Edit Csapó

Functionalization of gold nanoparticles with amino acid, β-amyloid peptides and fragment

Gold nanoparticles (Au NPs) were functionalized by cysteine (Cys), beta-amyloid peptides (Cys(0)Abeta(1-28), Cys(0)Abeta(1-40), Abeta(1-42)) and a pentapeptide fragment (Leu-Pro-Phe-Phe-Asp-OH (LPFFD-OH)). Optical absorption spectra of these systems were recorded and the plasmon resonance maximum values (lambda(max)) of the UV-vis spectra together with the transmission electron microscopy (TEM) images were also analysed. Both TEM images and the appearance of a new absorption band between approximately 720 and 750 nm in the visible spectra of the Au-cysteine and Au-LPFFD-OH systems most probably indicate that upon addition of these molecules to Au NPs-containing aqueous dispersions formation of aggregates is occurred. The wavelength shift between the two observed absorption bands in cysteine- and pentapeptide-modified Au NPs systems are Deltalambda=185 and 193 nm, respectively. These results suggest that the monodisperse spherical gold nanoparticles were arranged to chained structure due to the effect of these molecules. For confirmation of the binding of citrate and cysteine onto the plasmonic metal surface (1)H NMR measurements were also performed. (1)H NMR results may suggest that the citrate layer on the metal surface is replaced by cysteine leading to a formation of organic double layer structure. In the presence of beta-amyloid peptides the aggregation was not observed, especially in the Au-Cys(0)Abeta(1-40) and Au-Abeta(1-42) systems, however compared to the cysteine or LPFFD-OH-containing gold dispersion with Cys(0)Abeta(1-28) measurable less aggregation were occurred. The spectral parameters clearly suggest that Abeta(1-42) can attach or bind to the surface of gold nanoparticles via both the apolar and the N-donors containing side-chains of amino acids and no aggregation in the colloidal gold dispersion was observed.

Effect of pH on stability and plasmonic properties of cysteine-functionalized silver nanoparticle dispersion.

Citrate-stabilized spherical silver nanoparticles (Ag NPs) with d=8.25±1.25 nm diameter were prepared and functionalized with L-cysteine (Cys) in aqueous dispersion. The nanosilver-cysteine interactions have been investigated by Raman and (1)H NMR spectroscopy. The effect of pH on stability of biofunctionalized Ag NPs was investigated. The cysteine-capped nanosilver dispersions remain stable at higher pH (pH>7), while the degree of aggregation increased as the pH decreased. Below pH ~7, the characteristic surface plasmon band of bare silver nanoparticles was back-shifted from λ(measured)(bareAgNP)=391 nm to λ(measured)(1)=387-391 nm, while the presence of a new band at λ(measured)(2)=550-600 nm was also observed depending on pH. Finite element method (FEM) was applied to numerically compute the absorption spectra of aqueous dispersions containing bare and cysteine-functionalized Ag NPs at different pH. Both the dynamic light scattering (DLS) measurements, Zeta potential values and the transmission electron microscopic (TEM) images confirmed our supposition. Namely, electrostatic interaction arose between the deprotonated carboxylate (COO(-)) and protonated amino groups (NH(3)(+)) of the amino acid resulting in cross-linking network of the Ag NPs between pH ~3 and 7. If the pH is measurable lower than ~3, parallel with the protonation of citrate and L-cysteine molecules the connection of the particles via l-cysteine is partly decomposed resulting in decrease of second plasmon band intensity.

Interaction of biofunctionalized gold nanoparticles with model phospholipid membranes

AbstractThe understanding of the interaction of nanoparticles with cell membranes and the penetration of these nano-objects through cell wall is highly required for their biomedical application. In this work were aimed at the study of the interaction of gold nanoparticles with model phospholipid membranes prepared at the air/water interface in a Langmuir trough. Spherical (10 and 15xa0nm mean diameter) and rod-like gold (aspect ratio: 2.8) nanoparticles were synthesized and biofunctionalized with l-cysteine and l-glutathione. The gold nanoparticles were characterized by TEM images and UV–Vis absorbance measurements. The interaction of the biofunctionalized gold nanoparticles with the model monolayer membrane was studied by surface pressure versus surface area compressional isotherms and by the measurement of the change in surface pressure of a preformed model membrane. The effect of the initial surface pressure of the preformed membrane was evaluated to determine the maximum insertion pressure and synergy. We have found that the driving forces of the bioconjugated Au nanoparticle (NP) or Au nanorod (NR) penetration into the monolayer membrane is mostly determined by electrostatic interaction and orientational van der Waals forces. Monolayer films were transferred with Langmuir–Blodgett technique onto solid substrates and the nanoparticles were visualized with AFM technique.n Figureᅟ

Determination of binding capacity and adsorption enthalpy between Human Glutamate Receptor (GluR1) peptide fragments and kynurenic acid by surface plasmon resonance experiments.

The interaction between kynurenic acid (KYNA) and two peptide fragments (ca. 30 residues) of Human Glutamate Receptor 201-300 (GluR1) using surface plasmon resonance (SPR) spectroscopy was investigated. Because of the medical interest in the neuroscience, GluR1 is one of the important subunits of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPAR). AMPARs are ionotoropic glutamate receptors, which are mediating fast synaptic transmission and are crucial for plasticity in the brain. On the other hand, KYNA has been suggested to have neuroprotective activity and it has been considered for apply in therapy in certain neurobiological disorders. In this article the adsorption of the GluR1201-230 and GluR1231-259 peptides were studied on gold biosensor chip. The peptides were chemically bonded onto the gold surface via thiol group of L-cysteine resulted in the formation of peptide monolayer on the SPR chip surface. Because the GluR1231-259 peptide does not contain L-cysteine the Val256 was replaced by Cys256. The cross sectional area and the surface orientation of the studied peptides were determined by SPR and theoretical calculations (LOMETS) as well. The binding capability of KYNA on the peptide monolayer was studied in the concentration range of 0.1-5.0 mM using 150 mM NaCl ionic strength at pH 7.4 (±0.02) in phosphate buffer solutions. In order to determine the binding enthalpy the experiments were carried out between +10°C and +40°C. The heat of adsorption was calculated by using adsorption isotherms at different surface loading of KYNA on the SPR chip.

Optimization of the Field Enhancement and Spectral Bandwidth of Single and Coupled Bimetal Core-Shell Nanoparticles for Few-Cycle Laser Applications

We have theoretically studied and optimized the field enhancement and temporal response of single and coupled bimetal Ag/Au core–shell nanoparticles (NPs) with a diameter of 160xa0nm and compared the results to pure Ag and Au NPs. Very high-field enhancements with an amplitude reaching 100 (with respect to the laser field centered at 800xa0nm) are found at the center of a 2-nm gap between Ag/Au core–shell dimers. We have explored the excitation of the bimetal core–shell particles by Fourier transform-limited few-cycle optical pulses and identified conditions for an ultrafast plasmonic decay on the order of the excitation pulse duration. The high-field enhancement and ultrafast decay makes bimetal core–shell particles interesting candidates for applications such as the generation of ultrashort extreme ultraviolet radiation pulses via nanoplasmonic field enhancement. Moreover, in first experimental studies, we synthesized small bimetal Ag/Au core–shell NPs and compared their optical response with pure Au and Ag NPs and numerical results.

Comparative Study of Plasmonic Properties of Cysteine-Functionalized Gold and Silver Nanoparticle Aggregates

The absorptance spectra of gold and silver nanoparticle (NP) aqueous dispersions were measured by UV–visible spectroscopy and computed numerically by finite element method. Both NPs were functionalized by l-cysteine amino acid (Cys) in order to develop aggregate-based localized surface plasmon resonance biosensors. Absorptance spectra measured at an analogous pH value of ∼4.9 were compared, where Au-Cys conjugates have moderately split spectra with two commensurate maxima, while Ag-Cys conjugates exhibit the most pronounced secondary peak according to the highest degree of aggregation. The purpose of our theoretical study was to determine the simplest linear chain-like and wavy aggregate geometries, which result in maxima matching the measured peaks. The aggregates were characterized by N number and d diameter of NPs, g gap between the NPs, and t thickness of the l-cysteine covering. By tuning the angle of incidence and E-field oscillation direction in p-polarized light with respect to the aggregates, the contribution of longitudinal and transversal modes was varied. The comparison of measurements and computations revealed that spectra measured on bioconjugate dispersions include effects of numerous aggregates with various geometries, illuminated from different directions and are influenced by inter-aggregate coupling. Inspecting the normalized E-field distribution surrounding the aggregates, it was shown that fundamentally different multipolar modes can be identified at primary and secondary absorptance maxima, due to coupled plasmonic resonances on NPs.

Kinetic and Thermodynamic Evaluation of Kynurenic Acid Binding to GluR1270-300 Polypeptide by Surface Plasmon Resonance Experiments

This work clearly demonstrates an evaluation process that is easily performed and is simply based on the fitting of temperature-dependent surface plasmon resonance (SPR) sensorgrams to provide detailed thermodynamic characterization of biologically relevant interactions. The reversible binding of kynurenic acid (KYNA) on human glutamate receptor (GluR1) polypeptide (GluR1270-300)-modified gold surface has been studied at various temperatures under physiological conditions by two-dimensional SPR experiments. The registered sensorgrams were fitted by using different kinetic models without application of any commercial software. Assuming that the association of GluR1270-300-KYNA complex is first order in both reactants, the association (ka) and dissociation (kd) constants as well as the equilibrium constants (KA) and the Gibbs free-energy change (ΔG°) were given at 10, 20, 30, and 40 °C. Moreover, the enthalpy (ΔH° = -27.91 kJ mol(-1)), entropy (ΔS° = -60.33 J mol(-1) K(-1)), and heat capacity changes (ΔCp = -1.28 kJ mol(-1) K(-1)) of the model receptor-ligand system were also calculated using a spreadsheet program. Negative values of ΔG° and ΔH° indicate the exothermic formation of a stable GluR1270-300-KYNA complex, because the |ΔH| > |TΔS| relation suggests an enthalpy-driven binding process. The negative ΔH° and ΔS° values strongly support the formation of a salt bridge between KYNA and the positively charged residues of the polypeptide (Arg, Lys) at pH 7.4, confirmed by molecular docking calculations as well.

Targeting of the kynurenic acid across the blood-brain barrier by core-shell nanoparticles.

Core-shell nanoparticles (CSNPs) were developed to get over therapeutic amount of kynurenic acid (KYNA) across the blood-brain barrier (BBB). Bovine serum albumin (BSA) was used as core for encapsulation of KYNA and the BSA/KYNA composite was finally encapsulated by poly(allylamine) hydrochloride (PAH) polymer as shell. In the interest of the optimization of the synthesis the BSA and KYNA interaction was studied by two-dimensional surface plasmon resonance (SPR) technique as well. The average size of d~100 nm was proven by dynamic light scattering (DLS) and transmission electron microscopy (TEM), while the structure of the composites was characterized by fluorescence (FL) and circular dichroism (CD) spectroscopy. The in vitro release properties of KYNA were investigated by a vertical diffusion cell at 25.0 °C and 37.5 °C and the kinetic of the release were discussed. The penetration capacity of the NPs into the central nervous system (CNS) was tested by an in vitro BBB model. The results demonstrated that the encapsulated KYNA had significantly higher permeability compared to free KYNA molecules. In the neurobiological serial of in vivo experiments the effects of peripherally administered KYNA with CSNPs were studied in comparison with untreated KYNA. These results clearly proved that KYNA in the CSNPs, administrated peripherally is suitable to cross the BBB and to induce electrophysiological effects within the CNS. As the neuroprotective properties of KYNA nowadays are proven, the importance of the results is obvious.

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.