The development of structure-switching, electrochemical, aptamer-based sensors over the past ∼10 years has led to a variety of reagentless sensors capable of analytical detection in a range of sample matrices. The crux of this methodology is the coupling of target-induced conformation changes of a redox-labeled aptamer with electrochemical detection of the resulting altered charge transfer rate between the redox molecule and electrode surface. Using aptamer recognition expands the highly sensitive detection ability of electrochemistry to a range of previously inaccessible analytes. In this review, we focus on the methods of sensor fabrication and how sensor signaling is affected by fabrication parameters. We then discuss recent studies addressing the fundamentals of sensor signaling as well as quantitative characterization of the analytical performance of electrochemical aptamer-based sensors. Although the limits of detection of reported electrochemical aptamer-based sensors do not often reach that of gold-standard methods such as enzyme-linked immunosorbent assays, the operational convenience of the sensor platform enables exciting analytical applications that we address. Using illustrative examples, we highlight recent advances in the field that impact important areas of analytical chemistry. Finally, we discuss the challenges and prospects for this class of sensors.

Combining specific recognition capabilities with the excellent spatiotemporal resolution of small electrodes represents a promising methodology in bioanalytical and chemical sensing. In this paper, we report the development of reproducible electrochemical, aptamer-based (E-AB) sensors on a gold microelectrode platform. Specifically, we develop microscale sensors (25 μm diameter) for two representative small molecule targets–adenosine triphosphate and tobramycin. Furthermore, we report on the challenges encountered at this size scale including small-magnitude signals and interference from the irreversible reduction of dissolved oxygen and present methods to circumvent these challenges. Through the electrochemical deposition of dendritic gold nanostructures, we demonstrate microscale sensors with improved performance by increasing signal-to-noise and consequently sensitivity. Finally, we report on the use of the nonspecific adsorption of serum proteins as an additional layer of surface passivation for stable sensor performance. The sensor development here represents general guidelines for fabricating electrochemical, folding aptamer-based sensors on small-scale electrodes.