Preparation of novel pH sensitive phase separating polymers and its application in fluorescence immunoassay

Poly(N-isopropylacrylamide-methylacrylic acid) [P (NIP-co-MAA)], a linear w ater-soluble pH precipitating synthetic polymer, was used as a novel separa ting carrier for the reactants in immunoassay. The P(NIP-co-MAA) precipitat es out of water below a critical pH 5. 6 at 37 degrees C, and redissolved w hen the solution pH is above 6. 1. This characteristic of the P (NIP-co-MAA ) made it possible to carry out the immunochemical steps of the assay in tr ue solution and then to quickly separate the resulting procucts from the re action mixtures, The above approach was applied to an assay for the sandwic h immunoassay of hepatitis B surface antigen (HBsAg). Sensitivity of this m ethod was close to that of traditional ELISA using same reactants, However, the assay was much faster (assay time decreased from 100-120 min to 45 min ). This method has been applied to the determination of the HBsAg levels in human blood serum with satisfactory results. This general technique may al so be used for a wide variety of separation processes in addition to immuno assay, in which a specific component is to be isolated for analysis, recove ry, or disposal.