Polyaniline-gold nanoparticle-based biosensor targeting miR-21-5p for early diagnosis of leptospirosis.

Blood-based disease diagnosis facilitates the early-stage detection of leptospirosis because leptospires were present in the blood in the first 5 to 10 days after exposure. We present a sensor employing polyaniline (PANI) and gold nanoparticles (AuNPs) for the specific detection of miR-21-5p in individuals with leptospirosis. The electropolymerization of PANI on glassy carbon electrodes (GCEs) creates a porous and durable coating that remains stable over extended periods without mechanical damage. To enhance the biosensor's performance, we functionalized the sensor surface with gold nanoparticles through electrodeposition, which facilitated an electroactive surface and selective binding of the thiolated probe. Our data confirmed that the thiolated DNA probe (anti-miRNA-21) exhibits a higher affinity for the target miRNA-21 and serum samples from individuals with leptospirosis compared to non-complementary sequences and healthy serum samples. The biosensor demonstrated remarkable sensitivity with a detection range spanning from 1 aM to 50 nM, boasting a limit of detection (LOD) of 1 aM and a limit of quantification (LOQ) of 4.59 aM. This represents an unprecedented achievement in ultra-low-level miRNA-based biosensors for diagnosing leptospirosis. Early-stage disease detection is crucial for effective disease management and timely treatment. Such an approach holds promise for point-of-care testing in remote settings to facilitate the early diagnosis of leptospirosis.