Various tissue glues have drawback such as toxicity, causing inflammatory reactions or insufficient bonding strength. The present invention is directed to methods of form tissue adhesion by administering to tissues compositions comprising proteins conjugated to one or more novel photosensitizers and irradiating the composition. The composition may further comprise one or more proteins not conjugated to the photosensitizer. Additionally, the present invention relates to compositions and methods wherein increased ratios of protein to photosensitizer enhance weld strength.