Controlling Mixed-Protein Adsorption Layers on Colloidal Alumina Particles by Tailoring Carboxyl and Hydroxyl Surface Group Densities

We show that different ratios of bovine serum albumin (BSA) and lysozyme (LSZ) can be achieved in a mixed protein adsorption layer by tailoring the amounts of carboxyl (−COOH) and aluminum hydroxyl (AlOH) groups on colloidal alumina particles (<i>d</i>₅₀ ≈ 180 nm). The particles are surface-functionalized with −COOH groups, and the resultant surface chemistry, including the remaining AlOH groups, is characterized and quantified using elemental analysis, ζ potential measurements, acid–base titration, IR spectroscopy, electron microscopy, nitrogen adsorption, and dynamic light scattering. BSA and LSZ are subsequently added to the particle suspensions, and protein adsorption is monitored by in situ ζ potential measurements while being quantified by UV spectroscopy and gel electrophoresis. A comparison of single-component and sequential protein adsorption reveals that BSA and LSZ have specific adsorption sites: BSA adsorbs primarily via AlOH groups, whereas LSZ adsorbs only via −COOH groups (1–2 −COOH groups on the particle surface is enough to bind one LSZ molecule). Tailoring such groups on the particle surface allows control of the composition of a mixed BSA and LSZ adsorption layer. The results provide further insight into how particle surface chemistry affects the composition of protein adsorption layers on colloidal particles and is valuable for the design of such particles for biotechnological and biomedical applications

Modulation of Silica Nanoparticle Uptake into Human Osteoblast Cells by Variation of the Ratio of Amino and Sulfonate Surface Groups: Effects of Serum

To study the importance of the surface charge for cellular uptake of silica nanoparticles (NPs), we synthesized five different single- or multifunctionalized fluorescent silica NPs (FFSNPs) by introducing various ratios of amino and sulfonate groups into their surface. The zeta potential values of these FFSNPs were customized from highly positive to highly negative, while other physicochemical properties remained almost constant. Irrespective of the original surface charge, serum proteins adsorbed onto the surface, neutralized the zeta potential values, and prevented the aggregation of the tailor-made FFSNPs. Depending on the surface charge and on the absence or presence of serum, two opposite trends were found concerning the cellular uptake of FFSNPs. In the absence of serum, positively charged NPs were more strongly accumulated by human osteoblast (HOB) cells than negatively charged NPs. In contrast, in serum-containing medium, anionic FFSNPs were internalized by HOB cells more strongly, despite the similar size and surface charge of all types of protein-covered FFSNPs. Thus, at physiological condition, when the presence of proteins is inevitable, sulfonate-functionalized silica NPs are the favorite choice to achieve a desired high rate of NP internalization

Effective Bacterial Inactivation and Removal of Copper by Porous Ceramics with High Surface Area

In this study, we present porous ceramics combining the antibacterial effect of copper with an integrated copper removal adsorbent. After preparing and characterizing the antibacterial copper-doped microbeads and monoliths (CuBs and CuMs), their antibacterial efficiency is probed against different nonpathogenic and pathogenic bacteria (<i>Bacillus subtilis</i>,<i> Escherichia coli</i>,<i> Staphylococcus aureus</i>, and <i>Pseudomonas aeruginosa</i>). An antibacterial efficiency of 100% is reached within 15 min to 3 h for all tested strains under static conditions. Dynamic tests with <i>B. subtilis</i> and <i>E. coli</i> showed high antibacterial efficiency up to 99.93% even at continuous flux. To avoid any adverse effects on the environment, continuous removal of released copper-ions is accomplished with porous, high surface area monolithic adsorbents (MAds). MAds are prepared similarly to the CuMs but without adding copper during the manufacturing process. MAds reduce the amount of copper released from the CuMs ≥ 99% during the first 15 min, ≥90% up to 2 h, and after 22 h of continuous filtration up to 56% of the released copper is removed

Straightforward Processing Route for the Fabrication of Robust Hierarchical Zeolite Structures

Strong hierarchical porous zeolite structures are prepared by a sol–gel method using freeze gelation. Instead of conventional binders in powder form, such as bentonite or kaolin, it has been proven that using a freeze gelation method based on a colloidal silica sol is a more straightforward and easier-to-use-approach in fabricating highly mechanically stable zeolite monoliths. The resulting zeolite slurries possess superior rheological properties (not being pseudoplastic) and show low viscosities. This low viscosity of the slurry enables an increase in the solid content without compromising the extraordinary good flow behavior for casting applications. Additionally, in comparison to conventional powdery binders, zeolite samples prepared by using a colloidal silica sol exhibit a significantly higher mechanical strength. This mechanical strength can be further improved by either increasing the zeolite content or increasing the silica to zeolite ratio. Increasing the zeolite content leads to an increased volumetric adsorption capacity for CO₂ as the test gas, resulting from the increased amount of zeolite particles per unit volume. In addition, a higher solid content of the zeolite monoliths leads to higher compression strengths, while showing the same elastic deformation and brittle failure characteristics. In turn, increasing the silica to zeolite ratio does not affect the volumetric adsorption capacity for CO₂. Nevertheless, higher silica contents lead to a significant increase in the elastic deformation and absorbed work until failure. Therefore, the proposed processing route based on freeze gelation presents an easy and unique tool to tune the mechanical and gas adsorptive properties of hierarchically structured zeolite monoliths, according to the application requirements

Self-Assembly and Shape Control of Hybrid Nanocarriers Based on Calcium Carbonate and Carbon Nanodots

We describe a platform for the synthesis of functional hybrid nanoparticles in the submicrometer range with tailorable anisotropic morphology. Fluorescent carbon dots (CDs) and poly­(acrylic acid) (PAA) are used to modify the crystallization and assembly of calcium carbonate (CaCO₃). Carboxylic groups on CDs sequester calcium ions and serve as templates for CaCO₃ precipitation when carbonate is added. This creates primary CaCO₃ nanoparticles, 7 nm in diameter, which self-assemble into spheres or rods depending on the PAA concentration. At increasing polymer concentration, oriented assembly becomes more prevalent yielding rod-like particles. The hybrid particles show colloidal stability in cell medium and absence of cytotoxicity as well as a loading efficiency of around 30% for Rhodamine B with pH-controlled release. Given the morphological control, simplicity of synthesis, and efficient loading capabilities the CD-CaCO₃ system could serve as a novel platform for advanced drug carrier systems

Interaction of the Physiological Tripeptide Glutathione with Colloidal Alumina Particles

Understanding of the molecular interactions of alumina particles with biomolecules is fundamental for a variety of biotechnological processes. To study the interactions of polypeptides with alumina particles, we have investigated the adsorption and desorption behavior of the physiologically relevant tripeptide glutathione (GSH, γ-glutamylcysteinylglycine) onto colloidal α-alumina particles (CPs). The adsorption of GSH to positively charged alumina particles was rapid, increased proportionally to the concentration of CPs, and shifted the isoelectric point of the CP to a less alcaline pH. Desorption of particle-bound GSH was achieved by increasing the ionic strength after adding salt to the suspension, suggesting that adsorption of GSH to alumina is governed by electrostatic interactions. The presence of negatively charged and GSH-structurally related molecules such as glutamate, γ-glutamylcysteine, γ-glutamylglutamate, or methyl-S-GSH prevented the binding of GSH to the positively charged alumina surface in a concentration dependent manner, while positively charged and net-uncharged molecules and GSH esters did not affect GSH adsorption to alumina CPs. These data suggest that exclusively electrostatic interaction via the carboxylate groups of GSH governs its binding to alumina particles

Enhancing Cellular Uptake and Doxorubicin Delivery of Mesoporous Silica Nanoparticles via Surface Functionalization: Effects of Serum

In this study, we demonstrate how functional groups on the surface of mesoporous silica nanoparticles (MSNPs) can influence the encapsulation and release of the anticancer drug doxorubicin, as well as cancer cell response in the absence or presence of serum proteins. To this end, we synthesized four differently functionalized MSNPs with amine, sulfonate, polyethylene glycol, or polyethylene imine functional surface groups, as well as one type of antibody-conjugated MSNP for specific cellular targeting, and we characterized these MSNPs regarding their physicochemical properties, colloidal stability in physiological media, and uptake and release of doxorubicin <i>in vitro</i>. Then, the MSNPs were investigated for their cytotoxic potential on cancer cells. Cationic MSNPs could not be loaded with doxorubicin and did therefore not show any cytotoxic and antiproliferative potential on osteosarcoma cells, although they were efficiently taken up into the cells in the presence or absence of serum. In contrast, substantial amounts of doxorubicin were loaded into negatively charged and unfunctionalized MSNPs. Especially, sulfonate-functionalized doxorubicin-loaded MSNPs were efficiently taken up into the cells in the presence of serum and showed an accelerated toxic and antiproliferative potential compared to unfunctionalized MSNPs, antibody-conjugated MSNPs, and even free doxorubicin. These findings stress the high importance of the surface charge as well as of the protein corona for designing and applying nanoparticles for targeted drug delivery

Adsorption and Orientation of the Physiological Extracellular Peptide Glutathione Disulfide on Surface Functionalized Colloidal Alumina Particles

Understanding the interrelation between surface chemistry of colloidal particles and surface adsorption of biomolecules is a crucial prerequisite for the design of materials for biotechnological and nanomedical applications. Here, we elucidate how tailoring the surface chemistry of colloidal alumina particles (<i>d</i>₅₀ = 180 nm) with amino (−NH₂), carboxylate (−COOH), phosphate (−PO₃H₂) or sulfonate (−SO₃H) groups affects adsorption and orientation of the model peptide glutathione disulfide (GSSG). GSSG adsorbed on native, −NH₂-functionalized, and −SO₃H-functionalized alumina but not on −COOH- and −PO₃H₂-functionalized particles. When adsorption occurred, the process was rapid (≤5 min), reversible by application of salts, and followed a Langmuir adsorption isotherm dependent on the particle surface functionalization and ζ potential. The orientation of particle bound GSSG was assessed by the release of glutathione after reducing the GSSG disulfide bond and by ζ potential measurements. GSSG is likely to bind via the carboxylate groups of one of its two glutathionyl (GS) moieties onto native and −NH₂-modified alumina, whereas GSSG is suggested to bind to −SO₃H-modified alumina via the primary amino groups of both GS moieties. Thus, GSSG adsorption and orientation can be tailored by varying the molecular composition of the particle surface, demonstrating a step toward guiding interactions of biomolecules with colloidal particles