Bio-inspired multifunctional catecholic assembly for photo-programmable biointerface

Antimicrobial Efficiency and Surface Interactions of Quaternary Ammonium Compound Absorbed on Dielectric Barrier Discharge (DBD) Plasma Treated Fiber-Based Wiping Materials

The physicochemical interactions between alkyldimethylbenzylammonium chloride (ADBAC) as disinfectant and three commercial wiping materials made from 100% polyester (PET), 55%cellulose/45%PET (blend), and 100% cellulose were investigated after treatment with dielectric barrier discharge (DBD) plasma at atmospheric pressure. Wipe material type in terms of cellulose content, liquor ratio, and immersion time demonstrated a significant influence on the adsorption of ADBAC. The higher the content of cellulose in the material, the higher is the adsorption of ADBAC active ingredient. The antimicrobial tests confirm that the ADBAC adsorbed on pure cellulosic material is inactivated losing its bactericidal activity, while 100% PET and blend wipes showed good antimicrobial efficacy. XPS analysis demonstrates the strong interactions of ADBAC with the plasma-generated oxygen species in the polyester-containing wipes surface. Unexpectedly, plasma-treated blend wipe displays a reverse antimicrobial effect compared to untreated samples, performing better in Gram-negative bacteria. The best result was obtained in the plasma treated 100% polyester wipe showing an improvement of about 20% in Gram-positive bacteria and an excellent performance in Gram-negative ones. This method allows the unprecedented use of pure polyester as effective wiping material for surface disinfection eliminating the major drawback of pure polyester, its high hydrophobicity.

Functional Biointerfaces Based on Mixed Zwitterionic Self-Assembled Monolayers for Biosensing Applications

Surface modification for biosensors has focused attention for improvement of their sensitivity and specificity, particularly for the detection in complex medium. In this work, we have synthesized zwitterionic carboxybetaine-thiols (CB-thiols) and sulfobetaine-thiols (SB-thiols) for modification of gold substrates to form a functional self-assembled monolayer (SAM) for the immunoassay in a surface plasmon resonance (SPR) biosensor. X-ray photoelectron spectroscopy (XPS), contact angle goniometer, and cyclic voltammetry were applied for characterizations of elemental composition, surface wettability, and packing density, respectively. The antifouling properties of the SAMs were accessed by quantitative analysis of protein and bacterial adsorption. The results from the SAMs with a single component indicated that the SB-thiol SAM provides better surface hydrophilicity, fouling resistance, and packing density as compared to the CB-thiol SAM, likely due to the ionic association of CB moieties. However, the CB-thiol with the functional carboxylate group plays a critical role in postmodification of biomolecules via commercially available amine coupling chemistry. Thus, the mixed SAMs were prepared to integrate the unique characteristics from CB- and SB-thiols to control compositions and surface properties. The immunoassay was performed in the SPR biosensor, showing that the zwitterionic mixed SAM enables immobilization of biorecognition elements (BREs), and improved sensitivity and specificity. Consequently, the work reveals excellent and attractive versatility, antifouling, and functionalizable properties of zwitterionic mixed SAMs comprising CB- and SB-thiols for biosensing applications. This surface chemistry is expected to be applicable to monitor specific molecular recognition events.

Controlled Silanization Using Functional Silatrane for Thin and Homogeneous Antifouling Coatings

Organosilicons for surface modification are gaining prominence because of their easy and rapid preparation, high availability, and effective modification for varying interfacial properties. However, their implementation has been humbled by poor control of the packing density, thickness, and molecular structures due to the uncontrollable hydrolysis and condensation. This study reports for the first time new functional silatrane chemistry for the precision deposition of a thin and homogeneous zwitterionic coating. Sulfobetaine silatrane (SBSiT) has a tricyclic caged structure and a transannular N → Si dative bond, which shows excellent chemical stability in the presence of water and an acid-modulated hydrolysis characteristic. Results from X-ray photoelectron spectroscopy indicate the progressive deposition of SBSiT on a silicon surface. Characterization using atomic force microscopy and ellipsometry shows the uniform and thin SBSiT films on silicon surfaces. The superior antifouling properties of SBSiT coatings were demonstrated by resisting bacterial and protein adsorption. More importantly, the stable and complete formation of the SBSiT coatings allows an accurate interpretation of the interfacial phenomena for sensing and nanomaterial applications.

Self-Propulsion and Shape Restoration of Aqueous Drops on Sulfobetaine Silane Surfaces

The motion of droplets on typical surfaces is generally halted by contact line pinning associated with contact angle hysteresis. In this study, it was shown that, on a zwitterionic sulfobetaine silane (SBSi)-coated surface, aqueous drops with appropriate solutes can demonstrate hysteresis-free behavior, whereas a pure water drop shows spontaneous spreading. By adding solutes such as polyethylene glycol, 2(2-butoxy ethoxy) ethanol, or sodium n-dodecyl sulfate, an aqueous drop with a small contact angle (disappearance of spontaneous spreading) was formed on SBSi surfaces. The initial drop shape was readily relaxed back to a circular shape (hysteresis-free behavior), even upon severe disturbances. Moreover, it was interesting to observe the self-propulsion of such a drop on horizontal SBSi surfaces in the absence of externally provided stimuli. The self-propelled drop tends to follow a random trajectory, and the continuous movement can last for at least 10 min. This self-propelled random motion can be attributed to the combined effects of the hysteresis-free surface and the Marangoni stress. The former comes from the total wetting property of the surface, while the latter originates from surface tension gradient due to fluctuating evaporation rates along the drop border.

Effect of elimination on antifouling and pH-responsive properties of carboxybetaine materials

α- and β-substituted methyl carboxybetaine materials are developed to investigate the occurrence of elimination in the ethylene intercharge arm in a harsh basic solution.

Quantitative Measurement of Ligand Exchange with Small-Molecule Ligands on Iron Oxide Nanoparticles via Radioanalytical Techniques

Ligand exchange on the surface of hydrophobic iron oxide nanoparticles is a common method for controlling surface chemistry for a desired application. Furthermore, ligand exchange with small-molecule ligands may be necessary to obtain particles with a specific size or functionality. Understanding to what extent ligand exchange occurs and what factors affect it is important for the optimization of this critical procedure. However, quantifying the amount of exchange may be difficult because of the limitations of commonly used characterization techniques. Therefore, we utilized a radiotracer technique to track the exchange of a radiolabeled ¹⁴C-oleic acid ligand with hydrophilic small-molecule ligands on the surface of iron oxide nanoparticles. Iron oxide nanoparticles functionalized with ¹⁴C-oleic acid were modified with small-molecule ligands with terminal functional groups including catechols, phosphonates, sulfonates, thiols, carboxylic acids, and silanes. These moieties were selected because they represent the most commonly used ligands for this procedure. The effectiveness of these molecules was compared using both procedures widely found in the literature and using a standardized procedure. After ligand exchange, the nanoparticles were analyzed using liquid scintillation counting (LSC) and inductively coupled plasma-mass spectrometry. The labeled and unlabeled particles were further characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS) to determine the particle size, hydrodynamic diameter, and zeta potential. The unlabeled particles were characterized via attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and vibrating sample magnetometry (VSM) to confirm the presence of the small molecules on the particles and verify the magnetic properties, respectively. Radioanalytical determination of ¹⁴C-oleic acid was used to calculate the total amount of oleic acid remaining on the surface of the particles after ligand exchange. The results revealed that the ligand-exchange reactions performed using widely cited procedures did not go to completion. Residual oleic acid remained on the particles after these reactions and the reactions using a standardized protocol. A comparison of the ligand-exchange procedures indicated that the binding moiety, multidenticity, reaction time, temperature, and presence of a catalyst impacted the extent of exchange. Quantification of the oleic acid remaining after ligand exchange revealed a binding hierarchy in which catechol-derived anchor groups displace the most oleic acid on the surface of the nanoparticles and the thiol group displaces the least amount of oleic acid. Thorough characterization of ligand exchange is required to develop nanoparticles suitable for their intended application.

Surface modification with zwitterionic cysteine betaine for nanoshell-assisted near-infrared plasmonic hyperthermia

Nanoparticles decorated with biocompatible coatings have received considerable attention in recent years for their potential biomedical applications. However, the desirable properties of nanoparticles for in vivo uses, such as colloidal stability, biodistribution, and pharmacokinetics, require further research. In this work, we report a bio-derived zwitterionic surface ligand, cysteine betaine (Cys-b) for the modification of hollow gold-silver nanoshells, giving rise to hyperthermia applications. Cys-b coatings on planar substrates and nanoshells were compared to conventional (11-mercaptoundecyl)tri(ethylene glycol) (OEG-thiol) to investigate their effects on the fouling resistance, colloidal stability, environmental tolerance, and photothermal properties. The results found that Cys-b and OEG-thiol coatings exhibited comparable antifouling properties against bacteria of gram-negative Pseudomonas aeruginosa (P. aeruginosa) and gram-positive Staphylococcus epidermidis (S. epidermidis), NIH-3T3 fibroblasts, and bovine serum albumin. However, when the modified nanoshells were suspended at a temperature of 50°C in aqueous 3M NaCl solutions, shifts in the extinction maximum of the OEG-capped nanoshells with time were observed, while the corresponding spectra of nanoshells capped with Cys-b generally remained unchanged. In addition, when the nanoshells were continuously exposed to NIR irradiation, the temperature of the solution containing nanoshells capped with Cys-b increased to a plateau of 54°C, while that of the OEG-capped nanoshells gradually decreased after reaching a peak temperature. Accordingly, the Cys-b nanoshells were conjugated with anti-HER2 antibodies for targeted delivery to HER2-positive MDA-MB-453 breast cancer cells for hyperthermia treatment. The results showed the selective delivery and effective photothermal cell ablation with the antibody-conjugated Cys-b nanoshells. Therefore, this work demonstrated the promise of bio-derived zwitterionic Cys-b as a stable and biocompatible surface coating for materials in nanomedicine.