Temperature-Compensated and Sensitivity-Enhanced Biosensor for the Detection of EGFR Exon-20 Gene in Non-Small Cell Lung Cancer

Ultrasensitive detection of the epidermal growth factor receptor (EGFR) gene in non-small cell lung cancer (NSCLC) remains a critical challenge for early diagnosis and targeted therapy. While fiber-optic biosensors offer promising sensing capabilities, their performance is fundamentally limited by the temperature fluctuation and insufficient limit of detection (LOD). In this work, an approaching 4-fold amplification of EGFR-binding spectral shifts is achieved through the Vernier effect (VE) in the cascaded Sagnac interferometer (SI) and Mach-Zehnder interferometer (MZI), whose free spectral ranges (FSRs) are deliberately mismatched. Temperature compensation is achieved through a contour-based differential demodulation method enabled by integrating a fiber Bragg grating (FBG) into the biosensor, which effectively decouples temperature variations from the deoxyribonucleic acid (DNA) molecular hybridization signals. Functionalized with mercaptoethylamine (MEA)-mediated self-assembled monolayers and single-stranded probe DNA (pDNA) specific to the EGFR gene, the biosensor achieves 53.7-fold specificity discrimination with the 25.1593 nm wavelength redshift for complementary DNA (cDNA) versus 0.4683 nm for non-complementary DNA (nonDNA), caused by refractive index (RI) changes resulting from DNA hybridization between pDNA and cDNA. The biosensor achieves a prominent LOD of 0.03363 pM for the synthetic EGFR gene in the buffer, surpassing existing interferometric biosensors by four orders of magnitude. This work not only establishes a new paradigm for overcoming the temperature drift in photonic biosensing but also employs the VE to significantly enhance the LOD, offering transformative potential for early diagnosis of NSCLC in clinical settings.