Maximal interaction of electromagnetic radiation with corona virions

Absorption and scattering of the impinging electromagnetic waves are the two fundamental operations describing the energy exchange of any organic or inorganic particle with its environment. In the case of virion cells, substantial extinction power (counting both absorbing and scattering effects) is a prerequisite for performing a variety of coupling actions against the viral particles, and thus is a highly sought-after feature. By considering realistic dispersion for the dielectric permittivity of proteins and a core-shell modeling allowing for rigorous formulation via Mie theory, we report optical extinction resonances for corona virions at mid-infrared range that are not significantly perturbed by changes in the object's size or the background host. Our findings indicate the optimal regime for interaction of photonic radiation with viral particles, and may assist towards the development of equipment for thermal damage, disintegration, or neutralization of coronavirus cells.

Figure 1

(a) Illustrative representation revealing the coronavirus morphology when viewed via electron microscope. Both the gray core and the brown spikes that adorn the outer surface of the virus (imparting the look of a corona surrounding the virion) are made of proteins. The image was taken from the Public Health Image Library [34]. It is free of any copyright restrictions. (b) The adopted model in the present study; the spikes are replaced by an isotropic shell of permittivity ${\varepsilon }_s$ and thickness $(b-a)$ surrounding a homogeneous core of permittivity ${\varepsilon }_c$ and radius $a$; the structure is hosted by a background medium of permittivity ${\varepsilon }_b$. The virion is bombarded by an electromagnetic (EM) pulse of high intensity and central wavelength $\lambda$.

Figure 2

Dispersive permittivities $\varepsilon$ as functions of the incident wavelength $\lambda$. (a) Real and imaginary parts of the permittivity ${\varepsilon }_c$ for protein (diisopropylamine, DIPA). The data is obtained from a well-established source [31] and expanded to short wavelength limit, based on a lossless material assumption [49]. (b) Real parts of the background permittivity ${\varepsilon }_b$ for alternative hosts: Air, human blood, and human organs (like the liver). The various backgrounds are assumed to be lossless, and the corresponding data has been obtained from reliable experimental measurements [32, 33].

Figure 3

The extinction power $P_{\mathrm{ext}}$ by the virion normalized by the incident power through the spherical cross section $P_{\mathrm{inc}}$ for various backgrounds ${\varepsilon }_b$, as a function of: (a) the core-shell radii ratio $a/b$ ($s=0.5$) and (b) the filling factor $s$ of the shell ($a/b=0.7$). Plot parameters: $\lambda =250\mathrm{nm}$, $b=80\mathrm{nm}$. The effect of the material contrast is identified.

Figure 4

The extinction power $P_{\mathrm{ext}}$ by the virion normalized by the incident power through the spherical cross section $P_{\mathrm{inc}}$ as a function of the incoming wavelength $\lambda$ for: (a) various host environments ${\varepsilon }_b$ ($b=60\mathrm{nm}$), (b) various external sizes $b$ of the virions (in blood). Plot parameters: $a/b=0.7$, $s=0.5$. The strong local optimum at mid-infrared ($\lambda \cong 3370\mathrm{nm}$) is spotted, regardless of background and size.

Figure 5

Spatial distribution of the total electric field $|\mathbf{E}/E_0{|}^2$ across $zx$ and $zy$ planes when the incoming pulse travels along $+z$ axis for: (a),(b) $\lambda =3370\mathrm{nm}$ (optimal mid-infrared wavelength) (c),(d) $\lambda =2200\mathrm{nm}$ (arbitrary smaller wavelength). Plot parameters: $a/b=0.7$, $s=0.5$, $b=65\mathrm{nm}$, human blood background. The blue lines indicate the boundaries between two different media.

Figure 6

Field concentration at shorter wavelengths. Spatial distribution of the total electric field $|\mathbf{E}/E_0{|}^2$ across $zy$ plane when the incoming pulse travels along $+z$ axis for: (a) $\lambda =350\mathrm{nm}$, (b) $\lambda =700\mathrm{nm}$. Plot parameters: $a/b=0.7$, $s=0.5$, $b=100\mathrm{nm}$, human blood background. The blue lines indicate the boundaries between two different media.

Figure 7

Effect of aspect ratio on the field concentration at optimal mid-infrared wavelength. Spatial distribution of the total electric field $|\mathbf{E}/E_0{|}^2$ across $zx$ plane when the incoming pulse travels along $+z$ axis for: (a) $a/b=0.6$, (b) $a/b=0.7$, (c) $a/b=0.8$, (d) $a/b=0.9$. Plot parameters: $s=0.6$, $b=80\mathrm{nm}$, $\lambda =3367\mathrm{nm}$, human blood background.