Chemical sensors based on multiresponsive block copolymer hydrogels

In order to realize a chemical sensor with a high signal reproducibility, a thermo-shrinking photo cross-linkable co- and terpolymer of N-isopropylacrylamide (NIPAAm), 2-(dimethyl maleimido)- N-ethylacrylamide (DMIAAm) as the chromophore and poly(2-vinylpyridine) (P2VP) (or N, N-dimethylacrylamide (DMAAm), respectively) has been used as chemo-mechanical transducer. Commercially available pressure sensor chips with a flexible thin silicon bending plate have been employed as mechano-electrical transducer for the transformation of bending plate deflection into an corresponding electrical output signal. A thin film of the photo cross-linkable hydrogel has been deposited onto the backside of the silicon bending plate and irradiated with UV light. The aqueous solution to be measured has been pumped through inlet tubes into the silicon chip cavity and induces swelling or shrinking processes of the hydrogel. Changes in the polymer composition have allowed to vary the gel volume phase transition temperature ( T c) from 25 °C for P2VP-block-P(NIPAAm-co-DMIAAm) to 43 °C for NIPAAm-DMIAAm-DMAAm terpolymer. The combination of the temperature-sensitive PNIPAAm with a pH-sensitive P2VP component allowed us to realize a pH sensor with a long-term stable signal in the pH range between 2 and 5. In addition, the sensitivity of the sensors with regard to concentration changes of different inorganic solutes has been studied. The influence of an initial gel-conditioning procedure on the signal value as well as the sensitivity of the proposed chemical sensors was investigated. Measurement conditions necessary for high signal reproducibility and a long-term stability were determined.