17 Jun 2002
Researchers have used near-infrared pulses from a femtosecond laser source to dissect chromosomes.
Exclusive from Opto & Laser Europe magazine
The technique pioneered by Karsten König and colleagues from the Friedrich Schiller University in Jena enables the manipulation of DNA samples within living cells without causing any damage to the surrounding cell material.
The researchers used high-numerical-aperture objectives from a scanning microscope to focus a Ti:sapphire Coherent Vitesse laser. The diffraction-limited spots reached light intensities of several terawatts per square centimeter. The 800 nm, 80 MHz source had a 170 fs pulse length. Single-point exposure and line scans were used to make submicron cuts in the chromosomes.
König said: "The cut size is smaller than the diffraction-limited spot size, because only the centre of the spot provides sufficient photon density to induce highly localized multiphoton-induced ionization." He claims that the 85 nm cuts in DNA are the smallest ever reported. "Most of the cuts we made were in the 200 to 400 nm range, which is still less than 40% of the diffraction-limited spot diameter."
Compared with conventional ultraviolet and visible nanosecond laser pulses, the near-infrared femtosecond laser pulses have several advantages: higher light-penetration depth; no out-of-focus absorption or plasma shielding effects; and no significant transfer of heat or mechanical energy to surrounding structures.
König and his colleagues have set up a company, Jenlab, to commercialize the technology. They foresee a range of applications for the scalpel, including intracellular surgery, DNA probe designs, and highly localized gene transfer.