Carboxylate-Terminated Electrode Surfaces Improve the Performance of Electrochemical Aptamer-Based Sensors

Electrochemical aptamer-based (EAB) sensors are a molecular measurement platform that enables the continuous, real-time measurement of a wide range of drugs and biomarkers in situ in the living body. EAB sensors are fabricated by depositing a thiol-modified, target-binding aptamer on the surface of a gold electrode, followed by backfilling with an alkanethiol to form a self-assembled monolayer. And while the majority of previously described EAB sensors have employed hydroxyl-terminated monolayers, a handful of studies have shown that altering the monolayer headgroup can strongly affect sensor performance. Here, using 4 different EAB sensors, we show that the mixed monolayers composed of mixtures of 6-carbon hydroxyl-terminated thiols and varying amounts of either 6- or 8-carbon, carboxylate-terminated thiols lead to improved EAB sensor performance. Specifically, the use of such mixed monolayers enhances the signal gain (the relative change in the signal seen upon target addition) for all tested sensors, often by several fold, both in buffer and whole blood at room temperature or physiological temperatures. Moreover, these improvements in gain are achieved without significant changes in the aptamer affinity or the stability of the resulting sensors. In addition to proving a ready means of improving EAB sensor performance, these results suggest that exploration of the chemistry of the electrode surface employed in such sensors could prove to be a fruitful means of advancing this unique in vivo sensing technology.