III.1 Surface Modification - Chemical and Biochemical

    Contact between proteins and surfaces is a common occurrence in a wide variety of contexts, ranging from drug delivery systems to sensors to prosthetics. A less commonly realized and examined aspect is the potential use of the self-assembling nature of polypeptide monomers to achieve regular patterns of protein two-dimensional crystals on solid surfaces through cooperative adsorption from appropriate solution. We are carrying out experimental and modeling/simulation studies to gain a deeper understanding of the nature of the phenomena involved in achieving the objective of patterned protein film formation on semiconductor and ceramic surfaces over reasonable local area in microns.

A. Silicon

Following are illustrations of some of our work done on the self assembly of organic chains onto Silicon surfaces to form self-assembled monolayers (SAMs).

AFM image of 3-bromopropyl-tricholoro-silane 0028BPTS) SAM modified Si(001) surface

AFM image of octadecyl-tricholorosiloxane (ODS) SAM modified Si(001) surface

Application to Protein Absorption

    We are carrying out studies for adsorption of a mutant chaperonin (TF55) protein on 3-bromopropyl-tricholrosilane (BPTS) modified Si(001) as shown in the schematic below (left picture). The chaperonin is provided by NASA AMES Laboratory (Dr. J. Trent). Compared to the bare Si surface, BPTS significantly improves adsorption efficiency of the chaperonin by covalently attaching to exposed cysteine group on chaperonin through thiol-ether linkage. This is manifested in the high coverage of chaperonin seen in the AFM image of such a sample (right picture). This research is supported by the National Nanotechnology Initiative under the DURINT (Defense University Research Initiative in Nanotechnology) program.

B. GaAs

Following are illustrations of some of our work done on the self assembly of organic chains onto GaAs surfaces to form self-assembled monolayers (SAMs).

AFM image of 1-octadecanethiol (ODT) SAM modified GaAs (001) surface

AFM image of 1, 6-Hexanedithiol (HDT) SAM modified GaAs (001) surface

Application to Nanocrystal adsorption

SAM molecules with thiol end can be used as bi-linkers between nanocrystals such as CdSe, InAs, ZnSe, etc and semiconductor surfaces. The SAM enables the adsorption of nanoparticles on surface.

Schematic of CdSe nanoparticles adsorbed onto GaAs substrate through HDT SAM

AFM image of CdSe nanoparticles adsored on HDT modified GaAs surface

II. Insulating substrates - Glass and Alumina

A. Glass

                Schematic of APTS SAM adsorption on Glass

Optical fluorescence images of plain (left), and APTS reacted glass surface (right) treated with Fluorescein Isothiocyanate (FITC).

AFM images of plain (left), and APTS reacted glass surface (right) treated with Fluorescein Isothiocyanate (FITC).

The uniformity of the surface coverage of the SAM over macroscopic areas ~1 mm2 and over nano-scale areas ~ 100 nm2 is evident from these images.

B. Alumina

Generic type SAM on Alumina - COOH(CH2) nR

Optical fluorescence images of plain (left), and Aminocaproic acid reacted Alumina surface (right) treated with Fluorescein Isothiocyanate (FITC).

AFM images of plain (left), Aminocaproic acid reacted Alumina (Sapphire) surface (right) treated with Fluorescein Isothiocyanate (FITC).

    Application to Peptide Immobilization and Cell Adhesion

We are carrying out the controlled adsorption of peptide chains that induce the attachment and growth of hippocampal neuronal cells such as neurons and glia on glass and alumina substrate surfaces subsequently rendering them biocompatible. Non-conducting substrates such as glass and alumina form the platforms for most prosthetic implant devices. Our strategy employs controlled adsorption of specific neuronal cells through modification of the surfaces of prosthetic implant electrode arrays by designed organic, self-assembling, bi-linkers that at one end bind covalently (and thus strongly, for mechanical stability) to the prosthesis surface and at the other end contain specific cell receptor recognition peptide in a conformation that enables adsorption of specific neuronal cells through receptor-ligand recognition and binding. The penta-peptide IKVAV has been identified as a sequence that is recognized by the neuron cell surface receptor. Similarly, KHIFSDDSSE is a peptide sequence that is recognized by the glial cell, specifically astrocyte surface receptors. We therefore chose to modify our surfaces with organic molecules designed to immobilize each of these peptides and subsequently expose them to neural cell culture environments to compare the cell adhesion / repulsion induced by such peptide modified surfaces.

Schematic illustrating selective cell adhesion onto peptide modified prosthetic surface.

Optical fluorescence using peptide conjugated dye, TAMRA (top panel) and AFM (lower panel) images of glass surface without peptide (left) and surface reacted with peptide (right).

DURINT Project
    - Nanocrystal/Eptaxial 2D integration
    - Surface Modification (Chemical & Biochemical) (Current Page)
    - Nanoscale Simultaneous Morphological & Optical Imaging

Back to top