AVS 50th International Symposium
    Biomaterial Interfaces Monday Sessions
       Session BI-MoM

Paper BI-MoM7
Using Nanografting to Position with Predictable Orientation, De-novo Proteins on Gold

Monday, November 3, 2003, 10:20 am, Room 307

Session: Protein-Surface Interactions
Presenter: Y Hu, Princeton University
Authors: Y Hu, Princeton University
M. Case, Princeton University
G. McLendon, Princeton University
T.K. Vanderlick, Princeton University
D. Vanderah, National Institute of Standards and Technology
B. Nickel, Princeton University
M. Mrksich, University of Chicago
G.Y. Liu, University of California, Davis
G. Scoles, Princeton University
Correspondent: Click to Email
An extensive research effort has been trying to make biosensors at the nanometer scale, especially selective detection devices with molecular recognition sites. We have approached this problem from a unique angle by using nanografting, which is to use an AFM tip to remove thiol molecules from a designated area of a self-assembled monolayer (SAM) while different thiol molecules from a contacting solution will self-assemble onto the exposed gold sites. By incorporating cysteine residues at the end of the peptide chains of [Fe(V@suba@L@subd@C-long)@sub3@]@super2+@, the proteins acquire the possibility to stand vertically on a gold surface. By using nanografting, the proteins could be patterned into islands about tens of nm wide and their properties could be measured in a differential way using the surrounding SAM as a reference. The height of these islands measures 3.2nm±0.4nm which, added to the 2.2 nm of the C@sub18@ SAM, corresponds well with the model height of the proteins. Effectively maximizing the signal-to-noise ratio of biosensors depends also on the ability to prevent protein nonspecific surface adsorption. It has been found that SAMs of thiols containing short oligomers of the ethylene glycol group prevent the adsorption of most proteins under a wide range of conditions. However the mechanism has not been clearly explained. It is observed that both SH(CH@sub2@)@sub11@(EO)@sub3@-OH and SH(EO)@sub6@-(CH@sub2@)@sub17@-CH@sub3@ reversibly compressed to half of their height under small imaging forces(0-10nN) in ethanol or 2-butanol. When the force is increased to over ~50nN, irreversible compression happened. Moreover, when the solution is changed to water mixture, the SH(EO)@sub6@-(CH@sub2@)@sub17@-CH@sub3@ is found to decrease its height significantly, and become much less compressible. By offering a model to explain the compressibility changes observed, we hope to offer some insight into the protein resistant properties of PEG-containing layers.