FUNCTIONALIZED BIOINSPIRED MICROSTRUCTURED OPTICAL FIBER PORES FOR APPLICATIONS IN CHEMICAL VAPOR SENSING

Open Access
Author:
Calkins, Jacob Andrew
Graduate Program:
Chemistry
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
February 22, 2011
Committee Members:
  • John V Badding, Dissertation Advisor
  • John V Badding, Committee Chair
  • James Bernhard Anderson, Committee Member
  • Christine Dolan Keating, Committee Member
  • Venkatraman Gopalan, Committee Member
Keywords:
  • Light Scattering
  • Microstructured Optical Fibers
  • SERS
  • Waveguide Raman
  • Self-assembled Monolayers
Abstract:
Chemical vapor sensing for defense, homeland security, environmental, and agricultural application is a challenge, which due combined requirements of ppt sensitivity, high selectivity, and rapid response, cannot be met using conventional analytical chemistry techniques. New sensing approaches and platforms are necessary in order to make progress in this rapidly evolving field. Inspired by the functionalized nanopores on moth sensilla hairs that contribute to the high selectivity and sensitivity of this biological system, a chemical vapor sensor based on the micro to nanoscale pores in microstructured optical fibers (MOFs) was designed. This MOF based chemical vapor sensor design utilizes MOF pores functionalized with organic self‐assembled monolayers (SAMs) for selectivity and separations and a gold plasmonic sensor for detection and discrimination. Thin well‐controlled gold films in MOF pores are critical components for the fabrication of structured plasmonic chemical vapor sensors. Thermal decomposition of dimethyl Au(II) trifluoroacetylacetonate dissolved in near‐critical CO2 was used to deposit gold island films within the MOF pores. Using a 3‐mercatopropyltrimethoxysilane adhesion layer, continuous gold thin films as thin as 20‐30 nm were deposited within MOF pores as small as 500 nm in diameter. The gold island films proved to be SERS active and were used to detect 900 ppt 2,4 DNT vapor in high pressure nitrogen and 6 ppm benzaldehyde. MOF based waveguide Raman (WGR), which can probe the air/silica interface between a waveguiding core and surrounding pores, was developed to detect and characterize SAMs and other thin films deposited in micro to nanoscale MOF pores. MOF based WGR was used to characterize an octadecyltrichlorosilane (OTS) SAM deposited in 1.6 μm diameter pores iv to demonstrate that the SAM was well‐formed, uniform along the pore length, and only a single layer. MOF based WGR was used to detect a human serum albumin monolayer deposited on the OTS SAM and monitor in‐situ the combustion of an OTS SAM in high pressure oxygen. Light scattering, an optical characterization technique that provides ellipsometric data from micro to nanoscale cylinders, was developed in order to characterize highly smooth wires and MOF pores. Clean, bare gold wires etched from MOF pore templates were found to have angle dependent Ψ and Δ values that agree with numerically calculated and finite element modeled values over the full 340o angular collection range. Light scattering was shown to be sensitive to ellipticities in the cross‐section of silica, gold, and silicon wires down to 1%. Using alkanethiol SAMs deposited on gold wires, light scattering was demonstrated to be able to detect films as thin as 1.5 nm, and able to distinguish between a decanethiol (1.5 nm) and an octadecanethiol SAM (2.7 mn). The high sensitivity of light scattering will allow it to characterize SAMs and thin films on the inner surfaces of MOF pores. WGR and light scattering provide the analytical tools that will allow for the further development of organic SAMs and thin films within MOF pores for analyte selectivity and chromatographic separations. This high selectivity combined with the sensitivity of a 3‐ dimensional nanostructured gold plasmonic sensor allows for the fabrication of a chemical vapor sensor inspired by the field performance of moth sensilla hairs.