Tellurium Based Glasses for Bio-Sensing and Space Applications

Abstract

Te2As3Se5 (TAS) fibers are often used in bio-sensing applications requiring direct contact between the fiber and live cells. However, the toxicity and stability of chalcogenide glasses typically used in such bio-sensing applications are not well known. The stability and toxicity of TAS glass fibers were therefore examined. The surface of TAS fibers stored for up to three years in air were analyzed using X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICP-MS), and atomic force microscopy (AFM). It is shown that an oxide layer develops on the surface of TAS fibers stored in air. This oxide layer is highly soluble in water and therefore easily removed. Additional studies using cyclic voltammetry show that the fresh TAS glass surface is insoluble in water for at least a few days, and attenuation measurements show that oxidation does not affect the transmission properties of the glass fibers. It was also determined that old, oxidized fibers pose a toxic threat to cells, while washed and new fibers show no toxic effect. Therefore, it is concluded that a soluble oxide layer forms on the surface of TAS fibers stored in air and that this layer has a toxic effect on cells in an aqueous environment. However, through etching, the oxide layer and the toxicity can be easily removed.In other applications of telluride glasses, such as the search for possible signs of life on exoplanets, a glass transmitting further into the IR is required in order to detect molecules, such as CO2. A new family of Tellurium based glasses from the Ge-Te-I ternary system has therefore been investigated for use in space and bio-sensing applications. A systematic series of compositions has been synthesized in order to explore the ternary phase diagram in an attempt to optimize the glass composition for the fiber drawing and molding process. The resulting glass transition temperature range lies between 139°C and 174°C, with deltaT values between 64°C and 124°C. The most stable glass composition was found to be Ge20Te73I7. The Ge-Te-I glasses were found to have an effective transmission window between 2-20 microns, encompassing the region of interest for the identification of biologically relevant species such as carbon dioxide. Furthermore, the successful fibering and molding of the composition Ge20Te73I7 are shown. Lastly, an investigation into glass conductivity was completed resulting in a maximum conductivity value on the order of 10^-4 Ohm-1 cm-1 for the composition Ge20Te73I7.In an attempt to take advantage of the high conductivity of telluride glasses, a new approach to virus detection in an aqueous environment has been developed using the electrophoretic deposition of protein and viruses on the charged glass surface for in situ infrared characterization and identification. A proof of concept experiment has been completed using a germanium ATR plate and an indium tin oxide (ITO) plate as the experimental electrodes. Charged proteins and viruses were driven to the surface of the oppositely charged germanium ATR crystal, once a potential was applied to the system. FTIR/ATR spectroscopy was used before and throughout electro-deposition to enable the in situ observation of the deposition with time. This technique resulted in the successful deposition and removal of the protein Bovine Serum Albumin (BSA), and deposition of the virus MS2, a bacteriophage that infects only bacteria, with an applied voltage of only 1.1V. Furthermore, based on analysis of the ATR spectra, distinct spectral features were identified for the protein and virus showing the potential for identification and characterization of biological molecules in an aqueous environment. A Ge20Te73I7 ATR plate was synthesized but unsuccessfully applied as an electrode in these experiments, likely due to an inconsistent conductivity along the plate. A glass from the Ge-As-Te system with a lower but more consistent conductivity was thereafter synthesized and successfully used as an electrode and sensing element in the electro-deposition experiment.