Nanopatterned Monolayers of Bioinspired, Sequence-Defined Polypeptoid Brushes for Semiconductor/Bio Interfaces

The ability to control and manipulate semiconductor/bio interfaces is essential to enable biological nanofabrication pathways and bioelectronic devices. Traditional surface functionalization methods, such as self-assembled monolayers (SAMs), provide limited customization for these interfaces. Polymer brushes offer a wider range of chemistries, but choices that maintain compatibility with both lithographic patterning and biological systems are scarce. Here, we developed a class of bioinspired, sequence-defined polymers, i.e., polypeptoids, as tailored polymer brushes for surface modification of semiconductor substrates. Polypeptoids featuring a terminal hydroxyl (−OH) group are designed and synthesized for efficient melt grafting onto the native oxide layer of Si substrates, forming ultrathin (∼1 nm) monolayers. By programming monomer chemistry, our polypeptoid brush platform offers versatile surface modification, including adjustments to surface energy, passivation, preferential biomolecule attachment, and specific biomolecule binding. Importantly, the polypeptoid brush monolayers remain compatible with electron-beam lithographic patterning and retain their chemical characteristics even under harsh lithographic conditions. Electron-beam lithography is used over polypeptoid brushes to generate highly precise, binary nanoscale patterns with localized functionality for the selective immobilization (or passivation) of biomacromolecules, such as DNA origami or streptavidin, onto addressable arrays. This surface modification strategy with bioinspired, sequence-defined polypeptoid brushes enables monomer-level control over surface properties with a large parameter space of monomer chemistry and sequence and therefore is a highly versatile platform to precisely engineer semiconductor/bio interfaces for bioelectronics applications.


Scheme S2.
Biotinylation of polypeptoids at the N-terminus.The same PP1 sample, after two days in ACN/H2O solution:

Figure S7 .
Figure S7.Potential esterification of the -OH group on the first monomer with TFA during cleavage (peak at 3.27 min observed in LC trace, with + 96 g mol -1 as compared to the theoretical molecular weight of PP1), which fully reverse after ~ two days in ACN/H2O solution.

2 DNA
Origami and Streptavidin Immobilization on Polymer Brush Modified Surfaces and Chemical Contrast Nanopatterns

Figure S11 .
Figure S11.Top: Schematic of the DNA origami nanostructure (from tilibit nanosystems) and morphology of deposited DNA origami nanostructures on bare Si substrates.Bottom: DNA origami binding density on bare Si (3 nM) vs. on PP3 brush monolayer and PP4 brush monolayer modified Si substrates (1 nM).

Figure S14 .
Figure S14.Backfill test with the biotinylated polypeptoid (biotin-PP1) brush, which demonstrates sufficient brush interpenetration happens during the backfill step, and the interpenetrated biotinylated polypeptoid brushes bind large amounts of streptavidin proteins.

Table S1 .
Comparison of brush monolayer thickness and water contact angle of the correspondingly modified Si substrate surface between -OH and -COOH functionalized polymers.
a Polymer brush monolayers are prepared on Si wafers with a 250 nm thermal oxide layer, with the thermal oxide layer thickness measured via ellipsometry before polymer grafting.