High levels of molecular orientation of surface azo chromophores can be optically induced even in a wet biological environment.

We have developed polyelectrolyte multilayer bio-films containing azobenzene chromophores that enhance reversible photo-orientation upon irradiation with linearly polarized light, to effect surface photo-switching of adjacent biological systems. When conditions of film preparation and irradiation were optimized, we could observe the highest measured birefringence to date in amorphous systems (Δn > 0.2). This birefringence change to probe orientation was also for the first time measured and determined to be stable completely underwater, permitting optimization for in situ applications immersed in biological conditions.