Poly(N-isopropylacrylamide) layers on silicon wafers as smart DNA-sensor platforms

The aim of this study is to create thermo-responsive ('smart') biosensor (array) platforms. Poly(N-isopropylacrylamide) (poly(NIPA)) carrying two different functional groups (-SH and -COOH) at two ends was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Self-assembled monolayers (SAMs) with amino-terminated groups on the Si(001) surfaces were prepared using 3-aminopropyltrimethoxysilane (APTS). Ellipsometric measurements showed that monolayers with a thickness of about 1.10 nm were formed when the dipping time is about 1 h, while more profound agglomerations were observed for longer time periods and APTS solutions with higher concentrations. Poly(NIPA) molecules were then covalently attached to the silicon surfaces via APTS molecules. Afterwards, 5'-thiolated oligodeoxynucleotide-probes were immobilized onto these thiol-terminated poly(NIPA) layers on the surface by disulfide bond formation. An ellipsometer was used for detection (by hybridization) of the target oligos (the complementary of the probe oligos) within the aqueous media at two different temperatures, 25 degrees C and 45 degrees C, which are below and above the "Lower Critical Solution Temperature" (LCST) of poly(NIPA), respectively. Hybridization at low temperatures was significantly higher than those observed at higher temperatures. No respond (no hybridization) was monitored when the target is a non-complementary oligo sequence. These preliminary studies demonstrated that this approach can be used switch off and on the surface reactions on smart surface by using an external stimulus (temperature in this case).