Abstract
Conventional pin-to-point continuous wave Helium Corona plasma discharge was successfully used in Soft Plasma Polymerization (SPP) processes to immobilize into water and onto glass polymerized bioactive Cerrena unicolor laccase coatings. The coatings were tested for bioactivity and durability under water wash. The coatings showed up to 59% bioactivity relative to the native laccase in water deposition, undoubtedly due to damage to and fragmentation of monomer molecules by the active, energetic species in the plasma. However, plasma deposited laccase coatings on glass delivered 7 times the laccase activity of the same non-plasma deposition process in the coating after water wash. This latter result would seem to be due to the ability of the plasma to both crosslink monomer and more strongly bond it to the glass surface by a combination of surface cleaning and the creation of active, high energy sites in both glass and laccase molecules. FTIR analysis indicated that the core copper containing moieties at the centre of the molecule largely remain undamaged by this plasma type so that bonding and cross-linking reactions are likely to mainly involve species around the outer perimeter of the molecule. The chemical composition and structure of laccase biocoatings deposited by Corona SPP are described. The combination of the coating performance parameter values for retained activity and durability under water wash indicates that a relatively simple Corona plasma process for deposition of biocoatings, which directly polymerizes the monomer with no added matrix or encapsulant material, may offer enhanced solutions for biocatalyst, sensor or lab-on-a-chip applications.
Highlights
Plasma techniques have become increasingly popular as surface engineering tools in recent years, in particular for deposition of functional coatings
Experiment laccase solution in water toCorona plasma.pin‐to‐plane laccaseThe in water experimental factors were the applied voltage used for plasma generation and the timeexperimental of the covering a glass slide was subjected to pure Helium Corona pin-to-plane jet plasma
The slide with its laccase solution covering was placed below the end of the Corona jet as per Figure 2 and exposed to a pure Helium Corona plasma for 30 or 60s at varying applied voltages and at a constant Helium flow rate of 10 L/min
Summary
Plasma techniques have become increasingly popular as surface engineering tools in recent years, in particular for deposition of functional coatings. A significant step in film deposition has been the development of atmospheric pressure, room temperature Soft Plasma Polymerization (SPP) processes. SPP is the plasma deposition of organic compounds where the original monomer is put down as a cross-linked, thin-film coating without major degradation or denaturing of the original monomer, namely without losing significant functional groups from the molecule [2]. The mechanism of SPP is complex and includes reactions both in the gas/plasma phase and on the surface of the solid substrate receiving the coating. These processes have been studied on non-bioactive organic precursors [3], Polymers 2018, 10, 532; doi:10.3390/polym10050532 www.mdpi.com/journal/polymers
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