A programmable benchtop photocrosslinking chamber for controlled bioconjugation

Ultraviolet (UV) photochemical reactions have become ubiquitous in the biomedical sciences, where they are frequently used to conjugate biomolecules in a process known as photo-crosslinking. Such processes play an important role in the fields of drug discovery, biomarker validation, and bioprinting. Typically, these photochemical reactions are conducted using commercially available UV irradiation sources which are bulky and expensive. Handheld units are a popular substitute but tend to cause excessive heating of the sample. Additionally, currently available UV sources are not designed to be user-friendly for performing bioconjugation in Eppendorf tubes, making them less practical for efficient and precise biomedical experiments. Here we present an open-source, low-cost (approximately $250), and customizable UV irradiation system that allows for simultaneous processing of up to six 1.5 mL Eppendorf tubes. Our system uses uniformly arranged 365 nm UV LEDs that irradiate the bottom of the tube with a polished aluminum sleeve for even distribution of light throughout the tube volume, resulting in higher efficiency and a 50% reduction in sample heating compared to commercial mercury lamp blanket exposure systems. The modular design allows LEDs of other wavelengths to be easily installed for broader photoreaction applications. Using this user-friendly system, we demonstrate the efficient conjugation of photocrosslinkable nanobodies to antibodies in 5 min without causing photobleaching of the fluorophores, thus enabling immunofluorescent imaging for biomedical applications.