Temperature-regulated non-monotonic behavior of DNA immobilization on poly(N-isopropylacrylamide) (PNIPAm)-grafted surface

Immobilizing single-stranded DNA (ssDNA) probes onto transducer surface is the initial step to construct DNA biosensors, and its surface density is crucial for the performance of the designed sensors. Here, we report the surface density of Cy3-labeled DNA probes immobilized on poly(N-isopropylacrylamide) (PNIPAm)-grafted indium-tin oxide (ITO) surface shows temperature-regulated behavior by combining experiment and molecular theory. DNA immobilization gets hindered by the hydrophilic PNIPAm layer grafted on ITO surface at 25 oC, and the surface density of DNA probes gets monotonically decreased as PNIPAm surface coverage rises. However, DNA immobilization shows non-monotonic variation depending on the PNIPAm surface coverage at 45 oC. More specifically, the immobilized DNA probes get facilitated by the hydrophobic PNIPAm layer at low surface coverage, and the largest surface density of DNA probes reaches 1.4-fold that of the bare ITO surface, but DNA immobilization gets blocked by the hydrophobic PNIPAm layer at high surface coverage. The temperature-regulated behavior of DNA immobilization on PNIPAm-grafted surface may be exploited for design of thermo-responsive DNA biosensors and self-assemblies based on DNA probes.