Optical sensing of nanoparticles employing porous silicon thin films

Abstract

With the increasing consumption of nanomaterials in a variety of applications, our environment becomes more and more exposed to different kinds of (possibly toxic) nanomaterials having variable sizes and shapes, raising up the requirement to sense and monitor the presence of nanomaterials. Here, we propose and demonstrate a porous-silicon based optical sensing platform, capable of sensing nanoparticles of a given distribution of sizes and shapes, but independent of their chemical, mechanical, or electrical properties. A white light optical interference technique has been utilized to transduce nanoparticles trapped in the porous matrix into an optical signal. We have found an unusual optical sensing response that substantially increases the sensing bandwidth of the porous-silicon based optical sensor, which follows a Hill-equation type behavior that is characterized by a logarithmic response at low nanoparticle's concentration and saturation at high concentrations. These universal characteristics of the sensors are explained by the anomalous and limited diffusion of the nanoparticles via a quasi-1D geometry of the pore's matrix. Very low concentration of nanoparticles, of the order of few μg/ml, has been measured by this sensing technique.