Applied Surface Science 282 (2013) 709–713 Contents lists available at SciVerse ScienceDirect Applied Surface Science j ourna l ho me page: www.elsevier.com/locate/apsusc Surface modification of piezoelectric aluminum nitride with functionalizable organosilane adlayers Edmund Chan a , Nathan Jackson b , Alan Mathewson b , Paul Galvin b , Ali B. Alamin Dow c , Nazir P. Kherani c , Christophe Blaszykowski a , Michael Thompson a,∗ a Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada, M5S 3H6 b Tyndall National Institute, University College Cork, Lee Maltings, Cork, Ireland c Department of Electrical and Computer Engineering, University of Toronto, 10 King’s College Road, Toronto, Ontario, Canada, M5S 3G4 a r t i c l e i n f o Article history: Received 4 March 2013 Received in revised form 3 June 2013 Accepted 6 June 2013 Available online 14 June 2013 Keywords: Aluminum nitride Organosilane adlayer Surface modification Piezoelectric (bio)sensor a b s t r a c t The world of biosensors is expanding at a rapid pace with an ever-increasing demand for more sensitive miniaturized devices. Acoustic wave biosensors are not spared from this trend. In this domain, the search for enhanced sensitivity is increasingly oriented toward the rational design of new piezoelectric materials with superior properties to substitute for prevalent quartz. With respect to surface chemistry, construc- tion of the biorecognition element, more often than not, requires the use of bifunctional molecules that can spontaneously assemble on the substrate and form organic surfaces readily biofunctionalizable in a subsequent, ideally single step. In this context, we present herein the surface modification of aluminum nitride (AlN) with alkyltrichlorosilane cross-linking molecules bearing a functionalizable benzenethio- sulfonate moiety. This latter feature is next demonstrated through the straightforward, preactivation-free immobilization of thiolated biotin probes. To date, AlN has only received little attention in the field of piezoelectric biosensors despite its many attractive properties and the perspective to operate devices at ultra-high frequencies (GHz) with unprecedented sensitivity. To our knowledge, this work describes one of the first examples of direct surface derivatization of AlN with bifunctional trichlorosilane molecules. It also constitutes a first step toward the development of electrodeless GHz piezoelectric biosensing platforms based on AlN and trichlorosilane surface chemistry. © 2013 Elsevier B.V. All rights reserved. 1. Introduction In (bio)sensor technology, the conversion of (bio)chemical events into measurable signals requires the development of trans- ducing technologies capable of being interfaced with appropriate surface chemistry in an intimate overall structure. Among the var- ious sensor systems that have been engineered, those based on bulk acoustic wave (BAW) physics and the unique properties of quartz occupy a large place [1–3]. The traditional configuration is found in thickness shear mode (TSM) devices, which rely on the use of contact metal electrodes plated on a piezoelectric quartz substrate to instigate acoustic resonance, generally at 5 or 9 MHz [4]. Device sensitivity is frequency-dependent and can be expected to be enhanced from ∼ 18 to ∼ 5 ng cm -2 Hz -1 between these frequencies [4]. Thinning the quartz resonator (i.e., increasing its fundamental frequency) is indeed one option to enhance sensitiv- ity [5]. Another strategy consists in operating at higher harmonic that is at higher resonant frequency [5]. In our laboratory, we ∗ Corresponding author. E-mail address: mikethom@chem.utoronto.ca (M. Thompson). have successfully combined both features in the electromagnetic piezoelectric acoustic wave sensor (EMPAS) [5–11], an electrode- free new configuration in which resonance is remotely driven by an external electromagnetic field associated with a planar spiral coil placed at proximity to the quartz substrate [5,6]. The supe- rior analytical sensitivity of the EMPAS over the TSM was shortly demonstrated thereafter [6], so was the miniaturazability of the sensing platform, more recently [8]. Through harmonic tunability and the use of 20 MHz quartz substrates, the EMPAS can be oper- ated up to the ultra-high frequency of 1.06 GHz (53rd harmonic) [8,10], with a theoretical sensitivity of 21 pg cm -2 Hz -1 at this fre- quency. This represents an increase in sensitivity of three orders of magnitude compared to a conventional TSM device operated at 5 MHz. Even higher sensitivity (15 pg cm -2 Hz -1 ) was recently reported for a wireless-electrodeless quartz crystal microbalance (WE-QCM) biosensor working with 9.7 m-thick, 170 MHz quartz resonators [12]. In this case, resonance was generated by a line antenna placed outside the WE-QCM cell. An attractive but challenging alternative to develop electrode- free BAW biosensing platforms with high(er) sensitivity consists in replacing natural quartz with man-made materials possessing, among others, superior piezoelectric properties. We have already 0169-4332/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsusc.2013.06.039