Selective Detection of Chemical and Biological Toxins Using Gold-Nanoparticle-Based Two-Photon Scattering Assay

Possible terrorist threats on water supplies are causes for concern given the easy availability of numerous biological and chemical toxins that could be used by a terrorist organization. In this article, we report gold-nanoparticle-based two-photon light-scattering (TPS) assay, for the label-free detection of arsenic and Salmonella bacteria separately, with excellent detection limit and selectivity over other analytes. Our experimental results show that arsenic can be detected quickly and accurately without any tagging, in 100-ppt level with excellent discrimination against other heavy metals. We have demonstrated that our TPS assay is capable of measuring the amount of arsenic in Bangladesh, West Bengal, and Nevada well water as well as in Mississippi river water. We have also shown that gold-nanoparticle-based TPS assay are capable for label-free detection of Salmonella typhimurium (S. typhimurium) with excellent detection limit (10³ bacteria/mL) and high selectivity over other pathogens. The mechanism of TPS assay working principle has been discussed. Our results demonstrate the potential for a broad application of nanotechnology in practical defense applications.