Characterizing the Assembly and Functional Properties of Gene-Length Mixed DNA Monolayers on Electrodes for Cell-Free Expression

Abstract

Gold electrodes are attractive substrates for bioelectronic and cell-free synthetic biology platforms because they are conductive, chemically stable, biocompatible, and readily functionalized through thiol-gold chemistry. Here, gene-length DNA monolayers assembled on planar gold electrodes as reusable templates for cell-free protein expression are investigated. Using thiol-modified sfGFP genes, DNA surface density is shown to be tunable by changing the DNA concentration during incubation, with the immobilized genes able to support cell-free sfGFP expression directly from the electrode surface. Further, the effects of applied voltage, storage, repeated reactions, reducing agents, and protein fouling on monolayer stability and expression output are examined. While some conditions lead to loss of reusable expression activity, dense chemisorbed monolayers can retain partial function under neutral, non-reducing conditions and are relatively robust to protein exposure. In contrast, low-density physisorbed monolayers show a stronger relationship between DNA loss and expression output. Finally, when using gold-mediated fluorescence quenching to monitor changes in DNA conformation, surface-bound DNA demonstrates electrophoretic addressability. Together, these results establish DNA- functionalized planar electrodes as a promising foundation for modular, addressable cell-free expression platforms.