Scanning force microscopy as a tool for bioelectronics

Before biomolecules can become common components in hybrid bio-electronic/semiconductor integrated circuits, a better understanding is required of their properties in the significantly non-biological environmental conditions under which silicon-based circuits operate. We use the scanning force microscope (SFM) to study the properties of the biomolecule bacteriorhodopsin (BR). We have demonstrated the ability to pattern BR at the micron length scale through the use of a new soft-lithography based technique which is applicable to a wide range of electrophoretic molecules, both biological and not. We have shown that we can measure the photoresponse of oriented purple membrane (PM) multilayers with an SFM and we have done so under conditions similar to those of a semiconductor chip. We find that the hydration level of the multilayer has a drastic effect on the induced photovoltage. We have developed an analytical model of the photoresponse which gives a complete qualitative explanation of the results. We have looked at the more general question of what physical information about a sample we can extract from an SFM. Specifically, we have looked at non-linear effects in the oscillation of the SFM cantilever and we have demonstrated the ability to measure a range of higher mode oscillations and to produce images showing higher mode contrast between PM and mica as well as the variation of different higher mode signals with tip-sample distance