Fig. 1.

Electrochemical aptamer-based (E-AB) sensors generate a detectable electrochemical signal via a binding-induced conformational change in a redox-reporter-modified, electrode-bound aptamer. (Left) In the absence of the target, the aptamer is relatively unfolded and extended. Target binding induces a conformational change, leading in turn to a change in the electron transfer rate of the methylene blue reporter. (Right) Binding of the tryptophan /inorganic receptor complex produces decreases the electrochemical signal in a manner quantitatively related to the concentration of tryptophan in the solution.