Sensors and Actuators B 182 (2013) 147–155 Contents lists available at SciVerse ScienceDirect Sensors and Actuators B: Chemical journal h om epage: www.elsevier.com/locat e/snb Enhanced dimethyl methylphosphonate (DMMP) detection sensitivity by lead magnesium niobate-lead titanate/copper piezoelectric microcantilever sensors via Young’s modulus change Qing Zhu a,1 , Wei-Heng Shih a , Wan Y. Shih b,∗ a Department of Materials Science and Engineering, Drexel University, Philadelphia, PA 19104, USA b School of Biomedical Engineering, Science, and Health System, Drexel University, Philadelphia, PA 19104, USA a r t i c l e i n f o Article history: Received 28 September 2012 Received in revised form 14 February 2013 Accepted 15 February 2013 Available online 6 March 2013 Keywords: Piezoelectric cantilever sensor Dimethyl methylphosphonate a b s t r a c t We have examined the detection of dimethyl methylphosphonate (DMMP) using lead magnesium niobate-lead titanate (PMN-PT) piezoelectric microcantilever sensor (PEMS) coated with various pla- nar and particulate receptor coatings. We showed that a two-order-of-magnitude enhancement in the flexural-mode resonance frequency shift, f, in DMMP detection that was not accountable for by mass loading alone could be achieved by using a planar Cu 2+ adsorbed 11-Mercaptoundecanoic Acid (MUA/Cu 2+ ) or planar 3-mercaptopropyltrimethoxysilane (MPS) coated PEMS. We also showed that the enhancement of f of PEMS was a result of the Young’s modulus change in the PMN-PT layer induced by the surface stress generated by the binding of DMMP on a continuous receptor coating. Furthermore, the Young’s modulus-change enhanced f in PEMS with a planar receptor coating was shown to be inversely proportional to the product of the average Young’s modulus and thickness of the PEMS and independent of the PEMS lateral dimension. We also showed that with an array of three PEMS, one uncoated, one coated with planar MUA/Cu 2+ and the other with planar MPS, the detection f pattern for DMMP was distinctively different from those of acetone and ammonia. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Chemical warfare agents (CWA) were used in World War I and resulted in 1.3 million casualties [1]. Since then they have been used in numerous incidents, for examples, sulfur mustard in the Iran–Iraq war, nerve agents against the Kurdish opposition in Iraq, and the attacks by Aum Shinrikyo sect in Japan [2]. After the 9–11 attack and the subsequent anthrax scare, use of CWA in terrorism activities has become a major homeland security concern and there has been an urgent need for rapid, real time, in situ CWA detections in both civilian and military environments. Current analytical techniques for nerve gas detection include gas chromatography–mass spectrometry [3], passive Fourier trans- form infrared spectroscopy [4], and Raman spectroscopy [5]. They are unsuitable for portable in situ detection. To meet the challenge, researchers have been working on a wide range of sensing tech- nologies, including electrochemical sensors [6–8], quartz crystal microbalance (QCM) [9–11], surface acoustic wave (SAW) devices ∗ Corresponding author. E-mail address: shihwy@drexel.edu (W.Y. Shih). 1 Current address: FUJIFILM Dimatix, Inc., 2250 Martin Avenue, Santa Clara, CA 95050, USA. [12–17], semiconducting metal oxide (SMO) devices [18–22], and microelectromechanical systems (MEMS) [23–34]. Despite that these techniques can provide relatively rapid and specific nerve gas detection, there are still limitations hindering their applica- tions. For example, SMO sensors require the detection be done at an elevated temperature. QCM and SAW are in the centime- ter size range, not ideal for array sensing. Although silicon-based microcantilever sensors have many advantages such as high sen- sitivity, rapid response, and array capability, they rely on a finely aligned optical system to detect less than sub-nanometer displace- ments for signal transduction, not suitable for portable detection [28,35]. Piezoelectric microcantilever sensors (PEMS) is a new type of sensors that consist of a highly piezoelectric layer bonded to a nonpiezoelectric layer whose mechanical resonance can both be excited and detected by simple electrical means. With receptors immobilized or coated on a PEMS surface, binding of target ana- lytes can shift a PEMS resonance frequency. Detection of target analytes is achieved by electrically monitoring the PEMS resonance frequency shift, offering the potential of real-time, in situ detection of chemical and biological systems including nerve gas. Earlier studies with piezoelectric cantilevers longer than 3 mm in length indicated that piezoelectric cantilevers were mass sen- sors [36] in that binding of analytes to the sensor surface changed 0925-4005/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2013.02.064