ORIGINAL PAPER Cystic fibrosis: a label-free detection approach based on thermally modulated electrochemical impedance spectroscopy Hany Nasef & Valerio Beni & Veli C. Őzalp & Ciara K. O’Sullivan Received: 18 November 2009 / Revised: 3 January 2010 / Accepted: 17 January 2010 / Published online: 14 February 2010 # Springer-Verlag 2010 Abstract Cystic fibrosis is one of the most common genetically inherited diseases in northern Europe, with the DF508 mutation being the most common, and among the Caucasian population being responsible for almost 70% of cases. In this work, we report on the use of thermally modulated electrochemical impedance spectroscopy for the discrimination of the DF508 mutation from the wild-type sequence. DNA probes (15 and 21 bases long) were immobilised on the surface of gold electrodes and the variation of the charge-transfer resistance was monitored as a function of hybridisation. Two sets of targets were used in this work: synthetic 15-mer sequences and two single- stranded synthetic analogues of PCR products 82 (mutant) and 85 (wild type) bases long. Hybridisation with short targets resulted in very sequence specific charge-transfer- resistance variation with a discrimination factor at room temperature between fully complementary and mismatched sequences of approximately fivefold. However, in the case of the single-stranded synthetic PCR product analogues, a lower discrimination factor was recorded (1.5-fold). The effect of temperature was investigated to improve discrim- ination and the use of a posthybridisation wash at elevated temperature resulted in a fivefold improvement in the discrimination factor. Using an electrode array with probes immobilised against each of the mutant and wild-type sequences, we achieved an unequivocal detection of the DF508 mutation. Keywords Electrochemical impedance spectroscopy . Cystic fibrosis . Label-less detection . DNA sensor . DF508 Introduction Cystic fibrosis is one of the most common life-shortening, childhood-onset inherited diseases, which manifests itself as an inherited defect of chloride transport in the epitheli- um, resulting in damage to lung, sweat glands and the pancreatic glands, causing progressive disability and, for most, early death [1–5]. The incidence of cystic fibrosis is one in 2,500 live births in the Caucasian population [2, 3]. Moreover, cystic fibrosis is the most common genetic disease among the population of European descent; one in 22 people carry one gene for cystic fibrosis [6]. Cystic fibrosis is caused by mutations in a gene called the cystic fibrosis transmembrane conductance regulator (CFTR). The CFTR protein is a transport protein that functions as an ion channel and is involved in the regulation of the production of sweat, digestive juices and mucus. Although most people without cystic fibrosis have two functional copies of the CFTR gene, only one is needed to prevent cystic fibrosis; cystic fibrosis develops when neither gene works normally. Therefore, cystic fibrosis is classified as an autosomal recessive disease. The name “cystic fibrosis” refers to the characteristic “fibrosis” (tissue scarring) of the biliary tract (“cystic” being a generic term for all that is related to the biliary vesicle and/or the bladder), and was first thus named in the 1930s [1, 5, 6]. H. Nasef : V. Beni (*) : V. C. Őzalp : C. K. O’Sullivan (*) Nanobiotechnology & Bioanalysis Group, Departament d’Enginyeria Quimica, Universitat Rovira i Virgili, Avinguda Països Catalans 26, 43007 Tarragona, Spain e-mail: valerio.beni@urv.cat e-mail: ciara.osullivan@urv.cat C. K. O’Sullivan Institucio Catalana de Recerca i Estudis Avançats, Passeig Lluis Companys 23, 08010 Barcelona, Spain Anal Bioanal Chem (2010) 396:2565–2574 DOI 10.1007/s00216-010-3489-y