Analytica Chimica Acta 787 (2013) 36–49 Contents lists available at SciVerse ScienceDirect Analytica Chimica Acta jou rn al h om epage: www.elsevier.com/locate/aca Review Advanced vapor recognition materials for selective and fast responsive surface acoustic wave sensors: A review Adeel Afzal a,b,∗ , Naseer Iqbal a , Adnan Mujahid a,c , Romana Schirhagl a,d a Institute of Analytical Chemistry and Food Chemistry, University of Vienna, Waehringerstrasse 38, 1090 Vienna, Austria b Affiliated Colleges at Hafr Al-Batin, King Fahd University of Petroleum and Minerals, P.O. Box 1803, 31991 Hafr Al-Batin, Saudi Arabia c Institute of Chemistry, University of the Punjab, 54590 Lahore, Pakistan d Department of Physics, ETH-Zurich, Schafmattstrasse 16, 8093 Zurich, Switzerland h i g h l i g h t s • Surface acoustic wave (SAW) sensors for detection of organic vapors are presented. • A variety of materials used as vapor recognition layers on SAW devices are reviewed. • Limitations and challenges of SAW organic vapor sensors are discussed. • The directions for future exploratory research in SAW vapor sensors are identified. g r a p h i c a l a b s t r a c t a r t i c l e i n f o Article history: Received 21 January 2013 Received in revised form 18 April 2013 Accepted 2 May 2013 Available online 13 May 2013 Dedicated to Prof. Franz L. Dickert on the occasion of his 70th birthday. Keywords: Carbon nanotubes Molecular recognition Nanomaterials Polymers Surface acoustic wave Vapor sensors a b s t r a c t The necessity of selectively detecting various organic vapors is primitive not only with respect to regular environmental and industrial hazard monitoring, but also in detecting explosives to combat terrorism and for defense applications. Today, the huge arsenal of micro-sensors has revolutionized the tradi- tional methods of analysis by, e.g. replacing expensive laboratory equipment, and has made the remote screening of atmospheric threats possible. Surface acoustic wave (SAW) sensors – based on piezoelectric crystal resonators – are extremely sensitive to even very small perturbations in the external atmosphere, because the energy associated with the acoustic waves is confined to the crystal surface. Combined with suitably designed molecular recognition materials SAW devices could develop into highly selective and fast responsive miniaturized sensors, which are capable of continuously monitoring a specific organic gas, preferably in the sub-ppm regime. For this purpose, different types of recognition layers ranging from nanostructured metal oxides and carbons to pristine or molecularly imprinted polymers and self- assembled monolayers have been applied in the past decade. We present a critical review of the recent developments in nano- and micro-engineered synthetic recognition materials predominantly used for SAW-based organic vapor sensors. Besides highlighting their potential to realize real-time vapor sensing, their limitations and future perspectives are also discussed. © 2013 Elsevier B.V. All rights reserved. Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2. SAW sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 2.1. History and merits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 ∗ Corresponding author. Tel.: +966 03 722 4958x2263; fax: +966 03 722 6149. E-mail addresses: aa@aafzal.com, dr.adeelafzal@gmail.com (A. Afzal). URL: http://www.aafzal.com (A. Afzal). 0003-2670/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.aca.2013.05.005