Spectroscopy in heterogenous media and applications for bioprocess and environmental monitoring

Diffuse reflectance measurements and photon migration studies with near infrared (NIR) diode lasers were employed to elucidate experimental methods for determining absorption and scattering coefficients and species concentrations in heterogenous media. Measurements were performed at a number of wavelengths utilizing several laser sources some of which were widely tunable. In order to establish the applicability of simple photon migration models derived from radiation transport theory and to check the experimental boundary conditions of our measurements, simple light scattering solutions ( such as suspensions of titanium dioxide, latex particles, and solutions of milk powder) containing dyes ( such as nile blue, isosulfan blue) were investigated. The results obtained from diffuse-reflectance studies at different source-detector distances were in accordance with predictions from simple photon diffusion theory. Applications of reflectance measurements for monitoring of cell growth during fermentation processes and for in-situ investigations of soils are presented.