A) Schematics of electrochemical aptamer sensors on planar (left) and nanoporous (right) electrodes. The structure‐switching aptamer, end‐labeled with a methylene blue (MB) reporter, is unfolded in the absence of its target, doxorubicin (DOX). This situates MB far from the electrode, yielding minimal signal. DOX binding induces aptamer folding, bringing MB close to the electrode and producing an increase in current. B) Scanning electron microscopy (SEM) images of the nanoporous electrode. Upper and lower panels show top and side views, with scale bars of 100 and 50 nm, respectively. C) Impact of pore size on signal gain. Bottom panels show SEM images of the various nanoporous electrodes. Error bars in the x‐direction represent the standard deviation of different nanopores captured in the corresponding SEM images. Error bars in the y‐direction represent the standard deviation of the signal gain of three replicates.