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.