Trapping Of Gold Nanoparticles Research Articles

Off-resonance high-performance surface-enhanced Raman scattering-active substrate by trapping gold nanoparticles using Bessel beam

The surface-enhanced Raman scattering (SERS) technique provides outstanding molecular fingerprint identification and high sensitivity of analytes. Herein, colloidal sphere-shaped gold nanoparticles (Au-NPs) trapped in concentric rings of the Bessel beam generated from the optical fiber-based negative axicon has been reported as a SERS substrate. With the trapping of Au-NPs, the SERS ability of colloidal Au-NPs improved, and the average enhancement factor (AEF) of the rhodamine-6G (R6G) and 4-aminothiophenol (4-ATP) molecules can reach up to the order of 107. Control experiments were also carried out with the trapping of Au-NPs by Gaussian beam illumination, without any illumination of the light and with the trapping of Au-NPs by the Bessel beam illumination on a silver (Ag)-coated silicon (Si) substrate with a self-assembled monolayer (SAM) of 4-ATP. Theoretical studies were also carried out using the finite element method (FEM) to identify the hotspots generated in the gaps formed between the Au-NPs, leading to an enhancement in the SERS signal of the molecules, and the results were consistent with the experimentally determined AEFs. The obtained results demonstrate that the proposed SERS technique is stable. This study has significant potential applications in clinical diagnosis, food safety, environment safety, chemical sensing, and biosensing.

Simultaneous Force and Darkfield Measurements Reveal Solvent-Dependent Axial Control of Optically Trapped Gold Nanoparticles

Single molecule force spectroscopy using optical tweezers (OT) has enabled nanoresolved measurements of dynamic biological processes but not of synthetic molecular mechanisms. Standard OT probes made from silica or polystyrene are incompatible with trapping in organic solvents for solution phase chemistry or with force-detected absorption spectroscopies. Here, we demonstrate optical trapping of gold nanoparticles in both aqueous and organic conditions using a custom OT and darkfield instrument which can uniquely measure force and scattering spectra of single gold nanoparticles (Au NPs) simultaneously. Our work reveals that standard models of trapping developed for aqueous conditions cannot account for the trends observed in different media here. We determine that higher pushing forces mitigate the increase in trapping force in higher index organic solvents and lead to axial displacement of the particle which can be controlled through trap intensity. This work develops a new model framework incorporating axial forces for understanding nanoparticle dynamics in an optical trap. These results establish the combined darkfield OT with Au NPs as an effective OT probe for single molecule and single particle spectroscopy experiments, with three-dimensional nanoscale control over NP location.

Optical concentration of gold nanoparticles as a new concept of analytical sensitivity

Concentration procedures have always been implemented when trace analysis of compounds in real matrices is contemplated. A variety of concentration strategies have been reported aiming at decreasing the limits of detection (LODs). The optical concentration of the substance in solution is one of the novel concepts for the enhancement of the analytical sensitivity. In this study, the optical concentration has been measured by the trapping of gold nanoparticles ( nm) dispersed in water at low-concentrations at the focal volume of the laser beam. The influence of factors such as the time of gold nanoparticle trapping, the size of the nanoparticles, the intensity of the laser beam, their solution concentration have been reported on the accumulation of gold nanoparticles in the solution. The results showed at different laser intensities, the capacity of the optical trap changed. At low concentrations of gold nanoparticles, the signal increased linearly with the concentration until the capacity of the optical trap was filled. Also, the best optical concentration efficiency was observed when the time of trapping increased to a period of 40 s. Under the optimum conditions, the relative concentration increase of gold nanoparticles was calculated across the range of to particles at the focal volume of the laser beam for the range from particle/mL of gold nanoparticles in the solution at a laser intensity of mW. This approach may be used to quantitatively determine of gold nanoparticles, supermolecules, and other nanoparticles.

Plasmonic enhancement in gold coated inverse pyramid substrates with entrapped gold nanoparticles

Significant increase of plasmonic surface enhancement has been observed in gold coated micron sized inverse pyramids entrapping a gold nanoparticle. The amplification of both surface enhanced Raman and fluorescence signals was found and it was dependent on the size of the trapped gold nanoparticle. The enhancement was found to be 50 times higher for the 250nm diameter nanosphere, compared to the 50nm one. Finite differential time domain simulations were performed to determine the near-field distribution in the structure and showed that when the nanoparticle protrudes into the hotspot zone of the void, coupling of the electromagnetic field occurs and the plasmon-related near-field enhancement is concentrated into the close vicinity of the nanoparticle, mainly into the gaps around the contact points of the curved sphere and the flat pyramid surfaces.

Modulation of nanoparticle uptake, intracellular distribution, and retention with docetaxel to enhance radiotherapy.

One of the major issues in current radiotherapy (RT) is the normal tissue toxicity. A smart combination of agents within the tumor would allow lowering the RT dose required while minimizing the damage to healthy tissue surrounding the tumor. We chose gold nanoparticles (GNPs) and docetaxel (DTX) as our choice of two radiosensitizing agents. They have a different mechanism of action which could lead to a synergistic effect. Our first goal was to assess the variation in GNP uptake, distribution, and retention in the presence of DTX. Our second goal was to assess the therapeutic results of the triple combination, RT/GNPs/DTX. We used HeLa and MDA-MB-231 cells for our study. Cells were incubated with GNPs (0.2 nM) in the absence and presence of DTX (50 nM) for 24 h to determine uptake, distribution, and retention of NPs. For RT experiments, treated cells were given a 2 Gy dose of 6 MV photons using a linear accelerator. Concurrent treatment of DTX and GNPs resulted in over 85% retention of GNPs in tumor cells. DTX treatment also forced GNPs to be closer to the most important target, the nucleus, resulting in a decrease in cell survival and increase in DNA damage with the triple combination of RT/ GNPs/DTX vs RT/DTX. Our experimental therapeutic results were supported by Monte Carlo simulations. The ability to not only trap GNPs at clinically feasible doses but also to retain them within the cells could lead to meaningful fractionated treatments in future combined cancer therapy. Furthermore, the suggested triple combination of RT/GNPs/DTX may allow lowering the RT dose to spare surrounding healthy tissue. This is the first study to show intracellular GNP transport disruption by DTX, and its advantage in radiosensitization.

Three dimensional DNA nanotracks: A novel method for ultrasensitive and visible mercury (II) detection

Three Dimensional DNA nanotracks (3D DNA Nanotracks) based on Hg (II)-responsive exponential amplification reaction (EXPAR) integrated with DNA hydrogels for ultrasensitive and visual Hg (II) detection were developed. The 3D DNA Nanotracks could be successfully installed in the presence of Hg (II). Briefly, Hg (II) triggered the EXPAR reaction and produced substantial amounts of single-stranded DNA (ssDNA). The ssDNA as the initiator stimulated the visual DNA hydrogel, which trapped gold nanoparticles (AuNPs) in its networks. Therefore, Hg (II) could be visually determined using the Hg (II)-responsive EXPAR for the signal amplification, identification, and transformation. The hydrogel was used as the visual and quantitative readout, and the limit of detection (LOD) of the biosensor was determined to be as low as 2.8 pM.

Nanozyme-Catalyzed Cascade Reactions for Mitochondria-Mimicking Oxidative Phosphorylation.

Multiple-enzyme-involving cascade reactions that yield bioenergy are necessary in natural oxidative phosphorylation. However, in vitro applications are hampered by the sensitivity of catalytic activity to environmental adaptation. Herein, we explore nanozyme-catalyzed cascade reactions in an assembled hybrid architecture for mitochondria-mimicking oxidative phosphorylation. Hollow silica microspheres containing trapped gold nanoparticles were synthesized to promote two enzyme-like catalytic reactions that transform glucose into gluconic acid in the presence of oxygen. The resulting transmembrane proton gradient drives natural ATP synthase reconstituted on the surface to convert ADP and inorganic phosphate into ATP. The assembled architecture possesses high activity for oxidative phosphorylation, comparable to that of natural mitochondria. This study provides a new natural-artificial hybrid prototype for exploring bioenergy supply systems and holds great promise for ATP-powered bioapplications.

Nanozyme‐Catalyzed Cascade Reactions for Mitochondria‐Mimicking Oxidative Phosphorylation

AbstractMultiple‐enzyme‐involving cascade reactions that yield bioenergy are necessary in natural oxidative phosphorylation. However, in vitro applications are hampered by the sensitivity of catalytic activity to environmental adaptation. Herein, we explore nanozyme‐catalyzed cascade reactions in an assembled hybrid architecture for mitochondria‐mimicking oxidative phosphorylation. Hollow silica microspheres containing trapped gold nanoparticles were synthesized to promote two enzyme‐like catalytic reactions that transform glucose into gluconic acid in the presence of oxygen. The resulting transmembrane proton gradient drives natural ATP synthase reconstituted on the surface to convert ADP and inorganic phosphate into ATP. The assembled architecture possesses high activity for oxidative phosphorylation, comparable to that of natural mitochondria. This study provides a new natural–artificial hybrid prototype for exploring bioenergy supply systems and holds great promise for ATP‐powered bioapplications.

Trapping of Au nanoparticles in a microfluidic device using dielectrophoresis for surface enhanced Raman spectroscopy.

Dielectrophoresis (DEP) is the electrokinetic movement of non-charged particles when they are subjected to a non-uniform electric field. This is a growing area of research, which can be used for trapping, concentrating and separating different particles. Some work has been reported with the intention of trapping metal particles to optimize the surface enhanced Raman spectroscopy (SERS) effect. In this paper, we use DEP with insulating structures (iDEP) to generate a non-uniform electric field for trapping gold nanoparticles (AuNP). The system was coupled to a Raman spectrometer for the detection of Crystal Violet by utilizing the SERS effect.

Trapping of gold nanoparticles within arrays of topological defects: evolution of the LSPR anisotropy

We demonstrate how the localized surface plasmon resonance (LSPR) of gold nanoparticles is affected by their trapping within topological defect cores. Using aligned arrays of smectic edge dislocations, we evidence a reversal of the LSPR anisotropy, when the nanoparticle concentration increases. We combine UV–visible spectroscopy with simulations to show that this reversal is related to a transformation of the nanoparticle organization. When the concentration increases, the organization varies from nanoparticle chains parallel to the dislocations to anisotropic nanoparticle ribbons, larger in the direction perpendicular to the dislocations, moreover denser perpendicular to the dislocation than parallel to the dislocations. This transformation may be associated with the localized presence of dense arrays of aligned dislocations, inducing a compression between the NPs, but only in the direction perpendicular to the dislocations.

Imaging and Analysis of Single Optically Trapped Gold Nanoparticles Using Spatial Modulation Spectroscopy.

The extinction cross sections and spectra of single nanoparticles can be directly measured by moving the particle in and out of a tightly focused laser beam. This technique, known as spatial modulation spectroscopy, yields detailed information about the size, shape, and environment of the particles. These experiments are typically done on particles immobilized on a substrate. Here we demonstrate for the first time the use of spatial modulation spectroscopy to interrogate single, optically trapped nanoparticles in solution. Gold nanoparticles as small as 15 nm were trapped and imaged. The experiments were performed by modulating the position of the probe laser beam while scanning it over the trapped particle with a galvo-scanning mirror system. This technique opens up the possibility of precisely measuring the optical properties of single nanoparticles in liquid environments, free from the influence of a surface.

Laser-induced breakdown of an optically trapped gold nanoparticle for single cell transfection

The cell selective introduction of therapeutic agents remains a challenging problem. Here we demonstrate spatially controlled cavitation instigated by laser-induced breakdown of an optically trapped single gold nanoparticle of diameter 100 nm. The energy breakdown threshold of the gold nanoparticle with a single nanosecond laser pulse at 532 nm is three orders of magnitude lower than water, which leads to nanocavitation allowing single cell transfection. We quantify the shear stress to cells from the expanding bubble and optimize the pressure to be in the range of 1-10 kPa for transfection. The method shows transfection of plasmid DNA into individual mammalian cells with an efficiency of 75%.

Dielectrophoretic trapping of nanoparticles with an electrokinetic nanoprobe

Electrophoresis 2013, 34, 1922-1931. DOI: 10.1002/elps.201300004 The main figure shows a three-dimensional, branched fractal pattern of gold nanoparticles created via dielectrophoresis. Initially, a silver-gallium nanoneedle is mounted on the end of a pulled glass capillary and coated with a thin layer of gold. A conductive coverslip (not pictured) is used to complete the point-and-plate system. A droplet containing suspended non-spherical gold nanoparticles (35 nm mean diameter) of various shapes is introduced. At an AC signal of 200 kHz and 0.6 Vrms the gold nanoparticles are attracted to the probe via positive dielectrophoresis. Subsequent particle-particle electrokinetic interactions, including pearl-chaining, produce the resulting pattern. The inset figures (top, middle) are magnified images showing the trapped gold nanoparticles. The last inset image (bottom) shows a gold nanowire created from two electrodes.

Optical trapping of metal-dielectric nanoparticle clusters near photonic crystal microcavities

We predict the formation of optically trapped, metal-dielectric nanoparticle clusters above photonic crystal microcavities. We determine the conditions on particle size and position for a gold particle to be trapped above the microcavity. We then show that strong field redistribution and enhancement near the trapped gold nanoparticle results in secondary trapping sites for a pair of dielectric nanoparticles.

Manipulation of gold nanorods with dual-optical tweezers for surface plasmon resonance control

Gold nanorods are too tiny to be manipulated using conventional mechanical methods. In this paper, we demonstrate the trapping, transferring, positioning and patterning of gold nanorods with dual-optical tweezers. The convenient manipulations are achieved by taking advantage of the longitudinal surface plasmon resonance of gold nanorods and the anisotropic optical trapping forces formed by two linearly polarized Gaussian beams. The trapped gold nanoparticles are positioned extremely firmly and quickly on a substrate compared with randomly dispersed ones. It is observed that gold nanorods show advantages over gold nanospheres with regard to positioning speed and stability. More importantly, versatile plasmon coupling effects have been achieved in some patterned nanorods.

Convenient formation of nanoparticle aggregates on microfluidic chips for highly sensitive SERS detection of biomolecules

Microfluidic chips combined with surface-enhanced Raman spectroscopy (SERS) offer an outstanding platform for rapid and high-sensitivity chemical analysis. However, it is nontrivial to conveniently form nanoparticle aggregrates (as SERS-active spots for SERS detection) in microchannels in a well-controlled manner. Here, we present a rapid, highly sensitive and label-free analytical technique for determining bovine serum albumin (BSA) on a poly(dimethylsiloxane) (PDMS) microfluidic chip using SERS. A modified PDMS pneumatic valve and nanopost arrays at the bottom of the fluidic microchannel are used for reversibly trapping gold nanoparticles to form gold aggregates, creating SERS-active spots for Raman detection. We fabricated a chip that consisted of a T-shaped fluidic channel and two modified pneumatic valves, which was suitable for fast loading of samples. Quantitative analysis of BSA is demonstrated with the measured peak intensity at 1,615cm(-1) in the surface-enhanced Raman spectra. With our microfluidic chip, the detection limit of Raman can reach as low as the picomolar level, comparable to that of normal mass spectrometry.

Heat Profiling of Three-Dimensionally Optically Trapped Gold Nanoparticles using Vesicle Cargo Release

Irradiated metallic nanoparticles hold great promise as heat transducers in photothermal applications such as drug delivery assays or photothermal therapy. We quantify the temperature increase of individual gold nanoparticles trapped in three dimensions near lipid vesicles exhibiting temperature sensitive permeability. The surface temperature can increase by hundreds of degrees Celsius even at moderate laser powers. Also, there are significant differences of the heat profiles in two-dimensional and three-dimensional trapping assays.

Direct Measurements of Heating by Electromagnetically Trapped Gold Nanoparticles on Supported Lipid Bilayers

Absorption of electromagnetic irradiation results in significant heating of metallic nanoparticles, an effect which can be advantageously used in biomedical contexts. Also, metallic nanoparticles are presently finding widespread use as handles, contacts, or markers in nanometer scale systems, and for these purposes it is essential that the temperature increase associated with electromagnetic irradiation is not harmful to the environment. Regardless of whether the heating of metallic nanoparticles is desired or not, it is crucial for nanobio assays to know the exact temperature increase associated with electromagnetic irradiation of metallic nanoparticles. We performed direct measurements of the temperature surrounding single gold nanoparticles optically trapped on a lipid bilayer, a biologically relevant matrix. The lipid bilayer had incorporated fluorescent molecules which have a preference for either fluid or gel phases. The heating associated with electromagnetic radiation was measured by visualizing the melted footprint around the irradiated particle. The effect was measured for individual gold nanoparticles of a variety of sizes and for a variety of laser powers. The temperatures were highly dependent on particle size and laser power, with surface temperature increments ranging from a few to hundreds of degrees Celsius. Our results show that by a careful choice of gold nanoparticle size and strength of irradiating electromagnetic field, one can control the exact particle temperature. The method is easily applicable to any type of nanoparticle for which the photothermal effect is sought to be quantified.

Direct Measurement of Heating by Optically Trapped Gold Nanoparticles Using Molecular Sorting in a Lipid Bilayer

Gold nanoparticles have are extremely useful as multi-functional and sensitive probes for investigation and manipulation of biological systems. Particles, as small as tenths of nanometers, can be visualized, optically manipulated, and used as controlled force transducers. Their high absorbance also makes them excellent converters of electromagnetic radiation into thermal energy. If the heating can be quantified it can also be advantageously used to perform controlled thermal treatment. We performed a direct measurement of the heating associated with optical trapping of individual gold nanospheres. A trapped gold nanosphere was embedded in a two dimensional supported gel phase lipid bilayer with incorporated fluorescent molecules which preferentially located, e.g., in the gel phase. Visualization of the melted region gave direct information about the temperature profile around the irradiated particle. The heating is highly dependent on particle size and laser power, with surface temperatures increasing from a few to hundreds of degrees Celcius. This quantification allows for creating controlled and localized temperature gradients which can be utilized for destruction of unwanted biological material such as cancer cells, to create local temperature gradients in lipid bilayers, or for nano-engineering purposes.

From droplets to devices

Single-electron behaviour has been observed in devices that can be made by simply trapping gold nanoparticles between two droplets of liquid metal.