In-situ monitoring of potential enhanced DNA related processes using electrochemical quartz crystal microbalance with dissipation (EQCM-D) Xueling Quan a, ⁎, Arto Heiskanen a , Maria Tenje b , Anja Boisen a a Department of Micro- and Nanotechnology, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark b Department of Measurement Technology and Industrial Electrical Engineering, Lund University, SE-22100 Lund, Sweden abstract article info Article history: Received 18 July 2014 Received in revised form 14 August 2014 Accepted 28 August 2014 Available online xxxx Keywords: Potential pulse assisted functionalization Thiolated DNA functionalization DNA hybridization Vertically aligned DNA conformation EQCM-D The effect of applied potential pulses on DNA functionalization (thiolated single stranded DNA) and hybridization processes has been monitored in-situ on gold surfaces using electrochemical quartz crystal microbalance with dissipation (EQCM-D). The applied potentials were chosen with respect to the potential of zero charge (E pzc ) of the gold surfaces: a positive potential to attract the negatively charged DNA molecules and a negative potential to enhance the vertical alignment due to electrostatic repulsion. The obtained results clearly show that both DNA modification and hybridization are strongly enhanced by applying potential pulses. Based on the EQCM-D results, we present a model to explain the influence of the potential pulsing. Aside from the effect of applied potentials on DNA related processes, this work also demonstrates the versatility of the combination of electrochemistry and quartz crystal microbalance with dissipation in facilitating real-time in situ monitoring of such processes. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Functionalization of metal electrodes using, e.g., self-assembled monolayers of alkanethiols (SAM) [1,2] and monolayers of DNA [3–5], has been widely applied for construction of bio/chemical systems that serve as structural or functional parts of biosensors, molecular electron- ic devices, and drug delivery systems. In such applications, especially in nanotechnology, it is crucial to improve the molecular level quality and reproducibility of monolayers and shorten the functionalization time. Applied potential has been shown to enhance deposition of alkanethiol SAMs [6–8], immobilization [9] and hybridization [10,11] of DNA as well as conformational modulation of DNA layers [12,13], introducing new possibilities for molecular level control of surface functionalization. Ad- ditionally, Ma and Lennox have shown that a moderate anodic potential (from +200 mV to +600 mV vs Ag/AgCl) applied to an Au electrode, induced a rapid and complete adsorption of thiol molecules [6]. Quartz crystal microbalance with dissipation (QCM-D) technique, which measures simultaneously changes in both mass (change in the resonance frequency, Δf) and viscoelastic properties (change in the dissipation factor, ΔD) in real-time, is widely used for charactering the properties of DNA layers [14–16]. Electrochemical QCM-D technique applying gold coated quartz crystals provides an effective tool to study electrochemically assisted adsorption/desorption phenomena combined with in situ monitoring of changes in surface load and morphology [17–19]. The combination of electrochemistry and mass/ morphology based probing provides detailed information of surface phenomena in comparison with other techniques, such as surface plas- mon resonance [20], X-ray photoelectron spectroscopy [3], fluorescence detection [21], neutron reflectivity measurements [22], and atomic force microscopy (AFM) [23]. To our best knowledge, there are no published studies demonstrat- ing the effect of potential pulse assisted immobilization of thiolated single stranded DNA followed by subsequent DNA hybridization com- bined with in situ real-time monitoring of the processes. In this commu- nication, using EQCM-D technique, we demonstrate the synergistic effect of applied potential pulses above and below the potential of zero charge (E pzc ) on DNA related processes and present a model explaining the effect. Based on the presented results, we propose such potential pulse protocols as a new paradigm for constructing micro- and nanodevices relying on DNA modifications and hybridization. 2. Materials and methods 2.1. Chemicals HS-ssDNA and complementary probes with 21 base pairs were obtained from DNA Technology A/S (Denmark). The sequences of the thiolated single strand DNA (HS-ssDNA) probe with 7551.3 Da molar mass and complementary target DNA with 6875.8 Da molar mass were 5′-SH-(CH2)6-TGCTGTTTGAAGATGCTGGTA-3′ and 5′-TACCAGCATCTT CAAACAGCA, respectively. All other reagents used in the experiments Electrochemistry Communications 48 (2014) 111–114 ⁎ Corresponding author at: Department of Micro- and Nanotechnology, Technical University of Denmark, Ørsteds Plads 345E, DK-2800 Kongens Lyngby, Denmark. Tel.: +45 45255890; fax: +45 45887762. E-mail address: xueling.quan@nanotech.dtu.dk (X. Quan). http://dx.doi.org/10.1016/j.elecom.2014.08.029 1388-2481/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom