Synopsis: DNA Damage from “Eye-Safe” Wavelengths

A study on the biological impact of far-infrared laser pulses shows that longer, supposedly safer, wavelengths can cause breaks in the backbone of DNA.
Synopsis figure
Krithika Dota and Deepak Mathur/ Tata Institute of Fundamental Research

Lasers that emit at far-infrared wavelengths are often considered “eye-safe,” making them attractive for open-air applications such as laser radar, range-finding, and military targeting. However, new research may raise concerns about the safety of these long wavelengths. Experiments reported in Physical Review Letters show that femtosecond pulses from far-infrared lasers can cause breaks in exposed DNA strands.

Safety regulations for lasers are based in large part on protecting the retina from intense, focused light that can burn that sensitive tissue. At far-infrared wavelengths (greater than about 1400 nanometers), the light is mostly absorbed by water in the front of the eye, thus preventing it from reaching the retina. For this reason, acceptable laser power exposure is higher for far-infrared lasers than for visible and near-infrared lasers.

However, the threat from lasers is not limited to over-heating, but also includes photoinduced chemical changes. In a previous study, Deepak Mathur of the Tata Institute of Fundamental Research and his colleagues showed that laser pulses at 800 nanometers could cause “nicks” or breaks in DNA through the generation of free electrons and hydroxyl (OH) radicals in the surrounding water medium. They have now performed similar experiments with femtosecond (terawatt) laser pulses at 1350 and 2200 nanometers. After about 3 minutes of exposure, analysis showed that roughly 95% of the targeted DNA molecules had single-strand or double-strand breaks. The team found that they could reduce the damage by introducing “scavenger” molecules that deactivate hydroxyl radicals. From this, they surmise that the DNA damage comes primarily from rotationally “hot” OH molecules formed in the strong optical fields of the pulses. However, it remains to be shown whether these DNA-attacking hydroxyl radicals form at the lower powers found in commercial applications. – Michael Schirber


Features

More Features »

Announcements

More Announcements »

Subject Areas

OpticsBiological Physics

Next Synopsis

Related Articles

Focus: How to Locate a Nanoparticle with Sub-angstrom Precision
Optics

Focus: How to Locate a Nanoparticle with Sub-angstrom Precision

Laser tricks allow nanoparticle position measurements with a record 0.6-angstrom uncertainty, which will be useful in future nanotech devices. Read More »

Viewpoint: Record Distance for Quantum Cryptography
Optics

Viewpoint: Record Distance for Quantum Cryptography

An optical-fiber-based quantum cryptography scheme works over a record distance of 421 km and at much faster rates than previous long-distance demonstrations. Read More »

Synopsis: Pinning down the Chemistry of Photosynthetic Water Splitting  
Biological Physics

Synopsis: Pinning down the Chemistry of Photosynthetic Water Splitting  

A time-resolved x-ray study indicates that certain chemical changes of oxygen atoms during photosynthesis occur in a different order than current models predict. Read More »

More Articles