THE prospect of filming DNA at work inside living cells has come closer with a technique for capturing images of biomolecules that uses ordinary light.
Researchers at Osaka University in Japan were able to resolve features a few dozen atoms across by combining two existing techniques that beat the diffraction limit of ordinary light microscopes 鈥� the principle that you can鈥檛 resolve objects smaller than half the wavelength of light. They hope their technique could be fine-tuned to provide a reliable way of imaging individual molecules or structures such as DNA base pairs.
Satoshi Kawata鈥檚 team scanned bundles of DNA strands with laser beams, causing the molecules to emit photons 鈥� a phenomenon known as anti-Stokes Raman scattering. The photons have a characteristic frequency determined by the way atoms vibrate within the molecules, so a spectrometer can tell what type of molecule the beams are focusing on (Physical Review Letters, DOI 10.1103/PhysRevLett.92.220801). The team then further improved the resolution by placing a nanometre-sized metal point at the focus of the laser beams. The metal point interacts with the beams鈥� electric fields to increase their intensity, thereby improving the signal.
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The technique does not damage the molecules it is imaging, which could give it unique advantages, says Vahid Sandoghdar at the Swiss Federal Institute of Technology in Zurich. 鈥淚t could be used to capture images in vivo,鈥� Sandoghdar told New Scientist. 鈥淚t is very positive and encouraging.鈥�
Sandoghdar adds that the technique should be able to distinguish between different kinds of biomolecules more reliably than existing imaging techniques. The main disadvantage, however, is that the signal is relatively weak and so requires amplification and the use of very sensitive sensing equipment.