photocrosslinking

Photocrosslinking is the formation of covalent bonds between polymer chains or biomolecules upon exposure to light. It typically uses ultraviolet or visible light to activate a crosslinking moiety or a photoinitiator/photosensitizer that generates reactive species, which then form crosslinks. The approach provides spatial and temporal control, allowing in situ solidification, patterning, and modification under mild conditions.

Chemistries used in photocrosslinking include: radical crosslinking of polymers with acrylate or methacrylate groups initiated by Type I or Type II photoinitiators; photo-dimerization or photocycloaddition of reactive groups such as coumarin, diazirine, or diarylethene units; and photochemical crosslinking of nucleic acids and proteins using psoralen under UVA to form interstrand links, or via photoaffinity groups such as benzophenone that react with nearby C–H or N–H bonds upon irradiation. Common photoinitiators include benzoin ethers, benzophenone, and acetylphosphine oxides, with many systems designed to operate under visible light to minimize damage to delicate samples.

Applications span materials science and biology. In materials chemistry, photocrosslinking enables hydrogel formation for tissue engineering and drug delivery, photo-patterning of surfaces and microstructures, and the creation of biocompatible adhesives. In biology, it is used to stabilize and map biomolecular interactions, capture protein–RNA and protein–protein contacts, and study transient complexes in cells.

Limitations include limited light penetration in thick samples, potential photodamage to light-sensitive molecules, cytotoxicity or perturbation from initiators, and oxygen inhibition in radical systems. Careful choice of wavelength, initiator, and reactive groups is essential to balance efficiency with biocompatibility.