Sensors and Actuators B 175 (2012) 173–178 Contents lists available at SciVerse ScienceDirect Sensors and Actuators B: Chemical journa l h o mepage: www.elsevier.com/locate/snb Love-wave sensor array to detect, discriminate and classify chemical warfare agent simulants D. Matatagui a , M.J. Fernández a , J. Fontecha a , J.P. Santos a , I. Gràcia b , C. Cané b , M.C. Horrillo a,∗ a Instituto de Física Aplicada, CSIC, Serrano 144, 28006 Madrid, Spain b Instituto de Microelectrónica de Barcelona, CSIC, Campus UAB, 08193 Bellaterra, Spain a r t i c l e i n f o Article history: Received 30 September 2011 Received in revised form 7 February 2012 Accepted 20 February 2012 Available online 27 February 2012 Keywords: Love wave Gas sensor SAW Chemical warfare agent (CWA) Sensor array a b s t r a c t An array made up of Love wave sensors based on quartz/SiO 2 is proposed as a detection system for chem- ical warfare agents (CWA). The array is composed of one reference and six devices coated with different polymers means of spray coating technique. The system has been tested with well-known CWA simu- lants: dimethylmethyl phosphonate (DMMP), dipropyleneglycol methyl ether (DPGME), dimethylmethyl acetamide (DMA), dichloroethane (DCE), dichloromethane (DCM), and dichloropentane (DCP), detecting very low concentrations, such as 40 ppb of DMMP, a simulant of sarin nerve gas. Additionally, principal component analysis (PCA) as a data pre-processing and discrimination technique, and probabilistic neural networks (PNN) as a pattern classification technique, have been applied, obtaining a clear discrimination and a correct classification. © 2012 Elsevier B.V. All rights reserved. 1. Introduction During the last years, it has been demonstrated that the chem- ical warfare agents (CWAs) are powerful weapons and a threat for civil safety in the industrial countries. These chemical agents can be developed in an easy way from chemical products that are usu- ally used in the industries, which are not difficult to get for any citizen. In addition, these weapons are extremely aggressive for human health. CWA have been used twice in Japan, 1994 in Matsumoto and in 1995 in Tokyo, where the citizens were attacked with the sarin gas [1]. Others chemical warfare agents as distilled mustard (HD), nitro- gen mustard (HN) phosgene (CG), and soman (GD) are potential threats to public health. The need to control these weapons has led to the use of some techniques such as chromatography, mass spectrometry or ion mobility spectroscopy [2,3]. A suitable gas sensor array can detect concentrations below the median lethal dose of these agents (LD50: dose required to kill half the members of a tested population) in real time and in situ. Arrays of acoustic wave devices are widely used in sensing appli- cation, such as medical analysis [4,5], environmental fields [6] and food quality [7–9]. Some types of acoustic wave sensors [10–16] are: quartz crystal microbalances, devices based on Rayleigh waves, ∗ Corresponding author. Tel.: +34 91 5618806; fax: +34 91 5631794. E-mail address: carmenhorrillo@ifa.cetef.csic.es (M.C. Horrillo). acoustic plated modes, transverse surface waves and Love waves. Love wave sensors [17–19] are suitable to detect CWAs due to the high sensitivity, fast response, real time detection, stability and low cost. Chemical warfare agents are really dangerous and for security reasons are only measured in especial installations. Therefore, CWA simulants have been used instead of these ones, which closely mimic the chemical structures of real CWA without their associated toxicological properties [20–23] 2. Materials and methods 2.1. Love-wave devices Our Love-wave devices (Fig. 1) are delay lines (DL) with size 9 mm × 4 mm × 0.5 mm and two ports. They are based on a shear horizontal surface acoustic wave (SH-SAW) propagated on the ST-cut quartz perpendicular to the x crystallographic axis. This SH- SAW, with a wavelength  = 28 m, is generated and detected by interdigital transducers (IDTs) which are made by standard litho- graphic technique depositing a 200 nm thickness aluminum layer by mean of RF sputtering. A double electrode structure is repeated 75 times (N = 75) to form each IDT [24]. The spacing center to cen- ter between IDTs, Lcc, is 150  and the acoustic aperture, W, is 75 . Finally, the SH-SAW is guided in a film of SiO 2 deposited by plasma- enhanced chemical vapor deposition (PECVD) in order to obtain a Love wave. The highest sensitivity is found for a thickness of SiO 2 of about 3 m, being the synchronous frequency around 163 MHz. 0925-4005/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2012.02.061