Physicists from Cornell University in Ithaca, N.Y., have discovered a way to identify single molecules by their vibration signature. The advance could lead to new ways to study biological molecules such as DNA. For more than a decade, scientists have investigated the use of scanning tunneling microscopes to examine the bonds that hold atoms together in molecules. The method -- vibrational spectroscopy -- studies the energy produced by the vibration of molecular bonds, which are created when a positively charged nucleus of one atom pulls negatively charged electrons in another atom. As this occurs, electrons and protons in one atom repel the electrons and protons in the second atom. This attraction and resistance results in a constant push-pull, which creates a vibration. The vibration is unique for each possible arrangement of atoms in a molecule, making the molecule easily identifiable. The new method employs a specially designed scanning tunneling microscope, with a tip that can narrow to just one atom, suspended at less than a billionth of a meter. Using the new instrument, researchers can focus on one atom at a time. Previously, researchers had difficulty keeping the microscope steady enough for precise measurements.