COVID-19: Zapped by Laser

Is it possible to shine a light on infected tissue, and only kill the viruses, leaving healthy tissue intact? A father-son team combined physics and biology to prove that it is indeed possible.

Kong-Thon Tsen, a physics professor at Arizona State University, was talking with his son Shaw-Wei Tsen, a pathology student at Johns Hopkins, about antiviral treatments. If a vaccine is not available for a viral illness, treatment options are extremely limited.

“We have demonstrated a technique of using a laser to excite vibrations on the shield of a virus and damage it, so that it’s no longer functional,” said Tsen senior. “We’re testing it on HIV and hepatitis right now.”

Tsen and Tsen have demonstrated that their laser technique (see ) can break up the protein shell of the mosaic tobacco virus. When completed, the treatment leaves only a harmless film of molecules.

The ultra-short pulse ( ) laser releases energy in pulses just one femtosecond long; that’s one millionth of a nanosecond. The USP laser can kill the virus using a principle called “forced resonance.” Every virus has a unique molecular structure; for each virus, there is a unique frequency that will cause it to vibrate. It is analogous to the way that a fine crystal glass will resonate, or vibrate at a particular frequency.

If you increase the volume at that particular frequency, the glass will vibrate violently enough to shatter. Similarly, by putting more energy in to the USP laser, the virus shakes itself apart.

So far, their technique has only been used in test tubes; animal trials must follow, with human trials further into the future.

This device seems almost too good to be true; it sounds like something a science fiction writer might think of. As a matter of fact, Robert J. Sawyer did think about it, writing in Hybrids (Neanderthal Parallax)

Methods

Femtosecond laser irradiation

Proposed model for USP laser-induced viral capsid defect

The excitation source employed in this work was a diode-pumped continuous wave mode-locked Ti-sapphire laser. The laser produced a continuous train of 60 fs pulses at a repetition rate of 80 MHz. The output of the second harmonic generation (SHG) system of the Ti-sapphire laser was used to irradiate the sample. The excitation laser was chosen to operate at a wavelength of λ = 425 nm and with an average power of approximately 120 mW. It has a pulse width of full-width at half maximum = 100 fs. A lens was used to focus the laser beam into a spot within the sample volume. MCMV virus was irradiated at a final concentration of about 5×106 TCID50/ml. A magnetic stirring device was used to facilitate exposure of the sample to the laser beam. Irradiation was carried out at 22°C and with the single laser beam excitation. After laser irradiation, samples were immediately stored at −80°C.

Results

USP laser-treated virus is internalized by host cells

For all experiments, we used a GFP-expressing MCMV described in a previous report. Samples of MCMV were irradiated using a 425nm femtosecond laser. Laser-inactivated virus showed an approximate 5-log reduction in viral titers by TCID50 assay, to a level near the limit of detection. To determine whether virions were internalized by host cells, we used electron microscopy to view viral particles within murine embryonic fibroblast cells that had been infected with control (untreated) MCMV or USP laser-treated MCMV for 2 h. In both control and laser-treated groups, we observed the presence of MCMV virions within cells . To confirm these findings, we labeled control or laser-treated MCMV with a fluorescent dye, PKH26. Murine fibroblast cells were infected with PKH26-labeled control or laser-treated MCMV for 2 h before imaging by fluorescence microscopy. In both control and laser-treated groups, we found fluorescent virus particles within cells . These results were further confirmed by PCR detection of MCMV genomic DNA in cells infected with both control and laser-treated MCMV (). Therefore, laser treatment does not alter the ability of MCMV virions to be internalized by cells.

Electron microscopy shows cellular internalization of USP laser-treated MCMV
Fluorescence microscopy shows cellular internalization of USP laser-treated MCMV

Conclusion

  • We reveal evidence supporting a functional capsid defect in viruses inactivated by ultrashort pulsed laser treatment.
  • USP laser targeting of capsids is a unique mechanism with advantages against rapidly mutating or drug-resistant pathogens.
  • USP laser treatment has applications in pathogen reduction, antiviral treatments, and vaccine development.

I am scattered, and then that last hundred pages, bam!, I am a laser

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