Comparison of voltammetric methods used in the interrogation of electrochemical aptamer-based sensors

Electrochemical aptamer-based (EAB) sensors are the first continuous molecular measurement technology that is both (1) able to function in situ in the living body and (2) independent of the chemical reactivity of its targets, rendering it generalizable to a wide range of analytes. Comprised of an electrode-bound, redox-reporter-modified aptamer, signal generation in EAB sensors arises when binding to this target-recognizing aptamer causes a conformation change that, in turn, alters the rate of electron transfer to and from the redox reporter to the electrode surface. A range of electrochemical approaches, including both voltammetric (e.g., cyclic, square wave, and alternating current voltammetry) and non-voltammetric (e.g., chronoamperometry, electrochemical phase interrogation) methods have been used to monitor this change in transfer rate, with square wave voltammetry having dominated recent reports. To date, however, the literature has seen few direct comparisons of the performance of these various approaches. In response we describe here comparisons of EAB sensors interrogated using square wave, differential pulse, and alternating current voltammetry. We find that, while the noise associated with AC voltammetry (in vitro in 37°C whole blood) is exceptionally low, neither this approach nor differential pulse voltammetry support accurate drift correction under these same conditions, suggesting that neither approach is suitable for deployment in vivo. Square wave voltammetry, in contrast, matches or surpasses the gain achieved by the other two approaches, achieves good signal-to-noise, and supports high-accuracy drift correction in 37°C whole blood. Taken together, these results finally confirm that square wave voltammetry is the preferred pulsed voltammetric method for interrogating EAB sensors in complex biological fluids.