Selective antigen–antibody recognition on SPR sensor based on the heat-sensitive conformational change of poly(N-isopropylacrylamide)

We describe the modulation of biointerface by an external stimulus with a smart polymer-modified electrode. Poly(N-isopropylacrylamide) (PNIPAAm) shows a rapid reversible hydrophilic/hydrophobic transition of its conformation in response to the temperature variation across its lower critical solution temperature (LCST). This phenomenon changes the physical appearance of the polymer, helical and linear form, at the biorecognition interface. The chip surface was double functionalized with the PNIPAAm and a model ligand, biotin, and the antigen–antibody affinity reaction was observed and traced by surface plasmon resonance (SPR) spectroscopy. The amount of anti-biotin antibody binding on the chip surface was controlled specifically by the structural transformation of PNIPAAm by the temperature variation. By using two reaction channels on a single SPR sensor chip, the difference of the bound antibody concentration in the consequence of the structural transformation was found to be 3.73 × 10−13 mol cm−2, supporting the possibility of site-selective protein immobilization/patterning for multiplexed analysis.