We propose and experimentally demonstrate an in-line interferometer, which is based on a capillary spliced between two single mode fibers (SMFs) with a certain of transverse offset. As two main modes, LP01 and LP11, are excited and propagate in the capillary wall, they will interfere with each other when they meet again in the output-SMF. Due to the characteristic of polarization dependent in the LP11 mode, the proposed capillary-based interferometer can be designed for twist sensing. Experimental results show that our proposed capillary-based interferometer can provide sensitivities higher than 90 pm/° in both anticlockwise and clockwise twist in the range of 10° – 90°.
We propose a tilted fiber grating (TFG) sensor for ammonium ion detection in aqueous solution. The sensor is made by coating a nano-film of polyvinylidene-fluoride-bromothymol-blue (PVDF-BTB) over the TFG surface. As the ammonium ion can react with the bromothymol blue, the smoothness of the PVDF-BTB film will be destroyed, leading to the transmission spectrum changing correspondingly. The reaction strength between the ammonium ion and the bromothymol blue is proportional to the concentration of ammonium ion. Therefore, through monitoring the change of a selected cladding mode in the transmission spectrum with time, we can measure the concentration of ammonium ion. Experimental results show that our sensor can detect ammonium ion in concentration as low as 1 mg/L within 140 seconds, and after that the intensity variation of the monitored mode almost keeps stable, which agrees with the theoretical analysis. Furthermore, through monitoring the core mode during the experiment, we can eliminate the temperature-induced cross-sensitivity, thus improving the measured accuracy of the sensor. Our proposed TFG sensor for ammonium ion detection has advantages of simple structure, easy fabrication and comparable performances.
We proposed and experimentally demonstrated a metal coated tilted fiber grating (TFG) for calmodulin detection. The sensor was designed as a reflective probe type by depositing a gold mirror in the down-stream of the TFG. A 50-nmthick gold nanocoating was radio-frequency magnetron sputtered over the fiber surface of an 18° TFG, and the transient receptor potential channels were bond onto the metal surface for calmodulin detection. The experimental results demonstrated that our biosensor can detect calmodulin with concentration as low as 1 μM. This result was better than that obtained using the isothermal titration calorimetry method. In addition, with the use of a custom-designed microfluid system, the volume of sample solution required by our biosensor was only 20 μL. Our proposed sensor is simple to fabricate and easy to implement, and it can be used for rapid, label-free, and microliter-volume biomolecule detection
We have proposed and experimentally demonstrated a plasmonic tilted fiber Bragg grating (TFBG) biosensor for labelfree detection of small biomolecule S-adenosyl-L-homocysteine (AdoHcy) in different concentrations. The biosensor is designed as a reflective probe type with a 50-nm-thick gold film coating over the fiber surface of an 18° TFBG, together with a surface functionalization with protein lysine methyltransferase Set7 working as bio-detector. The sensor is fabricated without any destruction of fiber structural integrity, thereby ensuring the stability and reproducibility. The experimental results demonstrated that our biosensor can detect biomolecule AdoHcy with concentration as low as 1 nM. We have also measured AdoHcy in different concentrations, including 0.01, 0.1 and 10 nM, and the results indicated that as the AdoHcy concentration increases, the association ratio between AdoHcy and Set7 arises correspondingly, agreeing with the theory.
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