# A Target-Displaced Aptamer–cDNA Duplex Strategy on ERGO for Ultrasensitive Turn-On Electrochemical Detection of Ochratoxin A

## TL;DR

A new electrochemical sensor detects ochratoxin A with high sensitivity by using a DNA-based strategy that amplifies the signal when the toxin is present.

## Contribution

The study introduces a novel turn-on electrochemical aptasensor using a target-displaced aptamer–cDNA duplex on ERGO for ultrasensitive OTA detection.

## Key findings

- OTA binding triggers G-quadruplex formation, accelerating electron transfer and producing a strong signal-on response.
- The ERGO-based platform enables ultrasensitive OTA detection with a linear range of 10 fM to 100 pM and an LOD of 0.67 fM.
- The sensor shows high selectivity, reproducibility, and stability for reliable OTA monitoring.

## Abstract

What are the main findings?
A turn-on electrochemical aptasensor was developed using a target-induced displacement of an aptamer–cDNA duplex on an ERGO-modified electrode.OTA binding triggers G-quadruplex formation of the aptamer, leading to accelerated electron transfer and a pronounced signal-on response.

A turn-on electrochemical aptasensor was developed using a target-induced displacement of an aptamer–cDNA duplex on an ERGO-modified electrode.

OTA binding triggers G-quadruplex formation of the aptamer, leading to accelerated electron transfer and a pronounced signal-on response.

What are the implications of the main findings?
The duplex displacement and G-quadruplex folding strategy enables highly sensitive and low-background electrochemical detection of OTA.The ERGO-based, linker-free platform provides an electron-transfer catalyst and large surface area, leading to ultrasensitive detection of OTA.

The duplex displacement and G-quadruplex folding strategy enables highly sensitive and low-background electrochemical detection of OTA.

The ERGO-based, linker-free platform provides an electron-transfer catalyst and large surface area, leading to ultrasensitive detection of OTA.

Ochratoxin A (OTA) is a highly toxic mycotoxin commonly detected in food and agricultural products, requiring sensitive analytical methods for reliable monitoring. Herein, we report an ultrasensitive turn-on electrochemical aptasensor for OTA detection based on a target-induced displacement of an aptamer–complementary DNA (cDNA) duplex assembled on an electrochemically reduced graphene oxide (ERGO)-modified glassy carbon electrode (GCE). In the absence of OTA, a methylene blue (MB)-labeled aptamer hybridized with cDNA is immobilized on the ERGO surface via π–π stacking interactions, forming a rigid duplex that suppresses electron transfer and yields a low electrochemical signal. Upon OTA binding, the aptamer undergoes a conformational transition into a G-quadruplex structure, leading to dissociation of the cDNA strand. This target-induced folding brings the MB redox tag into close proximity to the ERGO surface, markedly accelerating electron transfer and enhancing the cathodic reduction current of MB, thereby producing a pronounced signal-on response in square-wave voltammetry (SWV). The ERGO-modified electrode provides a conductive and stable interface without chemical linkers. Under optimized conditions, the aptasensor shows a linear response to OTA from 10 fM to 100 pM with an ultralow LOD of 0.67 fM, together with high selectivity, good reproducibility, and satisfactory stability. This work demonstrates a simple and effective turn-on aptasensing strategy for sensitive electrochemical detection of OTA.