Cindy Berrie

Bioanalytical chemistry, protein-surface interactions, surface chemistry, scanning probe microscopy, nanoscale fabrication, physical chemistry.

The fundamental investigations of the nanoscale properties of materials in our laboratory are intended to enable the design and implementation of future nanobiodevices. Success of these devices requires that all of the different aspects of design of the material (including the protein adsorption, mechanical stability, and electrical signal transport) be optimized. In particular, research in our group has focused on the effect of nanoscale structure on 1) biomolecule adsorption, 2) friction and adhesion, and 3) electrical conductivity of organic molecules. In all of these cases, we are interested in designing model systems in which the nanoscale structural and chemical variations can be achieved.

Biomolecule Adsorption: Our research group has been investigating protein adsorption at surfaces in a number of systems to both elucidate fundamental aspects of biomolecule-surface interactions and exploit them to facilitate the study of important biological problems. One system we have studied is the plasma protein fibrinogen, a large, abundant protein critically involved in blood-clotting. We have investigated fibrinogen adsorption and conformation at the single molecule level on both hydrophobic and hydrophilic surfaces and shown, through atomic force microscopy (AFM) imaging, that the shapes of the molecules on the two types of surfaces are dramatically different. Our work provides direct evidence for a powerful structural model that can explain both the aggregation state and shapes of the adsorbed molecules. In addition, we have obtained direct evidence that this protein has significant initial mobility on hydrophobic surfaces which results in unique structural features of the film and is likely be important in the dynamic interactions and activity in this system. We are currently investigating the effect of nanoscale patterning on the adsorption of fibrinogen on surfaces as well as using surface plasmon resonance to investigate the kinetics of adsorption in this system.

Another system of interest in our group is F1 ATPase, the non-membrane-bound part of the larger ATPase complex that synthesizes ATP when driven by a proton gradient across the membrane. The amazing efficiency and power of this nanoscale motor have led to speculation that this molecule could form the basis for potential nanobiodevices. However, this would require dramatic improvement in the ability to control the position, orientation, conformation, and activity of the protein. In collaboration with Prof. Mark Richter, we are engineering the surface with nanoscale sites that will bind individual molecules in the desired orientation by controlling the chemistry both inside and outside these patterned domains. We have demonstrated sub-complex resolution of the F1 ATPase molecules through AFM imaging in solution, allowing the determination of the orientation of the absorbed proteins. We are currently working to develop nanoscale patterns of thes protein molecules which are functionally active through nanoscale surface engineering.

Friction and Adhesion: The tribological attributes (friction and adhesion) of materials used in coating micro- or nano-mechanical devices are critical in determining their performance and wear characteristics. Further, the nanoscale structure of the two contacting surfaces influences the properties. We have been developing methods for producing well-characterized, nanoscale-structured thin films, where the variation in topography and chemistry can be independently controlled down to a few nanometers. We have been able to show that we can pattern both vertically and laterally down to nanometer dimensions. In addition, we have developed methods for coating AFM cantilevers in order to investigate the influence of nanoscale chemical and topographic structure on the friction and adhesion between an AFM probe tip and the sample. We have shown that it is possible to observe the contrast in frictional properties in these films at the nanometer length scale using adhesion and friction force measurements. We are currently using these patterned films and functionalized tips to determine the influence of the nanoscale chemical variations on the friction and adhesion properties of the film.

Electronic Conductivity: The drive to smaller and smaller device sizes in electronics has made the possibility of molecular-scale electronics very attractive. However, we do not yet understand how to assemble organic molecules into the architectures required for devices and what those architectures should be (i.e., how the charge transport works). We are probing this by examining the influence of domain size of organic molecules on the conductivity of the molecules. This information is going to be critically important in the design of devices in which these molecules must be assembled into working systems. Our approach is to investigate nanostructured arrays of conducting organic molecules as a function of domain size and composition using a conductive-probe AFM. We have developed the patterning methods needed to create these precise, nanostructured domains and have preliminary data showing the contrast in electronic properties between these nanostructured domains and an alkyl monolayer serving as the background matrix. In addition, we have (with Prof. Mikhail Barybin) demonstrated ordered monolayer formation of isocyanoazulenes (a novel class of molecules of interest for their nonlinear optical and electronic properties).