As a proof-of-principle demonstration, DOPA molecules with different chirality are selected for the electrochemical recognition measurements. The oxidation behavior of DOPA molecules has been well documented at the surface of various solid electrodes, which makes the understanding of our data easier and more consolidated. At first, cyclic voltammetry (CV) curves were recorded to confirm the happening of DOPA oxidation with PdGa-A as the working electrode. In the absence of L-DOPA (Fig. ), the broad oxidation peak between 0.6 and 1 V vs. Ag/AgCl can be attributed to the formation of Pd-O or Pd-OH bonding. The strong reduction peak between 0 -0.3 V can be indexed to the strong H adsorption process at the surface of Pd-based compounds. When 4 mM of L-DOPA was introduced into the solution, a strong oxidation peak is observed at around 0.78 V, suggesting the oxidation of L-DOPA at the crystal surface. Other investigated samples including PdGa-B and Pt films exhibit the same behaviors towards DOPA oxidation (Fig. ). As a comparison, 2H-MoS2 single crystals can not drive the oxidation reaction because the (001) basal planes are catalytically inert to electrochemical reactions. As a result, no oxidation peaks are found under the same measurement condition in the presence of DOPA (Fig. ).