An electrochemical aptamer-based (E-AB) biosensor has the ability to generate an electrochemical signal in response to specific target binding in vivo The signal is measured by a change in Faradaic current passed through an electrode. E-AB sensors are advantageous over previously reported aptamer-based sensors, such as fluorescence generating aptamers, due to their ability to detect target binding in vivo with real-time measurements. An E-AB sensor is composed of a three-electrode cell: an interrogating electrode, a reference electrode, and a counter electrode. A signal is generated within the electrochemical cell then measured and analyzed by a potentiostat. There are several biochemical and electrochemical parameters to optimize signal gain for E-AB biosensors. The density packing of DNA