Density Of Gold Nanoparticles Research Articles

Isolation of Exosomes from Human Serum Using Gold-Nanoparticle-Coated Silicon Surface.

Exosomes, whose mean diameter ranges from 20 nm to 200 nm, are cell-secreted vesicles and are abundant in most biological fluids, such as blood, urine, tears, sweat, breast milk, etc. Exosomal size variations and their composition can be attributed to several factors, such as age, gender and disease conditions of the individual. Existing techniques, such as ultracentrifugation and density gradient ultracentrifugation, for exosome isolation are instrument-dependent, time-consuming and lack specificity. In the present work, a gold-nanoparticle (GNP)-coated silicon (Si) wafer, functionalized with polyethylene glycol (PEG) was used for conjugation with anti-CD63 antibody via EDC NHS chemistry and incubated with serum to immobilize the exosomes on the Si surface. The surface-immobilized exosomes were eluted and quantified by a nanoparticle tracking analyzer (NTA). It was observed that an increase in GNP density on the Si wafer increases the size range and total number of exosomes that are being isolated. Western blotting performed for proteins such as HSP 70 and calnexin confirmed the immobilization and elution of exosomes. The proposed technique can be used as an alternative to existing techniques, as it has several benefits such as reusability of the Si surface for several isolations, minimal instrumental requirement, isolation of exosomes in two hours and compatibility with the microfluidic platform, making the technique suitable for real-time application. The proposed method could be useful in isolating a specific subrange of exosomes by altering the size of the GNP used for coating the Si wafer.

Fabrication of gold nanoparticle decorated surfaces for controlled nucleation of plasmonic microbubbles

Plasmonic bubbles produced by water-immersed gold nanoparticles (GNPs) under a laser irradiation are of great relevance in numerous applications. Normally, plasmonic bubbles are produced on a well-fabricated GNP decorated sample surfaces, which rely on expensive devices and complex fabrication processes. In this study, we systematically investigate the fabrication of GNP decorated sample surfaces for optimized production of plasmonic bubbles. Sample surfaces are fabricated by thermal dewetting of a gold film coated on fused silica substrates under an annealing temperature up to 1200 °C. Both the size and density of GNPs can be well tuned by adjusting gold film thickness and annealing temperature. The optical absorption of sample surfaces is also experimentally and numerically investigated, from which the optimal parameters of fabrication are determined. More importantly, for the first time, we find that the high annealing temperature leads to the formation of nanoindents beneath GNPs, resulting in the partial enwrapment of GNPs into fused silica substrates. This helps to stabilize GNPs on sample surfaces. With the fabricated sample surfaces, the nucleation and growth dynamics of giant initial bubbles and ordinary plasmonic bubbles can be well tuned. No apparent damage has been observed on the sample surfaces after the violent bubble nucleation. The increased stability of GNPs is important for plasmonic bubble related applications.

Monte Carlo investigation of the effect of gold nanoparticles’ distribution on cellular dose enhancement

PurposeIn recent decades‎, ‎radiotherapy has became one of the most useful and cost effective tools in cancer treatment‎. Having a number of unique characteristics made gold nanoparticles (GNPs) as promising candidates in achieving dose enhancement in tumor and improving the radiation treatment outcome‎. ‎Considering the widely documented tendency of GNPs to localize around the nucleus‎, ‎the distribution model of GNPs in the medium needs to be investigated in detail and to be well quantified‎. MethodsThe MCNPX Monte Carlo code was used to simulate particle transport in cells‎. ‎A single cell‎, ‎including an ellipsoidal cytoplasm with a centrally located sphere surrounded by a cube as the medium was modeled‎. ‎The physical dose due to the irradiation of 10–100 keV monoenergetic photons was calculated in the nucleus‎. To investigate the effect of the approach used for distribution of GNPs in the medium on dose enhancement factor‎ (‎DEF)‎, three models have been proposed‎: ‎filling the medium and the cytoplasm with either a gold-water mixture or a homogeneously distributed GNPs‎, ‎and the heterogeneous model by simulating spheres of GNPs localized in the cytoplasm‎. ResultsThe results show an overestimation of dose enhancement caused by gold-water mixture rather than that of homogeneous distribution‎. The DEFs for the heterogeneous model‎, ‎while follow the same behavior of two other models against various primary energies‎, ‎quantitatively demonstrate a significant distinction‎. ‎This model was also examined by studying the effect of concentration (the ratio of the mass of GNPs to the mass of the medium)‎, ‎size and density of‎ GNPs on nucleus dose enhancement‎. ‎It was found that though the values calculated for DEF strongly depend on concentration of GNPs‎, ‎for a given concentration‎, ‎they would not considerably be affected by changing the GNPs' size‎. As a criterion to assess their density around the nucleus‎, ‎the distance between two typical GNPs was found to be a key determinant factor to predict and to control dose enhancement in the target volume‎. For the primary photons of 30 keV‎, ‎our results showed a negligible difference between the DEFs calculated due to the cell orientation in the medium‎. ‎By extending the heterogeneous model for ten different locations of nucleus in the cell‎, ‎the energy dependence behavior of DEF was observed‎. ConclusionsThe results obtained emphasize the importance of accurate modeling of the distribution of GNPs in cell to demonstrate the more precise potential of gold in improving radiotherapy treatments‎.

Self-assembled gold nanoparticles as saturable absorber for low-threshold all-solid-state pulsed 2 μm laser

In order to overcome the shortcomings of un-uniformity of two-dimension (2D) material based saturable absorbers (SAs) and improve the performance of consequently generated laser pulses, a kind of gold nanoparticles (GNPs) based SAs was synthesized and employed to form 2 μm low-threshold pulsed laser. Two SA samples with different density of GNPs were fabricated and their modulation performance was compared under similar condition. Using Tm:YAP as gain medium, the constructed passively Q-switched 2 μm all-solid-state laser could deliver the shortest laser pulses with duration of 580 ns, repetition rate of 129 kHz and an average output power of 601 mW by using the first SA sample (with high GNPs density), corresponding to a pulse energy of 4.37 μJ and a peak power of 6 W. Laser pulses with a high pulse energy of 6.1 μJ and a peak power of 7.5 W were obtained with the second sample (with low GNPs density). Besides, the formed Q-switched lasers showed very low thresholds because of the large third-order nonlinear coefficient of GNPs. These results showed that the GNPs could be a promising SA for 2 μm wavelength band.

Nano-assembling and optical properties of sub-100 nm raspberry-like nanoparticles

The optical properties of sub-100 nm raspberry-like nano-systems composed of highly monodisperse silica particles and large gold nanoparticles (GNPs) is studied experimentally. The nanoparticles (NPs) were prepared by a self-assembly method, and the pH of each solution was determined by measuring the ζ-potential to ensure the stability of the nano-systems. Dynamic light scattering measurements show a narrow size distribution of NPs, and fairly dispersed particles in solution. The obtained nanoraspberries was also studied by transmission electron microscopy, which shows that the GNPs closely packed on the surface of silica particles. This effect induced a broadening and a shift of the absorption band to higher wavelengths, with an increase in GNPs density. It was also observed that the reduced size of silica particles resulted in a shortening of the inter-particles distance, which has favoured the generation of many hot spots in the gaps between GNPs. The tenability of obtained plasmon bands may have benefits in SERS probe, photocatalysis and fluorescence-based bioimaging.

TU-E-201B-08: K-Edge Imaging Using a Gold Nanoparticle Contrast Agent and a CT System with Photon Counting Detectors

Purpose: To investigate the feasibility of imaging a goldnanoparticle (GNP) contrast agent for detection of vulnerable plaque using a CT with photon countingdetectors and energy resolution. Materials and Methods: Simulation was performed for material decomposition based on the likelihood maximization method. The simulations were based on single‐slice parallel beam geometry. The beam energy was set to 120 kVp in order to provide high enough photon flux for energies above the k‐edge of the gold (80.7 keV). A CdZnTe detector with 5 different energy bins was used. Both ideal and more realistic detectors were used in the simulation. The phantom used for the simulation contained polymethyl‐methacrylate (PMMA), calcium, and GNP. The concentration of calcium in plaque was adjusted in such a way that the linear attenuation coefficients of GNP and calcium were approximately equal. It is expected in patients with an unstable plaque that goldnanoparticles would occupy portions of calcified tissue. Thus, the simulation of these three materials allows the simulation of the situations which are clinically relevant. Results: In reconstructed images after decomposition only gold was visualized without any traces of PMMA or calcium. The minimum detectablegold density for ideal detector was found to be ∼300 μg/cm3. The minimum detectable density increased by a factor of two as imperfections were added to the detector during simulation. However, the minimum detectable GNP density was far less than the amount of GNP that is accumulated in the plaque. The effect of dose, beam energy, and gold concentration on the image quality was also studied. Conclusions: These studies show the feasibility of using GNP as a contrast agent to detect vulnerable plaque.

Electrodeposition of large size gold nanoparticles on indium tin oxide glass and application as refractive index sensor

Large size gold nanoparticles (GNPs) were directly deposited onto the indium tin oxide (ITO) glass surface by cyclic voltammetric method. The GNPs on ITO substrate were characterized by means of scanning electron microscopy (SEM), UV–vis spectroscopy and X-ray diffraction (XRD). The nucleation and growth steps were controllable in the GNPs deposition procedure. The addition of chloride ion in the electrolysis affected the size and density of GNPs on the ITO surface. The response of refractive index for various organic solvents was also investigated. The sensitivity of refractive index increased as GNPs became larger.

Direct electrodeposition of gold nanoparticles onto indium/tin oxide film coated glass and its application for electrochemical biosensor

A novel electrochemical deposition method for growth of gold nanoparticles (GNPs) on indium tin oxide (ITO) thin film coated glass was investigated. The resulting electrode surface was characterized by SEM, UV–Vis spectroscopy and electrochemical methods. The GNPs directly attached on the electrode surface with a quasi-spherical shape and their sizes of diameters were in the range of 20–35 nm with a quite symmetric distribution. With increasing electrodeposition cycles of cyclic voltammetry, the density of GNPs on ITO electrode surface was increased. The potential utility of the GNPs modified ITO electrode was investigated. Superoxide dismutase (SOD) was successfully immobilized on GNPs modified ITO electrode and the direct electron transfer between enzyme and electrode surface realized. The enzyme electrode exhibited a rapid and high response to superoxide anion.

Electrical detection of human immunoglobulins G from human serum using a microbiosensor

A biosensor for the electrical detection of human antibodies from serum has been fabricated and experimentally demonstrated. The device is based on the immobilization of proteins used as probes between a set of microelectrodes. Incubation with diluted human serum was followed by incubation with anti-human secondary antibodies labeled with gold nanoparticles (GNPs) and then precipitation of silver on the nanoparticles. The output of the device was defined as the percentage of short-circuited microelectrodes after silver deposition independently of the gap conductance. Two model probes were studied: protein A and goat antibodies. The effects of the microgap spacing (5, 10, 15 or 20 μm) and the duration of the silver treatment were examined. The data obtained showed that a large spacing (20 μm) led to poor sensitivity. Alternately, 5 μm gaps led to high sensitivity and saturation of the signal. Interestingly, 10–15 μm gaps enabled a non-saturated and distinct signal for both probes that was correlated with the GNP density between the microgaps as determined by atomic force microscopy. Different capture efficiencies could be easily distinguished. The biosensor described here is easy to use and thus can be applied to real detection experiments.