Optical switching of protein interactions on photosensitive–electroactive polymers measured by atomic force microscopy

The ability to switch the physico-chemical properties of conducting polymers opens up new possibilities for a range of new applications. Appropriately functionalised materials can provide routes to multi-modal switching, for example in response light and/or electrochemical stimuli; this capability is important in the field of bionics, wherein remote control of the properties of materials opens new possibilities. For example, the ability to actuate a film via photonic stimuli is particularly interesting as it facilitates the modulation of interactions between surface host binding sites and potential guest molecules. In this work, we studied two different poly-terthiophenes: one was functionalized with a spiropyran photoswitch (pTTh-SP) and the second with a non photoswitchable methyl acetate moeity (pTTh-MA). These substrates were exposed to several cycles of illumination with light of different wavelengths and the resulting effect studied with UV-vis spectroscopy, contact angle and atomic force microscopy (AFM). The AFM tips were chemically activated with fibronectin (FN) and the adhesion force of the protein to the polymeric surface was measured. The pTTh-MA (no SP incorporated) showed a slightly higher average maximum adhesion (0.96 ± 0.14 nN) than the modified pTTh-SP surface (0.77 ± 0.08 nN), but after exposure of the pTTh-SP polymer to UV, the average maximum adhesion of the pTTh-MC was significantly smaller (0.49 ± 0.06 nN) than both the pTTh MA and pTTh-SP. These results suggest that hydrophobic forces are predominant indetermining the protein adhesion to the films studied and that this effect can be photonically tuned. By extension, this further implies that it should be possible to obtain a degree of spatial and temporal control of the surface binding behaviour of certain proteins with these functionalised surfaces through photoactivation/ deactivation, which, in principle, should facilitate patterned growth behaviour (e.g. using masks or directional illumination) or photocontrol of protein uptake and release