Transforming diatomaceous earth into sensing devices by surface modification with gold nanoparticles

Diatomaceous earth, or diatomite, is produced through the accumulation of diatom (Bacillariophyceae) skeletons (i.e. cell walls called frustules) made of amorphous silica. The porous, highly symmetrical structure and microscopic size of diatom cell walls make them ideal constituents of sensing devices and analytical chips. Here, we propose chemical methods to purify diatom frustules extracted from diatomaceous earth. Using photo deposition techniques, we grow gold nanoparticles on the surface of diatom skeletons and within the pores of the skeletons, where the size and density of nanoparticles can be controlled by changing the parameters of the synthesis. Resulting devices have an internal porous structure that can harvest molecules from a solution, and an external shell of gold nanoparticles that amplifies the electromagnetic field generated by the measurement laser in Raman or other spectroscopies. The combination of these effects enables the analysis of biological specimens, chemical analytes and pollutants in extremely low abundance ranges. The devices were demonstrated in the analysis of Bovine Serum Albumin in water with a concentration of 100 aM, and mineral oil with a concentration of 50 ppm.