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Refereed/Peer-reviewed An advanced multi-parameter optical fiber sensing technology for EGFR gene detection based on DNA hybridization technology is demonstrated in this paper. For traditional DNA hybridization detection methods, temperature and pH compensation can not be realized or need multiple sensor probes. However, the multi-parameter detection technology we proposed can simultaneously detect complementary DNA, temperature and pH based on a single optical fiber probe. In this scheme, three optical signals including dual surface plasmon resonance signal (SPR) and Mach-Zehnder interference signal (MZI) are excited by binding the probe DNA sequence and pH-sensitive material with the optical fiber sensor. The paper proposes the first research to achieve simultaneous excitation of dual SPR signal and Mach-Zehnder interference signal in a single fiber and used for three-parameter detection. Three optical signals have different sensitivities to the three variables. From a mathematical point of view, the unique solutions of exon-20 concentration, temperature and pH can be obtained by analyzing the three optical signals. The experimental results show that the exon-20 sensitivity of the sensor can reach 0.07 nm nM−1, and the limit of detection is 3.27 nM. The designed sensor gives a fast response, high sensitivity, and low detection limit, which is important for the field of DNA hybridization research and for solving the problems of biosensor susceptibility to temperature and pH.

Refereed/Peer-reviewed We demonstrate a multipoint optical fiber pressure sensor for high temperature operation using multimode interference. Each sensing element consists of a four-hole asymmetric multimode fiber acting as the pressure sensing fiber, spliced between two standard polarization-maintaining single mode fibers. Multiple sensing elements are serially connected for multipoint pressure sensing and demultiplexing is achieved using Fourier analysis. The spatial frequency associated with each sensing element is separated by having distinct optical path lengths. The pure silica material of the sensing fiber enables high-temperature operation. As a proof of concept, we demonstrate two-point pressure sensing at a temperature up to 900 °C with negligible crosstalk between the sensing elements and good stability. Our demonstrated sensor has potential applications in heavy industry where spatially resolved measurements of pressure at high temperature may lead to improvements in efficiency and safety.

Refereed/Peer-reviewed 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.

Nitric oxide plays a crucial role as a messenger in biological systems, but limitations in measurement are restricted due to its relatively low concentration and short half-life time. Here we report a novel approach to sensing nitric oxide by using an exposed core fiber with its core coated with CdTe/CdS core/shell quantum dots.This enables rapid detection and opens up the possibility of monitoring its production within biological systems.The detection mechanism is based on fluorescence quenching of CdTe/CdS quantum dots by nitric oxide, which can coordinate with Cd²⁺ directly as a ligand forming transition metal complexes. We demonstrate that CdTe/CdS quantum dots functionlization exposed core optical fibers can respond rapidly to nitric oxide in physiologicalenvironments with picomolar sensitivity. Refereed/Peer-reviewed

usc Abstract: A fiber Bragg grating was inscribed in an abrupt fiber taper using a femtosecond laser and phase-mask interferometer. The abrupt taper transition allows to excite a broad range of guided modes with different effective refractive indices that are reflected at different wavelengths according to Bragg’s law. The multimode-Bragg reflection expands over 30 nm in the telecom-C-band. This corresponds to a mode-field overlap of up to 30% outside of the fiber, making the device suitable for evanescent field sensing. Refractive index and temperature measurements are performed for different reflection peaks. Temperature independent refractive index measurements are achieved by considering the difference between the wavelength shifts of two measured reflection peaks. A minimum refractive index sensitivity of 16 ± 1 nm/RIU was obtained in a low refractive index regime (1.3475–1.3720) with low influence of temperature (−0.32 ± 0.06 pm/°C). The cross sensitivity for this structure is 2.0 × 10−5 RIU/°C. The potential for simultaneous measurement of refractive index and temperature is also studied. Refereed/Peer-reviewed

Refereed/Peer-reviewed Distributed sensing of micron-scale particles is achieved with an exposed-core microstructured optical fiber using optical frequency domain reflectometry. The reference and sample signals of the interferometer are generated in the same fiber path, which gives this fully fiber-integrated sensor the potential to be used as a portable probe for in-vivo sensing. This sensing concept has great advantages over reported single-point fiber sensors due to its distributed sensing property. We demonstrate the technique using 10 μm polystyrene beads, by detecting their locations along the fiber through backscatter of the exposed-core fiber’s evanescent field. A simplified theoretical model is proposed to estimate the relationship between the particle’s size and detection distance after considering the system’s inherent losses. The proposed sensing platform offers opportunities for distributed sensing of biological targets.