Calibration-Free, Seconds-Resolved In Vivo Molecular Measurements using Fourier-Transform Impedance Spectroscopy Interrogation of Electrochemical Aptamer Sensors

Abstract

Electrochemical aptamer-based (EAB) sensors are capable of measuring the concentrations of specific molecules in vivo, in real time, and with a few-second time resolution. For their signal transduction mechanism, these sensors utilize a binding-induced conformational change in their target-recognizing, redox-reporter-modified aptamer to alter the rate of electron transfer between the reporter and the supporting electrode. While a variety of voltammetric techniques have been used to monitor this change in kinetics, they suffer from various drawbacks, including time resolution limited to several seconds and sensor-to-sensor variation that requires calibration to remove. Here, however, we show that the use of fast Fourier transform electrochemical impedance spectroscopy (FFT-EIS) to interrogate EAB sensors leads to improved (here better than 2 s) time resolution and calibration-free operation, even when such sensors are deployed in vivo. To showcase these benefits, we demonstrate the approach's ability to perform real-time molecular measurements in the veins of living rats.

Nucleic acid-based wearable and implantable electrochemical sensors

“…Conventional nucleic acid-based sensor designs involving a redox reporter have relied on dual-frequency SWV measurements, which have been found to limit the time resolution of the sensor to approximately 6 to 22 s. 105 To accelerate electrochemical interrogation and further approach real-time sensing, fast Fourier transform electrochemical impedance spectroscopy (FFT-EIS) was used. 105 FFT-EIS simultaneously captures the impedance at multiple frequencies in under 2s to evaluate the electron transfer rate without the need for individual sensor calibration and drift correction. This finding emphasizes the need for ongoing exploration of analytical electrochemistry techniques in the biosensor space.…”

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

“…Similar to the dual reporter approach, researchers have employed dual frequency approaches for calibration-free sensing with E-AB sensors utilizing the strong dependence of E-AB sensor signaling to the interrogating square wave voltammetric frequency . Plaxco and co-workers have introduced a method where sensor responses at two different square wave voltammetric frequencies are considered. , Chen and co-workers have used this method to explore calibration-free approaches to enhance the dynamic range of E-AB sensor performance, altering the testing temperatures in different complex biological media. , Even though this approach has shown great E-AB sensor performance for estimating the unknown target concentration, the requirement to collect sensor responses at two different frequencies reduces the time resolution of the measurements. − …”

High‐Precision Viral Detection Using Electrochemical Kinetic Profiling of Aptamer‐Antigen Recognition in Clinical Samples and Machine Learning

“…In the context of electrochemical biosensing, affinitybased assays using structure-switching aptamers overcome the need for washing steps and offer single-pot operation. [15][16][17][18] However, a large fraction of aptamers selected through systematic evolution of ligands by exponential enrichment (SELEX), despite high affinity and selectivity, do not result in sufficient structural changes to translate target binding to a measurable electrochemical signal change. [19,20] As such there is an unmet need for universal aptamer-based electrochemical assays, structureswitching or not, that operate in a wash-free and single-pot manner.…”

“…Using a trimeric aptamer that demonstrates higher affinity biorecognition [21] compared to its monomeric counterparts [22] and is capable of target extraction in solution, [23] we aimed to meet the first two conditions noted above. Monitoring target binding on electrode surfaces is possible using electrochemical impedance spectroscopy (EIS); [16,[24][25][26][27] however, this technique scans through a large range of frequencies for a single measurement, which takes several minutes to complete and is not suitable for real-time monitoring. [11,[27][28][29] To meet the third condition above, we aimed at measuring electrochemical impedance at a single frequency [27,30] to monitor processes such as target binding or target-ligand dissociation or degradation directly on the electrode surface.…”