Microcontact printing of proteins on mixed self-assembled monolayers

Microcontact printing of proteins from an elastomeric stamp has been demonstrated on a limited number of substrates. This work explores the generality of this method of patterning proteins by examining the role of surface wettability of both the substrate and the stamp in microcontact printing. The substrates used in this study consisted of two-component, mixed self-assembled monolayers (SAMs) of alkanethiols on gold presenting -CH3 and polar groups -COOH, -OH, or -(OCH2CH2)(6)OH. We found that protein adsorbed on a stamp successfully transfers onto a mixed SAM only when the mole fraction of polar functionality on the SAM exceeded a particular threshold. Although the mole fraction of polar groups required was different for each of the three types of mixed SAMs, the advancing water contact angles on these surfaces nearly coincided. Moreover, the minimum wettability of the SAM needed for the transfer of proteins decreased when the wettability of the stamp was decreased. Our findings suggest that the difference in wettability between the surfaces of the stamp and substrate is the dominant parameter that determines the successful microcontact printing of proteins.