Accelerated Electron Transfer in Nanostructured Electrodes Improves the Sensitivity of Electrochemical Biosensors

Abstract

Electrochemical biosensors hold the exciting potential to integrate molecular detection with signal processing and wireless communication in a miniaturized, low-cost system. However, as electrochemical biosensors are miniaturized to the micrometer scale, their signal-to-noise ratio degrades and reduces their utility for molecular diagnostics. Studies have reported that nanostructured electrodes can improve electrochemical biosensor signals, but since the underlying mechanism remains poorly understood, it remains difficult to fully exploit this phenomenon to improve biosensor performance. In this work, electrochemical aptamer biosensors on nanoporous electrode are optimized to achieve improved sensitivity by tuning pore size, probe density, and electrochemical measurement parameters. Further, a novel mechanism in which electron transfer is physically accelerated within nanostructured electrodes due to reduced charge screening, resulting in enhanced sensitivity is proposed and experimentally validated. In concert with the increased surface areas achieved with this platform, this newly identified effect can yield an up to 24-fold increase in signal level and nearly fourfold lower limit of detection relative to planar electrodes with the same footprint. Importantly, this strategy can be generalized to virtually any electrochemical aptamer sensor, enabling sensitive detection in applications where miniaturization is a necessity, and should likewise prove broadly applicable for improving electrochemical biosensor performance in general.

Tailoring electrode surface charge to achieve discrimination and quantification of chemically similar small molecules with electrochemical aptamers

“…Signal gain is the baseline-subtracted ratio between the SWV peak generated in the presence of the target molecule to that produced in the absence of target; we used this value to quantify analyte concentrations in the sample. 3,19,33 We found that the signal gain produced by 10 μM DOX (the maximum clinically relevant concentration) increased by ∼36% on the C6-OH SAM relative to the C6-COOH SAM—from 129% to 176% ( Fig. 2A , upper plot).…”

“…There have been many innovations in selecting high-affinity aptamers using directed evolution, [11][12][13][14] and also in improving the signaling of these aptamers by rationally designing switches 15,16 and engineering electrode interfaces to tune transduction. [17][18][19][20][21] However, one major challenge is that these sensors often suffer from poor specificity, such that the presence of structurally-similar interferents and metabolites can potentially make accurate molecular quantification of the target difficult or impossible. This is because the specificity of molecular detection is heavily dependent on the aptamer's capacity to discriminate between chemically similar targets, and it can be exceedingly difficult to generate aptamers that exhibit such excellent selectivity while also achieving a robust target-induced conformational change.…”

“…22,23 In recent work, we showed that the use of a nanoporous rather than a planar electrode improved the sensitivity of a sensor based on a doxorubicin (DOX) aptamer. 19 This was because the highly-confined nanoporous structures extended the EDL, strengthening electrostatic effects near the electrode. 24,25 We further hypothesized that altering the EDL composition could confer the benefit of introducing contrast between different targets.…”

Real-time monitoring of drug pharmacokinetics within tumor tissue in live animals

“…We recently reported that nanoporous structured electrodes offer greatly improved electrochemical detection sensitivity relative to planar electrodes, with a higher SNR due to reduced charge screening effects ( 38 ). This enhanced sensitivity is important in this context, because in vivo experiments intrinsically have high background noise.…”

DNA Walkers for Biosensing Development

“…[ 2 , 8 , 91 , 92 , 93 ] To improve the sensitivity of biosensors, a variety of strategies have been raised to amplify signals, such as enzymatic reactions, DNA nanotechnology, and so on. [ 94 , 95 ] Among them, DNA walker‐based biosensors exhibit superior performance in biosensing. The programmability of DNA nanotechnology enables the design of walking behaviors that specifically respond to different biological targets.…”