A simple and robust refractive index (RI) sensor based on a Mach-Zehnder interferometer has been demonstrated. A section of optical microfiber drawn from silica fiber is employed as the sensing arm. Because of the evanescent field, a slight change of the ambient RI will lead to the variation of the microfiber propagation constant, which will further change the optical length. In order to compensate the variation of the optical length difference, a tunable optical delay line (ODL) is inserted into the other arm. By measuring the delay of the ODL, the ambient RI can be simply demodulated. A high RI sensitivity of about 7159  μm/refractive index unit is achieved at microfiber diameter of 2.0 μm.

Abstract. Optical fiber technology has significantly bolstered the growth of photonics applications in basic life sciences research and in biomedical diagnosis, therapy, monitoring, and surgery. The unique operational characteristics of diverse fibers have been exploited to realize advanced biomedical functions in areas such as illumination, imaging, minimally invasive surgery, tissue ablation, biological sensing, and tissue diagnosis. This review paper provides the necessary background to understand how optical fibers function, to describe the various categories of available fibers, and to illustrate how specific fibers are used for selected biomedical photonics applications. Research articles and vendor data sheets were consulted to describe the operational characteristics of conventional and specialty multimode and single-mode solid-core fibers, double-clad fibers, hard-clad silica fibers, conventional hollow-core fibers, photonic crystal fibers, polymer optical fibers, side-emitting and side-firing fibers, middle-infrared fibers, and optical fiber bundles. Representative applications from the recent literature illustrate how various fibers can be utilized in a wide range of biomedical disciplines. In addition to helping researchers refine current experimental setups, the material in this review paper will help conceptualize and develop emerging optical fiber-based diagnostic and analysis tools.

All-in-fiber optofluidics is an analytical tool that provides enhanced sensing performance with simplified analyzing system design. Currently, its advance is limited either by complicated liquid manipulation and light injection configuration or by low sensitivity resulting from inadequate light-matter interaction. In this work, we design and fabricate a side-channel photonic crystal fiber (SC-PCF) and exploit its versatile sensing capabilities in in-line optofluidic configurations. The built-in microfluidic channel of the SC-PCF enables strong light-matter interaction and easy lateral access of liquid samples in these analytical systems. In addition, the sensing performance of the SC-PCF is demonstrated with methylene blue for absorptive molecular detection and with human cardiac troponin T protein by utilizing a Sagnac interferometry configuration for ultra-sensitive and specific biomolecular specimen detection. Owing to the features of great flexibility and compactness, high-sensitivity to the analyte variation, and efficient liquid manipulation/replacement, the demonstrated SC-PCF offers a generic solution to be adapted to various fiber-waveguide sensors to detect a wide range of analytes in real time, especially for applications from environmental monitoring to biological diagnosis.

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In this paper, we report an optical fiber Sagnac interferometer (OFSI)-based temperature sensor constructed by a selectively filled polarization-maintaining photonic crystal fiber (PM-PCF). The transmission spectrum of the OFSI is in sinusoidal form and is sensitive to temperature. Simulation results predicted a higher sensitivity by selective filling than nonselective filling. In experiments, we used an extremely low-cost process to realize the selective filling. A sensitivity of 2.58 nm= C was achieved with an 11.7-cm-long PM-PCF. The sensitivity dependence on the infiltration length ratio was also investigated.

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A novel magnetic field sensor using tilted fiber Bragg grating (TFBG) interacting with magnetic fluid is proposed and experimentally demonstrated. The TFBG is surrounded by magnetic fluid whose complex refractive index changes with external magnetic field. The guiding properties of cladding modes excited by the TFBG are therefore modulated by the external magnetic field. As a result, the magnetic field strength measurement is successfully achieved within a range up to 196 Gauss by monitoring extinction ratio of cladding mode resonance. Furthermore, temperature variation can be obtained simultaneously from the wavelength shift of the TFBG transmission spectrum.

Background: Stress fracture is one of the most common overuse injuries in athletes. Overloaded mechanical stimulation is an important factor affecting stress fractures, but the mechanism is unclear. Methods: MC3T3-E1 cells and a polycaprolactone (PCL) scaffold were co-cultured, and finite element analysis (FEA) was used to analyze the load-carrying capability. Cell proliferation was investigated with CCK-8 assays. An alkaline phosphatase (AKP) activity assay was used to evaluate cell differentiation. Cell apoptosis was analyzed using Hoechst/ PI double-labeling, Caspase-3 activity and lactate dehydrogenase (LDH) activity assays. Realtime PCR and Western blotting were used to examine the gene and protein expression, respectively, of Caspase-3 and Caspase-9. Assays of the intracellular calcium with fluorescent probe technique and extracellular ATP with fluorometric assay kit were used to analyze the changes in the intracellular calcium concentration induced by calcium channel opening and the release of ATP, respectively, at different operation times. Results: When the apparent strain reached 10000 µε, the strain scope of fber at levels greater than 4000 µε was 60%. Overloading for 4 days and operation times of 0.5 h and 2 h increased the cell number and AKP secretion. However, apoptosis genes were activated at the same time, and the operation time of 2 h had a significantly greater effect than 0.5 h. At 8 days, the cell numbers were greater for the operation time of 0.5 h than for 2 h, and the 2-h groups had the fastest apoptosis rate. Overloading for 1 day increased intracellular calcium levels and ATP release. The increase in intracellular calcium could be blocked by the addition of N-ethylmaleimide (NEM) or Hank's medium. Overloading for 8 days increased intracellular calcium levels but decreased extracellular ATP, and verapamil blocked the increase in intracellular calcium. Conclusion: We found that a simultaneous ‘double effect’ on osteoblasts was induced by overloading, which promoted cell proliferation, differentiation and apoptosis. Short-term overloading could open the cell membrane calcium channels and release calcium stores to elevate intracellular calcium levels, thereby promoting the proliferation and differentiation of cells to a greater extent than the effect of apoptosis. For long-term overloading, calcium channel opening in the membrane could lead to overloading of intracellular calcium levels, inducing an apoptosis effect that is greater than the effect on proliferation and differentiation.