Enhanced Contrast Agent for X‐Ray Imaging Using Gold–Silicon Core–Shell Nanostructures

X-ray computed tomography (CT) requires an optimal compromise between image quality and patient dose. While high image quality is an important requirement in CT, the radiation dose must be kept minimal to protect the patients from ionizing radiation-associated risks. The use of probes based on gold nanoparticles (AuNPs) along with active targeting ligands for specific recognition of cancer cells may be one of the balanced solutions. Herein, we report the effect of folic acid (FA)-modified AuNP as a targeted nanoprobe on the contrast enhancement of CT images as well as its potential for patient dose reduction. For this purpose, nasopharyngeal KB cancer cells overexpressing FA receptors were incubated with AuNPs with and without FA modification and imaged in a CT scanner with the following X-ray tube parameters: peak tube voltage of 130 KVp, and tube current–time products of 60, 90, 120, 160 and 250 mAs. Moreover, in order to estimate the radiation dose to which the patient was exposed during a head CT protocol, the CT dose index (CTDI) value was measured by an X-ray electrometer by changing the tube current–time product. Raising the tube current–time product from 60 to 250 mAs significantly increased the absorbed dose from 18 mGy to 75 mGy. This increase was not associated with a significant enhancement of the image quality of the KB cells. However, an obvious increase in image brightness and CT signal intensity (quantified by Hounsfield units [HU]) were observed in cells exposed to nanoparticles without any increase in the mAs product or radiation dose. Under the same Au concentration, KB cells exposed to FA-modified AuNPs had significantly higher HU and brighter CT images than those of the cells exposed to AuNPs without FA modification. In conclusion, FA-modified AuNP can be considered as a targeted CT nanoprobe with the potential for dose reduction by keeping the required mAs product as low as possible while enhancing image contrast.

Flexible design of hybrid polymer nanoassemblies consisting of nonlinear optical (NLO) polymer nanosheets and gold nanoparticle alignment was done to elucidate near-field effects of localized surface plasmon (LSP) coupling, which was generated from coupled gold nanoparticles, on enhanced second harmonic generation (SHG) from nonlinear optical (NLO) dyes in hybrid nanoassemblies. Structurally well-defined hybrid polymer nanoassemblies comprising NLO polymer nanosheets and aligned gold nanoparticles were fabricated using bottom-up approaches: Langmuir-Blodgett (LB) technique and nanoparticle adsorption. Two hybrid polymer nanoassembled structures were particularly examined: a single-layer NLO polymer nanosheet and gold nanoparticle monolayer (single-layer structure) exhibiting intralayer LSP coupling, and a single-layer NLO polymer nanosheet sandwiched between two-layer gold nanoparticle monolayers (sandwich structure). The latter enables interlayer LSP coupling between the two gold nanoparticle monolayers. Dependence of SHG intensity on the distance between the NLO layer and nanoparticle layer was examined according to the LB layer structure and gold nanoparticle size variation. The SH light intensity from the NLO polymer nanosheet decreased almost exponentially with increasing spacer distance between the NLO polymer nanosheet and gold nanoparticle monolayer in both single-layer and sandwich structures. The decay length depends strongly on the gold nanoparticle size, indicating effective spatial distance for enhanced SHG from NLO polymer nanosheets. Theoretical calculations were used to study the enhancement mechanism. Finite difference time domain (FDTD) calculations reproduced the exponential behavior of SH light intensity as a function of separation distance, which confirmed the importance of coupled gold nanoparticle formation and parallel geometry of near-field coupling of the coupled gold nanoparticles with NLO polymer nanosheets for efficient SHG enhancement. Dipole-type LSP coupling along the long axis of adjacent gold nanoparticles at the fundamental frequency dominates enhancement of SHG from NLO dyes oriented parallel to the long axis of LSP coupling, which occurs at the center of the Au NPs.

In this article, the idea of employing lossy mode resonances (LMR) concertedly for gas sensing along with the reversible interaction of metal oxides with gases has been investigated. Fabrication and characterization of a LMR-based fiber optic probe with successive coatings of indium-tin oxide (ITO) film and nanoparticles over the unclad core of the fiber have been carried out for the detection of hydrogen gas (H2). The results have been compared with the probes having individual coatings of ITO thin film and nanoparticles. For calibrating and comparing, the wavelength interrogative spectra have been recorded for varying concentrations of H2 gas exploiting the sensor probes. A red shift of the spectrum has been observed with the increase in the concentration of the gas. The results uphold the fact that the LMR-based sensor with both thin film and nanoparticles layer has better sensitivity to H2 gas than the probes with the layer of either nanoparticles or thin film. A collective study on the three probes for different gases has predicted a maximum level of sensitivity for the probe with layers of thin film and nanoparticles along with the high selectivity and repeatability of the results for H2 gas. In addition to high sensitivity and selectivity, the proposed sensor can be used for online monitoring and remote sensing of the gas because of the fabrication of the probe on the optical fiber.

Numerical studies of microwave propagation properties in a conical horn and an adjustable waveguides, and for plasmas generated under disk-plate windows of a 220mm diameter and in a vacuum chamber are studied by a finite-difference time-domain (FDTD) method including plasma equations. In the numerical studies, a TM01-mode microwave of 2.45GHz at a power of 1kW is supplied from the top of the conical horn waveguide. In addition, numerical results by the FDTD method are compared with experimental results, and a validity of the numerical results is investigated. From the numerical results, it is found that the TM01-mode microwave changes its field shape and propagates along inner surfaces of the conical horn and the adjustable waveguides. Then electromagnetic fields of the TM01-mode microwave concentrate at the center surfaces of the disk-plate windows [quartz (εr=3.8), alumina (εr=9.7), and WG20 (εr=20.0)]. A diameter of higher concentration is within 80mm, and the orientation of electric field is almost vertical to the disk-plate window. The diameters within 80mm are equivalent to a diameter at a higher electron density in an oxygen plasma experiment in the volume mode at 1kW and 133Pa with a quartz window. When heights of the adjustable waveguide are changed from 64to244mm, peaks of electric fields in the heights, where microwave power is estimated to be strongly absorbed into the plasmas, appear and peak positions of the electric fields are observed periodically in surface-wave mode plasmas as well as the volume mode plasmas. Heights of the peaks increase with increasing dielectric constant and peak-to-peak distances of the peak positions decrease with increasing dielectric constant. The peak positions agree to the minimum microwave power reflections tuned by a combination of an autotuning unit and adjustable waveguide heights in experiments. Furthermore, peak positions of relatively absorbed microwave powers in the surface-wave and volume mode plasmas calculated by Poynting vectors in the FDTD method are close to the peak positions. This means that microwave powers penetrate effectively the disk-plate windows near the peak positions. In addition, a relatively absorbed microwave power with an alumina disk-plate window (surface-wave mode plasma) is larger than that with the quartz disk-plate window (volume mode plasma). This comes from a reason that a larger electron density in the surface-wave plasma absorbs a larger quantity of the microwave power. From the above comparisons between results obtained by the FDTD method and experiments, a validity of the FDTD method including the plasma equations can be confirmed.

In this study, we demonstrate that the uptake rate of the surface-modified gold nanoparticles (GNPs) with folic acid by specific cells can be increased significantly, if the membranes of these cells have sufficient folic-acid receptors. Two human breast cancer cell lines were studied; one is MDA-MB-435S cell, and the other T-47D cell. The expression of the folic acid receptors of the former is much higher than that of the latter. These cells were incubated with media containing bare GNPs or GNPs conjugated with folic acid individually. Due to the unique optical behavior (i.e. surface plasmon resonance) of GNPs, the uptake amount of GNPs by cells can be identified by using the laser scanning confocal microscopy. Our experiments show that the uptake amount of GNPs in MDA- MB-435S cells is higher than that in T-47D cells for the same culture time, if the culture medium contains bare GNPs. Moreover, if the GNPs conjugated with folic acid are used for the culture, the uptake rate of GNPs by MDA-MB-435S cells is improved more. In contrast, the uptake rates of both GNPs are almost the same by T-47D cells. The phenomenon indicates that the uptake rate of GNPs can be improved via the ligand- receptor endocytosis, compared with the nonspecific endocytosis. Therefore, the uptake rate of GNPs conjugated with folic acid by MDA-MB-435S cells is higher than that of bare GNPs.

Illuminating a transparent mold under total internal reflection condition generates evanescent light. Near-field photolithography uses such light, and we simulated this exposure in two dimensions using the finite-difference time-domain (FDTD) method. Our simulation suggests the feasibility of resolving a 130 nm pitch grating pattern, which is finer than the diffraction limit of light. The simulation results showed fair agreement with our experimental results, confirming the strong influence of exposure light polarization to the distribution of optical near fields in photoresist films. This indicates that the FDTD simulation is promising to predict exposure results for designing molds. We further extended the simulation varying the thickness and refractive index of a photoresist film. Based on the simulation results, showing the good exposure contrast in the thin surface layer of the photoresist film, we suggested two methods to resolve a thick resist film: the multilayer resist method which allows us to use a sufficiently thin photoresist film, and the surface imaging technology which can completely dry develop a thick photoresist film even if its exposure area is confined in the surface layer.

In thin films of porphyrin (H2P) and gold nanoparticles (AuNPs), photoexcitation of porphyrins leads to energy and charge transfer to the gold nanoparticles. Alternating layers of porphyrins and octanethiol protected gold nanoparticles (dcore ∼3 nm) were deposited on solid substrates via the Langmuir−Schäfer method, forming bilayer films denoted as H2P/AuNP. Photoinduced electron transfer from the gold nanoparticle layer to the porphyrin layer was observed as a distinct photovoltage response of the H2P/AuNP film when studied via the time-resolved Maxwell displacement charge (TRMDC) method. Time-resolved fluorescence and absorption measurements of the H2P/AuNP film demonstrated a significant reduction of the lifetime of the excited singlet state of porphyrin caused by the gold nanoparticles. Transients of the charge transfer reaction were not observed in the time-resolved absorption measurements, which indicates that the quantum yield of the charge transfer is low in the H2P/AuNP film. Energy transfer from the excited singlet state of porphyrin to the gold nanoparticles is the main deactivation path of excited porphyrins in the H2P/AuNP film. The critical distance of the energy transfer was estimated to be 6.4 nm, based on the dependence of fluorescence quenching on the distance between the porphyrin and gold nanoparticle layers.

Design and Methodology: Materials with feature sizes spanning the nano- and micro-scale range have been sought after by materials scientists and engineers to address specific functional demands unmet by bulk materials, in fields ranging from energy to sensors. Surface-enhanced Raman scattering (SERS) based sensors for molecular detection rely on nano- and micro-structuring of metallic substrates to amplify the intrinsically weak Raman signal, however fabricating SERS substrates can be tedious and time consuming. Our vision was to create a versatile and simple approach to fabricate SERS substrates. Wrinkling of a thin film on a compliant substrate is a rapid and inexpensive fabrication method for controllably creating materials with features covering several lengthscales.[1] Bioprocessing and biosensing devices have been fabricated using wrinkling with sputtered thin films,[2–4]however we sought to develop a method to create tunable wrinkled materials for SERS without the use of complex, vacuum-based deposition systems. First, a layer of gold nanoparticles was formed on an amino-silane treated heat-shrinkable substrate using self-assembly. Then, wrinkling of the nanoparticle layer was induced by heating the coated polymer substrate over its glass transition temperature, causing the footprint of the substrate to be reduced to 16% of the original area, while exerting a compressive force on the gold nanoparticle layer. The mechanical stress was relieved through the buckling of the gold nanoparticle layer on the surface of the substrate. Original Data and Results: The wrinkling behaviour of the gold nanoparticle film was assessed before shrinking, after shrinking uniaxially (by physically constraining two sides of the substrate), and after shrinking biaxially using scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). Well-ordered uniaxial and biaxial nanoparticle wrinkles were produced across the entire surface of the substrate. In order to control the wavelength and amplitude of the resulting wrinkles, nanoparticles of different diameters (~12 nm, ~18 nm, and ~36 nm) were deposited as the film layer. In addition, we assessed the effect of depositing multiple layers of ~12 nm nanoparticles on the resulting wrinkled structures. We observed that by increasing the diameter of the nanoparticles or by increasing the number of deposited nanoparticle layers, the wavelength and amplitude of the wrinkles could be controllably increased (Figure 1). These wrinkle structured nanoparticle surfaces were applied as SERS substrates, using 4-mercaptopyridine as the target analyte. By tuning the wavelength and morphology of the wrinkled structures, using different sized nanoparticles or multiple nanoparticle layers, the enhancement factor of the various SERS substrates was altered and optimized. Conclusions:We have developed a benchtop all-solution-processing method to create wrinkled metallic nano-/microstructures, tunable in size and morphology, on polymer substrates. By altering the nanoparticle diameters and number of deposited layers, we were able to control the amplitude and wavelength of the resulting wrinkled structures. Moreover, using physical constraints during the shrinking/wrinkling process allows for further regulation of the wrinkle morphology. We have demonstrated that these structures can used to create optical sensors as they were successfully applied as tunable SERS substrates to specifically detect a target analyte, and we envision these nanoparticle polymer composites finding other applications in chemical sensors, biosensors, and optoelectronics. [1] A. Schweikart, A. Horn, A. Böker, A. Fery, Adv. Polym. Sci. 2010, 227, 75. [2] S. M. Woo, C. M. Gabardo, L. Soleymani, Anal. Chem. 2014, 86, 12341. [3] C. M. Gabardo, A. M. Kwong, L. Soleymani, Analyst 2015. [4] A. Hosseini, L. Soleymani, Appl. Phys. Lett. 2014, 105, 074102. Figure 1

Photonic crystal (PhC) can potentially result in enhanced optical properties around critical points in the photonic band gap. Of interest here are enhanced nonlinear optical effects. In this study, one and two dimensional nonlinear PhC were designed and fabricated using barium titanium oxide (BTO) thin films as the active medium. Nonlinear PhC made with barium titanate thin films potentially provide integrated devices with the advantages of wide tunability and high stability. Films 500 nm thick deposited on MgO substrates were utilized. Two dimensional PhC structures were defined by focused ion beams (FIB). Before patterning, a thin metal layer was deposited on the barium titanate layers in order to improve the conductivity of the samples. After writing the patterns, cylindrical air holes were generated in the thin film layers. The PhC lattice constant and the hole radius were selected in sub-micron region in order to satisfy the requirement of wave resonance. The PhCs with sub-micron features were characterized by the atomic force microscopy (AFM), scanning electron microscopy (SEM), and near field optical microscopy (NSOM). The transmission spectra of the PhC waveguides were calculated with a continuous wide band source that covered 1 to 2 micron wavelength. Simulations of the transmission characteristics were performed using the two dimensional finite difference time domain method (FDTD).

Surface-enhanced Raman spectroscopy (SERS) technique can achieve an ultra-high sensitivity (i.e., down to the single-molecule level) via coinage-metal nanostructures such as silver, gold, copper, etc. In this work, a geometry is proposed that consists of silver nanoparticles (AgNPs) decorated on cadmium chloride (CdCl2) annealed cadmium sulfide (CdS) thin film on a glass substrate. A strong SERS enhancement in AgNPs on CdCl2 annealed CdS thin films is achieved, which is twelve times larger than the scattering from the bare CdCl2 annealed CdS thin film. The improved SERS signal allows us to observe fundamental phonon processes in CdCl2 annealed CdS thin film. Moreover, a finite difference time domain (FDTD) method is used to understand the underlying SERS physics. By using the FDTD method, robust electromagnetic field localization in the nanogap between AgNPs and at the contact point of Ag NPs and CdS thin film is studied.

Most commercial computer aided design (CAD) software for microwave planar circuits is based on models of circuit elements that are valid for a limited range of dielectric constant. Therefore designing miniaturized circuits on high dielectric constant substrates requires a full wave analysis approach. This category of substrates mainly contains high dielectric ceramics stable with temperature and the substrates for high temperature superconducting (HTS) thin films. Despite the advances in the finite-difference time domain (FDTD) method applied to planar circuits the practical aspects of the case of high dielectric constant substrates have not been sufficiently studied. This paper presents a FDTD method which can be effectively applied for practical planar circuits on high dielectric substrates. The extension of the FDTD method to this case is very important for the design of high temperature superconducting devices for mobile and satellite communications.

Introduction: Metal nanoparticles such as gold and silver nanoparticles have attracted much interest during the last decades for their special chemical and physical properties. Gold and silver nanoparticles can be functionalized with active biologic moieties like antibodies, drugs and chemicals, enabling them to react with specific cells. Furthermore, penetration and cytotoxic effects of nanoparticles can be increased by electromagnetic waves such as infrared, ultraviolet, radiofrequency and microwave. Aim: The aim of this study was to evaluate the rate of cell cytotoxicity induced by folic acid-functionalized gold and silver nanoparticles with and without microwave irradiation on cancer cells from patients with acute myeloid leukemia (AML). Method: Patients with known AML (M1, M2, M3 and M4), all recently diagnosed by histopathology, special stains and immunohistochemistry, and 4 normal persons were enrolled in the study. The blood mononuclear cell fraction was separated, so that the final concentration of neoplastic myeloid cells and normal mononuclear cells in each tube was adjusted to about 400 cells/μL. For preparation of folate-functionalized gold and silver nanoparticles, folic acid was dissolved in deionized water, added to 1 mM HAuCl4 and 1 mM AgNO3 solution, and incubated at 50°C for 8 h. Scanning electron micrographs, ultraviolet-visible spectrophotometer and Fourier transform infrared (FTIR) were used for confirmation of the synthesis of functionalized nanoparticles. After preparation, nanoparticles were added to cancerous and normal cell suspensions, and then incubated at 37°C for 1 h. Another experiment was carried out in the same way but with exposure to microwave irradiation for 10 s so that its temperature reached at 50°C, and then incubated at 37°C for 1 h, after which cell cytotoxicity was evaluated with MTT test. All of the tests were duplicated, and paired t-test was used to compare the mean absorbance read-out in each of the above-mentioned groups of wells. Results: The sizes of functionalized gold and silver nanoparticles were approximately 25 nm to 32 nm. After synthesis of functionalized nanoparticles, the tubes containing HAuCl4 turned to red color, and the peak absorbance for gold nanoparticles was at 520 nm. For AgNo3 , it turned to yellow color with a peak absorbance at 420 nm. FTIR test showed connection of folic acid moieties to gold and silver surfaces. This study showed that functionalized gold nanoparticles were more toxic than functionalized silver nanoparticles on cancer and normal cells. Also, microwave irradiation was more synergic with functionalized gold nanoparticles. Furthermore, the most effectiveness score was 2.87 for functionalized silver nanoparticles without microwave irradiation and the minimum effectiveness score was 2.20 for functionalized silver nanoparticles with microwave. Conclusion: This study clearly demonstrated that although functionalized gold nanoparticles have high toxicity to cells, but silver nanoparticles without microwave irradiation are more effective because of less cytotoxic effect on normal cells.

Changes in the optical properties of Pd capped Pr thin film and nanoparticle layers prepared by vacuum evaporation and inert gas evaporation techniques, respectively, have been studied as a function of time during hydrogen loading and deloading. These samples were characterized by transmission electron microscopy, atomic force microscopy, x-ray diffraction, and spectrophotometery techniques. Absorption spectra of Pr thin film and nanoparticles samples in metal, and hydrogen loaded and deloaded states have been reported. It is observed that filling of octahedral sites in the dihydride phase results in changes in absorption coefficient values at 1.5–2.0eV and H content in the trihydride phase causes shift of the absorption edge. Enhanced surface area, loose topography, a larger number of interparticle boundaries due to small sizes, relatively loose adhesion to the substrate, and smaller structural changes in nanoparticle layers result in larger and faster changes in the optical properties during loading in comparison to thin film.

We have developed a novel nanoscale patterning method of self-assembled monolayer (SAM) using near-field light. This method utilizes the thermal desorption of constituent molecules of a SAM (e.g. the desorption temperature of Octadecanethiol on Au is 130～230 °C) through the irradiation with near-field light, which can make noncontact and noncontaminating patterning of the SAM at nanoscale. In this paper, the near-field photothermal effect is numerically analyzed by the finite difference time domain (FDTD) method, and the electromagnetic field intensity and temperature distributions are estimated. The sample consists of Au thin film as a bonding layer with thiolated molecules of SAM, Ti thin film as an adhesion layer for Au, and SiO2 substrate. In the analysis, the shape of the near-field optical fiber probe and the thickness of the thin film layer are considered. In the case of the thick Au layer with a double-tapered near-field optical fiber probe, the temperature of the fiber-tip becomes higher than that of Au surface. The strong heating of the probe tip causes a fatal damage of the coating metal of the fiber, therefore it is difficult to couple the high intensity laser into the near-field optical fiber probe in order to reach the desorption temperature. On the other hand, the desorption temperature can be achieved with the 10 nm-thick Au thin film. Moreover, in order to gain high optical intensity enhancements, the triple-tapered near-field optical fiber probe is utilized. Our simulations confirm extremely high temperature distribution on the sample surface by using the triple-tapered near-field optical fiber probe with 10 nm-thick Au thin film layer on 50 nm-thick Ti membrane.

We studied the effects of reflective supports on the surface-enhanced Raman scattering (SERS) by Au nanoparticles (NPs) placed on top of them. When Au NPs are placed on a flat Au or Pt thin film, the SERS intensity of 4-aminobenzenethiol is doubled from that of Au NPs on a Si wafer. This phenomenon can be explained, through finite difference time domain (FDTD) simulations, with a strongly enhanced electromagnetic (EM) field at the gap space between the Au NP and the metallic surface originating from the coupling of the localized surface plasmon of Au NPs with the reflected beam from the surface. When a nanostructured Pt thin film is used as the support, the SERS intensity is further enhanced. Interestingly, the SERS intensity in this case is higher than the sum of the intensities on Au NPs and the nanostructured Pt thin film, suggesting a synergistic effect between them. However, such enhancement cannot be explained by EM field strengths obtained by simulations. In this case, the explanation needs conside...