PDMS-based chemo-mechanical sensors and microfluidic devices

Freestanding thin films made of elastic polymer such as polydimethylsiloxane (PDMS) are highly sensitive compared to conventional Si-based freestanding structures. The adsorption of molecules leads to surface stress changes that induces mechanical deformation or "buckling" that can be used to indicate the presence of pollutants, pathogens, cancer markers, etc. PDMS membranes are fabricated to explore the chemomechanical sensing of single-stranded DNA (ssDNA). An extrinsic Fabry-Perot interferometer (EFPI) is employed to detect the center deflection of a thin film. Silane chemistry and gold nanoparticles are utilized to immobilize probe ssDNA onto PDMS surface. Detection of ssDNA is achieved at ∼ 1 mum deflection/muM ssDNA on a 3-mm-wide, 10 mum thick circular membrane. This sensitivity is much higher than that of Si-cantilevers or glass polymer cantilevers as reported in the literature. In order to optimize DNA probe binding on the Au-coated PDMS surface, end-grafting studies of ssDNA and dsDNA along with hybridization evaluation are conducted on Au/glass and nanoporous Au (np-Au) surfaces. The optimal probe and target binding conditions prove to be at high salt concentrations, which shield the electrostatic repulsion among DNA strands.;Besides DNA, protein is another important biochemical analyte for micro-total-analysis-systems (muTAS). Integrated microchip protein digestion and reversed-phase separation can potentially reduce the sample consumption and accelerate the separation in comparison to conventional tube digestion and packed-bead column separation. Methacrylate-polymer monoliths were synthesized in microfluidic glass devices to perform protein digestion and peptide desalting compatible with conventional LC/MS system, with higher sequence coverage than conventional packed-bed digestion and desalting columns.;PDMS and glass are two important materials for building miniaturized chemo-mechanical sensors and microfluidic protein digestion and separation systems. The various surface functionalization strategies enable novel applications of PDMS, glass and hybrid PDMS/glass microdevices.