Stimuli-Responsive Hydrogel Films Based on Crosslinked Chitosan

Electrochemical research has been particularly difficult at primarily undergraduate institutions (PUIs) because students entering a research lab in their freshman and sophomore years have no or little knowledge of analytical chemistry or physical chemistry, let alone electrochemistry. However, considering the limited resources and amount of time faced by students at PUIs, electrochemistry presents a great opportunity to expose the students to multi-disciplinary research that encompasses chemistry, biology, material science and engineering.  Here we report the development of a stimuli-responsive hydrogel film based on crosslinked chitosan on the surface of an electrode. The film shows a pH-responsive, switch-like behavior. The negatively charged redox probe, Fe(CN)₆^3-/4-, is found to be trapped and enriched in the catechol-crosslinked chitosan film under acidic conditions, and released into solution by either increasing pH or applying a negative voltage. The release of negative species from the film can be controlled by the amplitude and duration of the applied voltage. This pH- and voltage-responsive material has promising applications in biofabrications, biosensors and drug delivery systems. Future studies and incorporation of similar research in undergraduate curriculum will also be discussed.