Dániel Sebők

Structural, optical, and adsorption properties of ZnO2/poly(acrylic acid) hybrid thin porous films prepared by ionic strength controlled layer-by-layer method

ZnO(2)/poly(acrylic acid) sandwich structures were prepared by layer-by-layer (LbL) self-assembly. The structure and optical behavior of the hybrid films were controlled by changing the surface charge and conformation of the poly(acrylic acid). The buildup of the films was followed by UV-vis absorption and reflection spectroscopy, atomic force microscopy (AFM), X-ray diffraction (XRD), and quartz crystal microbalance (QCM) measurements. It was found that the ionic strength of the polymer solution had a great influence on the film thickness which, in turn, affected the optical properties. The water vapor adsorption isotherms of the films determined by QCM showed an adsorption hysteresis characteristic of porous thin layer structures. The adsorption of water molecules inside the films changed the effective refractive index resulting in a change of the reflection properties. This phenomenon is shown to be exploited for the application of the films as optical sensors. The polarizability of water molecules in the adsorption layer was also determined. It was found that polarization of water molecules in the adsorption layer is much lower than in the liquid water when the surface coverage (Theta) is low.

Bovine serum albumin-sodium alkyl sulfates bioconjugates as drug delivery systems.

Precipitation of bovine serum albumin (BSA) by anionic surfactants with alkyl chains of increasing lengths (octyl, decyl, dodecyl sulfates) was studied at room temperature, at pH 3.0, in isotonic sodium chloride solution. The particle size of albumin, the zeta potential, the surface charge and fluorescent properties of BSA-surfactant composites were investigated concerning addition of increasing amount of surfactant. The thermal stability of the systems was monitored by calorimetric analysis (DSC). The formation of the well-ordered structure in the self-assembly process in liquid phase was studied by XRD measurement. The structure of the precipitated BSA-surfactant nanocomposites was characterized by small-angle X-ray scattering (SAXS). Finally, ibuprofen (IBU) molecules were enclosed in BSA-surfactant bioconjugate systems and the release properties of the drug were investigated. It has been found out that, as a consequence to the increasing number of carbon atoms in the alkyl chains of the surfactant, the structure and the fluorescent properties of the aggregates formed can be controlled due to the increase in the hydrophobicity of BSA-surfactant composites. The bioconjugates are well applicable as carrier to realize controlled release of drug molecules.

Optical and structural properties of protein/gold hybrid bio-nanofilms prepared by layer-by-layer method

Lysozyme/gold thin layers were prepared by layer-by-layer (LbL) self-assembly method. The build-up of the films was followed by UV-vis-absorbance spectra, quartz crystal microbalance (QCM) and surface plasmon resonance (SPR) techniques. The structural property of films was examined by X-ray diffraction (XRD) measurements, while their morphology was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). It was found that gold nanoparticles (NPs) had cubic crystalline structure, the primary particles form aggregates in the thin layer due to the presence of lysozyme molecules. The UV-vis measurements prove change in particle size while the colour of the film changes from wine-red to blue. The layer thickness of films was determined using the above methods and the loose, porous structure of the films explains the difference in the results. The vapour adsorption property of hybrid layers was also studied by QCM using different saturated vapours and ammonia gas. The lysozyme/Au films were most sensitive for ammonia gas among the tested gases/vapours due to the strongest interaction between the functional groups of the protein.

Spherical LDH-Ag°-montmorillonite heterocoagulated system with a pH-dependent sol-gel structure for controlled accessibility of AgNPs immobilized on the clay lamellae.

Aqueous suspensions of spherical ZnMgAl-layered double hydroxides [LDH(sph)] and antibacterial silver nanoparticles (AgNPs) deposited on the lamellae of montmorillonite were used for the synthesis of composites, which behave like coherent gels at low pH (≲4.5) and incoherent sols at higher pH (≳4.5). The composition of the composite was chosen as LDH(sph)/Ag°-montm. = 25:75 wt % in order to ensure a sol-gel transition that can also be characterized by viscometry. This pH-sensitive heterocoagulated system consisting of oppositely charged colloid particles was suitable for the release of antimicrobial AgNPs immobilized on the clay lamellae via a pH-controlled gel-sol transition. The heterocoagulation process was also characterized by surface charge titration measurements. Spherical LDH/Ag°-montmorillonite composite samples were identified by X-ray diffraction (XRD) measurements. The morphological properties of the composites were studied, and the presence of the heterocoagulated structure was confirmed by scanning electron microscopy (SEM). The nanoscale structure of the LDH(sph)-Ag°-montmorillonite composite obtained was also verified by small-angle X-ray scattering (SAXS), and the rheological characteristics were studied at various pH values. The viscosity and yield value of the composite decreased by an order of magnitude upon increasing the pH from 3.0 to 5.5. The sol-gel transition of the composite suspension was reversible in the previously mentioned pH range.

Comprehensive study on the structure of the BSA from extended-to aged form in wide (2–12) pH range

In this work we studied the structure of the bovine serum albumin (BSA) and the protein-ligand interactions since researchers prefer to use them as carriers in drug delivery systems. Systematic study (between pH 2-12, in double distilled water and physiological salt solution) was carried out to determine the changes in the secondary and the tertiary structures of the BSA, the apparent molecular weight (Mw), the size (dLS) and the electrokinetic potential (ζ). At pH 7, the BSA has higher stability in the absence (ζ=-69mV, dLS=2.2nm, A2=1.4×10(-3)mlmol/g(2)) than in the presence of salt solution (ζ=-2.4mV, dLS=5.3nm, A2=-3.2×10(-4)mlmol/g(2)). The Mw strongly depends on the pH and the ionic strength (at pH 3 in the absence of salt, the Mw is 54.6kDa while in the presence of salt is 114kDa) which determines the geometry of the protein. The protein-ligand interactions were characterized by fluorescence (FL) and isothermal microcalorimetry (ITC) methods; these independent techniques provided similar thermodynamic parameters such as the binding constant (K) and the Gibbs free energy (ΔG).

Surface and Structural Properties of Gold Nanoparticles and Their Biofunctionalized Derivatives in Aqueous Electrolytes Solution

Gold nanoparticles reduced by sodium citrate (d ∼ 10 nm) and purchased gold colloid particles (d ∼ 500 nm) were examined and compared. The properties of both gold particles and their biofunctionalized derivatives with L-cysteine and L-glutathione were studied in the presence of sodium nitrate. The structural investigations indicated an aggregated inner structure. The isoelectric points of pure gold, citrate reduced gold, and functionalized gold were measured and compared. The low isoelectric point of pure gold/water interface was explained by considering the distribution and accumulation of H+ and OH− ions within the interfacial water layer, being more pronounced for OH− ions.

Determination of binding capacity and adsorption enthalpy between Human Glutamate Receptor (GluR1) peptide fragments and kynurenic acid by surface plasmon resonance experiments. Part 2: Interaction of GluR1270–300 with KYNA

In the course of our previous work, the interactions of two peptide fragments (GluR1201-230 and GluR1231-259) of human glutamate receptor (GluR1201-300) polypeptide with kynurenic acid (KYNA) were investigated by surface plasmon resonance (SPR) spectroscopy. Besides quantitation of the interactions, the enthalpies of binding of KYNA on certain peptide fragment-modified gold surfaces were also reported. In the present work, a third peptide fragment (GluR1270-300) of the glutamate receptor was synthesized and its interaction with KYNA was investigated by an SPR technique. This 31-membered peptide was chemically bonded onto a gold-coated SPR chip via a cysteine residue. The peptide-functionalized biosensor chip was analyzed by atomic force microscopy (AFM) and theoretical calculations were performed on the structure and dimensions of the peptide on the gold surface. In order to determine the isosteric heat of adsorption of the binding of KYNA on the peptide-functionalized gold thin film, SPR experiments were carried out between +10°C and +40°C. The results on the GluR1270-300-KYNA system were compared with the previously published binding parameters of the interactions of GluR1201-230 and GluR1231-259 with KYNA. The binding abilities of KYNA with all three peptide fragments immobilized on the gold surface were estimated by a molecular docking procedure and the binding free energies of these AMPA receptor subunits with KYNA were determined.

A redox strategy to tailor the release properties of Fe(III)-alginate aerogels for oral drug delivery

Iron(III)-crosslinked alginate aerogel beads (d = 3-5 mm) were prepared and loaded with ibuprofen by using the technique of adsorptive deposition from supercritical CO2. Additional formulations were prepared where the aerogels were co-impregnated by ibuprofen and ascorbic acid. The release of ibuprofen from the Fe(III)-alginate is much faster in pH = 7.4 (PBS) than in pH = 2.0 (HCl), which can be explained by the faster dissolution and higher swelling of the alginate matrix in PBS. By decreasing the size of the beads and using a higher G content alginate the release rate could be slightly increased. A marked acceleration of drug release was achieved in both HCl and PBS by incorporating ascorbic acid into the Fe(III)-alginate aerogel preparations. The explanation is that in aqueous media ascorbic acid in situ reduces the crosslinking Fe(III) to Fe(II). The latter does not interact strongly with alginate, which promotes the hydration of the chains, thus the erosion and dissolution of the carrier matrix.

Preparation of novel tissue acidosis-responsive chitosan drug nanoparticles: Characterization and in vitro release properties of Ca2+ channel blocker nimodipine drug molecules

ABSTRACT The pH‐responsive intelligent drug release facility of hydrophobically modified chitosan nanoparticles (Chit NPs) (d = 5.2 ± 1.1 nm) was presented in the case of poorly water soluble Ca2+ channel blocker nimodipine (NIMO) drug molecules. The adequate pH‐sensitivity, i.e. the suitable drug carrier properties of the initial hydrophilic Chit were achieved by reductive amination of Chit with hexanal (C6‐) and dodecanal (C12‐) aldehydes. The successful modifications of the macromolecule were evidenced via FTIR measurements: the band appearing at 1412 cm−1 (C–N stretching in aliphatic amines) in the cases of the hydrophobically modified Chit samples shows that the C–N bond successfully formed between the Chit and the aldehydes. Hydrophobization of the polymer unambiguously led to lower water contents with lower intermolecular interactions in the prepared hydrogel matrix: the initial hydrophilic Chit has the highest water content (78.6 wt%) and the increasing hydrophobicity of the polymer resulted in decreasing water content (C6‐chit.: 74.2 wt% and C12‐chit.: 47.1 wt%). Furthermore, it was established that the length of the side chain of the aldehyde influences the pH‐dependent solubility properties of the Chit. Transparent homogenous polymer solution was obtained at lower pH, while at higher pH the formation of polymer (nano)particles was determined and the corresponding cut‐off pH values showed decreasing tendency with increasing hydrophobic feature (pH = 7.47, 6.73 and 2.49 for initial Chit, C6‐chit and C12‐chit, respectively). Next the poorly water soluble NIMO drug was encapsulated with the C6‐chit with adequate pH‐sensitive properties. The polymer‐stabilized NIMO particles with 10 wt% NIMO content resulted in stable dispersion in aqueous phase, the formation of polymer shell increased in the water solubility/dispersibility of the initial hydrophobic drug. According to the drug release experiments, we clearly confirmed that the encapsulated low crystallinity NIMO drug remained closed in the polymer NPs at normal tissue pH (pH = 7.4, PBS buffer, physiological condition) but at pH < 6.5 which is typical for seriously ischemic brain tissue, 93.6% of the available 0.14 mg/ml NIMO was released into the buffer solution under 8 h release time. According to this in vitro study, the presented pH‐sensitive drug carrier system could be useful to selectively target ischemic brain regions characterized by acidosis, to achieve neuroprotection at tissue zones at risk of injury, without any undesirable side effects caused by systemic drug administration. Graphical abstract Figure. No Caption available.

Sensitive detection of aflatoxin B1 molecules on gold SPR chip surface using functionalized gold nanoparticles

Due to the warm and favourably humid climate of Southern Hungary, the maize is one of the most important crops. The protection against crop damage caused by fusarium and Aspergillus species is essential. Detection of aflatoxin B1 (AFB1) molecules in cereal crops by selective sensors is important, while they can cause serious diseases in humans and animals if they enter the food chain. Our main objective was to develop selective AFB1 sensor with increased sensitivity applying βCD-functionalized gold nanoparticles (AuβCD NPs) in surface plasmon resonance (SPR) measuring apparatus. The nanoparticles ca. 10 nm in diameter were prepared in the presence of thiol-modified cyclodextrin. The adsorption isotherms of AFB1 on bare, thiol-modified cyclodextrin and AuβCD NPs covered Au film surface were calculated using SPR platform. The AFB1 concentration can be quantitatively determined in the 0.001–23.68 ng/mL range. The AuβCD NPs were found to be highly sensitive and exhibited a remarkably low limit of detection (LOD; 1 pg/mL) without using other analytical reagents.