Nanosensors: From near field to far field applications

The DoD Center for Chemical Sensors Development at the University of Puerto Rico-Mayaguez has worked in developing sensors for threat agents for over 8 years. Work has continued under the ALERT DHS Center of Excellence. The approaches for sensing have covered many types of threat chemicals and some types of biological simulants, including high energetic materials, homemade explosives, mixtures and formulations, chemical agents simulants, toxic industrial chemicals and spore forming microorganisms. Sensing in the far field has been based in vibrational spectroscopy: Raman and infrared. Near field detection has been mainly based on nanotechnology enabled sensing platforms for Surface Enhanced Raman Scattering. Initial use of colloidal suspensions of silver and gold nanospheres eventually evolved to metallic and metal oxide nanorods and to particle immobilization, including sample smearing on substrates and drop-on-demand thermal inkjet printing of nanoparticles. Chemical reduction of metal ions has been substituted by clean photonic physical reduction that leaves the nanoactive surface highly exposed and overcomes the physico-chemical problem of double electrical layers posed by colloidal suspensions of nanoparticles. New avenues have open wide research endeavors by using laser techniques to form nanoprisms and interference based metallic nano-images and micro-images. UV based metal reduction on top of metal oxides nanostructures promises to provide the selectivity and sensitivity expected for the last 30-40 years. Various applications and experimental setups will be discussed.