Atmospheric-pressure plasmas for the preparation of functional thin films for biosensing David Rettke, Frank Hempeland and Laura Barillas Biosensing Surfaces, Leibniz Institute for Plasma Science and Technology (INP), Felix-Hausdorff-Strasse 2, 17489 Greifswald, Germany Physical plasma-assisted processes have replaced numerous industrial approaches based on heating and wet chemistry as they enable cleaning, activation and functionalization of virtually any surface within minutes, reducing process steps and avoiding hazardous procedures. Such approaches are characterized by excellent controllability of process parameters as well as cost efficiency and environmental friendliness, and work as a viable alternative for producing functional thin films needed in biosensors [1] . In particular, plasmas at atmospheric pressure (AP) enable rapid processing, scalability, and lower cost, as the plasma source dimensions can be reduced to a compact form factor and there is no need for vacuum equipment. The suitability of such plasmas for the preparation of thin films has been successfully demonstrated and subsequently used for electrochemical and optical biosensing [2][3] . This contribution addresses current developments in thin film fabrication using AP plasmas for improved modularity and performance of biosensors. Our current research focuses on the introduction of tailored functionalities for bioreceptor immobilization, nanocomposite fabrication, and microscale morphology manipulation. AP plasmas were used to clean and activate the surfaces and vinylic monomers were subsequently deposited using specially designed mist chambers [1] . Exposure of the monomers to the plasma yielded cross-linked matrices formed via plasma-initiated radical polymerization. Ambient air-fed microwave plasma sources used for cross-linking and functionalization of tetraacrylates produced thin films bearing a high density of carboxy-groups, which are well suited for bioreceptor immobilization. The same monomer in conjunction with argon-fed radiofrequency plasma sources resulted in densely cross-linked matrices containing acrylate groups, suitable for the subsequent introduction of other functional moieties using Michael-addition reactions, expanding the repertoire of accessible immobilization chemistries. In addition, stable nanocomposites have been developed. These thin films, in which vinyl-containing liquid admixtures carrying a mass fraction of up to 10% colloidal gold were likewise exposed to AP plasmas, presented a homogeneous distribution of the nanoparticles within the matrix. Lastly, the possibilities for tuning the morphology of plasma-polymerized films are highlighted. Tunability of the morphology was achieved by varying process parameters, such as the flow rate of the process gas and the composition of the monomer mixtures, allowing the preparation of either smooth or rough and porous thin films with a large surface area. Furthermore, hydrogels with highly ordered lamellar structures with adjustable size from the milli- to the lower micrometer-scale were fabricated employing plasma-initiated self-assembly phenomena. In summary, AP plasma-based processes offer promising opportunities for the production of functional materials for biosensing with tailored immobilization chemistry for the respective bioreceptor, embedded nanomaterials for improved sensor performance, and adaptability of the morphology to the respective detection principle. References 1. Barillas et al. Coatings, 2021, 11, 1336 2. Makhneva et al. ACS Appl Mater Interfaces, 2020, 12, 14, 17100–17112 3. Levien et al. Appl. Surf. Sci., 2022, 584, 152511
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