DNA hybridization in thermoresponsive polymer nanoparticles.

We achieve very high hybridization efficiencies by using a new method to immobilize DNA strands on the surface of thermoresponsive polymer nanoparticles. Hybridization efficiencies of about 70 % are obtained between the DNA immobilized in the particles and a complementary strand in solution, even at very low ionic strengths (1 mM). The polymer nanoparticles have a glassy poly(methylmethacrylate) (PMMA) core and a thermoresponsive shell of poly(N-isopropylacrylamide) (PNIPAM) containing positive charges. After a DNA strand labeled with a fluorescence probe is loaded onto the particles at room temperature, the temperature is increased above the volume phase transition temperature of the PNIPAM shell, TVPT approximately 28 degrees C. The collapse of the particle shell immobilizes the DNA while maintaining its availability for hybridization with a complementary strand. Förster resonance energy transfer (FRET) is used to detect the hybridization with a complementary DNA strand labeled with a FRET acceptor probe.