that perform certain biological functions, such as specific cell adsorption or interaction with a specific protein or analyte. [3] As part of a device, bioactive surfaces are commonly required to perform in complex biological media such as blood, saliva, or urine. [1,[4][5][6] These fluids typically contain numerous types of proteins and cells that may interfere with the performance of the bioactive surface by nonspecific adsorption. Such nonspecific adsorption by proteins and cells from biological media on a surface is called fouling. [7,8] Thus, the practical application of bioactive surfaces requires antifouling layers capable of preventing protein and cell fouling from complex biological media. [9,10] Antifouling coatings can be generated by immobilizing self-assembled monolayers (SAMs) or "grafted-to" or "graftedfrom" polymer coatings on a surface. [6,[11][12][13][14] SAMs are broadly applied to introduce different functionalities to the surfaces. [15,16] Notably, oligo(ethylene glycol)-terminated [4] and zwitterionic SAMs [17] can resist or decrease fouling from single-protein solutions and cell cultures. "Grafted-to" polymers based on ethylene glycol oxide, oxazoline, [18] N-(2-hydroxypropyl) methacrylamide (HPMA), [12] and zwitterionic moieties [19] have shown good resistance toward single-protein solutions and moderate-to-good resistance toward more complex biological media. The "grafted-from" approach, in which polymer chains are grown from a surface, allows the Surface-initiated photoinduced electron-transfer-reversible addition-fragmentation chain transfer (SI-PET-RAFT) is, for the first time, used for the creation of antifouling polymer brushes on gold surfaces based on three monomers: oligo(ethylene glycol) methyl ether methacrylate (MeOEGMA), N-(2-hydroxypropyl) methacrylamide (HPMA), and carboxybetaine methacrylamide (CBMA). These coatings are subsequently characterized by X-ray photoelectron spectroscopy (XPS) and ellipsometry. The living nature of this polymerization allows for the creation of random and diblock copolymer brushes, which are based on HPMA (superb antifouling) and CBMA (good antifouling and functionalizable via activated ester chemistry). The polymer brushes demonstrate good antifouling properties against undiluted human serum, as monitored by quartz crystal microbalance with dissipation (QCM-D) and surface plasmon resonance (SPR) spectroscopy in real time. The amount of immobilization of bioactive moieties, here an antibody immobilized using N-succinimidyl ester-1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (NHS-EDC) coupling, in the diblock and random copolymer brushes is monitored by SPR, and is analyzed with respect to the brush structure, and is shown to be superior in the diblock copolymer brush. This approach represents a scalable, robust, mild, oxygen-tolerant, and heavy-metal-free route toward the production of antifouling and functional copolymer brushes (on gold surfaces) that open up applications in biosensing and tissue engineering.

When proteins in aqueous solutions are exposed to solid substrates, they adsorb due to the dynamic interplay of electrostatic, van der Waals, and hydration interactions and do so in a rather irreversible fashion, which makes protein recovery troublesome. Here, we use a gold electrode as the solid substrate and modulate the surface potential to systematically induce protein adsorption as well as partial desorption. We use different methods such as surface plasmon resonance, atomic force microscopy, and electrowetting and show that biasing the electrode to more negative potentials (by −0.4 V compared to the open-circuit potential at pH 6) results in an increased adsorption barrier of 6 kJ mol–1 for the negatively charged protein β-lactoglobulin. Further, we clearly demonstrate that this is due to an increased double layer potential of −0.06 V and an increase in hydration repulsion. This indicates that an electric potential can directly influence surface interactions and thus induce partial β-lactoglobulin desorption. These observations can be the basis for biosensors as well as separation technologies that use only one trigger to steer protein ad- and desorption, which is low in energy requirement and does not generate large waste streams, as is the case for standard protein separation technologies.

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