Natalia Janiszewska

To provide antifouling bioactive surfaces for biosensing and cell culture, we synthesized and characterized copolymer brush interfaces with minimized nonspecific adsorption combined with adjustable high-capacity bioconjugation of functional protein and examined the interfacial protein state that determines its biological activity. Brushes were fabricated using surface-initiated atom transfer radical polymerization with silicon-grafted chains copolymerized from 2-(2-methoxyethoxy)ethyl methacrylate (OEGMA) and methacrylic acid (MAA) taken in different proportions. For all P(OEGMA_1-x-co-MAA_x) coatings (0 ≤ x ≤ 1), X-ray photoelectron spectroscopy revealed the molar fraction x of MAA in the brush equal to that of the reaction mixture. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) showed a copolymer composition that is uniform with depth in the brush coatings, confirming a successful random copolymerization. Bioconjugation of immunoglobulin G antibody (IgG) within the brushes, enabled by the activation of MAA segments with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide (EDC/NHS), was examined together with nonspecific IgG adsorption to the nonactivated brushes using ToF-SIMS and fluorescence microscopy. Protein loading was controlled by copolymer composition and protein solution concentration. The optimal composition x = 0.25 was selected for the brushes with maximum bioconjugation (∼0.4 g/cm³) and low nonspecific adsorption. Protein loads per brush volume were estimated from ToF-SIMS depth profiles that evidenced IgG immobilization within the brush. For all P(OEGMA_1-x-co-MAA_x) brushes with conjugated IgG antibody, the coatings with x = 0.25 provided the highest amount of bound antigen with an antigen binding ratio higher than that of the PMAA coatings. This observation was related to the different interfacial antibody states in both coatings (determined by the residue involvement in the coupling with the MAA segments and the dominant antibody orientation), which were investigated with multivariate principal component analysis of ToF-SIMS data. Finally, human fibroblast cell culture showed the biocompatibility of the developed copolymer brush coatings, further promoted by brush conjugation with fibronectin.

Carbyne-containing materials offer significant potential for biosensor applications due to their unique chemical and mechanical properties. In this study, carbyne-enriched carbon coatings deposited on SiO₂/Si chips using ion-assisted pulse-plasma deposition were evaluated for the first time as substrates for optical biosensing. At first, the carbyne-enriched coatings were characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, Atomic Force Microscopy, and the sessile drop method to assess their composition, structure, and wettability. After that, chips with carbyne-enriched coatings were modified with biomolecules through physical absorption or covalent bonding, and the respective biomolecular interactions were monitored in real-time by White Light Reflectance Spectroscopy (WLRS). In both cases, SiO₂/Si chips modified with an aminosilane were used as reference substrates. Physical adsorption was tested through immobilization of an antibody against C-reactive protein (CRP) to enable its immunochemical detection, whereas covalent bonding was tested through coupling of biotin and monitoring its reaction with streptavidin. It was found that the carbyne-enriched carbon-coated chips retained both their antibody adsorption capability and their covalent bonding ability for over 18 months, while the modified with aminosilane SiO₂/Si chips lost 90% of their antibody adsorption capacity and covalent bonding ability after two months of storage. These findings highlight the strong potential of carbyne-enriched carbon-coated chips as robust biosensing substrates, with applications extending beyond WLRS.

We have investigated the evolution of freshly cleaved NaCl(100) and KCl(100) surfaces exposed to the ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF₆) and repeatedly scraped using atomic force microscopy (AFM). The response of the two surfaces to the IL is completely different. On NaCl, the cleavage step edges are slightly eroded, and the surface is progressively smoothed by the AFM tip. These changes are accompanied by a continuous increase in the friction force. On KCl, a dramatic dissolution of the surface is observed immediately after bringing it into contact with the IL. The surface is then smeared along the fast scan direction in the area scratched by the tip and even beyond. An increase in the friction force is also observed but only in the beginning of the surface modification process. Crystallites (∼100-200 nm in size) are observed all over the unscratched areas of KCl but not of NaCl. This result is supported by molecular dynamics simulations and Raman spectroscopy, which indicate a much stronger interaction of the IL with the KCl surface and, respectively, the formation of a BMIM-PF₆ solid phase on it. The analysis performed on the model systems presented here could be extended to other ionic crystal surfaces in contact with ILs, the possible degradation of which must be evaluated in view of their use in catalysis and energy storage applications.

Stereochemistry may affect the physicochemical and biological properties of polymer films that are important for their applications, including substrates for the fabrication of protein microarrays. In this study, we investigated the effect of poly(methyl methacrylate) (PMMA) tacticity on the interaction of polymer thin films with proteins and on the phase separation process in blends with poly(tert-butyl methacrylate) (PtBMA). Thin films of isotactic, atactic, and syndiotactic PMMA were studied for topography, surface chemistry, and protein adsorption. Secondary ion mass spectrometry and contact angle measurements revealed a lower surface exposure of polar ester functional groups for iso-PMMA, resulting in the reduced adsorption of albumin and fibrinogen proteins. We also showed that changes in surface chemistry alter the orientation of proteins adsorbed on iso-PMMA through hydrophobic and electrostatic interactions. In addition, blends composed of PMMA and PtBMA, both of different tacticities, were investigated in terms of protein microarray fabrication. The two-dimensional domain structure was obtained by a phase separation process for at-PtBMA blends prepared on silicon substrates modified with amino-silane. Finally, for an isotropic and regular polymer pattern of iso-PMMA/at-PtBMA, the possibility of protein microarray formation on this blend was demonstrated, showing selective adsorption to PtBMA domains and perfect mirroring of the polymer patterns.