Novel nucleotide-responsive hydrogels designed from copolymers of boronic acid and cationic units and their applications as a QCM resonator system to nucleotide sensing

Hydrogels comprised of boronic acid monomer (3), cationic monomer (4), and crosslinker monomer (5) were prepared by radical copolymerization. These hydrogels could efficiently bind nucleotides such as AMP and ATP by a cooperative action of the boronic acid-cis-diol complexation and the electrostatic interaction between the cationic unit and the phosphate group. The binding processes were conveniently monitored by the swelling and deswelling behaviors of these hydrogels in aqueous solution. For the hydrogel with the specific monomer composition an interesting `charge inversion' was observable: with increasing AMP or ATP concentration, the cation-rich hydrogel was gradually charge neutralized, once shrunken at the neutral stage, and then swollen again because of the anion-rich charge state. These nucleotide-induced swelling and deswelling phenomena were reproduced on the gold surface of a QCM resonator. Therefore, the present system is not only interesting to consider nucleotide-induced mechanochemical properties, but also applicable as a sensor to the nucleotide detection.