Molecular control of biopolymer assembly on surfaces

To develop new material functions, understanding correlations between structure and function is important. Molecular control is a bridge to connect designed structures to desired properties or functionality. In the present study, several new technologies are integrated to accomplish this goal. Dip-pen nanolithography (DPN) has recently been developed as a powerful tool for the controlled deposition of molecules on surfaces in the nanometer scale range. Similarly, enzymatic method in polymer synthesis offers novel control of structure. (a) DPN/Enzymatic Nanowires - Horseradish peroxidase (HRP) catalyzed polymerization of phenolic compounds and aniline derivatives has advantages over traditional methods in the synthesis of conducting polymers. By combining this biocatalytic approach with DPN methods, controlled polymer nano-features were achieved in ambient and biocompatible conditions. Conducting Nanowires were formed by DPN with 4-aminothiophenol followed by catalysis with HRP/H2O. (b) SAMs/DPN/Nanowires - Self-assembled monolayers (SAMs) help in the patterning of other compounds, such as tyrosine derivatives and 1,4-phenyldiamine, which lack affinity to gold or silicon surfaces, so that they can be polymerized in situ. The conducting polyaniline can also be patterned on SAMs with potential for direct manufacture of electronic nanodevices. The polymerization of surface anchored monomers also provides new insight for regioselectivity in the polymerization process. The pre-oriented monomer patterns resulted in specific structural features of the polymer products which were not controllable in solution. Nanoscale surface patterning of caffeic acid demonstrated that the surface induced preorganization of monomers completely altered the structural details of the resulting polymers formed via biocatalysis. (c) DPN/Self-Assembly - Collagen peptides with specific alterations in primary sequence, have been used with DPN to study self-assembly to interrogate the influence of sequence chemistry on self organization on surfaces and subsequently how this change in organization impacts function. The results demonstrate a direct correlation between alterations in mineralization patterns with the changes in protein template features, reflective of a biological paradigm that can be exploited in the design of novel composite materials. The strategies to integrate nanoscale processing and synthesis systems, such as DPN and biocatalysis and/or self-assembly, suggest new directions in the fabrication and integration of synthetic and biological systems at nanometer scales.