Jielin Sun

Cleaning using nanobubbles: Defouling by electrochemical generation of bubbles

Here we demonstrate that nanobubbles can be used as cleaning agents both for the prevention of surface fouling and for defouling surfaces. In particular nanobubbles can be used to remove proteins that are already adsorbed to a surface, as well as for the prevention of nonspecific adsorption of proteins. Nanobubbles were produced on highly oriented pyrolytic graphite (HOPG) surfaces electrochemically and observed by atomic force microscopy (AFM). Nanobubbles produced by electrochemical treatment for 20 s before exposure to bovine serum albumin (BSA) were found to decrease protein coverage by 26-34%. Further, pre-adsorbed protein on a HOPG surface was also removed by formation of electrochemically produced nanobubbles. In AFM images, the coverage of BSA was found to decrease from 100% to 82% after 50 s of electrochemical treatment. The defouling effect of nanobubbles was also investigated using radioactively labeled BSA. The amount of BSA remaining on a stainless steel surface decreased by approximately 20% following 3 min of electrochemical treatment and further cycles of treatment effectively removed more BSA from the surface. In situ observations indicate that the air-water interface of the nanobubble is responsible for the defouling action of nanobubbles.

Evaluation of the radial deformability of poly(dG)-poly(dC) DNA and G4-DNA using vibrating scanning polarization force microscopy

Poly(dG)-poly(dC) DNA and G4-DNA are two types of synthetic molecules that are regarded as promising candidates for molecular nanodevices. In this work, vibrating scanning polarization force microscopy (VSPFM) was employed to study the radial deformability of these two molecules coadsorbed on a Ni(2+)-modified mica surface. The values of the radial compressive elastic modulus of these two types of molecules were found to be similar (approximately 5-10 MPa) when the external loading force was between approximately 0.04 and approximately 0.12 nN. However, G4-DNA molecules possessed higher stiffness than poly(dG)-poly(dC) DNA (approximately 20-40 vs approximately 10-20 MPa) when the loading force was larger than approximately 0.12 nN. The results will aid us in understanding these molecules mechanical performances.

Peptide nanofilaments used for replica-molding: A combination of "bottom-up" and "top-down"

A novel nanofabrication method that combines both bottom-up (template-assisted peptide self-assembling) and top-down (replica molding) techniques is introduced. A designer peptide, GAV-9 (NH2-VGGAVVAGV-CONH2), can epitaxially self-assemble into nanofilaments on the surface of mica, which is further used as the diversified masters for the application of replica molding. With in situ atomic force microscopy monitoring, several typical masters are fabricated by peptide self-assembling on the surface of mica. These masters can be easily molded into hard poly(dimethylsiloxane) surfaces, and then further replica-molded into polyurethane surfaces. The polymeric surfaces with regular 1D and 2D patterns on the nanometer scale are expected to have new applications in nanostructures fabrication.