Hybridization Related to Microcystis spp. Arzum Erdem,* Hakan Karadeniz, Pembe Ece Canavar, Gulsah Congur Ege University, Faculty of Pharmacy, Analytical Chemistry Department, 35100 Izmir, Turkey fax: + 90-232-388 5258; phone: + 90-232-311 5131 *e-mail: arzum.erdem@ege.edu.tr Received: July 10, 2011; & Accepted: September 26, 2011 Abstract The electrochemical monitoring of (i) label-free and (ii) indicator based DNA hybridization related to Microcystis spp. (MYC) DNA was explored in this study via multiwalled carbon nanotube (MWCNT) based screen printed graphite electrodes (SPEs). The effect of CNT modification onto SPE was firstly investigated by measuring the oxi- dation signals of guanine and adenine before/after DNA immobilization onto the surfaces of bare SPE, MWCNT- SPE and SWCNT-SPE in combination with differential pulse voltammetry. MYC-DNA hybridization was moni- tored by following two procedures and measuring the guanine oxidation signal and the reduction signal of cobalt- phenanthroline Co(phen) 3 3 + . Voltammetric results were complemented with electrochemical impedance spectrosco- py (EIS). Keywords: Electrochemical DNA biosensor, Screen printed electrodes, Microcystis spp., Microcystin, Carbon nanotubes, DNA hybridization DOI: 10.1002/elan.201100369 Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/elan.201100369. 1 Introduction Electrochemical DNA hybridization biosensors have an important role in early diagnoses of infectious agents, toxins and pathogens in various environments [1–3]. The monitoring of sequence-specific DNA hybridization event could occur in two ways: (a) directly based on guanine or adenine oxidation signals [4–6], (b) by using DNA inter- calators (some antibiotics, metal coordination complexes, etc.) which form complexes with the nitrogenous bases of DNA [7–11]. In sensor technology, there has been an attractive inter- est for the modification of transducers with carbon nano- tubes (CNT). Because of some advantages such as high surface area, fast heterogeneous electron transfer and long-range electron transfer, the modification of electro- des with CNTs played an important role in DNA sensing [9, 12–20]. In the study of Wang et al. [19], the DNA hy- bridization related to breast cancer BRCA1 gene was de- tected by using a multiwalled CNT (MWCNT) modified glassy carbon electrode (GCE) with a signal enhancement in guanine oxidation signal in comparison to the unmodi- fied GCE. A sensitive and low cost DNA biosensor based on CNT modified disposable graphite electrode (PGE) was introduced in the study of Erdem et al. [9] for the electrochemical detection of label free DNA hybridiza- tion related to Hepatitis B Virus (HBV). In the study of Caliskan et al. carboxylic acid function- alized single-walled carbon nanotubes (SWCNT) modi- fied PGEs were developed for electrochemical monitor- ing of label-free HBV DNA hybridization based on gua- nine oxidation signal and their voltammetric results were also found in a good agreement with the ones of Electro- chemical Impedance Spectroscopy (EIS) [20]. Nanomaterial based screen printed electrodes (SPE) become more important in biomolecular recognition since they can present a detection scheme with higher sensitivity and better reproducibility while keeping their long term stability, and manufacture repeatability [21, 22]. Electrochemical detection of calf thymus ssDNA and yeast tRNA with good reproducibility with MWCNT-SPE was investigated by Ye et al. [21]. The application of MWCNT-SPEs for electrochemical monitoring of DNA hybridization was introduced for specific sequences on HBV DNA by Karadeniz et al. [22] based on the changes in the oxidation signal of guanine. A novel electrochemi- cal approach for label-free detection of DNA primary se- quence has been proposed by Vagin et al. [23] using a dis- posable graphite screen-printed electrodes shielded with a thin layer of inert polymer plasticized with water-immis- cible polar organic. Microcystins are a family of cyclic polypeptides pro- duced by different species of cyanobacteria (bluegreen algae), which can form blooms in lakes and reservoirs. TOPICAL CLUSTER TOPICAL CLUSTER 502  2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Electroanalysis 2012, 24, No. 3, 502 – 511 Full Paper