Conjugation of gold nanoparticles to polypropylene mesh for enhanced biocompatibility

Polypropylene mesh materials have been utilized in hernia surgery for over 40 years. However, they are prone to degradation due to the body's aggressive foreign body reaction, which may cause pain or complications, forcing mesh removal from the patient. To mitigate these complications, gold nanomaterials were attached to polypropylene mesh in order to improve cellular response. Pristine samples of polypropylene mesh were exposed to hydrogen peroxide/cobalt chloride solutions to induce formation of surface carboxyl functional groups. Gold nanoparticles were covalently linked to the mesh. Scanning electron microscopy confirmed the presence of gold nanoparticles. Differential scanning calorimetry and mechanical testing confirmed that the polypropylene did not undergo any significantly detrimental changes in physicochemical properties. A WST-1 cell culture study showed an increase in cellularity on the gold nanoparticle-polypropylene mesh as compared to pristine mesh. This study showed that biocompatibility of polypropylene mesh may be improved via the conjugation of gold nanoparticles.     

One-step synthesis of star-like gold nanoparticles for surface enhanced Raman spectroscopy

In this paper we present a new protocol for the synthesis of Star-Like Gold Nanoparticles (SGNs) by a simple one-step, room temperature procedure not involving the use of seeds or surfactants, that can be performed in seconds in any laboratory without the need of special technologies. These particles exhibited excellent properties for Surface Enhanced Raman Spectroscopy (SERS) and, when compared with spherical nanoparticles with similar size and concentration, showed enhancing factors from 10 to 50 times higher depending on the dye and on the wavelength employed. SGNs could be used directly in suspension as single, non-aggregating particles and were shown to be active in a remarkably broad range of the light spectrum from green to near infrared. Moreover, SGNs were adsorbed on the surface of a silicon slide to prepare SERS active solid substrate. Despite the fact that the surface of the solid substrate was not perfectly homogeneous, the signals recorded from different positions acquired through DuoScan averaging mode show excellent reproducibility, demonstrating how this simple and cheap protocol can be applied in order to generate reliable and homogeneous SERS substrates.     

Localized-surface-plasmon enhanced emission from porous silicon by gold nanoparticles

The porous silicon (PS) samples, decorated by Au nanoparticles (NPs) possessing localized-surface-plasmon (LSP) resonance, are prepared by the conventional anodization method. Photoluminescence (PL) is studied systematically, in particular, its dependence on the excitation power. It is found that undecorated PS samples exhibit a saturation behavior in PL intensity with increasing the pumping laser power, while the luminescence of Au-decorated PS hybrid samples have a purely linear dependence on the excitation power. In the linear response region of PS samples, addition of metal NPs layer moderately suppresses the emission while, in the saturation region, the net emission is enhanced by approximately up to 4-fold. Several possible mechanisms are discussed. We believe that the observed PL enhancement in saturation region is dominantly due to the resonant coupling between the LSP of Au NPs and the electronic excitation of PS, which inhibits the nonradiative Auger recombination process at high excitation power. These results indicate that the plasmon effect could be useful for designing even more efficient optoelectronic devices such as super bright light emitting devices and solar cells with high efficiencies. Despite many challenges, Au NPs can potentially be applied to introduce LSP resonance for the future silicon-based optoelectronics or photonics.     

Multilayer enhanced gold film over nanostructure surface-enhanced Raman substrates

We have developed a novel class of gold multilayer, surface-enhanced Raman scattering (SERS) substrates that are capable of enhancing SERS signals by 15.3-fold over conventional gold film over nanostructure (GFON) SERS substrates, making them comparable in sensitivity to optimized silver film over nanostructure (SFON) substrates, while providing the long-term stability obtained from gold. They are fabricated by depositing 10 A thick silver oxide islands on conventional GFON substrates, followed by deposition of a second continuous gold layer. The silver oxide layer acts as a dielectric spacer between the two continuous gold films and produces significantly enhanced SERS signals, as compared to optimized single layer substrates of the same geometry or comparable substrates prepared by deposition of silver islands that are not oxidized. In addition to the enhanced sensitivity of these multilayer substrates, they also exhibit long SERS active shelf-lives (i.e., months), with no measurable degradation in SERS enhancement, and relative standard deviations in SERS enhancement of less than 5.2% across the substrate's surface.     

Surface enhanced coherent anti-stokes Raman scattering on nanostructured gold surfaces

Coherent anti-Stokes Raman spectroscopy (CARS) is a well-known tool in multiphoton imaging and nonlinear spectroscopy. In this work we combine CARS with plasmonic surface enhancement on reproducible nanostructured surfaces. We demonstrate strong correlation between plasmon resonances and surface-enhanced CARS (SECARS) intensities on our nanostructured surfaces and show that an enhancement of ～10(5) can be obtained over standard CARS. Furthermore, we find SECARS to be >10(3) times more sensitive than surface-enhanced Raman Spectroscopy (SERS). We also demonstrate SECARS imaging of molecular monolayers. Our work paves the way for reliable single molecule Raman spectroscopy and fast molecular imaging on plasmonic surfaces.     

Tuning gold nanorod-nanoparticle hybrids into plasmonic Fano resonance for dramatically enhanced light emission and transmission

We investigate the optical response of a gold nanorod array coupled with a semicontinuous nanoparticle film. We find that, as the gold nanoparticle film is adjusted to the percolating regime, the nanorod-film hybrids are tuned into plasmonic Fano resonance, characterized by the coherent coupling of discrete plasmonic modes of the nanorod array with the continuum band of the percolating film. Consequently, optical transmission of the percolating film is substantially enhanced. Even more strikingly, electromagnetic fields around the nanorod array become much stronger, as reflected by 2 orders of magnitude enhancement in the avalanche multiphoton luminescence. These findings may prove instrumental in the design of various plasmonic nanodevices.     

Synthesis and enhanced electrochemical properties of pod-shaped gold/silica nanoparticles

Pod-shaped gold/silica nanoparticles (PGSNPs) were prepared using perfluorooctanoic acid (PFOA) and cetyltrimethylammonium bromide (CTAB) as cotemplates. The PGSNPs were utilized to explore a novel biosensor through coupling myoglobin (Mb) with chitosan (Chi). Compared with Mb-Chi-PSNPs (pod-shaped silica nanoparticles)/GC modified electrode, Mb-Chi-PGSNPs/GC electrode exhibited a pair of much stronger redox peaks at − 0.28 V (vs. Ag/AgCl). Moreover, facilitated direct electron transfer of the metalloenzymes with smaller peak-to-peak separation (ΔEp) of about 46 mV was acquired on the PGSNPs-based enzyme electrode. The PGSNPs-based biosensor demonstrated significant electrocatalytic activity for the reduction of hydrogen peroxide with a wide linear range (1-540 µM) and high sensitivity (661 mA cm^− 2 M^− 1). Together, the Mb-Chi-PGSNPs film is one of ideal candidate materials for direct electrochemistry of redox proteins, and may find potential applications in biomedical, food, and environmental analysis and detection.     

Surface enhanced fluorescence of Rh6G with gold nanohole arrays

Five gold nanohole arrays with distinct aperture size were fabricated by magnetron sputtering technique. Fluorescence enhancements of Rh6G fluorophore in the close vicinity of gold nanohole arrays were observed. Up to 40 times increase of fluorescence intensity was obtained from gold nanohole arrays as compared with a smooth gold surface control sample. A double-peak curve was presented in the excitation spectrum of enhanced fluorescence emission when the excitation wavelength was scanning from 300 nm to 550 nm. It was found that smaller aperture size and proper excitation wavelength matching with the surface plasmon resonances condition were favorable for a better fluorescence enhancement.     

Surface enhanced Raman scattering from porous gold nanofibers of different diameters

Porous gold nanofibers of different diameters from 43 to 219 nm were fabricated using electrochemical deposition techniques. Gold-silver alloy were electrochemically deposited in the form of nanofibers within the porous alumina templates of various diameters and only a silver phase was chemically removed using nitric acid. Field-emission scanning electron microscope images of the resulting nanofibers show a high-quality nanoporous network with homogeneous pores. A notable surface-enhanced Raman scattering (SERS) has been observed for all porous gold nanofibers of which scattering efficiencies are distinctly higher than that of the smooth solid gold nanofibers without porosity. As the diameter of porous gold nanofibers decreases, the observed SERS efficiency gradually increases. Controlled fabrication of lateral width of gold nanofibers reveals promising application for high efficient and stable molecular sensing platforms.     

Fabrication of multifunctional polydopamine-coated gold nanobones for PA/CT imaging and enhanced synergistic chemo-photothermal therapy

Multimodal imaging-guided chemo-photothermal therapy is an excellent cancer treatment,which can not only efficiently against tumor,but also can offer precise treatment window and real-time monitoring of the treatment efficiency.In our work,polydopamine(PDA)-coated gold nanobones(AuNBs@PDA nanocomplexes)were designed for this approach.The AuNBs@PDA nanocomplexes have strong absorbance in the near infrared(NIR)region and higher photothermal conversion efficiency(75.48%)than gold nanobones alone,which was facilitated for photoacoustic imaging and photothermal therapy.Besides,the loading efficiency of doxorubicin(DOX)by AuNBs@PDA nanocomplexes could be up to about 70%and DOX release from AuNBs@PDA/DOX nanocomplexes sensitively response to the lower pH environment and NIR laser irradiation,which makes them become the excellent nano-carrier for the delivery of chemotherapy drug.In vitro and in vivo studies showed significant cytotoxicity and antitumor efficacy by the AuNBs@PDA/DOX nanoplatform with negligible side effects.Meanwhile,the nanoplatform was also successfully employed for computed tomography(CT)imaging,attributing to the high atomic number and high X-ray attenuation coefficient of gold.Therefore,we believed that the proposed PDA-coated gold nanobones would be a novel multifunctional theranostic nanoagent to realize the PA/CT imaging-guided chemo-photothermal therapy of cancer.     

Convective assembly of linear gold nanoparticle arrays at the micron scale for surface enhanced Raman scattering

A convective assembly technique at the micron scale analogous to the writing action of a “pipette pen” has been developed for the linear assembly of gold nanoparticle strips with micron scale width and millimeter scale length for surface enhanced Raman scattering (SERS). The arrays with interparticle gaps smaller than 3 nm are hexagonally stacked in the vicinity of the pipette tip. Variable numbers of stacked layers and clean surfaces of the assembled nanoparticles are obtained by optimizing the velocity of the pipette tip. The SERS properties of the assembled nanoparticle arrays rely on their stacking number and surface cleanliness.      

Quantitative enhanced Raman scattering of labeled DNA from gold and silver nanoparticles

Surface-enhanced resonance Raman scattering (SERRS) from silver nanoparticles using 514.5-nm excitation has been shown to offer huge potential for applications in highly sensitive multiplexed DNA assays. If the technique is to be applied to real biological samples and integrated with other methods, then the use of gold nanoparticles and longer wavelengths of excitation are desirable. The data presented here demonstrate that dye-labeled oligonucleotide sequences can be directly detected by SERRS using gold nanoparticles in a quantitative manner for the first time. The performance of gold and silver nanoparticles as SERRS substrates was assessed using 514.5-, 632.8-, and 785-nm excitation and a range of 13 commercially available dye-labeled oligonucleotides. The quantitative response allowed the limit of detection to be determined for each case and demonstrates that the technique is highly effective, sensitive, and versatile. The possibility of excitation at multiple wavelengths further enhances the multiplexing potential of the technique. The importance of effectively combining the optical properties of the nanoparticle and the dye label is demonstrated. For example, at 632.8-nm excitation, the dye BODIPY TR-X and gold nanoparticles make a strong SERRS combination with very little background fluorescence. This study allows the choice of nanoparticle and dye label for particular experimental setups, and significantly expands the applicability of enhanced Raman scattering for use in many disciplines.     

Surface enhanced absorption and transmission from dye coated gold nanoparticles in thin films

Absorption spectra of gold nanoisland thin film and the composite film of gold having thin coating of Methylene Blue and Rh6G dyes have been studied. Thin gold nanoisland film shows surface plasmon resonance (SPR) peak in the visible wavelength range, which shifts to near infrared with an increase in the thickness of the film. It was found that thin film of gold consists of nanoparticles of different size and shape, particularly nanorods of noncylindrical shapes. A linear relation was found between SPR peak wavelength and the aspect ratio of the nanoparticles in gold thin film. Effective medium refractive index of the gold film is estimated to be ~2.5, which decreases with an increase in film thickness. The coating of dyes on gold films splits the SPR peak with an enhanced absorption. Enhancement in absorption of composite film is maximal when the dye absorption peak coincides with the SPR peak; otherwise enhancement in transmission is observed for all the wavelength range. Absorption amplitude of composite film peaks increase with an increase in the gold film thickness, which tend toward saturation for film thickness of ≥6 nm. A correlation shows that absorption spectra can be described by the Maxwell Garnett theory, when the gold nanoparticles have a nearly spherical shape for very thin film (≤6 nm).     

Formation of gold nanoparticles in silicon suboxide films prepared by plasma enhanced chemical vapour deposition

Nanostructured materials fabricated by dispersing metal particles on the dielectric surface have potential application in the field of nanotechnology. Interfacial metal particles/dielectric matrix interaction is important in manipulating the structural and optical properties of metal/dielectric films. In this work, a thin layer of gold (Au) was sputtered onto the surface of silicon oxide, SiO_x (0.38 < x < 0.68) films which was deposited at different N₂O/SiH₄ flow rate ratios of 5 to 40 using plasma enhanced chemical vapor deposition (PECVD) technique prior to the annealing process at 800 °C. FTIR spectra demonstrate the intensity and full-width at half-maximum (FWHM) of Si-O-Si stretching peaks are significantly dependent on the N₂O/SiH₄ flow-rate ratio, η. The films deposited at low and high N₂O/SiH₄ flow rate ratios are dominated by the oxygen and silicon contents respectively. The size and concentration of Au particles distributed on the surface of SiO_x films are dependent on the N₂O/SiH₄ flow-rate ratio. High concentrations of Au nanoparticles are distributed evenly on the surface of the film deposited at N₂O/SiH₄ flow-rate ratio of 30. Crystallinity and crystallite sizes of Au are enhanced after the thermal annealing process. Appearance of surface plasma resonance (SPR) absorption peaks at 524 nm for all samples are observed as a result of the formation of Au particles. The annealing process has improved SPR peaks for all the as-deposited films. The energy gap of the as-deposited Au/SiO_x films are in the range of 3.58 to 4.38 eV. This energy gap increases after the thermal annealing process except for the film deposited at η = 5.     

Surface enhanced Raman scattering of neurotransmitter release in neuronal cells using antibody conjugated gold nanoparticles

This study demonstrated the potential feasibility of using antibody-conjugated gold nanoparticles as highly sensitive and homogeneous sensing probes for biological monitoring of neurotransmitters in neuronal cells. Bands at 1152 and 1322 cm(-1) were also similar to SERS of metal catecholates, and could be assigned to catechol ring vibration and carbon-oxygen stretches.     

Origin of the positional offset of FP-like enhanced transmission peaks in a one-dimensional gold grating

General transmission characteristics of a one-dimensional optically thick gold grating were investigated as functions of the grating structural parameters (period, slit width and grating thickness) in the spectral range from 0.4 μm to 9.9 μm. The positions (resonant wavelengths) of the Fabry–Perot (FP)-like enhanced transmission (ET) peaks depend not only on the grating’s period and thickness, but also on the slit width. These numerically calculated FP-like resonant positions are different from the simple FP predictions. The physical origin of these positional offsets is ascribed to the additional phases produced by the special ‘reflecting planes’, which are caused by oscillating dipoles located at the entrances and exits of the slits. For a particular order of FP-like resonance, the additional phase is found to be independent of the refractive index of the surrounding, but dependent on the grating’s structural parameters.     

A DNA duplex with extremely enhanced thermal stability based on controlled immobilization on gold nanoparticles

The effect of DNA loadings on the thermal stability of DNA duplex immobilized on gold nanoparticles has been investigated. The modestly loaded duplexes on the gold nanoparticles showed enhanced thermal stability, as compared to that of the free duplex (without gold nanoparticles). However, the highly loaded duplex showed stability similar to that of free duplex. The stability could be controlled over a wide temperature range simply by varying the salt concentration (over 50 degrees C). Additionally, the gold nanoparticles with modestly loaded oligonucleotides could be used as nanoprobes for effective and fast strand exchange reactions, based on the increased thermal stability of the immobilized duplex. These results indicate that the interaction between the duplex and the nanoparticle surface plays an important role in determining the stability of the duplex.