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Understanding the Role of Existing Technology in the Fight Against COVID-19
Published in Ram Shringar Raw, Vishal Jain, Sanjoy Das, Meenakshi Sharma, Pandemic Detection and Analysis Through Smart Computing Technologies, 2022
Raman spectroscopy is another highly sensitive and useful vibrational spectroscopy technique that allows non-destructive and real-time analysis of biological samples. A Raman spectrum is obtained by the process of scattering of light, whereas in FTIR, it is obtained by absorption of light by the matter. When a monochromatic (laser source) light is incident on the sample, the light may interact with the material either elastically or inelastically. In the elastic scattering, the incident photon is absorbed and reemitted with the same energy (frequency). This is known as Rayleigh scattering. On the other hand, in an inelastic scattering, the absorbed photon may be emitted with frequency higher or lower than the incident photon. The probability of inelastic scattering is very small compared to the Rayleigh scattering. The process of light scattering is shown in Figure 2.4. When the frequency of emitted photon (ν2) is less than the incident frequency (ν1), it is known as Stokes Raman scattering. When the frequency of emitted photon (ν2) is more than the incident frequency (ν1), it is known as anti-Stokes Raman scattering. This phenomenon is known as the Raman effect, and the observed effect is specific to the molecules causing the scattering. Thus, the Raman signals are used for determining the presence of molecules and their states using the inelastic scattering.
Photon Interactions with Matter
Published in Eric Ford, Primer on Radiation Oncology Physics, 2020
In the coherent scattering process the incident photon interacts with an electron (Figure 5.1.2). The photon causes the electron to oscillate up and down (recall that photons can be thought of as electromagnetic waves and it is the oscillating electric field that produces a force on the electron). An accelerating charged particle always produces an electromagnetic wave. This is something we will consider in more detail in a later chapter. Therefore, as the electron oscillates, a second wave (or photon) is produced. This wave emerges in some other direction. The wavelength (or energy) of the emerging wave is equal to that of the incoming wave. That is, no energy is gained or lost in this interaction. There are two flavors of coherent scattering: Thompson scattering, in which the photon scatters from a free electron, and Rayleigh scattering, in which it scatters from an electron bound in an atom. It is the wavelength-dependent process of Rayleigh scattering from molecules in the atmosphere that makes the sky appear blue on the earth.
Intrinsic Optical Properties of Brain Slices: Useful Indices of Electrophysiology and Metabolism
Published in Avital Schurr, Benjamin M. Rigor, BRAIN SLICES in BASIC and CLINICAL RESEARCH, 2020
Thomas J. Sick, Joseph C. LaManna
In brain slices, as in other tissues, scattering occurs primarily because of interactions of light with molecules, subcellular organelles, and cells. The degree of light scattering in any heterogenous medium is wavelength dependent, such that shorter wavelengths are more readily scattered than longer wavelengths. An often used example that demonstrates this principle well is the passage of sunlight through air containing particulate matter such as water droplets or dust. Shorter wavelength light (ultraviolet and blue) is scattered (the appearance of blue sky) and extinguished, while longer wavelengths (reds) are transmitted (the appearance of the red sunset). Figure 2 demonstrates the principle for light passing through a brain slice. There is proportionally more light extinction (decreased transmission) by the slice as the wavelength is decreased. Moreover, scattering is proportional to the size of the scattering particles or structures. Scattering by particles much smaller than the wavelength of the incident light has been termed Rayleigh scattering, while that resulting from structures similar in size to the incident light is termed Mie scattering. It is clear that neither Rayleigh nor Mie scattering alone will adequately describe scattering in complex tissues such as brain slices where the number, size, and shape of scattering structures vary considerably.
Impact of Aluminium phthalocyanine nanoconjugate on melanoma stem cells
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2023
Bridgette Mkhobongo, Rahul Chandran, Heidi Abrahamse
Gold nanoparticles absorb in the visible spectrum and their properties can be assessed using a variety of instruments and methods. The UV-Vis spectroscopy shows optical features, demonstrating that the collective electron oscillation in the AuNPs conduction band is in resonance with a particular wavelength of incident light. The information collected from this can be used to calculate the concentration and average size of the AuNPs. The functional groups can be identified using FTIR data, while the particle size and structural shape of AuNPs can be determined using Transmission Electron Microscopy (TEM) [51]. Resonance Rayleigh Scattering (RSS) is another method that can be used for characterisation. This elastic scattering process occurs whenever the frequency of the incident light is close to an absorption band [52].In PDT, one of the principal ways that light into tissue is attenuated is by scattering, limiting the penetration depth. Due to the substantial wavelength dependence of scattering intensity, longer excitation wavelengths are preferred to counteract this [53].
Retinal imaging biomarkers of neurodegenerative diseases
Published in Clinical and Experimental Optometry, 2022
Eirini Christinaki, Hana Kulenovic, Xavier Hadoux, Nicole Baldassini, Jan Van Eijgen, Lies De Groef, Ingeborg Stalmans, Peter van Wijngaarden
Hyperspectral imaging provides detailed information on the wavelengths of light reflected from the retina. Molecular and structural changes that influence the spectral composition of this reflected light may therefore be detected using hyperspectral imaging. In vitro and preclinical studies have suggested that low-order, soluble amyloid-beta oligomers cause Rayleigh scattering of light and thus a distinct reflectance pattern that can be captured with a hyperspectral camera.38,77–79 The use of retinal hyperspectral imaging for the detection of AD has been explored in three clinical studies. Overall, these have shown that retinal hyperspectral imaging can be used to differentiate people with AD from controls. In one study spectral differences were most pronounced in the early stages of the disease, in people with MCI (MMSE ≥22).80 Another study utilised a machine learning approach to analyse the hyperspectral images of the retina and calculate a hyperspectral score. This approach distinguished people with MCI and high brain amyloid-beta levels, measured using PET imaging, from control participants with low brain amyloid-beta levels.20 Finally, a study of people with clinically probable AD and control subjects indicated that a combinatorial approach with retinal hyperspectral imaging and OCT can increase the accuracy of a hyperspectral imaging-based classification model for the detection of AD.70 Larger replication studies are needed, as are studies to characterise the quantitative association between retinal imaging measure and brain levels of amyloid-beta.
Label-free identification and chemical characterisation of single extracellular vesicles and lipoproteins by synchronous Rayleigh and Raman scattering
Published in Journal of Extracellular Vesicles, 2020
Agustin Enciso-Martinez, Edwin Van Der Pol, Chi M. Hau, Rienk Nieuwland, Ton G. Van Leeuwen, Leon W.M.M. Terstappen, Cees Otto
The size of the trapped particles can be estimated by Mie theory based on the Rayleigh scattering. Rayleigh scattering depends on size and RI of the particles. It is known that the particle size distribution of EVs in body fluids are not normally distributed. Hence, the Rayleigh scattered light by EVs in blood will also not have a normal distribution. Indeed, the Rayleigh distributions of Figure 4 reveal a lognormal distribution, rather than a normal distribution. By comparing the EV values for the Rayleigh backscattering cross-section with the Mie model in Figure 5, it was estimated that the lowest size range of particles probed is between 80 and 320 nm. Detecting smaller particles is challenging because their signal is overwhelmed by the background noise (S7). The NTA distributions (S1–S4) suggest that the size range of the trapped EVs corresponds with the range up to 600 nm in the Mie model (Figure 5).