Fouling also strongly affects the optimal frequency at which the highest response can be obtained. Titration curves were obtained with the most sensitive "signal-on" and "signal-off" SWV frequencies based on the frequency response curves measured for each batch of sensors (Figure ). The maximally responsive signal-on frequency for both MCH and MCO based sensors determined at day 0 was 300Hz. After 3 days, the maximally responsive signal on frequency shifted to 750 Hz for MCH while it remained at 300 Hz for the MCO sensors. This demonstrates that biofouling alters electron transfer kinetics with the electrode surface, either in the analyte-bound or unbound states for aptamer molecules, which is consistent with results seen in the literature where the frequency of maximum electron transfer for the unbound aptamer is shown to shift during the initial 2-3 hour exponential fouling phase. Initial fouling likely occurs at monolayer defects leading to an increased charge transfer resistance, which would explain both the initial reduction in redox tag current and the initial shift in the frequency of maximum electron transfer toward lower SWV frequencies, as expected from the Lovrić formalism. Over multiple days, desorption of passivation molecules allows for replacement with foulants and rearrangement of the biofouled layer into a highly defective film, a process that occurs much more rapidly on MCH sensors than MCO sensors as previously discussed. The replacement of tightly-packed alkylthiolates with foulants increases electron transfer rates and thus increases the resulting maximally responsive frequency, as seen in Supplemental Figure .