Defect-driven Biocidal Enhancement of Cuprous Oxide

Non-stoichiometric metal-oxides are known for their enabling roles in energy conversion and storage devices, sensors and catalysts, among other applications. Indeed, the compound Cu_2-_dO (cuprous oxide or cuprite), which is copper-deficient in its native state, has been documented as a contact-kill antimicrobial material; however the origins of its biocidal effectiveness are not well understood. To this end, it is of interest to investigate how cuprite’s antipathogenic character scales with the density of copper vacancies; these defects are hypothesized to donate highly elevated local electrical potential that disrupts cell membranes and/or virus protein shells. In this work, commercial cuprous oxide powder (99.99%) was processed using high-energy cryomechanical milling to amplify lattice disorder and was subsequently incorporated into coatings. Coatings made from these processed powders demonstrate a self-sterilizing response to <i>E. coli</i> bacteria that is 4x (400%) faster than coatings made from unprocessed powder. No viable bacteria (&gt; 99.999% (5-log10) reduction) are detected in bioassays performed after two hours of exposure of <i>E. coli</i> to coatings of processed cuprous oxide, while a greater than 99% bacterial reduction is achieved within 30 minutes of exposure. Further, these coatings are hydrophobic and need no external energy input to activate their contact-kill capability. The upregulated antibacterial response of the processed powders is positively correlated with extensive induced crystallographic disorder and microstrain in the Cu₂O lattice, and is accompanied by color changes that are consistent with an increased semiconducting bandgap energy. Electron microscopy reveals that cryomilled powder consists of well-crystallized nanoscale regions enmeshed within a highly lattice-defective particle matrix. These results highlight avenues for further enhancement of the antipathogenic capability of this abundant, inexpensive, robust and easily handled metal-oxide powder for wider deployment in contact-kill surfaces.<br/><br/><b>Funding Acknowledgement: </b>This work was conducted at Northeastern University under the auspices of NSF DMR Grant #2029194 (for determination of fundamental materials aspects) and DEVCOM Soldier Center Contract Agreement W911QY-19-9-0011 (for experiments related to preparation of coatings).