Controlled Modification of Protein-Repelling Self-Assembled Monolayers by Ultraviolet Light: The Effect of the Wavelength

Exposure of protein-repelling oligo(ethylene glycol) (OEG) terminated alkanethiolate (AT) monolayers to ultraviolet (UV) light results in the damage of the OEG chains and photooxidation of the thiolate headgroups, which can be used for controlled tuning of protein-repelling properties within the so-called UV direct writing (UVDW) approach or for the preparation of mixed OEG-AT/specific-receptor films by so-called UV-promoted exchange reaction (UVPER). Using several model systems, we studied the effect of the wavelength (254–365 nm) on the course and efficiency of UVDW and UVPER applied to different OEG-AT matrices. The cross sections of the UV-induced damage were found to decrease significantly with increasing wavelength of UV light. In accordance with this behavior, the efficiencies of both UVDW and UVPER were maximal at a wavelength of 254 nm, somewhat lower at 313 nm, and lowest at 365 nm. Both UVDW and UVPER allowed a fine-tuning of protein affinity for nonspecific and specific adsorption, respectively, but UVDW did not occur below a certain, wavelength-dependent threshold dose. Performing UVPER below this dose enables us to suppress possible nonspecific adsorption of proteins even in the case of noncomplete exchange of the UV-damaged molecules of the primary OEG-AT matrix by receptor-bearing moieties. The obtained results are of direct relevance for the preparation of high-quality mixed OEG-AT/specific-receptor films and the fabrication of complex protein patterns by UVDW and UVPER lithography.