Research Letter Simultaneous insulation and modification of quartz tuning fork surface by single-step plasma polymerization technique with amine-rich precursors Gizem Kaleli Can, Hatice Ferda Özgüzar, and Gözde Kabay, Plasma Aided Biomedical Research Group (pabmed), Biomedical Engineering Division, Graduate School of Science and Technology, TOBB University of Economics and Technology, Ankara 06560, Turkey Pelin Kömürcü, Plasma Aided Biomedical Research Group (pabmed), Micro- and Nano-Technology Division, Graduate School of Science and Technology, TOBB University of Economics and Technology, Ankara 06560, Turkey Mehmet Mutlu, Biomedical Engineering Department, Engineering Faculty, Plasma Aided Biomedical Research Group (pabmed), TOBB University of Economics and Technology, Ankara 06560, Turkey Address all correspondence to Mehmet Mutlu at m.mutlu@etu.edu.tr (Received 3 February 2018; accepted 13 April 2018) Abstract Amine-based plasma polymer thin films (NH 2 -PPTFs) are favorable due to their potential ability for binding a variety of biomolecules, especially in biotechnologic studies. In this context, to understand the effect of different amine sources on quartz tuning forks’ (QTF) surface function- alization and isolation, we prepared PPTFs by single-step plasma polymerization process. The amino-group concentration of PPTF’s was pro- portionally increased by increasing discharge powers, whereas not affected from exposure time. It was observed that the resistivity increased with the increasing molecular weight of the precursor. In conclusion, NH 2 -PPTF-modified QTFs present as a great candidate for future bio- technologic applications. Introduction The plasma polymerization technique is a commonly used method to achieve tailor-made and ångström (Å) scale thin films. Plasma polymerization offers easily controllable, environmentally friendly, and inexpensive processing of various materials when compared with the wet chemical methods. It is known that the plasma-polymerized thin films (PPTFs) have a random network and highly cross- linked film density. [1,2] These advantageous properties make this technique a distinguished candidate for biotechno- logic applications. [3] Ideally, thin films must possess some properties such as high stability, slow aging process, and uniformity. [4–6] So far, to achieve these features, precursors such as ethylenediamine, [5,7,8] amylamine, [2,3] heptylamine, [9] cyclopropylamine, [10] trans-1,2- diaminocyclohexane [11–13] were studied by employing plasma polymerization and amine-based PPTFs (NH 2 -PPTFs) have been produced for biotechnologic applications because of pro- viding covalent bonding with biomolecules such as proteins, enzymes, or living cells. [4,14] In order to achieve an active surface for biomolecule immobilization, amine-rich coatings are crucial, especially in biosensing studies. [15] Among biosensing technologies, mass sensitive devices are highly preferred due to their high precision and sensitivity. Although piezoelectric-based quartz crystal (QC) transducers are highly used for the preparation of mass sensitive biosensor infrastructures, quartz tuning forks (QTFs) are more advantageous due to their high-frequency stability, sharp frequency response, low response time, high-quality factor (Q F ) (at vacuum ∼10 3 –10 5 ), [16,17] and cost-effectiveness compared with QC microbalances. However, the main challenge with QTFs is their inability to work in liquids with high dielectric permeability due to short circuit. Any insulation or passivation layer can over- come this problem, and then QTFs can be used in any liquid medium. So far, no reports have been published about the insula- tion and functionalization of QTFs by plasma polymerization technique. With this motivation, for the first time in the literature, the effect of plasma-polymerized amine-rich thin films over QTF surfaces were investigated. Precursors, amylamine (amy), n-heptylamine (hep), or diaminocyclohexane (dach), were selected for simultaneous electrical insulation and surface functionalization. Experiments were performed in radio frequency-generated low-pressure plasma (RF/LP) and low- frequency-generated low-pressure plasma (LF/LP) systems, respectively. Processing parameters were modulated with respect to characterization studies and frequency shifts. Experimental QTF modification and insulation via plasma polymerization Substrates were selected as QTF prongs and third-class soda lime glass microscope slides for plasma modification. All contact angle (CA) measurements were conducted on glass microscope MRS Communications (2018), 8, 541–549 © Materials Research Society, 2018 doi:10.1557/mrc.2018.79 MRS COMMUNICATIONS • VOLUME 8 • ISSUE 2 • www.mrs.org/mrc ▪ 541 https://doi.org/10.1557/mrc.2018.79 Downloaded from https://www.cambridge.org/core. TOBB, on 16 Jan 2019 at 10:18:18, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.