Biosensors and Bioelectronics 28 (2011) 189–194 Contents lists available at ScienceDirect Biosensors and Bioelectronics j our na l ho me page: www.elsevier.com/locate/bios MEMS biosensor for detection of Hepatitis A and C viruses in serum Erman Timurdogan a , B. Erdem Alaca b , I. Halil Kavakli c , Hakan Urey a,∗ a Koc University, Electrical and Electronics Engineering, Rumeli Feneri Yolu, 34450 Sariyer, Istanbul, Turkey b Koc University, Mechanical Engineering, Rumeli Feneri Yolu, 34450 Sariyer, Istanbul, Turkey c Koc University, Chemical and Biological Engineering, Rumeli Feneri Yolu, 34450 Sariyer, Istanbul, Turkey a r t i c l e i n f o Article history: Received 9 May 2011 Received in revised form 27 June 2011 Accepted 9 July 2011 Available online 19 July 2011 Keywords: Optical microelectromechanical systems (MOEMS) Microcantilevers Biosensor Magnetic actuator Dynamic-mode operation Hepatitis viruses a b s t r a c t Resonant microcantilever arrays are developed for the purpose of label-free and real-time analyte mon- itoring and biomolecule detection. MEMS cantilevers made of electroplated nickel are functionalized with Hepatitis antibodies. Hepatitis A and C antigens at different concentrations are introduced in undiluted bovine serum. All preparation and measurement steps are carried out in the liquid within a specifically designed flowcell without ever drying the cantilevers throughout the experiment. Both actuation and sensing are done remotely and therefore the MEMS cantilevers have no electrical con- nections, allowing for easily disposable sensor chips. Actuation is achieved using an electromagnet and the interferometric optical sensing is achieved using laser illumination and embedded diffraction grat- ings at the tip of each cantilever. Resonant frequency of the cantilevers in dynamic motion is monitored using a self-sustaining closed-loop control circuit and a frequency counter. Specificity is demonstrated by detecting both Hepatitis A and Hepatitis C antigens and their negative controls. This is the first report of Hepatitis antigen detection by resonant cantilevers exposed to undiluted serum. A dynamic range in excess of 1000 and with a minimum detectable concentration limit of 0.1 ng/ml (1.66 pM) is achieved for both Hepatitis A and C. This result is comparable to labeled detection methods such as ELISA. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Detection of pathogens in liquid medium has significant appli- cations in medicine (for the monitoring of biomarkers in body fluids) and in public health (for the monitoring of disease agents in water). For point-of-care (POC) diagnostics applications, compact and label-free sensors that can operate directly with body fluids without requiring expertise are desired. There are many methods for biosensing (Arlett et al., 2011). MEMS cantilever sensors are promising candidates with good performance and rapid measurement times. Dynamic cantilever operation is based on detecting the frequency change in response to accreted mass on the cantilever surface (Gupta et al., 2006). Although mass detection limits on the order zeptograms can be achieved in vacuum (Yang et al., 2006), damping due to the liquid environment is a major drawback of the dynamic-mode operation (Hansen and Thundat, 2005). The associated decrease in the qual- ity factor of the resonator turns liquid-phase measurements into a challenge. Usual practice, the so-called “dip & dry” method, has been to measure samples in air after the cantilevers are treated with target molecules. This leads to (i) loss of ability to work with acti- ∗ Corresponding author. Tel.: +90 212 338 1474; fax: +90 212 338 1548. E-mail address: hurey@ku.edu.tr (H. Urey). vated microbes (Nugaeva et al., 2005), (ii) decreased appeal for POC applications (Skottrup et al., 2008), (iii) loss of insight into actual kinetics of biochemical surface reactions (Kwon et al., 2009), (iv) wetting or change in stiffness due to surface adhesion or stress and (v) decrease in affinity due to drying (Nugaeva et al., 2005). Despite the low quality factor, commercial AFM cantilevers have been used in the detection of Vibrio cholera O1 in solution (Sungkanak et al., 2010). Manalis (Lee et al., 2010) addressed the liquid operation challenge by operating the cantilever in air and building the liquid channels inside the cantilever. This method works well but is able to work with only very small sample volumes in small channels. Damping effect in liquid environment can be reduced by operating the micro-cantilevers at higher order vibration modes (Timurdogan et al., 2010b). Millimeter-size piezoelectric cantilevers operated in higher-order modes have also been used to overcome damp- ing issues in liquid environment. Although going from micron to millimeter-scale inherently reduces natural frequency and thereby worsens the detection limits, utilizing higher-order modes allowed detection of 50–100 cells/ml concentrations of Escherichia coli O157:H7 in broth and beef samples (Campbell et al., 2007). Detec- tion limits can be further decreased to 10 cells/ml if measurements are carried out in PBS buffer (Maraldo et al., 2007). Similar per- formance in solution is demonstrated on Cryptosprodium parvum oocyst and Giardia lamblia parasite (Campbell and Mutharasan, 2008; Xu and Mutharasan, 2010). Instead of the higher order vibra- 0956-5663/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.bios.2011.07.014