19 May 1999 Phys. A light within. CARS microscopy with the latest improvements allows the mitochondria in these live cells to be imaged without adding any dyes. To study cells under a microscope, researchers often mark specific cell structures with stains or fluorescent dyes.
Some proteins even light up without the addition of a dye.
But not all components of cells can be made to fluoresce by these methods. The 17 May PRL describes a laser-based method for imaging parts of a live cell in three dimensions based on the vibrations within molecules in the cell. The authors plan to study molecules that can't be seen using fluorescence or for which artificial dyes would interfere with the observations. Andreas Zumbusch, now of the Ludwig Maximilians University in Munich, Germany, Gary Holtom of the Pacific Northwest National Laboratory in Richland, WA, and Sunney Xie, now of Harvard University, wanted to image cellular components that don't tolerate dyes or fluoresce on their own. The idea of CARS microscopy is to detect molecules whose atoms vibrate at a specific frequency, such as the stretching frequency characteristic of carbon-hydrogen bonds, which are common to the long hydrocarbon chains found in cell membranes.