Coated Gold Nanoparticles Research Articles

Fluorescence Determination of L-Cysteine in Wound Dressings by Fluoroscein Coated Gold Nanoparticles

ABSTRACTA new method for the fluorimetric determination of L-cysteine in wound care dressings is reported using coated fluorescein gold nanoparticles. The procedure was performed with a continuous flow manifold to automate the process to improve the precision. Aqueous gold nanoparticles (size: 10.5 ± 1.2 nm) that were noncovalently adsorbed to fluorescein were employed for the determination of L-cysteine. The fluorescence of the fluorescein-gold nanoparticle compound was lower than the fluorescein fluorescence and increased in the presence of L-cysteine due to fluorescence resonance energy transfer. The fluorescence of the solution containing the fluorescein-gold nanoparticles was enhanced by a factor of 7.5 following the addition of L-cysteine. This effect was not observed when other amino acids were introduced. This fluorescence enhancement was used for the determination of L-cysteine. Good linearity was observed from 0.8 to 4.1 µM of L-cysteine, and the detection limit was 0.1 µM. The method was successfully employed to determine L-cysteine in wound care dressings.

Surface Adsorption and Molecular Modeling of Biofunctional Gold Nanoparticles for Systemic Circulation and Biological Sustainability

Fundamental aspects of protein complex coated gold nanoparticles (Au NPs) were presented for their possible use in systemic circulation in terms of pharmaceutical formulations. For this purpose, protein complexes of bovine serum albumin (BSA), lysozyme (Lys), and zein with an industrial important bioactive polymer diethylaminoethyl dextran (DEAE) were studied in the presence of Au NPs. Surface adsorption of such complexes magnified DEAE–protein interactions which were easily monitored spectroscopically under the effect of temperature and reaction time. In vitro synthesis of Au NPs allowed a simultaneous adsorption of the DEAE–protein complex on the NP surface to achieve colloidal stability, which was dramatically influenced by the nature of the DEAE–protein complex. The DEAE–BSA complex demonstrated strong favorable mainly electrostatic interactions followed by DEAE–Lys, while DEAE–zein interactions were predominantly influenced by the hydrophobic nature of zein. At the molecular level, the interactions w...

Di-Sulfide Linked Polyethylenimine Coated Gold Nanoparticles as a Non-Viral Gene Delivery Agent in NIH-3T3 Mouse Embryonic Fibroblast.

Di-sulfide linked polyethylenimine coated gold nanoparticles (ssPEI-GNPs) of 20 nm size was prepared in order to deliver the genes to target site. DLS and TEM analysis demonstrated that the GNPs have average size of 13 nm in diameter. Upon coating the GNPs with ssPEI in the weight ratio of 1:3, the average hydrodynamic diameter of the ssPEI-GNPs was found to 19±1.14 nm and a zeta potential value 41±1.23 mV was observed. TEM analysis of ssPEI-GNPs demonstrated that the nanoparticles have spherical morphology. Thermogravemetric analysis of the prepared ssPEI-GNPs showed that the estimated composition of the ssPEI coated over the GNPs was approximately 5% (w/w). Gene expression capabilities of the nanoparticles were confirmed by fluorescent microscopy and luciferase assay, which demonstrated the transgene delivery capability of the ssPEI-GNPs. These results demonstrate that ssPEI-GNPs could be used as gene delivery agent.

Mesostructured TiO2 Gated Periodic Mesoporous Organosilica-Based Nanotablets for Multistimuli-responsive Drug Release.

A multistimuli-responsive drug carrier is designed and successfully synthesized by self-assembly of thiol-modified periodic mesoporous organosilica (PMO) nanoparticles, coated gold nanoparticles (AuNPs), and mesostructured titanium dioxide (TiO2). Dye-loaded PMO-Au@TiO2 nanotablets are shown to respond to environmental changes (pH, temperature, and light) to achieve controlled release.

Evidence for a C14 Frank-Kasper Phase in One-Size Gold Nanoparticle Superlattices.

The Frank-Kasper phases were already known in 1982 when quasi-crystals were discovered, but their complex architectures are now considered as making a link between simple close-packed periodic structures and some quasi-periodic ones. These tetrahedrally close packed structures are observed in many materials from elements to intermetallics as well as self-assembled soft materials like micellar systems, dendritric liquid crystals, star polymers, and more recently block copolymers or heated gold nanocrystal superlattices. We report here the existence of a Frank-Kasper phase with hexagonal symmetry (MgZn2 type, also labeled C14) in superlattices of monodisperse hydrophobically coated gold particles at room temperature obtained from suspensions in various solvents. The existence of such a structure in this system is analyzed in terms of geometrical parameters including gold core diameter, ligand length, and grafting density and an energetic approach based on van der Waals attraction. Hydrophobically coated gold nanoparticles is a new system that exhibits a Frank and Kasper phase built by one-size objects. This result opens a route toward a nanoparticle superlattice with complex structures and thus original physical properties.

Probing the Surface Hydration of Nonfouling Zwitterionic and PEG Materials in Contact with Proteins.

Zwitterionic polymers and poly(ethylene glycol) (PEG) have been reported as promising nonfouling materials, and strong surface hydration has been proposed as a significant contributor to the nonfouling mechanism. Better understanding of the similarity and difference between these two types of materials in terms of hydration and protein interaction will benefit the design of new and effective nonfouling materials. In this study, sum frequency generation (SFG) vibrational spectroscopy was applied for in situ and real-time assessment of the surface hydration of the sulfobetaine methacrylate (SBMA) and oligo(ethylene glycol) methacrylate (OEGMA) polymer brushes, denoted as pSBMA and pOEGMA, in contact with proteins. Whereas a majority of strongly hydrogen-bonded water was observed at both pSBMA and pOEGMA surfaces, upon contact with proteins, the surface hydration of pSBMA remained unaffected, but the water ordering at the pOEGMA surface was disturbed. The effects of free sulfobetaine, free PEG chains with two different molecular weights, and PEG coated gold nanoparticles on the surface hydration of proteins were investigated. The results indicated that free sulfobetaine could strengthen the protein hydration layer, but free PEG chains greatly disrupt the protein hydration layer and likely directly interact with the protein molecules. In contrast to free PEG, the PEG chains anchored on the nanoparticles behave similarly to the pOEGMA surface and could induce strong hydrogen bonding of the water molecules at the protein surfaces.

The One Year Fate of Iron Oxide Coated Gold Nanoparticles in Mice.

Safe implementation of nanotechnology and nanomedicine requires an in-depth understanding of the life cycle of nanoparticles in the body. Here, we investigate the long-term fate of gold/iron oxide heterostructures after intravenous injection in mice. We show these heterostructures degrade in vivo and that the magnetic and optical properties change during the degradation process. These particles eventually eliminate from the body. The comparison of two different coating shells for heterostructures, amphiphilic polymer or polyethylene glycol, reveals the long lasting impact of initial surface properties on the nanocrystal degradability and on the kinetics of elimination of magnetic iron and gold from liver and spleen. Modulation of nanoparticles reactivity to the biological environment by the choice of materials and surface functionalization may provide new directions in the design of multifunctional nanomedicines with predictable fate.

Surfactant induced aggregation behavior of Merocyanine-540 adsorbed on polymer coated positively charged gold nanoparticles

Surfactant induced aggregation behavior of Merocyanine 540 adsorbed on polymer (PDD) coated gold nanoparticles (AuNP) is reported. The absorption band of the dye shifts to higher energy in the presence of free polymer and polymer coated AuNP implying aggregation. Addition of a negatively charged surfactant (SDS) induces multiple bands in the extinction spectrum of the dye adsorbed on nanoparticle surface. The highest (460nm) and lowest (564nm) energy bands of the dye become prominent at 10 and >50μM SDS concentrations respectively (dye: 10μM; AuNP: 100–200pM). Based on earlier results the high energy band is likely to originate from dye aggregates and the low energy band is likely to originate from dye monomers. This is attributed to the interplay between polymer–surfactant and polymer–dye interactions at the AuNP surface. The extinction spectra of dye adsorbed at AuNP surface remain unaffected in the presence of a positively charged (CTAB) or a neutral surfactant (Tx-100), at low surfactant concentrations. However at higher surfactant concentrations (>60μM) dye aggregation takes place which is attributed to dye–surfactant interactions. The fluorescence intensity of the dye quenched significantly but its lifetime increased in the presence of polymer coated AuNP. This is attributed to aggregation and reduction in the photoisomerization rate of the dye adsorbed on AuNP surface.

Characterization of hydrophilic coated gold nanoparticles via capillary electrophoresis and Taylor dispersion analysis. Part II: Determination of the hydrodynamic radius distribution – Comparison with asymmetric flow field-flow fractionation

In the first paper of this series we have shown for hydrophilic coated Au nanoparticles that capillary electrophoresis in combination with Taylor dispersion analysis in fused silica capillaries with an inner diameter of 75μm allows for the unbiased precise determination of the number-weighted mean hydrodynamic diameter, the zeta potential and the effective charge number, although mobility corrected double layer polarization has to be taken into account.In this second paper we investigate whether the modified approximate analytic expression developed by Ohshima (2001) permits the calculation of calibration lines and the concomitant conversion of electropherograms into number-weighted particle radius distributions. We show that with the method developed size distributions are obtained which are independent of the measurement conditions. These size distributions are much narrower than those obtained via dynamic light scattering and data evaluation by the CONTIN algorithm. Capillary electrophoresis together with the proposed data evaluation method reveals that the analyzed nanoparticle populations have very narrow size distributions with a width of 2–4nm. The hydrodynamic radius distributions of the coated NPs are only slightly broader than the solid particle radius distribution of the Au-NP cores. The presence of monomodal/bimodal size distributions is confirmed by asymmetric flow field-flow fractionation.

Radio-frequency capacitance spectroscopy of metallic nanoparticles

Recent years have seen great progress in our understanding of the electronic properties of nanomaterials in which at least one dimension measures less than 100 nm. However, contacting true nanometer scale materials such as individual molecules or nanoparticles remains a challenge as even state-of-the-art nanofabrication techniques such as electron-beam lithography have a resolution of a few nm at best. Here we present a fabrication and measurement technique that allows high sensitivity and high bandwidth readout of discrete quantum states of metallic nanoparticles which does not require nm resolution or precision. This is achieved by coupling the nanoparticles to resonant electrical circuits and measurement of the phase of a reflected radio-frequency signal. This requires only a single tunnel contact to the nanoparticles thus simplifying device fabrication and improving yield and reliability. The technique is demonstrated by measurements on 2.7 nm thiol coated gold nanoparticles which are shown to be in excellent quantitative agreement with theory.

Molecular simulations of mixed self-assembled monolayer coated gold nanoparticles in water.

Molecular dynamics simulations have been employed to study the hydration of a series of nanoparticles, each of which was coated with a mixed self-assembled monolayer (SAM) comprising methyl- and hydroxy-terminated alkane thiol chains. The mixing ratio of those chains are different for each nanoparticle. The simulations focused on the wetting behavior of the SAM-coated gold nanoparticles and the distribution and structure of their interfacial water molecules. The interactions of the mixed SAM-coated gold nanoparticles with water were analyzed by evaluating the radial distribution function, hydrogen bonds, the dipole orientations of the water molecules, and the water residence time in the interfacial region. The wettability of the mixed SAM-coated gold nanoparticles improved as the concentration of terminal hydroxy moieties was increased. The distribution and dynamics of the interfacial water molecules were found to be influenced by the mixing ratio of the terminal moieties of the SAM chains. The results of our simulations suggest that the surface interactions of the mixed SAM-coated gold nanoparticles with the aqueous medium can be modulated by systematically altering the mixing ratio of the terminal methyl and hydroxy moieties. This work may lead to new biological and technological applications and inspire the development of novel biomimetic materials. Graphical Abstract Mixed SAM-coated gold nanoparticles.

Initial in vitro and in vivo assessment of Au@DTDTPA-RGD nanoparticles for Gd-MRI and 68Ga-PET dual modality imaging.

Gadolinium chelate coated gold nanoparticles (Au@DTDTPA) can be applied as contrast agents for both in vivo X-ray and magnetic resonance imaging. In this work, our aim was to radiolabel and evaluate this gold nanoparticle with Ga-68, in order to produce a dual modality PET/MRI imaging probe. For a typical preparation of 68Ga-labeled nanoparticles, the Au@DTDTPA nanoparticles (Au@DTDTPA/Au@DTDTPA-RGD) were mixed with ammonium acetate buffer, pH 5 and 40 MBq of 68Ga eluate. The mixture was then incubated for 45 min at 65 AaC. Radiochemical purity was determined by ITLC. In vitro stability of both radiolabeled species was assessed in saline and serum. In vitro cell binding experiments were performed on integrin ανβ3 receptor-positive U87MG cancer cells. Non-specific Au@DTDTPA was used for comparison. Ex vivo biodistribution studies and in vivo PET and MRI imaging studies in U87MG tumor-bearing SCID mice followed. The Au@DTDTPA nanoparticles were labeled with Gallium-68 at high radiochemical yield (>95%) and were stable at RT, and in the presence of serum, for up to 3 h. The cell binding assay on U87MG glioma cells proved that 68Ga-cRGD-Au@DTDTPA had specific recognition for these cells. Biodistribution studies in U87MG tumor-bearing SCID mice showed that the tumor to muscle ratio increased from 1 to 2 h p.i. (3,71 ± 0.22 and 4,69 ± 0.09 respectively), showing a clear differentiation between the affected and the non-affected tissue. The acquired PET and MRI images were in accordance to the ex vivo biodistribution results. The preliminary results of this study warrant the need for further development of Au@DTDTPA nanoparticles radiolabeled with Ga-68, as possible dual-modality PET/MRI imaging agents.

Nanocomposite membranes of poly(ethylene glycol) diamine cured DGEBA/poly(vinylidene fluoride) reinforced with poly(methyl methacrylate) coated gold nanoparticles

The matrix material for hybrid membranes was prepared via curing of bisphenol A diglycidyl ether (DGEBA) with poly(ethylene glycol)diamine (DGEBA-c-PEGDA). The design of gold nanoparticles and poly(methyl methacrylate) coated gold nanoparticles (PMMA-AuNPs) as reinforcement was also considered. Morphology, size and distribution of PMMA-AuNPs were deliberated through transmission electron microscopy. The membranes of poly(vinylidene fluoride) (PVDF) and DGEBA loaded with PMMA-AuNPs were prepared by phase inversion method (DGEBA-c-PEGDA/PVDF/PMMA-AuNPs 0.1–1). Scanning electron microscopy was employed to study the fractured membrane surface and phase separated structure with nanopores were observed. The tensile strength was increased from 79.3 to 98.7 MPa when PMMA-AuNPs loading was increased from 0.1 to 1 wt.%. The glass transition temperature also improved with filler loading from 179 to 232°C. The membrane properties measured via membrane filtration set-up revealed increased pure water permeation flux, recovery and salt rejection for membrane with higher PMMA-AuNPs content. DGEBA-c-PEGDA/PVDF/PMMA-AuNPs membrane with 1 wt.% loading showed water flux of 50.2 mLcm−2 min−1 and salt rejection ratio of 88.8 %. Efficiency of the PMMA-AuNPs nanoparticles reinforced membranes for the removal of heavy metal ions was found to be 99 %.

Quantitative SHINERS analysis of temporal changes in the passive layer at a gold electrode surface in a thiosulfate solution.

Shell-isolated gold nanoparticles (SHINs) were employed to record shell-isolated nanoparticle-enhanced Raman spectra (SHINERS) of a passive layer formed at a gold surface during gold leaching from thiosulfate solutions. The (3-aminopropyl)triethoxysilane (APTES) and a sodium silicate solution were used to coat gold nanoparticles with a protective silica layer. This protective silica layer prevented interactions between the thiosulfate electrolyte and the gold core of the SHINs when the SHINs-modified gold electrode was immersed into the thiosulfate lixiviant. The SHINERS spectra of the passive layer, formed from thiosulfate decomposition, contained bands indicative of hydrolyzed APTES. We have demonstrated how to exploit the presence of these APTES bands as an internal standard to compensate for fluctuations of the surface enhancement of the electric field of the photon. We have also developed a procedure that allows for removal of the interfering APTES bands from the SHINERS spectra. These methodological advancements have enabled us to identify the species forming the passive layer and to determine that the formation of elemental sulfur, cyclo-S8, and polymeric sulfur chains is responsible for inhibition of gold dissolution in oxygen rich thiosulfate solutions.

An alternative assay to hydrophobic interaction chromatography for high-throughput characterization of monoclonal antibodies

The effectiveness of therapeutic monoclonal antibodies (mAbs) is governed not only by their bioactivity, but also by their biophysical properties. Assays for rapidly evaluating the biophysical properties of mAbs are valuable for identifying those most likely to exhibit superior properties such as high solubility, low viscosity and slow serum clearance. Analytical hydrophobic interaction chromatography (HIC), which is performed at high salt concentrations to enhance hydrophobic interactions, is an attractive assay for identifying mAbs with low hydrophobicity. However, this assay is low throughput and thus not amenable to processing the large numbers of mAbs that are commonly generated during antibody discovery. Therefore, we investigated whether an alternative, higher throughput, assay could be developed that is based on evaluating antibody self-association at high salt concentrations using affinity-capture self-interaction nanoparticle spectroscopy (AC-SINS). Our approach is to coat gold nanoparticles with polyclonal anti-human antibodies, use these conjugates to immobilize human mAbs, and evaluate mAb self-interactions by measuring the plasmon wavelengths of the antibody conjugates as a function of ammonium sulfate concentration. We find that hydrophobic mAbs, as identified by HIC, generally show significant self-association at low to moderate ammonium sulfate concentrations, while hydrophilic mAbs typically show self-association only at high ammonium sulfate concentrations. The correlation between AC-SINS and HIC measurements suggests that our assay, which can evaluate tens to hundreds of mAbs in a parallel manner and requires only small (microgram) amounts of antibody, will enable early identification of mAb candidates with low hydrophobicity and improved biophysical properties.

Colorimetric Logic Gates Based on Poly(2‐alkyl‐2‐oxazoline)‐Coated Gold Nanoparticles

A straightforward end‐capping strategy is applied to synthesize xanthate‐functional poly(2‐alkyl‐2‐oxazoline)s (PAOx) that enable gold nanoparticle functionalization by a direct “grafting to” approach with citrate‐stabilized gold nanoparticles (AuNPs). Owing to the presence of remaining citrate groups, the obtained PAOx@AuNPs exhibit dual stabilization by repulsive electrostatic and steric interactions giving access to water soluble molecular AND logic gates, wherein environmental temperature and ionic strength constitute the input signals, and the solution color the output signal. The temperature input value could be tuned by variation of the PAOx polymer composition, from 22 °C for poly(2‐npropyl‐2‐oxazoline)@AuNPs to 85 °C for poly(2‐ethyl‐2‐oxazoline)@AuNPs. Besides, advancing the fascinating field of molecular logic gates, the present research offers a facile strategy for the synthesis of PAOx@AuNPs of interest in fields spanning nanotechnology and biomedical sciences. In addition, the functionalization of PAOx with xanthate offers straightforward access to thiol‐functional PAOx of high interest in polymer science.

Layer-by-layer polymer coated gold nanoparticles for topical delivery of imatinib mesylate to treat melanoma.

The aim of this study was to investigate the feasibility of using layer-by-layer polymer coated gold nanoparticles (AuNP) as a carrier for topical iontophoretic delivery of imatinib mesylate (IM). AuNP were prepared by the Turkevich method and were stabilized and functionalized using polyvinylpyrrolidone and polyethylene imine. The functionalized AuNP were then sequentially coated with anionic poly(styrenesulfonate) and cationic polyethylene imine and loaded with IM. The layer-by-layer polymer coated AuNP (LbL-AuNP) showed average particle size and zeta-potential of 98.5 ± 4.3 nm and 32.3 ± 1.3 mV respectively. After LbL coating of AuNP, the surface plasmon resonance wavelength shifted from 518 to 530 nm. The loading efficiency of IM in LbL-AuNP was found to be 28.3 ± 2.3%, which was greatest for any small molecule loaded in AuNP. In vitro skin penetration studies in excised porcine ear skin showed that iontophoresis (0.47 mA/cm(2)) application enhanced the skin penetration of IM loaded AuNP by 6.2-fold compared to passive application. Tape stripping studies showed that iontophoresis of IM loaded LbL-AuNP retained 7.8- and 4.9-fold greater IM in stratum corneum and viable skin respectively compared with iontophoresis of free IM. LbL-AuNP were taken up rapidly (15 min) by B16F10 murine melanoma cells. Furthermore, IM loaded LbL-AuNP significantly (p < 0.001) decreased B16F10 cell viability compared to free IM. We have shown for the first time that IM can be delivered by topical application using LbL coated gold nanoparticles to treat melanoma.

Effect of maleimide-functionalized gold nanoparticles on hybrid biohydrogels properties

Nanoparticle cross-linking. Nanocomposite hydrogels with remarkable viscoelastic properties are prepared using maleimide coated gold nanoparticles as co cross-linkers for furan modified gelatin.

Measuring antibody coatings on gold nanoparticles by optical spectroscopy

Coating thickness estimates of coated gold nanoparticles was achieved to avoid reduction of diagnostic sensitivity from excess antibody.

Implications of sample aging on the formation of internally etched silica coated gold nanoparticles

Local refractive index sensitivity modelling using the plasmonic properties of gold nanospheres assists in the elucidation of the nanoparticle-rattle formation as a function of sample age and storage conditions.