Aptamer-Based Scanning Electrochemical Microscopy for Specific and Localized Detection of Analyte Concentration

Scanning electrochemical microscopy (SECM) is an excellent electroanalytical technique for the localized detection of analytes, providing high spatial resolution through precise positioning and controlled scanning of an electrode over a sample substrate. However, the applicability of this method is largely limited to redox active analytes with biosensor-based detection strategies remaining scarce, other than a few examples using enzymes as the bioreceptor. In this study, we introduce aptamer-based (AB)-SECM in which electrochemical aptamer-based biosensors are used as the imaging probe, and this new imaging mode is demonstrated for the localized detection of dopamine and adenosine triphosphate (ATP) released from a model micropore system. This study describes the fabrication and characterization of the model micropore system that is imaged using the amperometric feedback mode of SECM. This substrate is then imaged using AB-SECM using an imaging probe (electrode 25–35 μm in diameter) with immobilized target specific aptamers on the surface. The probe was positioned at a known distance from the micropore surface by recording an amperometric approach curve in which the oxidation of ferrocyanide through the sensor monolayer produced a negative feedback distance dependent response. For constant height imaging with AB-SECM, the probe was moved, and a square wave voltammogram (SWV) was recorded at each pixel. The obtained AB-SECM images showed a higher concentration of target analyte above the opening of the micropore with a decreasing concentration further from the pore. These results demonstrate the capability of AB-SECM for positioning of the probe at a known distance from a surface and for localized detection, which we envisage could be further adapted for performing chemical analysis at the single cell level.