Abstract:

Spectral interferometry is presented as a tool to monitor the swelling of polymers caused by organic gases or hydrocarbons in waste water as well as the adsorption and interaction of antigens and antibodies in immunoreactions. Modern diode-array technology allows the consequent observation of changes in optical pathlength on a fractional nanometer scale with subsecond repetition times. The theory of multiple-reflection principles in white-light interferometry determines the possibilities and limitations of this method. The optical set-up and some applications in gas sensing and label-free immunosensing are discussed with respect to the sensitivity, selectivity and limits of detection at present.

Abstract:

The application of a rapid scanning diode array spectrometer allows the time-resolved observation of the interferences caused by multiple reflections at the interfaces of thin films. This spectral interferometry enables the observation of changes in optical pathlengths and allows to separate volume-effects like polymer swelling from surface-effects like adsorption or deposition. Polymer/solvent interactions will give an example for an application of this method.

Abstract:

Oligomers with a dimethylsiloxane backbone coated as thin films on different substrate surfaces were thermally as well as photochemically cross-linked. The structure and the degree of cross-linking were examined spectroscopically. Diffusion of different gases in the thin polymer films was measured by time resolved infrared ATR-spectroscopy. The process of diffusion is almost immediately followed by a swelling of the polymer proportional to gas concentration. Therefore diffusion may also be measured by spectral interferometry, giving a very sensitive device for optical sensing of hydrocarbons. Furthermore, diffusion in polymers may be measured very accurately by spatially resolved UV/Vis-spectroscopy. Diffusion coefficients may also be determined indirectly from the equilibrium of monomers and excimers indicated by the fluorescence intensities. This method allows the in situ observation of the cross-linking process.

Abstract:

The principle of interferometry has been applied to thin polymer films as they swell by sorption of gases or as they interact with biochemical material. Modern diode array technology allows the monitoring of changes in optical path-length at a fractional nanometre scale. Observation of the interference spectra makes discrimination between thickness and Fresnel refractive index effects possible. Thus, very sensitive sensors can be developed for measuring concentrations of gaseous and liquid organic solvents as well as specific antigen-antibody interactions.