Light-activated spatiotemporal control over nanoreactor permeability†

Interactive materials can be responsive to a variety of stimuli, such as pH, redox, or light. Actuation with light offers excellent spatiotemporal control. Furthermore, it has the advantage that no waste is produced during the light activation process. Herein, we present a strategy to regulate the permeability of pH-responsive nanoreactors using a spiropyran photoacid. Upon light illumination, the photoacid drastically reduced the pH of the environment, which caused the nanoreactor to become permeable. Encapsulation of an enzyme within these nanoreactors therefore allowed for light-induced enzymatic conversion of substrate, and longer irradiation times resulted in an increase in product. Additionally, apart from temporal control, we showed that immobilization of the nanoreactors into a hydrogel matrix also allowed for excellent spatial control. By using a photomask approach, we demonstrated that only in illuminated regions of the hydrogel substrate was converted, due to the local activation of the nanoreactors. Furthermore, this approach could also be applied with higher resolution using confocal microscopy. Irradiating targeted areas with a 480 nm laser line allowed for photoisomerization of the spiropyran, simultaneously inducing permeability. This approach yields high-resolution spatial control over nanoreactor permeability and could potentially be utilized in controlled local synthesis of products or drug release.