Investigation of thin polymer layers for biosensor applications

► A polyimide waveguide material was investigated in aqueous solutions by in situ ellipsometry for biosensor applications. ► The large drift of the polyimide in solutions revealed water susceptibility and the need for suitable protection. ► The TiO2 ALD coat was promising as a shielding layer on the polyimide. ► The stable polyethyleneimine layer was proved on the polyimide which can be used as an immobilization layer in biosensors.