Biomimetic silica encapsulation of enzymes for replacement of biocides in antifouling coatings

摘要

Current antifouling technologies for ship hulls are based on metals such as cuprous oxide and co-biocides like zinc pyrithione. Due to the persistent adverse environmental effects of these biocides, enzyme-based antifouling paints are proposed as a bio-based, non-accumulating alternative. Here, a hydrogen peroxide-producing system composed of hexose oxidase (HOX, EC 1.1.3.5), glucoamylase (GA, EC 3.2.1.3) and starch is tested for the chemical and physical functionalities necessary for successful incorporation into a marine coating. The activity and stability of the enzymes in seawater was evaluated at different temperatures, and paint compatibility was assessed by measuring the distribution and activity of the enzymes incorporated into prototype coating formulations. We used a biomimetic encapsulation procedure for HOX through polyethylenimine-templated silica co-precipitation. The co-precipitation and formulation of a powder for mixing into a marine paint was performed in a one-step economical and gentle formulation process, in which silica co-precipitated HOX was combined with GA and starch to form the antifouling system. Silica co-precipitation significantly improved the stability and performance of the antifouling system in marine-like conditions. For example, encapsulation of HOX resulted in 46% higher activity at pH 8, and its stability in artificial seawater increased from retaining only 3.5% activity after 2 weeks to retaining 55% activity after 12 weeks. A coating comprising the full enzyme system released hydrogen peroxide at rates exceeding a target of 36 nmol cm~(-2) d~(-1) for 3 months in a laboratory assay, and had potential for prolonged action through incorporation in a self-polishing coating.