Programmable Dual-Phase Electrochemical Biosensor Combines Homogeneous CRISPR/Cas12a Activation with Interfacial Poly-G Signaling for miRNA-21 Detection

Sep 9, 2025Analytical chemistry

Dual-phase electrochemical sensor uses CRISPR activation and surface signaling to detect miRNA-21

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Abstract

A detection limit of 25 attomolar for miRNA-21 was achieved using a programmable dual-phase electrochemical biosensing system.

The system separates amplification from signal transduction to enhance efficiency and reproducibility.
Target-triggered polymerization and bidirectional strand extension generate double-stranded DNA amplicons.
CRISPR/Cas12a complexes are activated by the dsDNA, leading to the cleavage of reporter DNA on a gold electrode.
The exposed ends of the cleaved DNA initiate a specific extension reaction that produces a detectable signal.
The design offers excellent sequence specificity and reliable performance with human blood samples.

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Despite the promise of electrochemical biosensors in amplified nucleic acid diagnostics, existing high-sensitivity platforms often rely on a multilayer surface assembly and cascade amplification confined to the electrode interface. These stepwise strategies suffer from inefficient enzyme activity, poor mass transport, and inconsistent probe orientation, which compromise the amplification efficiency, reproducibility, and practical applicability. To address these limitations, we report a programmable dual-phase electrochemical biosensing system that decouples amplification from signal transduction. In the homogeneous phase, a palindromic allosteric hairpin probe undergoes target-triggered polymerization and bidirectional strand extension, generating double-stranded DNA (dsDNA) amplicons. These dsDNAs activate CRISPR/Cas12a complexes, which, in turn, cleave thiolated reporter DNA immobilized on a gold electrode. The exposed 3'-hydroxyl termini then initiate terminal deoxynucleotidyl transferase (TdT)-mediated polyguanine (poly-G) extension in the presence of dGTP. Methylene blue, selectively binding to G-rich sequences, produces a strong voltammetric signal proportional to the original miRNA-21 concentration. By integration of homogeneous amplification with localized electrochemical signal generation, this dual-phase design circumvents the drawbacks of interface-bound cascades while leveraging their sensitivity advantages. The system achieves a detection limit of 25 attomolar for miRNA-21, excellent sequence specificity, and reliable performance in human blood samples. This approach provides a robust and generalizable platform for nucleic acid diagnostics with high sensitivity, modularity, and operational simplicity.

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Programmable Dual-Phase Electrochemical Biosensor Combines Homogeneous CRISPR/Cas12a Activation with Interfacial Poly-G Signaling for miRNA-21 Detection

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