Home
Tags
No Tags
DEVELOPMENT OF SPECTROELECTROCHEMICAL WAVEGUIDE SENSORS
| Title: | DEVELOPMENT OF SPECTROELECTROCHEMICAL WAVEGUIDE SENSORS |
| Author: | Ross, Susan E |
| Description: | Incorporation of planar waveguide technology into spectroelectrochemical sensors with trimodal selectivity (partitioning, electrochemistry and spectroscopy) is described. The main advantage of planar waveguides is enhanced sensitivity due to the increased number of reflections over a multiple internal reflection (MIR) optic. Three planar waveguide designs have been fabricated and evaluated. In order of discussion, the three waveguide candidates are 1. an indium tin oxide (ITO) coated K+/Na+ ion-exchanged BK7 graded-index slab 2. an ITO coated GeO2-SiO2 step-index slab and 3. a gold coated K+/Na+ ion-exchanged BK7 graded-index channel. ITO or Au served as the electrode. The first candidate was selected since this design most closely resembled the prototype MIR optic, with which the sensor concept was successfully demonstrated earlier. In choosing GeO2-SiO2 as one of the waveguide designs, we wanted to reapply this telecommunication-oriented material for chemical sensing, especially in the near-UV wavelength region. The channel waveguide was of interest because of its possible microfabrication. In addition to the waveguide designs, alternative coupling methods to prism couplers were explored. Based on the fabrication scheme of Ramos, Choquette and Fell (Anal. Chem. 1996, 68, 1245), an embossed UV-cured polymer grating has been made and showed excellent results compared with our current sensor that is prism-coupled. Evaluation of the waveguide candidates was two-part: optical and spectroelectrochemical. We compared the optical properties, such as the refractive index, and the number of modes, at a near-UV wavelength of 441.6 nm (HeCd laser) for optical sensing of Fe(CN)6-3, a benchmark analyte in the demonstration of the selectivity concept, and at 632.8 nm (HeNe). All the waveguides that were fabricated were found to be multimode (3-5 modes) at both wavelengths. For demonstration of electromodulation of the optical signal with all three waveguide sensors, the chosen redox couple, Fe(CN)6-4/-3 partitioned into the anionic-selective film, poly(dimethyldiallylammonium chloride)-silica, which was spin-coated on the waveguide sensor, electrolyzed, and detected by ATR (attenuated total reflection). Only the ITO IE BK7 slab waveguide was shown to be quantifiable. Increased sensitivity and lower detection limits by several orders in magnitude, however, were achieved with the GeO2-SiO2 waveguide (vs. MIR optic). Attenuation of light by ITO, a potential-induced optical modulation of the electrode (ITO and Au), and film deposition were fabrication issues that were encountered with the different designs. |
| Permanent Link: |
http://rave.ohiolink.edu/etdc/view?acc_num=ucin971364855
http://hdl.handle.net/2374.OX/11088 |
| Date: | 2000 |
Files in this item
| Files | Size | Format | View |
|---|---|---|---|
|
There are no files associated with this item. |
|||