Investigation into the Optical Properties of Nanostructured Silica from Diatoms

Abstract

Abstract : The overall objective of this project was to investigate the optical properties of silica isolated from the unicellular algae known as diatoms. The diatom species used in this study were Cylindrotheca fusiformis, Cyclotella meneghiana, Navicula pelliculosa, and Nitzschia alba. Specific objectives were as follows: (1) grow the four different diatom species and prepare purified cell wall silica from them; (2) examine this material through scanning electron microscopy (EM) to determine overall cell dimensions and the dimensions of fine pores in the cell wall; (3) determine absorbance and fluorescence characteristics of the purified silica; (4) test a variety of dyes for their ability to stain diatom silica in vivo, and determine whether the dye treatment could survive the harsh acid treatment used for silica purification; and (5) determine whether material from any species had photonic band gap properties. Results show that two species had regularly repeating pore structures that could potentially generate photonic band gap phenomenon. Absorbance increased with decreasing wavelength, and fluorescence from native diatom silica was low. Out of 6 previously untested dyes, two, rhodamine B and rhodamine 6G, stained diatom silica. Rhodamine 123 was previously shown to stain diatom silica, and the authors showed that fluorescence of this dye survived the harsh acid treatment required to isolate the silica in pure form. Attempts to measure photonic band gap phenomenon from the silica were unsuccessful due to a high degree of scattering in the sample. (1 table, 4 figures, 8 refs.)