Gold Nanomaterials at Work in Biomedicine *
Valerio Voliani in Nanomaterials and Neoplasms, 2021
For a bulk metal with infinite sizes in all three dimensions, the ωp can be derived as ωp = (Ne2/εome)1/2 using the Drude model, where N is the number density of free electrons; e and me are the charge and effective mass of an electron [326, 327]. In practice, we have to evaluate an object that is confined by finite dimensions and surrounded by a medium with a specific dielectric constant. Since the light impinging on a metal surface can only penetrate to a certain depth (<50 nm for Au and Ag), only the free electrons on the surface of a metallic object will contribute to the plasmon resonance. For a metal-vacuum interface, application of the boundary condition results in a surface plasmon mode of frequency ωp/(2)1/2, where this plasmon mode represents a longitudinal surface charge density wave along the metal surface. When the collective oscillations of free electrons are further confined to a finite volume (e.g., within a metal nanoparticle), we will obtain a new plasmon mode, which is commonly referred to as LSPR. When vacuum is taken as the surrounding medium, the resonant frequency becomes ωp/(3)1/2 [325]. When the surrounding medium is no longer a vacuum, the resonant frequency will be determined by the dielectric constants of both the metal and the surrounding medium. For a spherical system, the analytical solutions are commonly referred to as the Mie theory.
Optics of the Skin
Henry W. Lim, Nicholas A. Soter in Clinical Photomedicine, 2018
Scattering by very small particles (defined as less than about the wavelength, that is, less than about 50 nm for visible light scattering) was first described in detail by Lord Rayleigh, and hence bears his name. Rayleigh, or molecular, scattering is weak, almost isotropic (equal in all directions), and strongly dependent on wavelength, varying inversely with the fourth power of wavelength. Thus, shorter wavelengths are much more strongly scattered by small particles or molecules. Scattering by particles about equal to the wavelength (i.e., between about and 10 times the wavelength) is called Mie scattering, after the physicist who first produced a solid theory describing it. Mie scattering is much stronger than Rayleigh scattering, is much less dependent on wavelength, and tends to be increasingly forward-directed for larger particles. Figure 1 shows the broad range of scattering behavior.
Hyperspectral Imaging of Diabetes Mellitus Skin Complications
Andrey V. Dunaev, Valery V. Tuchin in Biomedical Photonics for Diabetes Research, 2023
First, a solid biotissue phantom with predefined optical properties equal to those of bloodless human dermis was used to validate the ability of the proposed approach to measure blood oxygen saturation in the embedded vessels. The layout and the dimensions of the developed phantom are shown in Figure 8.4a and b. The phantom contains two tilted plain hollow channels (0.25 × 1 mm2 cross section) located at different angles. The embedding depth increases linearly from 0.3 to 2 mm for the superficial channel and from 0.3 to 4 mm for the deep one. A detailed description of the manufacturing and characterization of biotissue phantoms is given in Refs. [25–27]. In short, a polyvinyl chloride (PVC)-based matrix was used as a transparent host for ZnO nanoparticles introducing scattering. The proper amount of added scattering particles was estimated on the basis of Mie theory, taking into account their size distribution. The average diameter of the particles was 0.34 μm. To control the absorption coefficient of the phantom, a black plastic color composed of CI Pigment Black 7 was added. Two glass capillaries were installed at different angles, as described above, inside the phantom mold prior to solidification of the phantom. After solidification, the capillaries were gently removed, thus forming hollow channels. The channels were further connected via micropipette tips and plastic tubing to the syringe pump.
Solidification of hesperidin nanosuspension by spray drying optimized by design of experiment (DoE)
Published in Drug Development and Industrial Pharmacy, 2018
Qionghua Wei, Cornelia M. Keck, Rainer H. Müller
The particle size distribution of hesperidin nanosuspension was measured by using laser diffractometry (LD). A Mastersizer 2000 (Malvern Instruments, UK) was employed. The selected characterization parameters were the diameters d(v)10%, d(v)50%, d(v)90% and d(v)95%, which were calculated in volume-weighted diameters. A value of d(v)10% means that 10% of the particles in the tested samples are smaller than the given value, and this applies to the other parameters as well. Calculations were performed using the Mie theory of light scattering, which is based on the collected scattering intensity data, assuming the particles possess spherical shapes. The Mie theory has to be applied for size calculation when the particle size is below 5x the laser wavelength used in the instrument. In contrast to the Fraunhofer theory, this theory requires input of RI and IRI. The refractive index (RI) used was 1.57, and the imaginary refractive index (IRI) was 0.01 [21]. The samples were dispersed in water and measured with medium sonication.
Summary of numerical analyses for therapeutic uses of laser-activated gold nanoparticles
Published in International Journal of Hyperthermia, 2018
To evaluate the response of the nanoparticles to incident light, several models have been developed to calculate the absorption and scattering cross-sections. The first theory, known as Mie theory, was introduced in the early twentieth century. However, this theory is limited to spherical or cylindrical particles, which makes it inapplicable or rarely applicable given the variety of particle shapes produced, and the coupling effects encountered nowadays [63]. In addition to this fact, there are two additional assumptions based on which this theory is based: (i) the dielectric function of a nanoparticle and the surrounding environment are the same as bulk dielectric function, and (ii) the size of a nanoparticle is much smaller than the wavelength of the incident light [64]. According to the theory, the absorption and scattering coefficients are expressed as an infinite series of Ricatti–Bessel functions [65].
Improved resolution in extracellular vesicle populations using 405 instead of 488 nm side scatter
Published in Journal of Extracellular Vesicles, 2018
Mark J. McVey, Christopher M. Spring, Wolfgang M. Kuebler
Studying EVs can involve a wide variety of detection methods, yet one of the most popular and accessible techniques remains FCM. Current-generation high-sensitivity flow cytometers can detect EVs, but fundamental limitations such as challenges in effectively discriminating small EVs from the threshold of instrument noise provides confounding false-positive events for small particle detection and impacts the ability to accurately enumerate EVs due to poor representative sampling of the true EV population. These limitations have fuelled the need for technical advances that may reduce the discrimination threshold between genuine EV events and instrument noise at the lower end of the EV gate, thereby improving measurement sensitivity and detectability of smaller EV populations. For detection of particles of greater diameter than the excitation wavelength of laser light used by FCM such as cells (≫ 405 nm–488 nm) scattering of laser light is robust. However, as particles approach diameters at or below the wavelength of detection light sources, light scatter becomes critically limited. For these scenarios, Mie theory predicts that utilization of shorter wavelengths should significantly increase light scattering and allow for enhanced signal intensity and improved particle resolution.
Related Knowledge Centers
- Absorption
- Aerosol
- Rayleigh Scattering
- Refractive Index
- Scattering
- Rayleigh–Gans Approximation
- Anomalous Diffraction Theory
- Attenuation Coefficient
- Localized Surface Plasmon
- T-Matrix Method