Ultrasensitive <i>Helicobacter pylori</i> DNA Hybridization Detection Based on a No-Core-Fiber Offset Mach–Zehnder Interferometer Enhanced by a MoS ₂ Nanointerface

The specific and sensitive detection of <i>Helicobacter pylori</i> (<i>H. pylori</i>) is of great significance for the clinical diagnosis of gastropathy, but conventional detection methods for <i>H. pylori</i> lack sufficient sensitivity and accuracy with complicated operation, especially for low-density <i>H. pylori</i> infection. To break through the limitation, a label-free fiber optic Mach-Zehnder interferometer (MZI) was used for in situ real-time detection of <i>H. pylori</i> deoxyribonucleic acid (DNA) hybridization. One microcavity fabricated by no-core-fiber lateral offset splicing served as the sensing arm of MZI and the light guided in the fiber as the reference. Owing to the direct interaction between microfluidics and opening cavity mode as well as the enhancement caused by the MoS₂ nanointerface, the refractive index (RI) sensitivity can reach as high as -17,051 nm/RIU. The probe DNA is immobilized on the MoS₂-functionalized fiber surface by electrostatic interaction to specifically capture target DNA (tDNA). Results show that the sensor exhibits a good log-linear response to tDNA in the concentration range of 1 fM-100 pM, with a high sensitivity of 0.79 nm/logfM and low limit of detection of 0.89 fM, which is more than 2 orders of magnitude lower than that of other fiber optic sensors. As the interference dip at the longer wavelength exhibits higher RI, temperature sensitivities than that at the shorter, dual-parameter demodulation are feasible, and the compensation of temperature-induced cross-sensitivity can be realized. Moreover, the sensor with the advantages of easy fabrication, fast response, good specificity, stability, and reusability can be universally applied for ultralow concentration DNA detections applied in biological fields.