Single Voltammetric Sweep Calibration-Free Interrogation of Electrochemical Aptamer-Based Sensors Employing Continuous Square Wave Voltammetry

Abstract

Continuous square wave voltammetry (cSWV) is a technique that enables the continuous collection of current data (at 100 kHz) to maximize the information content obtainable from a single voltammetric sweep. This data collection procedure results in the generation of multiple voltammograms corresponding to different effective square wave frequencies. The application of cSWV brings significant benefits to electrochemical aptamer-based (E-AB) sensors. The E-AB sensor platform permits continuous real-time monitoring of small biological molecules. Traditionally, E-AB sensors report only on changes in analyte concentration rather than absolute quantification in matrices when basal concentrations are not known a priori. This is because they exhibit a voltammetric peak current even in the absence of a target. However, using a dual-frequency approach, calibration-free sensing can be performed effectively, eliminating the sensor-to-sensor variation by taking ratiometric current responses obtained at two different frequencies from two different voltammetric sweeps. In employing our approach, cSWV provides a great advantage over the conventionally used square wave voltammetry since the required voltammograms are collected with a single sweep, which improves the temporal resolution of the measurement when considering the current at multiple frequencies for improved accuracy and reduced surface interrogation. Moreover, we show here that using cSWV provides significantly improved concentration predictions. E-AB sensors sensitive to ATP and tobramycin were interrogated across a wide range of concentrations. With this approach, cSWV allowed us to estimate the target concentration, retaining up to an ±5% error of the expected concentration when tested in buffer and complex media.