An electrochemical protein detection method using a peptide aptamer microarray . A sample containing five different proteins is shown on the left, and an array of 12 different peptide aptamers is shown on the right (not to scale). Large gray spheres represent the aptamer scaffold protein; small colored spheres represent the aptamer variable regions, which confer binding specificity to cognate target proteins; and large colored shapes represent the cognate target proteins of the aptamers with matching colors. Protein detection is illustrated only for the first row of peptide aptamers. The binding of a protein to its cognate peptide aptamer perturbs the electrochemical properties of the layer above the electrode, which alters the impedance and its phase, as measured by applying an electrical signal of varying frequency to each electrode. An alteration in impedance is proportional to the amount of captured protein.