Developing aptamer-based microelectrode sensors for use in scanning electrochemical microscopy (SECM)

Debashis Sen, Olivia Stuehr, Jamma Lucky, Robert A. Lazenby

Florida State Univrsity

While scanning electrochemical microscopy (SECM) has traditionally measured direct electron transfer of various analytes, enzymatic biosensors have recently been employed in this technique to map the fluxes of compounds (such as glucose, lactate, ATP, and d-serine) released from live cells or model micropore systems. However, the limited availability of enzymes for certain bioanalytes restricts the wider applicability of this technique. In this work, we explore the possibility of using aptamers, which are synthetic nucleic acids with a broad range of target analytes, as scanned probes in SECM. To develop this methodology for localized detection of concentration flux originating from a model micropore system, a 25 µm diameter gold ultramicroelectrode was used. We demonstrate the ability to position the sensor probe using the steady state current due to ferrocyanide oxidation. To use the microelectrode aptasensors, three techniques were investigated for their feasibility in mapping surfaces in constant height mode SECM: cyclic voltammetry (CV), square wave voltammetry (SWV), and chronoamperometry (CA). A dopamine sensor was calibrated over a relevant range of target analyte concentrations using the techniques, which yielded different time resolutions ranging from a few milliseconds to several seconds. Although all three methods produced a comparable binding affinities (i.e. K_d value of approximately 10 µM), SWV demonstrated the highest sensitivity and lowest limit of detection (LOD). To enhance the spatial resolution, electrodeposition was performed on a 2 µm Pt microelectrode for 60 s, and we anticipate that the developed small-scale aptamer-based sensor probe and the fast interrogation methods will enable the localized detection of analyte concentrations released from a model micropore system.