Nanotechnology-Based Detection of Explosives and Biological Agents Simulants

Nanotechnology based detection of threat agents, such as explosives and biological agents, has been a top research priority at the Center for Chemical Sensors Development at the Department of Chemistry of the University of Puerto Rico-Mayaguez (UPRM). Nanoparticles are of fundamental interest since they possess unique size-dependent properties are quite different from the bulk state. When a bulk metal is reduced in size, its properties begin to change dramatically because the constituent electrons begin to suffer the effects of quantum confinement. One of these important properties deals with the extraordinary enhancement of the intensities of Raman scattering events in chemical systems called surface enhanced Raman scattering (SERS). Until very recently, only aromatic moieties containing strong chromophores or highly delocalized pi electrons would experience such an enhancement, when in close proximity to a silver or gold nanometallic assembly. In other cases, this SERS condition was not sufficient to satisfy the enhanced Raman scattering requirements because of Coulombic repulsions do not allow an intimate contact with the colloidal suspension of nanoparticles. Recent work in the research group includes optimization of particle size, agglomeration rate and ionic strength of the SERS active aqueous colloidal metallic suspensions. Results have led to extend existing benchmarks limits of detection of 10^-7 M to 10^-8 M (10^-15 g) in DNT and to 10^-12 M (10^-19 g) in the case of TNT. Other works include preparation and testing of bimetallic nano-interalloys: Au/Ag and metallic-semiconductor SERS active colloidal substrates: Ag/TiO₂. Group members have prepared silver and gold nanorods and nanolayers in an effort to change the sensing platform: from aqueous media to solventless detection.