Nanoscale adhesion, friction and wear studies of biomolecules on silicon based surfaces.

Protein layers are deployed over the surfaces of microdevices such as biological microelectromechanical systems (bioMEMS) and bioimplants as functional layers that confer specific molecular recognition or binding properties or to facilitate biocompatibility with biological tissue. When a microdevice comes in contact with any exterior environment, like tissues and/or fluids with a variable pH, the biomolecules on its surface may get abraded. Silicon based bioMEMS are an important class of devices. Adhesion, friction and wear properties of biomolecules (e.g., proteins) on silicon based surfaces are therefore important. Adhesion was studied between streptavidin and a thermally grown silica substrate in a phosphate buffered saline (PBS) solution with various pH values as a function of the concentration of biomolecules in the solution. Friction and wear properties of streptavidin (protein) biomolecules coated on silica by direct physical adsorption and a chemical linker method were studied in PBS using the tapping mode atomic force microscopy at a range of free amplitude voltages. Fluorescence microscopy was used to study the detailed wear mechanism of the biomolecules. Based on this study, adhesion, friction and wear mechanisms of biomolecules on silicon based surfaces are discussed.

Morphology and adhesion of biomolecules on silicon based surfaces.

Biomolecules such as proteins, on silicon based surfaces are of extreme importance in various applications including microfabricated silicon implants, in the fabrication of microdevices with protein compounds (e.g., biosensors), and therapeutics. Morphology of silicon based surfaces with and without biomolecules and their adhesion with the substrate govern performance and reliability of the biological application. In this research, step by step morphological changes of silicon as well as adhesion during its surface modification have been studied using atomic force microscopy. To improve adhesion between biomolecules and the silicon based surfaces, chemical conjugation as well as surface patterning have been used. Changes in adhesion as a result of surface modification have been analyzed with the help of contact angle measurements. Phase imaging technique was used to confirm the presence of biomolecules on the surface. To understand the relationship between morphology and local values of adhesion, adhesion mapping and local stiffness mapping were carried out.