Multiresponsive hydrogel based on polyacrylamide functionalized with thymine derivatives

Abstract

A novel multiresponsive hydrogel based on polyacrylamide functionalized with thymine derivatives has been demonstrated. In this study, thymines are grafted to the polyacrylamide chains by introducing thymines to the acrylamide precursors. Based on the photodimerization/cleavage of grafted thymines, the reversible sol–gel transition can be operated by alternate irradiation with 365 and 240 nm UV light. More importantly, thymine-functionalized polyacrylamide can combine with each other by the formation of a thymine(T)–Hg²⁺–thymine(T) complex to form a hydrogel in the presence of Hg²⁺. The formed hydrogel can gradually dissolve with the dissociation of the T–Hg²⁺–T complex by a series of external stimuli such as pH, thymine and thiol compounds. Subsequently, Ru(bipy)₃²⁺ dye-doped silica nanoparticles (FSiNPs) are selected as model guests and loaded into hydrogel to demonstrate multiresponsive controlled release behavior. Moreover, the FSiNPs loaded with Hg²⁺-cross-linked hydrogel can be employed as a sensor for the detection of cysteine biomolecule. These results indicate that thymine-functionalized polyacrylamide can not only realize a multiresponsive gel–sol transition but also has a promising application in the field of controlled release and biochemical analysis.