Saccharide-sensitive phase transition of a lectin-loaded gel

Abstract

A GEL system that swells and shrinks in response to specific molecules could serve as the basis for technological applications of polymer gels, for example as sensors, drug-delivery devices and actuators. Here we describe a lectin-loaded polymer gel that undergoes distinct swelling behaviour in response to different saccharides. The gel consists of a covalently cross-linked polymer network of N-isopropylacrylamide in which the lectin, concanavalin A, is immobilized. Concanavalin A displays selective binding affinities for certain saccharides. The gel undergoes a volume phase transition at ∼34 °C. When the saccharide dextran sulphate is added (as the sodium salt DSS) to the gel, it swells to a volume up to five times greater at temperatures close to this transition, and the transition itself changes from discontinuous to continuous. Replacing DSS with the non-ionic saccharide α-methyl-D-mannopyranoside brings about collapse of the gel back to almost its native volume. This process is reversible and repeatable. These results point to a general principle for the design of such molecule-specific systems.