Surface plasmons resonance technique for the detection of nicotine in cigarette smoke T. Abdallah a,* , S. Abdalla b , S. Negm b , H. Talaat a a Department of Physics, Faculty of Science, Ain Shams University, 62 Abbas Elakkad Nasr City, Cairo 1615, Egypt b Department of Physics and Mathematics, Faculty of Engineering, Zagazig University (Shoubra), Cairo, Egypt Received 3 December 2001; received in revised form 31 August 2002; accepted 7 October 2002 Abstract We have employed the surface plasmon resonance (SPR) as a sensor technique for the selective detection of nicotine in real time. The SPR was generated via a prism coupler in a Kretschmann configuration where Ag films of thickness 40 to 42:5  0:5 nm were evaporated on the base of the prism. The active material for the interaction with nicotine is a thin film of dioctyl phthalate (DOP) with sodium–tetraphenylborate or DOP with nicotine–tetraphenylborate or DOP only deposited on the Ag film. The angular scan for attenuated total reflection (ATR) spectra shows a shift of the SPR maximum coupling angle and a broadening of the Lorentzian line shape, due to the interaction of nicotine molecules with the active layer. The observed data shows that the SPR technique is a fast and accurate method for the detection of nicotine in air due to cigarette smoke. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Surface plasmon; Thin film; Nicotine 1. Introduction The surface plasmon (SP) sensors [1] offers a sensitive monitoring system for environmental control and that of polluting agent, that responds with perfect and instantaneous selectivity to a particular target chemical substance, in our case nicotine molecules. Such chemical sensor functions by detecting and rapidly responding to the presence or con- centration of an analyte at the interface between the sensor and the sample matrix or gas. Though nicotine in cigarette smoking is considered to be stimulator for adrenaline but it has a sedative effect and may eventually lead to addiction. Nicotine also could be toxic and may lead to nicotine poisoning. The main source of nicotine is tobacco, and is reported to account for one-third of all cancer [2]. Previous work to detect nicotine [3] involved a complex system of liquid membrane electrode based on the use of ion-association complexes of nicotinium cation with tetra- phenylborate counter anions in nitrobenzene solvent as ion- exchange sites. In this work, we have employed a more simple system of surface plasmon resonance (SPR) optical technique that uses an inherently surface phenomenon for the detection of the chemical interactions, which has been used with great interest during the last two decades [1]. Surface plasmon polaritons [4] are interface electromag- netic modes propagating along the interface between two different media, where one of the media is a metal and the other is a dielectric (e.g. air). The dispersion relation for a surface plasmon propagating along the interface is given by k SP ¼ o c   ðe m ðoÞe a Þ ðe m ðoÞþ e a Þ   1=2 (1) where k SP is the complex wave vector, o the angular fre- quency, c the velocity of light, e m (o) the complex dielectric constant of the metal, and e a is the dielectric constant of the ambient (1). These (EM) modes propagate in a wave like manner along the interface between two media but decrease exponentially in amplitude with distance from the interface, i.e. surface EM modes involving photons coupled to surface plasmons [4]. It is, however, not possible to set up a surface plasmon at the interface by using a direct reflection technique, i.e. with light incident from the ambient (the less dense medium) because k SP in Eq. (1) is always larger than the wave vector in the ambient, k a ¼ðo=cÞðe a Þ 1=2 . One way to overcome the problem is to employ the attenuated total reflec- tion (ATR) technique in the Kretschmann configuration [5]. Sensors and Actuators A 102 (2003) 234–239 * Corresponding author. Tel.: þ20-101-505001; fax: þ20-248-42560. E-mail address: tam16mar@hotmail.com (T. Abdallah). 0924-4247/03/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved. PII:S0924-4247(02)00390-4