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 thermo-responsive 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 (1mm). The polymer nanoparticles have a glassy poly(methylmethacrylate) (PMMA) core and a thermo-responsive 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 ≈ 288C. The collapse of the particle shell immobilizes the DNA while maintaining its availability for hybridization with a complementary strand. Fc̈rster resonance energy transfer (FRET) is used to detect the hybridization with a complementary DNA strand labeled with a FRET acceptor probe.