Novel biosensors made of polymers may offer advantages over conventional
technology such as possibility of mass production and tunability of the
material properties. With the ongoing work on the polymer photonic chip
fabrication in our project, simple model samples were tested parallel
for future immobilization and accessing conditions for applications in
typical aqueous buffers. The model samples consist of a thin, high
refractive index polyimide film on top of TEOS on Si wafer. These model
samples were measured by in situ spectroscopic ellipsometry using
different aqueous buffers. The experiments revealed a high drift in
aqueous solutions; the drift in the ellipsometric parameters (delta,
psi) can be evaluated and presented as changes in thickness and
refractive index of the polyimide layer. The first molecular layer of
immobilization is based on polyethyleneimine (PEI). The signal for the
PEI adsorption was detected on a stable baseline, only after a long
conditioning. The stability of polyimide films in aqueous buffer
solutions should be improved toward the real biosensor application.
Preliminary results are shown on the possibilities to protect the
polyimide. Optical Waveguide Lightmode Spectroscopy (OWLS) has been used
to demonstrate the shielding effect of the thin TiO2 adlayer
in biosensor applications.