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Laser Blasts Viruses In Blood

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A new use for lasers has been discovered— zapping viruses out of blood. The technique, which holds promise for disinfecting blood for transfusions, uses a low-power laser beam with a pulse lasting just fractions of a second.

Researchers are using lasers to zap viruses out of the blood. (Credit: Image courtesy of Johns Hopkins Medical Institutions)

Johns Hopkins University student Shaw-Wei David Tsen says it was during a stroll in the park with his father that the idea was born. Tsen, an immunology researcher in the laboratory of T.C. Wu at Hopkins’ Kimmel Cancer Center, sought a new method to rid isolated blood of dangerous pathogens, including the viruses HIV and hepatitis C. He says current techniques using UV irradiation and radioisotopes can leave a trail of mutated or damaged blood components.

Using ultrasonic vibrations to destroy viruses was one possibility, but his father, Kong-Thon Tsen, a laser expert at Arizona State University, had a better idea: Lasers, unlike ultrasound, can penetrate energy-absorbing water surrounding the viruses and directly vibrate the pathogen itself.

The researchers aimed a low-power laser with a pulse lasting 100 femtoseconds (10-13 second) into glass tubes containing saline-diluted viruses that infect bacteria, also known as bacteriophages. The amount of infectious virus within each cube plummeted 100- to 1000-fold after the laser treatment. “I had to repeat the experiment several times to convince myself that the laser worked this well,” says the younger Tsen.

His laser is different from those emitting a continuous beam of visible light. “Our laser repeatedly sends a rapid pulse of light and then relaxes, allowing the solution surrounding the virus to cool off,” Tsen says. “This significantly reduces heat damage to normal blood components.”

Building on the idea that vibration wrecks a virus’ outer shell, the scientists found that their low-power laser selectively destroys viruses and spares normal human cells around them, while stronger beams kill almost everything.

Father and son speculate that laser vibrations could destroy drug-resistant and -sensitive viruses alike.

Wu says that the technique his student developed “could potentially be used to control communicable diseases by giving infusions of laser-treated blood products.”

The scientists published their results in the July 13 issue of the Journal of Physics: Condensed Matter. They will continue their studies using different viruses.

Says Wu, “We believe this work on bacterial viruses is promising, but the real test will be with more serious pathogens like HIV and hepatitis.”

The National Science Foundation funded the research.

Additional collaborators include Chih-Long Chang and Chien-Fu Hung from Johns Hopkins and Juliann G. Kiang from the Uniformed Services University of the Health Sciences.

Virol J. 2007 Jun 5;4:50.

Inactivation of viruses by coherent excitations with a low power visible femtosecond laser.

Tsen KT, Tsen SW, Chang CL, Hung CF, Wu TC, Kiang JG.

Department of Physics, Arizona State University, Tempe, AZ 85287, USA.

BACKGROUND: Resonant microwave absorption has been proposed in the literature to excite the vibrational states of microorganisms in an attempt to destroy them. But it is extremely difficult to transfer microwave excitation energy to the vibrational energy of microorganisms due to severe absorption of water in this spectral range. We demonstrate for the first time that, by using a visible femtosecond laser, it is effective to inactivate viruses such as bacteriophage M13 through impulsive stimulated Raman scattering. RESULTS AND DISCUSSION: By using a very low power (as low as 0.5 nj/pulse) visible femtosecond laser having a wavelength of 425 nm and a pulse width of 100 fs, we show that M13 phages were inactivated when the laser power density was greater than or equal to 50 MW/cm2. The inactivation of M13 phages was determined by plaque counts and had been found to depend on the pulse width as well as power density of the excitation laser. CONCLUSION: Our experimental findings lay down the foundation for an innovative new strategy of using a very low power visible femtosecond laser to selectively inactivate viruses and other microorganisms while leaving sensitive materials unharmed by manipulating and controlling with the femtosecond laser system.

Written by huehueteotl

September 6, 2007 at 9:03 am

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