Spectroscopy of biological compounds with inelastic electron tunneling

Metal-insulator-metal electron tunnel junctions can be doped with a solution of an organic compound by placing a drop of the solution on the insulator and spinning of the excess. Electrical measurement of the second derivative of voltage with respect to current, as a function of applied voltage, then gives a spectrum of vibrational modes equivalent to an infrared or Raman spectrum, but with the use of only micrograms of sample.