Temperature-Compensated DNA Hybridization Detection with an Ultralow Detection Limit Based on a Mach–Zehnder Interferometer

Overcoming temperature-induced signal drift remains a fundamental challenge in developing reliable DNA biosensors, particularly for low-concentration DNA detection, where uncompensated temperature fluctuation severely compromises the detection accuracy. We propose a novel biosensing platform integrating a cascaded Mach-Zehnder interferometer (MZI) fabricated using a 6.8 μm taper-waist thin single-mode fiber (TTSMF) with a fiber Bragg grating (FBG). The temperature compensation is achieved through a contour-based differential demodulation method that effectively decouples temperature fluctuation from the DNA molecular hybridization. Functionalized with mercaptoethylamine (MEA)-mediated self-assembled monolayers and probe DNA (pDNA) immobilization, the biosensor achieves 100-fold specificity discrimination with 5.91 nm complementary DNA (cDNA) redshift versus 0.059 nm for noncomplementary DNA (nonDNA), caused by refractive index (RI) changes resulting from DNA hybridization between pDNA and cDNA revealed by a molecular theory. The compensated DNA biosensor demonstrates an ultralow detection limit of 1.274 × 10^-12 mol/L (M) with 1.0564 × 10^-12 M resolution, outperforming existing interferometric DNA biosensors by 2 orders of magnitude. The DNA biosensor not only exhibits excellent sensing performance through its innovative structure but also enables real-time temperature compensation, paving the way for reliable detection of disease-associated DNA biomarkers and offering transformative potential for early diagnosis of genetic disorders in clinical settings.