This area of our research focuses on the development of chemical modification strategies for controlling the specific and non-specific adsorption of biopolymers (e.g., synthetic polypeptides, proteins and DNA molecules) onto metal surfaces. The formation of biologically active biopolymer monolayers at metal surfaces is an essential step in the fabrication of a number of important bioanalytical devices such as biochemical sensors, bioelectronic switches and gates, chemical separation and purification surfaces, and enzymatically controlled electrochemical interfaces. The biochemical activity of the adsorbed molecules often differs from what is observed in solution; our goal is to optimize this activity with the appropriate surface chemistry and minimize any interferences due to non-specific adsorption.

How does one chemically modify a metal surface in order to control the adsorption of biopolymers? Figure 1 depicts the three general routes for controlling biopolymer adsorption on gold surfaces with self-assembled monolayers (SAMs) of n-alkanethiols.

Figure 1. Schemes for the creation of specific adsorption sites on modified gold surfaces.

The formation of alkanethiol SAMs at gold surfaces has been one of the most successful chemistries for the modification of gold surfaces, and offers a simple and attractive method of surface modification at the single monolayer level. The specific adsorption of a biological target molecule onto a metal surface can occur either by (A) the incorporation of alkanethiols terminated with an adsorption site into the SAM, (B) the covalent chemical attachment of an adsorption site to a SAM via reaction with a pendant functional group, or (C) the adsorption of a synthetic biopolymer onto the SAM that has adsorption sites incorporated into its structure. Using scheme A, SAMs have been used to control of the adsorption of enzymes, antibodies and DNA molecules onto metal surfaces. This method is viable as long as (i) the specific adsorption site does not interact with the thiol prior to adsorption, (ii) the chemical functionality that serves as the specific adsorption site does not interfere with the self-assembly process, and (iii) the modified alkanethiol does not segregate from other alkanethiols and inhibit the formation of mixed monolayers on the surface.

Development of attachment chemistry and fabrication methodologies for creating DNA microarrays on gold surfaces. A crucial aspect in the formation of surface array biosensors is the careful fabrication of well-characterized, robust DNA microarrays. Using a combination of self assembly of an amine-terminated alkanethiol (MUAM), chemical protection/deprotection reactions and photopatterning, we created a seven step fabrication methodology for the creation of DNA microarrays on gold surfaces. A crucial step in the fabrication process is the creation of a temporary hydrophobic background using an fmoc-protected amine-terminated surface to pin and separate the nanoliter volumes of DNA solution onto the array elements during the attachment step. The final array background is modified with polyethylene glycol (PEG) in order to avoid the non-specific adsorption of biopolymers onto the gold surface. This process has been patented (US 6,127,129) and is currently licensed by several biotechnology companies. In addition to array fabrication, we have explored alternate methods for the attachment of biopolymers onto gold surfaces, including a recent demonstration of disulfide linkages to surfaces. This new attachment chemistry allows for the reversible chemisorption of oligonucleotides and polypeptides.

Our recent papers in this area are:

• Emily A. Smith, William D. Thomas, Laura L. Kiessling, and Robert M. Corn,
  "Surface Plasmon Resonance Imaging Studies of Protein-Carbohydrate Interactions,"
  J. Am. Chem. Soc., 125 6140-6148 (2003).



• Greta J. Wegner, Hye Jin Lee, Gerard Marriott, and Robert M.Corn,
  "Fabrication of Histidine-Tagged Fusion Protein Arrays for Surface Plasmon Resonance Imaging Studies of Protein-Protein and Protein-DNA Interactions,"
  Analytical Chem., 75 4740-4746 (2003).



• Greta J. Wegner, Hye Jin Lee and Robert M. Corn,
  "Characterization and Optimization of Peptide Arrays for the Study of Epitope-Antibody Interactions Using Surface Plasmon Resonance Imaging,"
  Analytical Chem., 74 5161-5168 (2002).



• Emily A. Smith, Matt J. Wanat, Yufei Cheng, Sergio V. P. Barreira, Anthony G. Frutos and Robert M. Corn
  "Formation, Spectroscopic Characterization and Application of Sulfhydryl-Terminated Alkanethiol Monolayers for the Chemical Attachment of DNA onto Gold Surfaces,"
  Langmuir, 17 2502-2507 (2001).



• Bryce P. Nelson, Timothy E. Grimsrud, Mark R. Liles, Robert M. Goodman, and Robert M. Corn,
  "Surface Plasmon Resonance Imaging Measurements of DNA and RNA Hybridization Adsorption onto DNA Microarrays,"
  Analytical Chem., 73 1-7 (2001).



• Anthony G. Frutos, Jennifer M. Brockman and Robert M. Corn,
  "Reversible Protection and Reactive Patterning of Amine and Hydroxyl-Terminated Self-Assembled Monolayers on Gold Surfaces for the Fabrication of Biopolymer Arrays,"
  Langmuir, 16 2192-2197 (2000).
  Abstract



• Jennifer M. Brockman, Anthony G. Frutos and Robert M. Corn,
  "A Multi-Step Chemical Modification Procedure to Create DNA Arrays on Gold Surfaces for the Study of Protein-DNA Interactions with Surface Plasmon Resonance Imaging,"
  J. Am. Chem. Soc., 121 8044-8051 (1999).
  Abstract