Paper BI-ThP4
PNA-PEG Modified Silicon Platforms as Functional Bio-Interfaces for Applications in DNA Microarrays and Biosensors

Thursday, October 23, 2008, 6:00 pm, Room Hall D

Bio-functional interfaces on semiconductor materials enjoy increasing interest in basic and applied sciences because of the many possible applications of these structures in, e.g., proteomics, micro-array technology and biosensors. For DNA sensing applications single stranded DNA or peptide nucleic acid (PNA) is commonly covalently immobilized via a linker onto the surface which has been pre-modified with a thin organic film before. Here, high hybridization efficiency is generally strived for, together with a maximum suppression of unwanted, nonspecific interactions between target DNA and the sensor surface. We report on the synthesis and characterization of two novel types of PNA interfaces on silicon/siliconoxide substrates featuring poly(ethyleneglycol) (PEG)_n as molecular spacer and backfilling. As type one, phosphonate self-assembled monolayers were derivatized with a 12mer PNA oligomer via modification with and post-functionalization of a maleimide-terminated poly(ethyleneglycol) spacer (PEG₄₅). Similarly, a type two modification consisted of silane self-assembled monolayers which were functionalized with PNA via modification with a maleimide-terminated PEG₄₅ spacer and were also subsequently modified with a shorter methoxy-terminated PEG₁₂ (back-filling). X-ray photoelectron spectroscopy (XPS) analysis confirmed binding of PEG and PNA to the phosphonate and silane films and indicated that additional PEG chains were tethered to the surface during the backfilling process. We carried out hybridization experiments in the presence of matching and mismatching, fluorescently labeled DNA and found that both types of bio-functional surfaces were effective in the hybridization of matching DNA while significantly reducing non-specific adsorption. To verify the suppression of DNA adsorption on PEG-only modified surfaces and to extend the scheme towards laterally patterned structures we employed micro-molding techniques, i.e., pressed DNA-coated PDMS stamps onto a surface which comprised of alternating PNA functionalized, and non-functionalized regions, respectively, in a grid-like manner. These studies confirmed that hybridization took place selectively at the PNA functionalized regions only, while physisorption at the probe-less PEG-functionalized regions was drastically reduced.