Detecting Electron Transport of Amino Acids by Using Conductance Measurement

The single molecular conductance of amino acids was measured by a scanning tunneling microscope (STM) break junction. Conductance measurement of alanine gives out two conductance values at 10^-1.85 G₀ (1095 nS) and 10^-3.7 G₀ (15.5 nS), while similar conductance values are also observed for aspartic acid and glutamic acid, which have one more carboxylic acid group compared with alanine. This may show that the backbone of NH₂-C-COOH is the primary means of electron transport in the molecular junction of aspartic acid and glutamic acid. However, NH₂-C-COOH is not the primary means of electron transport in the methionine junction, which may be caused by the strong interaction of the Au-SMe (methyl sulfide) bond for the methionine junction. The current work reveals the important role of the anchoring group in the electron transport in different amino acids junctions.