Mechanism of super oxygen-resistant radical polymerization enabling polymerization-based signal amplification for biosensors


Alan Aguirre-Soto


Alan Aguirre-Soto, Jisam Wong, Kaja Kaastrup, Hadley D. Sikes

Author Affiliation: 

Massachusetts Institute of Technology


Despite being inhibited by oxygen, radical chain polymerization is the most versatile and robust polymer synthesis method to date. Oxygen inhibits the radical-initiated chain polymerization of vinyl monomers, which becomes a major problem when polymerizing thin-films at interfaces. Chemical methods to overcome interfacial oxygen inhibition include: 1) adding chain transfer agents; 2) increasing initial viscosity; and 3) producing excess radicals. But these methods may not be sufficient or applicable in many instances, in which expensive purging of oxygen comes to be the last resort. However, none of these alternatives suffice when polymerizing thin PEG-based hydrogels to amplify the signal from biomolecular recognition events at interfaces under ambient conditions for point-of-care medical diagnostics. Interestingly, it has been discovered that the visible-light activated radical co-polymerization of (meth)acrylate monomers and N-vinylpyrrolidone induced by eosin Y and triethanolamine withstands up to 100-1000 times excess oxygen with even micromolar concentrations of eosin Y. Nevertheless, the chemical mechanism behind this outstanding oxygen resilience remains inconclusive. In this work, we propose a comprehensive mechanism explaining the super oxygen-resilient radical-initiated polymerization induced by eosin Y and triethanolamine in water at basic pH. We construct our mechanism from first principles combining kinetic modeling with spectroscopic characterization of the role of monomer(s), amine, oxygen, and eosin Y. We account for previously ignored pathways to uncover molecular engineering criteria that can enable the design of radical polymerization routes with even higher resistance to oxygen. Finding more effective methods to overcome oxygen inhibition will allow us to design more sensitive and specific diagnostics using polymerization-based signal amplification.