Tuning the signal-to-noise ratio: An electrokinetic strategy for high-fidelity SERS biosensing of microRNA-21.

BACKGROUND: MicroRNA-21 (miRNA-21) has emerged as a promising biomarker for early cancer diagnosis, yet its accurate quantification in complex biological matrices remains a significant challenge. Conventional SERS-based biosensors are inherently susceptible to non-specific adsorption of biomolecules and probe tags, which generates substantial background interference and severely compromises the signal-to-noise ratio (SNR) and detection fidelity. While various signal amplification strategies have been extensively explored, the critical issue of actively suppressing non-specific noise at the sensing interface has been largely overlooked, necessitating innovative approaches that can simultaneously enhance specific signals and minimize background interference.

RESULTS: We develop an electrokinetic SERS biosensor that actively modulates the SNR through two sequential voltage-gated steps in a sandwich-structured detection format. A positive potential preconcentrates the negatively charged miRNA-21 targets and SERS probes at the electrode interface, significantly increasing their local concentration and accelerating specific hybridization kinetics, while a subsequent reverse potential acts as an electrostatic filter to selectively desorb non-specifically adsorbed probes, effectively purifying the sensing interface. This synergistic combination of preconcentration and separation efficiently decouples specific signals from non-specific interference, achieving a wide linear detection range from 1.0 × 10-15 to 1.0 × 10-10 M with an ultralow detection limit of 0.48 fM. The biosensor exhibits excellent selectivity in discriminating single-base mismatches and demonstrates robust analytical performance in human serum samples, with recoveries ranging from 95.4% to 104%.

SIGNIFICANCE: This work introduces a novel paradigm for high-fidelity SERS biosensing by actively tuning the SNR through precise dual-action electrokinetic control. The strategy offers a generalizable, enzyme-free solution to the challenge of non-specific adsorption, critically enhancing both detection accuracy and practical applicability in complex biological matrices. The electrokinetic approach provides a versatile platform for reliable biomolecular analysis.