The desire to improve and decentralize diagnostic platforms to facilitate highly precise and personalized medicine has motivated the development of a large number of electrochemical sensing technologies. Such a development has been facilitated by electrochemistry's unparalleled ability to achieve highly specific molecular measurements in complex biological fluids, without the need for expensive instrumentation. However, for decades, progress in the field had been constrained to systems that depended on the chemical reactivity of the analyte, obstructing the generalizability of such platforms beyond redox- or enzymatically active clinical targets. Thus, the pursuit of alternative, more general strategies, coupled to the timely technological advances in DNA sequencing, led to the development of DNA-based electrochemical sensors. The analytical value of these arises from the structural customizability of DNA and its ability to bind analytes ranging from ions and small molecules to whole proteins and cells. This versatility extends to interrogation methods, as DNA-based sensors work through a variety of detection schemes that can be probed via many electroanalytical techniques. As a reference for those experienced in the field, and to guide the unexperienced scientist, here we review the specific advantages of the electroanalytical methods most commonly used for the interrogation of DNA-based sensors.

Electrochemical, aptamer-based (E-AB) sensors support continuous, real-time measurements of specific molecular targets in complex fluids such as undiluted serum. They achieve these measurements by using redox-reporter-modified, electrode-attached aptamers that undergo target binding-induced conformational changes which, in turn, change electron transfer between the reporter and the sensor surface. Traditionally, E-AB sensors are interrogated via pulse voltammetry to monitor binding-induced changes in transfer kinetics. While these pulse techniques are sensitive to changes in electron transfer, they also respond to progressive changes in the sensor surface driven by biofouling or monolayer desorption and, consequently, present a significant drift. Moreover, we have empirically observed that differential voltage pulsing can accelerate monolayer desorption from the sensor surface, presumably via field-induced actuation of aptamers. Here, in contrast, we demonstrate the potential advantages of employing cyclic voltammetry to measure electron-transfer changes directly. In our approach, the target concentration is reported via changes in the peak-to-peak separation, ΔE P, of cyclic voltammograms. Because the magnitude of ΔE P is insensitive to variations in the number of aptamer probes on the electrode, ΔE P-interrogated E-AB sensors are resistant to drift and show decreased batch-to-batch and day-to-day variability in sensor performance. Moreover, ΔE P-based measurements can also be performed in a few hundred milliseconds and are, thus, competitive with other subsecond interrogation strategies such as chronoamperometry but with the added benefit of retaining sensor capacitance information that can report on monolayer stability over time.

No abstract