Fiber ring laser biosensor based on no-core fibers for label-free DNA biomolecule measurements

An erbium-doped fiber ring laser based on a single-mode fiber–no-core fiber–single-mode fiber (SMF-NCF-SMF) structure was constructed and experimentally demonstrated for label-free DNA hybridization measurement. The SMF-NCF-SMF structure acts as a sensing element and a filter to select the laser wavelength. The proposed fiber ring laser sensor exhibits a high optical signal-to-noise ratio (SNR, >50 dB) and narrow full width at half maximum (FWHM, <0.05 nm). Its refractive index sensitivity is 116.8 nm per RIU in the range of 1.3406–1.3705, and its detection limit is 1.79 × 10⁻⁴ RIU. By continuously monitoring the laser wavelength, we successfully achieved label-free measurement of complementary DNA (cDNA) at concentrations as low as 1 μM. Subsequently, the specificity of the sensor was detected by non-complementary DNA (N-cDNA). Experimental results show that the fiber ring laser biosensor has the advantages of simple operation, label-free measurement, and high specificity. Furthermore, it shows a broad application prospect in several fields, especially in key areas such as medical diagnosis and cancer screening.