Responsive Polymers in the Fabrication of Enzyme-Based Biosensors

Polymers play a crucial role in the design, fabrication, and performance of enzyme-based biosensors. Critical roles include (1) bioconjugation/bioimmobilization, (2) biohosting, (3) biocompatibility to reduce biofouling, and (4) active transduction. The latter role of polymers as a transducer-active or stimuli-responsive component of the biotransducer of a biosensor has not been subject to critical review. Among the several polymers used are inherently conductive polymers (ICPs), responsive-hydrogels, polymeric redox-mediators, ferroelectric, piezoelectric, and pyroelectric polymers. Additionally, polymeric composites comprise an inert polymeric binder and a conductive inclusion such as ICP filers and carbonaceous materials (dots, tubes, sheets). The classic biosensor system is discussed, with a focus on roles of these polymers within the four main types of electrochemical biosensors (amperometric, conductometric, impedimetric, potentiometric). Both passive (physical support) and active roles of responsive polymers within electrochemical biosensors are explored. Integration of responsive polymers in active roles in electrochemical biosensor systems has enabled dual- and multistimuli responsive biosensors capable of responses elicited by physical, chemical, or biological stimuli. Biosensor fabrication methods including microlithography and 3-D printing utilize existing technologies originally designed for inorganic materials to render bioactive, 4-D responsive biosensor electrodes. The pairing of new electrode architectures and chemistries including conjugation with carbon nanotubes, enzyme active site conjugation by boric acid, and direct molecular wiring has led to the development toward rapid, selective, miniaturized glucose sensors, leaving development toward wireless implantable biosensors an achievable goal.