Enzymatic Oxidation of Polyethylene & Peptide-Based Detection of Microplastics

Abstract

As humanity nears a century of steadily rising polyethylene (PE) production the associated environmental and societal costs are drawing increased concern. The recalcitrant nature of PE, while a distinct material advantage, poses a challenge to biotic degradation leading to prolonged environmental persistence. Here we present a screening of commercially available oxidative enzymes previously reported to oxidize the surface of PE with analysis performed by high-temperature 1H-NMR. This screening was conducted with the perspective gained from having previously characterized catalytically oxidized PE, which verified the efficacy of the 1H-NMR analytical method.

In total, five commercially sourced oxidoreductases and hemocyanin were tested on standardized PE and characterized by 1H-NMR. Despite multiple attempts with various radical mediators, only manganese peroxidase demonstrated potential oxidative activity against PE. These results underscore the need for carefully designed PE degradation experiments which utilize standardized PE, employ a range of analytical techniques, include the full spectra of the acquired data, and report all outcomes.

In addition to the screening of oxidative enzymes, we designed and tested five fluorescent peptide probes, produced using previously reported plastic binding peptides, to selectively identify the polymeric material of microplastics. Using both experimentation and computational modeling, tryptophan and phenylalanine were identified as key residues that mediate the binding of the peptides to the plastic surface. However, the produced hydrophobic interactions were determined to be largely non-specific when tested against PE, polyethylene terephthalate, polypropylene, and polystyrene.