Localized Detection of Analyte Concentrations Using an Electrochemical Aptamer Based Sensor Probe in Scanning Electrochemical Microscopy

Chemical analysis at the single-cell level will enable a better understanding of a range of cellular processes and cell heterogeneity, which can play an essential role in advancing clinical diagnostics. In this study, we used aptamer-based electrochemical biosensors as probes in scanning electrochemical microscopy (SECM) for the localized detection of analyte concentrations released from a glass micropore model system. Au nanostructures were deposited on 25 µm diameter Pt electrodes, that were used to fabricate the aptamer-based biosensor imaging probes targeting specific molecules. The probe was positioned at a known distance from the surface containing the micropore by recording an amperometric approach curve, whereby the oxidation of ferrocyanide that occurred through the sensor monolayer was used to provide a negative feedback distance-dependent response. Then, the probe was scanned across the surface containing the micropore in a raster pattern in the constant height mode. To create the SECM image, techniques including square wave voltammetry (SWV), cyclic voltammetry (CV), and chronoamperometry (CA) were performed every few microns (at distinct pixels) while the probe was held still. These methods were compared for their attributes for imaging, which included sensor response time, sensitivity, and limit of detection. The analyte concentration at each pixel was determined using calibration curves for each sensor, obtained before and after the imaging experiment. The SECM measurement using SWV showed a higher concentration of target analyte above the opening of the micropore, with decreasing concentration further from the pore. These results showed the localized detection of specific target analytes using an aptamer-based biosensor probe and a model micropore system filled with the analyte. We envision that the methodology being developed in this study will allow the measurement of the uptake or release of a range of analytes at the single-cell level.