Sensors and Actuators A 298 (2019) 111584 Contents lists available at ScienceDirect Sensors and Actuators A: Physical j ourna l h o mepage: www.elsevier.com/locate/sna Love-wave devices with continuous and discrete nanocrystalline diamond coating for biosensing applications L. Drbohlavová a,b,∗ , L. Fekete a , V. Bovtun a , M. Kempa a , A. Taylor a , Y. Liu c , O. Bou Matar c , A. Talbi c , V. Mortet a,b a FZU - Institute of Physics of the Czech Academy of Sciences, Prague, Czech Republic b Czech Technical University, Faculty of Biomedical Engineering, Kladno, Czech Republic c Univ. Lille, Centrale Lille, UVHC, ISEN, LIA LICS/LEMAC, IEMN UMR CNRS 8520, F-59000, France a r t i c l e i n f o Article history: Received 3 May 2019 Received in revised form 10 August 2019 Accepted 2 September 2019 Available online 4 September 2019 Keywords: Love-waves Acoustic-wave devices Nanocrystalline-diamond Phase velocity COMSOL simulations ST-cut quartz a b s t r a c t The integration of diamond layers brings biocompatibility and enhanced stability of biomolecules to Love wave devices for promising biosensor applications. Love-Wave Surface Acoustic Wave (LW-SAW) devices consisting of an ST-cut quartz substrate with a silicon oxide layer coated by a thin diamond layer have been fabricated. The effect of nucleation and growth of diamond on the properties of LW-SAW devices was studied. The Love-wave phase velocity was shown to be affected by the diamond coating and dependent on its thickness. Experimental results are in a good agreement with simulations carried out with COMSOL Multiphysics software. Deposition of isolated diamond grains results in a reduction in velocity in the Love waves, which is attributed to a mass loading effect. Conversely, coalesced diamond layers increase the stiffness of the surface, which results in faster propagation of the Love waves. Improved entrapment of the Love waves in the guiding layer was observed in the case of isolated diamond grains, which should ensure higher sensitivity for this type of coating. Diamond coated LW-SAW devices can be used for biosensing applications with appropriated functionalization of the diamond surface. © 2019 Elsevier B.V. All rights reserved. 1. Introduction Due to their high frequency selectivity, Surface Acoustic Wave (SAW) devices have been widely used in signal processing in the telecommunication industry, such as in TV sets, mobile phones and base stations [1–3]. Apart from these applications, SAW devices are gaining importance for physical, chemical and biological detection [4] thanks to their high sensitivity, compact size, low fabrication cost as well as wireless capabilities [1,3]. With surface function- alization, SAW devices can be used for rapid, label-free pathogen detection and point-of-care testing devices [1,5,6]. As bacterial or pathogen detection is performed in aqueous or buffered solutions, acoustic waves have to be polarized, in order to reduce the waves attenuation caused by liquid loading. Rayleigh surface acoustic wave devices (RSAW) are commonly used for gas sensing. They suffer from high attenuation due to particle displace- ment perpendicular to the surface causing this acoustic energy to be radiated into the liquid. However, devices using pure shear hor- ∗ Corresponding author at: FZU, Institute of Physics of the Czech Academy of Sciences, Prague, Czech Republic. E-mail address: drbohlavova@fzu.cz (L. Drbohlavová). izontal (SH) waves with a displacement parallel to the surface do not have radiation losses [5,7,8]. Love-wave surface acoustic wave sensors (LW-SAW) are electromechanical sensors based on a piezo- electric delay line with metallic interdigital transducers (IDTs) with a thin wave-guiding top layer. IDTs generate and receive pure SH waves confined in a thin guiding layer with a lower acoustic wave velocity than the piezoelectric substrate’s bulk [9–11]. The veloc- ity and amplitude of Love waves is influenced by the variation of the mechanical properties of the media at the sensor’s surface [12]. To date, the most common piezoelectric substrates for the generation of SH waves are ST-cut quartz (acoustic shear wave velocity is 5060 m/s), 64 ◦ YX lithium niobate (∼4600 m/s) or 36 ◦ YX lithium tantalate (4212 m/s) [4,13]. Commonly used materials for fabrication of the guiding layer are amorphous SiO 2 (2850 m/s), polymethylmethacrylate (1200 m/s) or ZnO (2747 m/s) [10,14]. LW-SAW sensors fabricated by combinations of the mentioned materials were successfully used to detect different biological ana- lytes, such as uric acid [4], bacteriophages [15,16], Influenza A virus [17], E. coli l-asparaginase [18], or bacterial nucleic acids [19,20]. Diamond is an attractive material for bio-sensing applications because of its chemical inertness, bio-compatibility and prolonged stability of covalently attached biomolecules [21,22]. The novelty of this research is the integration of a thin diamond layer onto Love- https://doi.org/10.1016/j.sna.2019.111584 0924-4247/© 2019 Elsevier B.V. All rights reserved.