Figure 1.

(A) Electrochemical aptamer-based (EAB) sensors exploit the binding-induced folding of a redox-reporter-modified aptamer that is covalently attached to an interrogating electrode via a self-assembled monolayer. (B) Target binding alters the efficiency with which the redox reporter (here methylene blue) approaches the electrode, producing an electrochemical signal easily measured using square wave voltammetry. (C) We fabricate indwelling EAB sensors using a 75 μm-diameter, 3 mm-long goldwire working electrode bundled with same-diameter platinum counter and silver/silver-chloride reference electrodes. (D) The completed sensor is small enough to be emplaced in the external jugular vein of a rat via a 22-gauge guide catheter.