We report a sharp photoinduced aqueous dissolution of the copolymer through phase transition based on the photochemical reaction of o-nitrobenzaldehyde (NBA) and the principle of polymer effect. We synthesized the copolymers having poly(N-isopropylacrylamide) main chain and NBA side chain at 4, 7, and 10 mol % functionalizations and analyzed their photoresponsive characteristics. Light with 365 nm wavelength converted NBA groups at copolymer side chains to carboxylic acid efficiently at the rate of 7.3 cm(2)/J, and in the case of 10 mol % functionalization, the irradiation dosage no more than 56 mJ/cm(2) induced sharp aqueous dissolution of the copolymer thin layer in pH 7.4 at 25 degrees C. As example applications, we demonstrated on-demand release of polyethylene beads and fluorescent-labeled albumins, which had been immobilized on a substrate surface via the copolymers, by the precisely controlled light irradiation using a microprojection system. Also, we examined application of the copolymers to the selective recovery of living cells from culture substrate under microscopic observation. As a result, mild light irradiation at room temperature triggered immediate detachment of the cultured adherent cells only in the irradiated areas without critical influence on their viability.