Highly sensitive electrochemical microfluidic thread-based nanobiosensor for lung cancer biomarker miRNA-21

This study presents the development of a microfluidic thread-based electrochemical nanobiosensor for the ultrasensitive detection of the lung cancer biomarker microRNA-21 (miR-21). The biosensor was constructed on nylon thread electrodes modified with poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)–MXene–gold nanoparticles (AuNPs) (PMA) nanocomposites. Capture probes (CPs) were immobilized on the thread electrode surface via Au-S bonds. A robust signal amplification was achieved through horseradish peroxidase (HRP) catalysis, activated upon the formation of a sandwich hybridization structure between the target miR-21 and biotin-labeled signal probes (SPs). The electrochemical properties of the nanobiosensors were characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Under optimized conditions, the biosensor exhibited a wide linear detection range from 1 fM to 1 nM, with an ultralow detection limit of 0.15 fM. It also demonstrated high specificity against mismatched sequences, good reproducibility, and acceptable stability. When applied to spiked human serum samples, the recovery rates ranged from 96.4% to 104.3%, confirming its potential for clinical sample analysis. The thread-based three-electrode system offers advantages over conventional screen-printed and glassy carbon electrodes, including adjustable electrode spacing and layout flexibility, low cost and a simple fabrication process. The proposed method provides a promising technological platform for developing sensitive, stable, and point-of-care (POC) diagnostic tools for miR-21 and other disease-related biomarkers.