Essential oils as solvents and core materials for the preparation of photo-responsive polymer nanocapsules

Light-triggered release of active ingredients from polymeric nanosized capsules can be employed in a wide range of applications, such as biomedicine, active packaging, and cosmetics. However, the preparation of core-shell polymeric nanocarriers typically involves the use of toxic organic solvents. To improve the sustainability and safety of nanocapsule applications, we demonstrate that natural essential oils can be used both as solvent and active material in light-responsive nanocapsules synthesized via miniemulsion polycondensation. The documented antimicrobial, anti-inflammatory, and antioxidant activity of essential oils enables the design of multipurpose light-responsive delivery platforms. The photo-responsive behavior of the capsules, achieved by means of photochromic azobenzene segments embedded in the capsule shell, is triggered by UV light irradiation (lambda(max) = 360 nm). Light-induced release kinetics of the essential oils and a fluorescent probe molecule, coumarin-6, is evaluated via UV-vis spectroscopy and spectrofluorimetry, respectively, demonstrating the efficiency and reliability of the release mechanism. Biological tests prove that the capsules are non-cytotoxic and readily internalized by cells, indicating the suitability of these smart nanocarriers for biological applications.