17th International Meeting on Chemical Sensors - IMCS 2018 406 Silver nanoplates on graphite substrates for ultrasensitive and label free Surface-Enhanced Raman Scattering (SERS) based detection of organophosphorous nerve agents in gas phase M. Lafuente 1 , D. Sanz 1 , M. Urbiztondo 2 R. Mallada 1,3 , M.P. Pina 1,3 , J. Santamaría 1,3 1 Nanoscience Institute of Aragon, University of Zaragoza, Department of Chemical & Environmental Engineering, Edif. I+D+i, Campus Rio Ebro, C/Mariano Esquillor, s/n, 50018 Zaragoza, Spain. 2 Centro Universitario de la Defensa de Zaragoza, 50090 Zaragoza, Spain 3 Networking Research Center on Bioengineering, Biomaterials and Nanomedicine, CIBER-BBN, 28029 Madrid, Spain. mapina@unizar.es Abstract A surface-enhanced Raman scattering (SERS)-based sensor has been developed for the label-free real-time gas phase detection of dimethyl methylphosphonate (DMMP); a surrogate molecule of the G- series nerve agents which are of particular concern due to its extreme toxicity, persistence and previous deployment. In particular, SERS substrates based on high density Ag nanoplates (LSPR at 700 nm) monolayers on graphite have been straightforwardly attained by electrostatically-driven adsorption technique. Unlike Au based counterparts, SERS measurements suggest the chemisorption of DMMP molecules to the Ag nanoplate surface, eventually leading to photoinduced decomposition products. These SERS substrates have demonstrated the capability for the reliable identification of DMMP in gas phase at 2.5 ppmV, with the advantages of simple operation and low cost. Key words: SERS, neurotoxic agents identification, gas phase, real time detection, sub-ppmV Introduction The G-series nerve agents, i.e. Tabun (GA), Sarin (GB), Soman (GD), are widely recognized as one of the most toxic group of chemical warfare agents (CWA) due to the presence of organophosphorus esters causing systemic effects predominantly on the central nervous system. Nowadays, the competing technologies for the rapid detection of chemical agents in gas phase face severe limitations in terms of specificity, portability, cost and simplicity. SERS is one of the leading techniques for label- free ultrasensitive vibrational fingerprinting of a variety of molecular compounds [1]. In the field of explosives and chemical threat detection [2- 3], SERS has been identified as key technology thanks to distinctive features such as: ultrahigh sensitivity, detection from a wide variety of matrices and quantification of multiple species in a single measurement, allowing real time detection in the field. SERS detection at trace concentration levels in gas phase is hampered by the fact that only a few molecules of interest are localized in very close vicinity (typically less than 10 nm) of the metal when localized surface plasmon nodes are excited. Many strategies address this problem, including the use of partition layers with low affinity and rapidly reversible binding sites [4-5] or the formation of stable complexes on the plasmonic surface [6]. In this work, real time SERS identification of DMMP has been demonstrated with Ag nanotriangle monolayers on graphite at 2.5 ppmV concentration. Their sensing performance has been assessed by comparison with Au based SERS substrates, already developed in our group [4]. Preparation and Characterization of SERS substrates The citrate capped Ag nanotriangles were synthesized according to published recipe [8]. The average edge length of Ag nanoplates is 38 nm (see Fig. 1) with the LSPR centred at 700 nm. The Ag assembly process was performed on graphite substrates previously coated with PDDA according to our previous works [4-5]. Graphite provides both DOI 10.5162/IMCS2018/AP4.3