Immobilization Of Gold Nanoparticles Research Articles

Covalent immobilization of gold nanoparticles on a plastic substrate and subsequent immobilization of biomolecules.

We propose a novel approach to stably immobilize gold nanoparticles (AuNPs) on a plastic substrate and demonstrate that the modified substrate is also capable of immobilizing biomolecules. To immobilize citrate-capped AuNPs, an acrylic substrate was simply dip-coated in a functional polymer solution to decorate the outermost surface with amino groups. Electrostatic interactions between AuNPs and the amino groups immobilized the AuNPs with a high density. The AuNP-modified acrylic substrate was transparent with a red tint. A heat treatment promoted the formation of amide bonds between carboxy groups on the AuNPs and amino groups on the substrate surface. These covalent bonds stabilized the immobilized AuNPs and the resulting substrate was resistant to washing with acid and thiol-containing solutions. The surface density of AuNPs was controlled by the surface density of amino groups on the substrate surface, which was in turn controlled by the dip-coating in the functional polymer solution. We attempted to immobilize functional biomolecules on the AuNPs-functionalized plastic surface by two different approaches. An enzyme (horseradish peroxidase) was successfully immobilized on the AuNPs through amide formation and 5′-thiolated DNA was also immobilized on the AuNPs through S–Au interactions. These chemistries allow for simultaneous immobilization of two different kinds of biomolecules on a plastic substrate without loss of their functional properties.

Alginate modified magnetic nanoparticles to immobilization of gold nanoparticles as an efficient magnetic nanocatalyst for reduction of 4-nitrophenol in water

This article displays synthesis of gold nanoparticles (Au NPs) decorated on sodium alginate (Alg) covered magnetite (Fe3O4@Alg-AuNPs) nanocomposite. Sodium alginate shell as a natural anionic polysaccharide on Fe3O4 microparticles core acted as a stabilizing agent for immobilization of Au NPs. Its catalytic performance was tested in the reduction of 4-nitrophenol to 4-aminophenol. The structural features of the synthesized nanocatalyst were investigated by Fourier-transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), Transmission electron microscopy (TEM), Energy Dispersive X-Ray Analysis (EDX), and Vibrating-sample magnetometer (VSM) studies. The catalytic activity of the material in the reduction process was quantitatively monitored using Ultraviolet–visible (UV–Vis) spectroscopy and it resulted excellent yields (99%) at short reaction time (1.5–4 min) in aqueous media at room temperature using very low catalyst load (1–3 mg). The kinetics study was also performed which afforded a good rate constant. Additionally, the catalyst showed high reproducibility as was easily retrievable and recoverable without noticeable loss in its catalytic activity.

Immobilization of Gold Nanoparticles on Poly(4-vinylpyridine)-Grafted Carbon Nanotubes as Heterogeneous Catalysts for Hydrogenation of 4-Nitrophenol

The organization of colloidal nanoparticles (NPs) on suitable supports is very significant for applications. In this work, a facile and robust method has been developed to directly attach gold NPs ...

Insights into the biomechanical properties of plasma treated 3D printed PCL scaffolds decorated with gold nanoparticles

Tissue engineered constructs having desired biomimetic and mechanical properties emerged due to the complexities involved in conventional skin grafting. They facilitate tissue regeneration without compromising mechanical properties. Herein, we report the fabrication of polycaprolactone (PCL) scaffold by fused deposition modeling and immobilization of gold nanoparticles onto the polymer surface after modifying the PCL surface using plasma polymerization. 3D printed PCL scaffolds inlaid with gold nanoparticles (Au-PCL) were characterized for their structural and mechanical properties using FESEM, and nano-indentation. The surface chemistry was analyzed using X-ray photon electron spectroscopy (XPS), wettability was determined using water contact angle studies and surface topography was imaged by atomic force microscopy (AFM). The surface modification of 3D printed scaffolds significantly improved their hydrophilicity suggesting that hydrophobicity which restricts the use of PCL in biological applications could be overcome by plasma modification. Nanoindentation studies showed that Au-PCL scaffolds exhibited remarkable enhancement in mechanical properties with reduced Young's modulus of 1.81 GPa. Biocompatibility was assessed by measuring cell viability, cell attachment and immune response. In vitro biocompatibility studies indicated good attachment of viable cells onto the gold nanoparticles incorporated 3D printed network. Immune response studies indicated that scaffolds did not enhance the production of pro-inflammatory cytokines such as TNF-α, IL-8 and IL-β. Collectively, plasma modification and surface immobilization of gold nanoparticles onto the 3D printed PCL scaffold is a simple and cost-effective technique to enhance the mechanical properties and biocompatibility of hydrophobic scaffolds like PCL, thereby making this technique a very promising tool for futuristic applications of scaffolds.

New composite stationary phase for chiral high-performance liquid chromatography

The new composite chiral stationary phase for high-performance liquid chromatography was prepared and characterized. Poly(styrene-divinylbenzene) microspherical particles with diameter of 3.3 micron were used as a matrix and coated with layer of 10 nm gold nanoparticles. Immobilized gold nanoparticles increased specific surface area of adsorbent and simplify covalent attachment of sulfur-containing compounds. In this work l-lysine conjugate with lipoic acid was synthesized, characterized and used for modification of gold nanoparticles. The prepared chiral selector was immobilized by the reaction of sulfur-containing groups from lipoic acid residue with gold surface of nanoparticles with formation of self-assembled monolayer. The prepared chiral stationary phase was characterized by nitrogen adsorption at low temperatures, diffuse reflection spectroscopy, scanning electron microscopy. The chromatographic retention of beta-blockers and profens was studied under conditions of reversed-phase HPLC. The possibility of enantiomers separation was demonstrated for flurbiprofen and ketoprofen racemates using 100 × 4.6 mm ID chromatographic column.

C, N Co-Decorated Alumina-Supported Au Nanoparticles: Enhanced Catalytic Performance for Selective Hydrogenation of Acetylene

The modifications of support for the dispersion and immobilization of gold nanoparticles were examined for the selective hydrogenation of acetylene to ethylene. The catalyst, denoted as Au/CNA, was prepared by the carbonization of C and N atom-containing organic precursors on Al2O3, which were subsequently used as supports for gold nanoparticles. The TOF value of Au/CNA was five times higher than that of Au/Al2O3 at 250 °C. The carbonization modification of Al2O3 support without N species showed almost no change in catalytic activity. Therefore, the improved catalytic performance of Au/CNA is related to the interactions of the N species on the CNA support with nano-gold particles. From the XPS analysis, electron transfer between gold and C, N co-doped species may play an important role in the high levels of Au active site utilization. This study may provide new avenues for the construction of organic/inorganic composite materials for efficient catalytic hydrogenation applications.

Enzyme-amplified SERS immunoassay with Ag-Au bimetallic SERS hot spots

Surface-enhanced Raman scattering (SERS) enables rapid detection of single molecules with high specificity. However, quantitative and sensitive SERS analysis has been a challenge due to the lack of reliable SERS-active materials. In this study, we developed a quantitative SERS-based immunoassay using enzyme-guided Ag growth on Raman labeling compound (RLC)-immobilized gold nanoparticle (Au NP)-assembled silica NPs (SiO2@Au-RLC@Ag). The enzyme amplified Ag+ reduction as well as Ag growth on the RLC-immobilized Au NP-assembled silica NPs (SiO2@Au-RLC), which resulted in a significant increase in SERS signal. In the presence of target antigens such as immunoglobulinG (IgG) or prostate-specific antigen (PSA), Ab1-Antigen-Ab2 immune complex with alkaline phosphatase triggered an enzyme- catalyzed reaction to convert 2-phospho-L-ascorbic acid (2-phospho-L-AA) to ascorbic acid (AA). As produced AA reduced Ag+ to Ag, forming an Ag hot spot on the surface of SiO2@Au-RLC, which enhanced the SERS signal of SiO2@Au-RLC@Ag in a solution with a target antigen concentration. The plasmonic immunoassay for IgG detection showed a high linearity of SERS intensity in the range of 0.6 to 9.0 ng/mL with a detection limit (LOD) of 0.09 ng/mL, while an LOD of 0.006 ng/mL was obtained for PSA. The results indicate that the sensitivity of our novel SERS-based immunoassay is higher than that of conventional enzyme-based colorimetric immunoassays.

Gold nanoparticle-glutathione-functionalized porous graphene oxide-based hydrophilic beads for the selective enrichment of N-linked glycopeptides.

A three-dimensional structured porous graphene oxide-polyethylenimine bead (pGP) is synthesized for immobilizing gold nanoparticles and modifying glutathione molecules (denoted as pGP/AuG). The pGP/AuG has open pore structure, honeycomb-like channels, and excellent hydrophilicity. By taking advantages of the porous structure, abundant binding sites, and multivalent interactions between glycopeptides and both glutathione molecules and free amino groups, the pGP/AuG is adopted to the selective enrichment of N-linked glycopeptides with low limit of detection (2fmol), high enrichment selectivity (1:500), binding capacity (333.3mg/g), recovery yield (91.3 ± 2.1%), and repeatability (< 6.0% RSD) using matrix-assisted laser desorption/ionization time of flight mass spectrometrydetection method. Furthermore, the practical applicability of pGP/AuG is evaluated, in which 209 N-glycosylated peptides corresponding to 128 N-glycosylated proteins are identified from 1μL human serum in three independent analysis procedures, suggesting the great potential for application in glycoproteome fields.Graphical abstract Schematic presentation of preparation for porous graphene oxide-based hydrophilic beads (pGP/AuG) with honeycomb-like microstructure. The pGP/AuG was successfully used for enriching and identifying glycopeptides from actual biological sample.

Immobilization of Au nanoparticles on poly(glycidyl methacrylate)‐functionalized magnetic nanoparticles for enhanced catalytic application in the reduction of nitroarenes and Suzuki reaction

We report a novel strategy for the synthesis of magnetic nanocomposite for highly efficient catalysis. Poly(glycidyl methacrylate) (PGMA) chains were grafted to the surface of magnetic nanoparticles (MNPs) through surface‐initiated reversible addition‐fragmentation chain transfer polymerization. Then, the oxirane rings in the PGMA chains were opened with 2,6‐diamino pyridine (DAP) molecules as ligands to prepare the solid support. Finally, this magnetic nanocomposite was used for the immobilization of gold nanoparticles. Fourier‐transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, transmission electron microscopy, scanning electron microscopy, gel permeation chromatography, vibrating sample magnetometry, and atomic absorption spectroscopy were used for characterization of the catalyst. The loading of gold nanoparticles on the solid support was 0.52 mmol/g. The catalytic activity of the prepared catalyst (MNP@PGMA@DAP@Au) was evaluated for the reduction of nitro compounds and C–C coupling reaction in water. The catalyst can be easily recovered and reused seven times without significant loss of catalytic activity.

A miRNA biosensor based on localized surface plasmon resonance enhanced by surface-bound hybridization chain reaction

The dysregulation of the concentration of individual circulating microRNAs or small sets of them has been recognized as a marker of disease. For example, an increase of the concentration of circulating miR-17 has been linked to lung cancer and metastatic breast cancer, while its decrease has been found in multiple sclerosis and gastric cancer. Consequently, techniques for the fast, specific and simple quantitation of microRNAs are becoming crucial enablers of early diagnosis and therapeutic follow-up. DNA based biosensors can serve this purpose, overcoming some of the drawbacks of conventional lab-based techniques. Herein, we report a cost-effective, simple and robust biosensor based on localized surface plasmon resonance and hybridization chain reaction. Immobilized gold nanoparticles are used for the detection of miR-17. Specificity of the detection was achieved by the use of hairpin surface-tethered probes and the hybridization chain reaction was used to amplify the detection signal and thus extend the dynamic range of the quantitation. Less than 1 h is needed for the entire procedure that achieved a limit of detection of about 1 pM or 50 amol/measurement, well within the reported useful range for diagnostic applications. We suggest that this technology could be a promising substitute of traditional lab-based techniques for the detection and quantification of miRNAs after these are extracted from diagnostic specimens and their analysis is thus made possible.

Seeded Growth Synthesis of Zirconia@Gold Particles in Aqueous Solution.

Metal-ceramic composite particles are of increasing interest due to their potential applications in photonic metamaterials as well as next-generation catalysts. The zirconia-gold system has received little attention due to the lack of controllable preparation methods. Well-known methods for the deposition of gold nanoshells on silica spheres, however, should be adaptable for similar zirconia-based materials. Here, we present a novel synthetic approach to the well-controlled deposition of gold on the surface of sol-gel derived zirconia mesoparticles by a stepwise method involving the immobilization of gold nanoparticles and repeated seeded-growth steps. We show that the immobilization efficiency is strongly enhanced by acidification with hydrochloric acid and additional employment of aminomethylphosphonic acid as coupling agent. The optimum conditions are identified and the subsequent incremental growth by seeded reduction of gold is demonstrated. The results shed light on the parameters governing the preparation of zirconia@gold composite particles and our synthetic approach provides a promising tool for future developments in complex nanomaterials design.

Revealing surface functionalities via microwave for the para-fluoro-Thiol click reaction

A fast and simple bottom-up methodology is reported to allow, thanks to a spontaneous phenomenon, the grafting of various materials on polymer substrates. In 60 s, the inert surface of polystyrene material is converted into a functional platform onto which organic molecules and metal particles can be anchored. A polystyrene (PS) matrix is blended with a small amount of a diblock copolymer additive engineered to both segregate at the material surface and be able to involve chemical reaction. Indeed, poly(pentafluorostyrene) (PSF) contains surface active fluorine atoms and the nucleophuge para-fluorine atom that allows nucleophilic substitution with thiols. Films of blend of PS matrix and PS-b-PSF additive are submitted to a microwave annealing to accelerate the spontaneous surface segregation of fluorine low surface energy atoms. XPS was performed to find that the optimal annealing conditions was a treatment at 30 W during 60 s. With this procedure, a blend of 5 w% in additive can lead to a surface composed of 13 at% of fluorine atoms corresponding to 55 w% of diblock. The pentafluorostyrene units decorating the surface were used as anchors to immobilize gold nanoparticles via the para-fluoro-thiol click reaction.

Quantifying the relationship between surfaces’ nano-contact point density and adhesion force of Candida albicans

It has been recently recognized that controlled surface structuring on the nanometer scale is a successful strategy to endow different materials with antimicrobial properties. Despite many studies on bacterial interactions with nanostructured surfaces, a quantitative link between surface topography and bacterial adhesion is still missing. To quantitatively link cell adhesion data with topographical surface parameters, we performed single-cell spectroscopy on chemically identical surfaces with controlled nano-contact point density achieved by immobilization of gold nanoparticles (AuNP) on gold thin films. Such materials surfaces have previously shown antimicrobial (anti-adhesive) efficacy towards Gram-negative Escherichia coli cells. In the current study, the influence of nano-structured surfaces on the surface coverage and adhesion forces of clinically relevant Candida albicans (C. albicans), the fungus primarily associated with implant infections, was investigated to validate their antimicrobial potency against different microbial cells. The adhesion forces of C. albicans cells to nanostructured surfaces showed a decreasing trend with decreasing contact-point density and correlated well with the results of the respective C. albicans cell counts. The surfaces with the lowest contact-point density, 25 AuNP/μm², resulted in an average adhesion force of 5 nN, which was up to 5 times lower compared to control and 61 AuNP/μm² surfaces. Further, detailed analyses of force-distance curves revealed that the work of adhesion, and thus the energy required to remove the C. albicans cell from the surface is up to 10 times lower on 25 AuNP/μm² surfaces compared to unstructured surfaces. These findings show that a controlled tuning of nanostructured surfaces in terms of accessible nano-contact points is crucial to generate surface structures with enhanced antimicrobial properties. The gained knowledge can be further exploited for the design of biomaterials surfaces to prevent adhesion of some most commonly encountered pathogens.

Fiber Optic Particle Plasmon Resonance Biosensor for Label-Free Detection of Nucleic Acids and Its Application to HLA-B27 mRNA Detection in Patients with Ankylosing Spondylitis.

We developed a label-free, real-time, and highly sensitive nucleic acid biosensor based on fiber optic particle plasmon resonance (FOPPR). The biosensor employs a single-strand deoxyoligonucleotides (ssDNA) probe, conjugated to immobilized gold nanoparticles on the core surface of an optical fiber. We explore the steric effects on hybridization affinity and limit of detection (LOD), by using different ssDNA probe designs and surface chemistries, including diluent molecules of different lengths in mixed self-assembled monolayers, ssDNA probes of different oligonucleotide lengths, ssDNA probes in different orientations to accommodate target oligonucleotides with a hybridization region located unevenly in the strand. Based on the optimized ssDNA probe design and surface chemistry, we achieved LOD at sub-nM level, which makes detection of target oligonucleotides as low as 1 fmol possible in the 10-μL sensor chip. Additionally, the FOPPR biosensor shows a good correlation in determining HLA-B27 mRNA, in extracted blood samples from patients with ankylosing spondylitis (AS), with the clinically accepted real-time reverse transcription-polymerase chain reaction (RT-PCR) method. The results from this fundamental study should guide the design of ssDNA probe for anti-sense sensing. Further results through application to HLA-B27 mRNA detection illustrate the feasibility in detecting various nucleic acids of chemical and biological relevance.

Performance of Single Mode Tapered Optical Fiber Sensor Based on Localized Surface Plasmon Resonance (LSPR) for Various Coating Time

Tapered optical fiber (TOF) sensor based on localized surface plasmon resonance is demonstrated for refractive index sensing application. The single-mode fiber (G652D) with 10/125 µm of core/core-cladding diameter was tapered by flame brushing method and achieved a waist diameter of approximately 15µm. Mercapto group (-SH) of 3-mercatoptopropyltrimethoxysilane (MPTMS) was utilized for immobilization of gold nanoparticles (AuNPs) by self-assemble monolayer (SAM) method on fiber surface. Evanescent field at the TOF sensing region excites the localized surface plasmons of AuNPs, with average mean diameter 15 ± 2 nm as evidence by scanning electron microscopy (SEM). The effect on deposition time was examined on three different samples; S1, S2 and S3 with 24h, 48h and 72h of coating time respectively. TOF sensor performance was evaluated with surrounding refractive indices ranges from 1.3324 to 1.4254. The sensing mechanism is based on the modulation of output light signal that represent by transmission shifting spectra. The optimum sensitivity was obtained for S2 at 18 nm/RIU with good repeatability, reversibility and stability.

Uniform intensity in multifocal microscopy using a spatial light modulator.

Multifocal microscopy (MFM) offers high-speed three-dimensional imaging through the simultaneous image capture from multiple focal planes. Conventional MFM systems use a fabricated grating in the emission path for a single emission wavelength band and one set of focal plane separations. While a Spatial Light Modulator (SLM) can add more flexibility as a replacement to the fabricated grating, the relatively small number of pixels in the SLM chip, cross-talk between the pixels, and aberrations in the imaging system can produce non-uniform intensity in the different axially separated image planes. We present an in situ iterative SLM calibration algorithm that overcomes these optical- and hardware-related limitations to deliver near-uniform intensity across all focal planes. Using immobilized gold nanoparticles under darkfield illumination, we demonstrate superior intensity evenness compared to current methods. We also demonstrate applicability across emission wavelengths, axial plane separations, imaging modalities, SLM settings, and different SLM manufacturers. Therefore, our microscope design and algorithms provide an alternative to the use of fabricated gratings in MFM, as they are relatively simple and could find broad applications in the wider research community.

Robust phase transfer, 3D-assembly and SERS application of multi-shaped gold nanoparticles

A robust, fast and versatile phase transfer approach to the transfer of large hydrophilic multi-shaped gold nanoparticles from aqueous to organic phase was systematically investigated. The procedure uses the amphiphilic surfactant bis-(amidoethylcarbamoylethyl) octadecylamine (C18N3), which consists of a long alkane chain to provide hydrophobic properties and terminal amine groups for hydrophilic properties. Furthermore, the 3D-assembly behavior, plasmonic properties and surface-enhanced Raman scattering properties of the hydrophobic multi-shaped gold nanoparticles derived from the phase transfer method on the surface of mercapto-silica colloidal spheres were systematically investigate. The surfaces of mercapto-silica spheres immobilize gold nanoparticles through strong coordination interactions between gold cations and thiol groups and allow the direct assembly of large multi-shaped nanoparticles on supporting colloidal spheres. The size of the gold nanoparticles used in both 3D-assembly and phase transfer is much larger (as large as 55 nm) than any known reports to date. This assembly strategy will provide the research community with a highly versatile, configurable, and reproducible process for the preparation of various structures and great flexibility in incorporating multiple nanoparticle components.

In situ formation and immobilization of gold nanoparticles on polydimethylsiloxane (PDMS) exhibiting catalase-mimetic activity.

We report a heterogeneous reaction to reduce HAuCl4 solution and form gold nanoparticles (AuNPs) on stainless steel needle surfaces. Through bubbling of nitrogen, AuNPs dispersed into the solution homogeneously. Subsequently, AuNPs were immobilized on the surface of polydimethylsiloxane (PDMS). The immobilized AuNPs exhibit catalase-mimetic activity in a 2 wt% H2O2 solution.

Gold nanoparticles for smart and recoverable catalyst using thermo-responsive core-crosslinked star polymer as the nanoreactor

In this work, a novel kind of temperature-responsive core cross-linked star (CCS) polymer, composing of poly(methoxypolyethylene glycol-co-di(ethylene glycol) ethyl ether acrylate) (P(PEGA-DEGA)) as thermo-responsive arm and poly(2-(dimethylamino)ethyl methacrylate) as functional core, was developed as nanoreactor for immobilizing gold nanoparticles for smart catalyst with facile recovery. The protonated imino groups in CCS polymer core could capture AuCl4- and simultaneously reduce it to Au NPs in aqueous solution, leading to the formation of P(PEGA-DEGA) CCS@Au composite. The whole procedure was carried out in aqueous media without using any toxic reducing agent, which is facile, efficient and green. The as-prepared CCS@Au composite exhibit a superior high catalytic activity for the reduction of 4-nitrophenol (4-NP), owing to that the soluble polymeric arms of the CCS polymers provides a homogeneous reaction system with fast mass transfer and thus facilitates interactions between Au NPs in the core and 4-NP. In addition, temperature-responsive catalyzing behavior was observed for the CCS@Au composite: the reaction rate enhanced with the elevation of the reaction temperature at first, but decreased when the temperature increased close to the LCSTs of the CCS@Au catalysts.

Thiol functionalized carbon ceramic electrode modified with multi-walled carbon nanotubes and gold nanoparticles for simultaneous determination of purine derivatives.

In this proof-of-concept study, a thiol-functionalized sol-gel-based carbon ceramic electrode (CCE) was developed. This CCE was further modified by immobilizing gold nanoparticles (AuNP) in the thiol-functionalized ceramic matrix as well as incorporating multi-walled carbon nanotubes (MWCNT) within the pores of this ceramic sol-gel. The proposed electrode (MWCNT-AuNP-CCE) was used for the simultaneous determination of purine derivatives, uric acid (UA), xanthine (XA) and caffeine (CA). The simultaneous detection of these compounds is essential because these purine derivatives often coexist in real samples. Moreover, since these analytes have the capacity to interchange structures, developing a simultaneous detector is important. This electrode was successfully characterized using environmental scanning electron microscopy (ESEM) with secondary and back scattering electron detectors, energy dispersive X-ray (EDX) analysis, transmission electron microscopy (TEM), and Fourier-transform infrared (FT-IR) spectroscopy. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) measurements were performed in phosphate buffer solution (0.1M PBS, pH6) at a potential window of 0.2 to 1.1V (vs. Ag/AgCl). The proposed modified electrode (MWCNT-AuNP-CCE) displayed three well-defined, stable and continuous oxidation peaks at 0.3, 0.7 and 1.0V for UA, XA, and CA, respectively. The resulting catalytic current at the surfaces showed a linear dependence to the concentrations of UA, XA and CA for up to 225, 225 and 1500μM, respectively. The limit of detection was determined to be 50, 63 and 354nM for UA, XA and CA, respectively. The analytical performance of MWCNT-AuNP-CCE was challenged with real samples such as human serum and urine with recoveries ranging between 98.1 and 102.6%. Moreover, the selectivity of sensor was further challenged with very similar purine molecules, theobromine and theophylline, which contain one less methyl group than CA. Overall, MWCNT-AuNP-CCE exhibited a promising platform for the future development of sensitive electrochemical sensors for the detection of purine derivatives in real samples.