Sensors and Actuators B 174 (2012) 187–194 Contents lists available at SciVerse ScienceDirect Sensors and Actuators B: Chemical journa l h o mepage: www.elsevier.com/locate/snb A novel magnetic particle-modified electrochemical sensor for immunosensor applications Zeynep Altintas, Sreenivasa Saravan Kallempudi 1 , Ugur Sezerman, Yasar Gurbuz ∗ Faculty of Engineering and Natural Sciences, Sabanci University, Orhanli, Tuzla, Istanbul 34956, Turkey a r t i c l e i n f o Article history: Received 25 May 2012 Received in revised form 15 August 2012 Accepted 22 August 2012 Available online 29 August 2012 Keywords: Capacitive biosensor Magnetic particle Multiple marker detection Precise disease diagnosis Biomarker a b s t r a c t In this study, a novel magnetic particle-modified capacitive sensor was reported for the detection of can- cer markers. A gold interdigitated (GID) capacitor transducer was modified using magnetic beads (MB) for signal enhancement and the optimal frequency range and magnetic bead amount were determined. The platform was initially tested using C-reactive protein (CRP) as the model analyte and the methodology was then transferred for multiple marker detection with the aim of precise disease diagnostics. For the first time, the protein biomarkers of lung cancer including carcinoembryonic antigen (CEA), epidermal growth factor receptor (hEGFR) and cancer antigen 15-3 (CA15-3) were investigated with a capacitive sensor. The threshold levels of the markers to indicate the cancer are higher than 5 ng mL -1 (CEA), 64 ng mL -1 (hEGFR) and 50 U mL -1 (CA15-3), respectively. CEA and hEGFR could successfully be detected in the con- centration range of 5 pg mL -1 to 1 ng mL -1 while CA15-3 was detected in the range of 1–200 U mL -1 with a high specificity. Our study demonstrates a highly specific capacitive immunoassay, presenting a potential alternative tool for early and precise diagnosis of cancer disease. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Cancer is a large group of different diseases that occur due to the unregulated cell growth. It may affect people of all ages and certain types of it arises more according to the gender, age or geo- graphical location at globe. 13% of all human deaths worldwide occur due to the cancer in 2007. The incidence and mortality rates of the cancer show a significant difference depending on the can- cer type. For example, the commonest cancer types include breast, lung, prostate and colon carcinomas; however, the rate of mortal- ity is quite low for breast and prostate cancers when compared with lung cancer [1]. Moreover, the mortality and incidence rates of lung cancer show similarity and this increases the importance of early diagnosis for the disease. It displays the highest mor- tality rate, 1.3 million people per year worldwide, compared to the other common cancers [2]. The treatment of the disease is a long and difficult process and the most crucial point for the best result is to diagnose the disease at an early stage. For this aim, there are many methods to apply that are chest X-ray, computer- ized tomography, magnetic resonance imaging, positron emission tomography, sputum cytology and biopsy although some of them are not suitable to all people due to the other pathologies that the ∗ Corresponding author. Tel.: +90 216 483 9533; fax: +90 216 483 9550. E-mail address: yasar@sabanciuniv.edu (Y. Gurbuz). 1 Sabanci University Nanotechnology Research and Application Centre (SUNUM), Sabanci University, Orhanli, Tuzla, Istanbul 34956, Turkey. patient has. Moreover, the patients can often experience a great pain and complication because of some diagnostic tools such as biopsy. Since the current diagnostic tools are also time consuming and were not applicable for early stage detection, a new sensitive and easily applicable method is necessary for cancer detection. With this approach, sensor technology has provided a promis- ing future for the detection of many important diseases through rapid, sensitive and easy applications [3–5]. Getting highly specific and sensitive results by this technology for the biomarkers from blood samples may provide both early and easy detection without painful and invasive techniques. With this aim, a novel mag- netic particle-modified capacitive platform was developed in this study. In recent years, numerous studies have been performed for the direct monitoring of biomolecular recognition processes at the surface of a capacitor transducer chip. Applications of these immunosensors for the determination of substances in serum could be demonstrated only for a few analytes due to the lack of sensi- tivity. The analytical sensitivity of these sensors is limited by the molecular weight of the analyte, so that smaller analyte molecules give only a moderate sensor response. Several methodologies have been reported to improve the detection sensitivity via elec- trode surface modification resulting in surface area enhancement and hence large quantities of immobilized capturing/recognition molecules [6–8]. However, detection limits comparable to those of conventional ELISA techniques could not be realized so far. In order to enhance the sensor signal, the use of solid-phase magnetic beads was proposed in the literature. 0925-4005/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2012.08.052