Real time device for biosensing: design of a bacteriophage model using love acoustic waves O. Tamarin a , S. Comeau b , C. De ´jous a, *, D. Moynet c , D. Rebie `re a , J. Bezian c , J. Pistre ´ a a IXL (CNRS UMR 5818-ENSEIRB-Universite ´ Bordeaux1), 351 Cours de la Libe ´ration, 33045 Talence, France b Cellule Adera/Bordeaux2 (Universite ´ Victor Segalen/Bordeaux2), 146 Rue Leo Saignat, 33076 Bordeaux, France c Immunologie Mole ´culaire et Parasitologie (Universite ´ Victor Segalen/Bordeaux2), 146 Rue Leo Saignat, 33076 Bordeaux, France Received 15 May 2002; received in revised form 27 November 2002; accepted 17 December 2002 Abstract Love wave sensors (ST-cut quartz substrate with interdigital transducers, SiO 2 guiding layer and sensitive coating) have been receiving a great deal of attention for a few years. Indeed, the wave coupled in a guiding layer confers a high gravimetric sensitivity and the shear horizontal (SH) polarization allows to work in liquid media. In this paper, an analytical method is proposed to calculate the Love wave phase velocity and the gravimetric sensitivity for a complete multilayer structure. This allows us to optimize the Love wave devices design in order to improve their gravimetric sensitivity in liquid media. As a model for virus or bacteria detection in liquids (drinking or bathing water, food...) we design a model using M13 bacteriophage. The first step is the anti-M13 (AM13) monoclonal antibody grafting, on the device surface (SiO 2 ). The second step is an immunoreaction in between the M13 bacteriophage and the AM13 antibody. The Love wave device allows to detect in real time the graft of the AM13 sensitive coating, as well as the immobilization of the M13 bacteriophages. With a pH change, the M13 bacteriophages can be removed from the sensor surface, in order to be numerated as plaque forming unit (pfu). Results on the sensitivity of Love waves are compared with similar immunological works with bulk acoustic wave devices, and demonstrate the high potentialities of Love waves sensors. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Biosensors; Immunodetection; Love wave; Real time detection 1. Introduction Nowadays, the field of sensors receives a great deal of attention, related to the growing market for specific detection tests in medical applications, food industries or environment. This kind of test needs devices that could work in a liquid medium. Moreover, an interest- ing challenge is to realize portable devices at low cost in order to make in situ measurement. For these reasons acoustic wave sensors in the field of gas and liquid medium detection received a big interest from the international scientific community as they can collect the previous interesting properties. Ballantine et al. (1997) published a book on acoustic sensors in 1997. In the biosensors domain, the first acoustic wave device able to work in liquid medium was quartz crystal microbalance (QCM). And nowadays, several authors use these acoustic devices for biological detections (Miura et al., 1993; Uttenthaler et al., 2001). The evolution of microtechnologies allows to investigate other types of acoustic wave devices. Among them, Shear Horizontal Acoustic Plate Mode (SH-APM) received a particular attention a few years ago (Dahint et al., 1996). They offered several advantages but were limited by a weak sensitivity. In the last years, a powerful device in term of sensitivity appeared: Love waves. Indeed, the wave energy trapping in a guiding layer confers a good sensitivity and the shear horizontal (SH) polarization allows to work in liquid media. For a (bio)chemical detection application, a sensitiveoverlay, specific to the species to detect, is added. Mounted in an oscillator * Corresponding author. Tel.:  /33-5-56-842848; fax:  /33-5-56- 371545. E-mail address: dejous@ixl.u-bordeaux.fr (C. De ´jous). Biosensors and Bioelectronics 18 (2003) 755 /763 www.elsevier.com/locate/bios 0956-5663/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0956-5663(03)00022-8