Selective functionalization of 3D matrices via multiphoton grafting and subsequent click chemistry

Grafting is a popular approach for adjusting the properties and functionalization of various surfaces. Conventional photoinduced grafting has been utilized on flat surfaces, porous monoliths, and hydrogels. By masking or illuminating only a portion of the sample, a certain degree of spatial and temporal control is possible, but the ability to use grafting to pattern in 3D is limited. Here, the laser-induced photolysis of an aromatic azide compound is employed for true 3D photografting within a poly(ethylene glycol) (PEG)-based matrix. Since the multiphoton interaction occurs only in a confined area within the laser focal spot, the localized immobilization of a selected molecule with high spatial resolution in 3D is possible. In contrast to the widely utilized chain-growth polymerization-based grafting, the approach is characterized by a single-molecule insertion mechanism. Successful binding of the fluorophore is confirmed by laser scanning microscopy. To test for the presence of latent azides and to determine the suitability for additional postmodification with arbitrary functional groups, the sample is further subjected to copper-catalyzed alkyne click-reaction conditions. The described 3D photografting method is simple, highly efficient, and universal. The presented results demonstrate the great potential of multiphoton-induced grafting for 3D site-specific functionalization. The use of aromatic azide compounds for selective multiphoton-induced photografting within a poly(ethylene glycol) (PEG)-based 3D matrix is reported. A highly selective molecule immobilization with good lateral resolution in 3D is achieved and patterns are further functionalized by means of a click reaction. The 3D site-specific functionalization method has potential applications in microarray-based proteome analysis, studies of cell-surface interactions, sensing applications, and drug screening.