Exploring aerosol-assisted plasma deposition of biocomposite antifouling films for biosensing

Abstract

Aerosol-assisted plasma deposition (AAPD) at atmospheric pressure is a plasma-based deposition process that uses aerosols to inject precursors into the plasma. This approach significantly expands the library of usable precursors, including compounds with a low vapor pressure, nanoparticle solutions or even biomolecules. In this thesis, we explore AAPD using an atmospheric pressure plasma jet as an alternative method for two essential steps in the fabrication process of a biosensor: the deposition of a poly(ethylene oxide)(PEO)-based antibiofouling coating and the immobilization of a bioreceptor. While AAPD provides interesting opportunities, fundamental insight in the deposition mechanism is required to develop AAPD processes that enable deposition of PEO-based antibiofouling coatings and the incorporation of bioreceptors in PEO-based layers. We investigate how the precursor properties and AAPD process conditions affect the composition, morphology and antifouling properties of PEO-based antibiofouling and PEO-based biocomposite films. In addition, we aim to explore the potential of AAPD to entrap bioreceptors in PEO-based layers and investigate how the film morphology relates to the sensor sensitivity. In chapter 2, we study the AAPD process of PEO-based antifouling films focusing on aerosol generation, droplet transport, impaction, spreading and polymerization. We examine the effects of volatility and viscosity for a set of poly(ethylene oxide) dimethacrylate precursors with varying ethylene oxide repeats. Increasing the number of ethylene oxide repeats reduces volatility, hereby improving the material balance by minimizing evaporation during transport and after impaction on the substrate. This results in more and larger droplets reaching the substrate, which influences the polymerization. The antifouling properties of the films can be improved by increasing the number of ethylene oxide repeats in the precursor, in agreement with an increasing PEO-character of the deposited films. In chapter 3, we investigate a promising route to further improve the antifouling properties with an alternative precursor: di(ethylene glycol) divinyl ether (2EGDVE), which can result in a higher PEO-character. However, as atmospheric pressure plasma jets operate in open air, air can enter the reaction area and inhibit polymerization. We investigate the mixing of air into the reaction area for two nozzle designs (a ring and a line nozzle) using a computational fluid dynamics model. The line nozzle performs better to keep air out of the reaction area, which resulted in less oxidized coatings with improved stability in water. The resulting coatings have excellent antifouling properties and could prevent the adhesion of human fibroblast cells, consistent with their high PEO character (65%). In chapter 4 we provide and analyze a proof-of-concept for the immobilization of a bioreceptor, glucose oxidase (GOx), in a PEO-based biocomposite thin film deposited by AAPD. The film morphology and biosensor sensitivity are tunable through the AAPD process conditions. We demonstrate how water evaporation during transport of the aerosol changes the water volume fraction (ϕH2O) in the droplets. Droplets with a high ϕH2O spread out upon impaction, forming disk-shaped features, while droplets with a low ϕH2O behave more like a solid upon impaction, leading to the formation of hemispherical features. The formation of disk-shaped features correlates with an increased sensitivity when the films are used in a first-generation glucose sensor. This work demonstrates how AAPD can become a viable technology for deposition of biocomposite thin films with tunable properties. A deeper understanding of the mechanisms during AAPD, especially regarding the role of the aerosol in the deposition process, is essential to enable AAPD of biocomposite thin films for biosensor fabrication.