In-situ DNA detection with an interferometric-type optical sensor based on tapered exposed core microstructured optical fiber

A label-free DNA biosensor based on exposed core microstructured optical fiber for in-situ real-time DNA detection has been presented and experimentally demonstrated. The sensor is fabricated by splicing a section of tapered exposed core fiber (ECF) between two single-mode fibers (SMFs), forming a multimode Mach-Zehnder interferometer (MZI). The ECF design provides the evanescent field with the sensitivity of a micro/nano optical fiber. In this paper, the ECF has a large cladding diameter (160 µm) but a small core (9 µm), and the core of the ECF is further reduced by tapering, which significantly improves the refractive index (RI) sensitivity. The sensor can detect local RI changes that occur on the surface of the optical fiber due to the binding of biomolecules. We immobilized probe DNA (pDNA) on the exposed side of the core to detect the complementary DNA (cDNA), demonstrating use for specific and label-free sensing of DNA hybridization. Experimental results show that the sensor can qualitatively detect cDNA with the sensitivity of 0.0618 nm/nM and a detection limit of 0.31 nM at a temperature of 25 °C. The proposed DNA biosensor has potential applications in fast developing fields such as medical diagnostics, cancer screening, drug testing, and environmental engineering.