Light-triggered DNA release by dynamic monolayer films

We illustrate a simple strategy to immobilize single and double strand DNA on a two-dimensional surface and to trigger their release under physiological conditions, under the exclusive control of light stimuli. A tailored azobenzene derivative has been self-assembled on transparent platinum electrodes to form cationic-terminated monolayer films. These monolayers encourage the binding of DNA with the metal surface through effective electrostatic interactions with the negatively charged polynucleotide backbone. Irradiation of the film with UVA light induces trans to cis isomerization of the photoresponsive azobenzene units leading to significant changes of surface hydrophilicity and decreasing the binding affinity for DNA, which is consequently released into the solution. It is shown that the amount of DNA released can be precisely tuned by controlling the illumination conditions and is strictly related to the photoinduced structural modi. cations at the film surface. After the release of DNA the functional monolayers can be recycled through illumination with visible light which causes the cis form of the azo-chromophore to revert to the trans form, restoring the initial conditions. Given the nonspecific nature of the Coulombic interactions the approach presented herein may, in principle, also be extended from polynucleotides to other negatively charged biomolecules, making these dynamic monolayers appealing model systems from the perspective of nanoscaled devices for biomedical applications where spatiotemporal control of biological material is required.