Controlled Release of Chol-TEG-DNA from Nano- and Micropatterned SU-8 Surfaces by a Spreading Lipid Film

Abstract

We report the controlled release of immobilized cholesteryl-tetraethyleneglycol-DNA (chol-DNA) from micropatterned SU-8 surfaces by a spreading lipid film. The release of chol-DNA is rapid and on the order of the spreading rate of the lipid film beta = 1-3 microm2/s ( approximately 10(5) molecules of DNA per second). The lipid film serves as a poor solvent for the DNA adduct, which upon contact redistributes into the aqueous phase. Thus, the release of DNA is accompanied by a change in surface hydrophobicity. The method can be used for creating arbitrary concentration profiles of DNA in solution over time or to dynamically change surface properties on demand in, for example, micro- and nanofluidic devices. Examples of DNA release from spiral, comb, meander, and triangular as well as from nanoscale SU-8 lanes are shown.

Thermodynamic Modeling of Solvent-Assisted Lipid Bilayer Formation Process

“…In contrast, repulsive forces in the hydrophobic chains and headgroups will be generated from the steric, hydration, and electrostatic effects when lipid molecules in the shape of inverted cones form SLBs, giving rise to an imbalance of the lipid lateral pressure and elevated bending energy at the molecular level. However, on hydrophobic substrates (e.g., alkanethiol-coated gold, fluoropolymers [38], and the epoxy SU-8 [39]), µ sm µ sb , inducing the formation of a supported lipid monolayer. This simple estimation of the Gibbs free energy indicates that SLBs form on hydrophilic surfaces and lipid monolayers form on hydrophobic surfaces.…”

Molecular phospholipid films on solid supports

“…13 Furthermore, monolayer spreading was found to compete with other densely surface-adhered hydrophobic molecules. 160 While a SAM of cholesteryl-tetraethyleneglycol-DNA molecules weakly adsorbed to the SU-8 surface does not have an influence on the spreading coefficient, 160 lipid monolayer spreading is somewhat slower on EPON 1002F, 21 but significantly faster on Teflon AF (12-20 mm 2 s À1 ). 156 Unlike large or giant multi-or unilamellar vesicles, very small lipid reservoirs, e.g.…”

“…13 Micromanipulation techniques were developed which allow for the deposition of lipid vesicles on designated areas of microand nanostructured SU-8. 13,160 Sanii and Parikh have placed a single bulk lipid source onto a composite hydrophilic/hydrophobic substrate and observed lipid bilayer and monolayer spreading simultaneously on the hydrophilic and hydrophobic areas. 12 This way, bilayer and monolayer spreading dynamics could be directly compared.…”

SU-8 free-standing microfluidic probes

“…These challenges are a consequence of the material properties and processing requirements of PDMS. These problems prompted us to investigate the possibility of employing the negative photoresist SU-8, which has been widely used in microsystems and coating applications, 11–15 for a scalable process with options for integration of additional features.…”