FABRICATION AND IMAGING OF 2-DIMENSIONAL PATTERNS OF PROTEINS ADSORBED ON SELF-ASSEMBLED MONOLAYERS BY SCANNING ELECTRON-MICROSCOPY

This paper describes methods for controlling both the concentration an d spatial distribution of proteins adsorbed onto patterned, self-assem bled monolayers (SAMs). Patterned SAMs were formed by the serial chemi sorption of two or more omega-functionalized alkanethiols (HS(CH2)(n)R ) on gold. Several techniques (microwriting, micromachining, stamping, and UV microlithography) were used to fabricate the patterned SAMs. T he most useful systems of patterned SAMs for studying the adsorption o f proteins are those in which spatially-defined areas that resist prot ein adsorption arc formed from oligo(ethylene glycol)-terminated thiol s (e.g., R = (OCH2CH2)6OH) and other areas that allow protein adsorpti on are formed from thiols terminated by nonpolar (R = CH3) and ionic ( R = CO2-, PO3H-, 2-imidazolo) groups. Scanning electron microscopy (SE M) allows characterization of patterns of proteins adsorbed on SAMs of alkanethiolates. The adsorbed proteins, when correctly prepared, form layers that appear to be homogeneous by SEM. When the protein layers are prepared differently, images obtained by SEM clearly show heteroge neity and defects in the layer of adsorbed proteins. The ability to as say the uniformity of coverage of surfaces by adsorbed proteins using SEM will be useful in studies involving protein adsorption.