Tapered Fiber Bioprobe Based on U-Shaped Fiber Transmission for Immunoassay.

In this paper, a tapered fiber bioprobe based on Mach-Zehnder interference (MZI) is proposed. To retain the highly sensitive straight-tapered fiber MZI sensing structure, we designed a U-shaped transmission fiber structure for the collection of optical sensing signals to achieve a miniature-insert-probe design. The spectrum responses from the conventional straight-tapered fiber MZI sensor and our proposed sensor were compared and analyzed, and experimental results showed that our proposed sensor not only has the same sensing capability as the straight-tapered fiber sensor, but also has the advantages of being flexible, convenient, and less liquid-consuming, which are attributed to the inserted probe design. The tapered fiber bioprobe obtained a sensitivity of 1611.27 nm/RIU in the refractive index detection range of 1.3326-1.3414. Finally, immunoassays for different concentrations of human immunoglobulin G were achieved with the tapered fiber bioprobe through surface functionalization, and the detection limit was 45 ng/mL. Our tapered fiber bioprobe has the insert-probe advantages of simpleness, convenience, and fast operation. Simultaneously, it is low-cost, highly sensitive, and has a low detection limit, which means it has potential applications in immunoassays and early medical diagnosis.

Ultrasensitive deafness gene DNA hybridization detection employing a fiber optic Mach-Zehnder interferometer: Enabled by a black phosphorus nanointerface.

The rapid and efficient detection of deafness gene DNA plays an important role in the clinical diagnosis of deafness diseases. This study demonstrates the ultrasensitive detection of complementary DNA (cDNA) by employing a nanointerface-sensitized fiber optic biosensor. The sensor consists of SMF-TNCF-MMF-SMF (abbreviated as STMS) structure with lateral offset. Besides, it is functionalized with a nanointerface of black phosphorus (BP) to enhance the light-matter interaction and eventually improve the sensing performances. Relying on this nanointerface-sensitized sensor, we successfully realize the in-situ detection of cDNA at concentrations ranging from 1 pM to 1 µM, with a sensitivity of 0.719 nm/lgM. The limit of detection (LOD) is as low as 0.24 pM, which is at least two orders of magnitude lower than those of existing methods. The sensor exhibits the advantages of simple operation, fast response, label-free measurement, excellent repeatability, and high selectivity. Our contribution suggests a convenient approach for deafness gene DNA detection and can be extended for general ultra-low concentration DNA detection applications.

Femtosecond laser written ultra-weak Fabry-Perot array for distributed absolute temperature profile sensing with high spatial resolution.

In this paper, high spatial-resolution distributed temperature sensing has been realized based on a femtosecond laser written ultra-weak Fabry-Perot Array (FPA). 50 identical Fabry-Perot cavities are fabricated in a 10 mm long optical fiber by femtosecond laser point-by-point written technology, and the corresponding spatial resolution is as high as 200 µm. Besides, by employing the total phase demodulation method, the optical path lengths (OPLs) in the ultra-weak FPA are successively demodulated based on the Rayleigh backscattering signal recorded by an optical frequency domain reflectometry (OFDR), and therefore the absolute temperature values instead of the relative ones can be obtained. When compared with the conventional single mode fiber-based OFDR, the proposed ultra-weak FPA presents both higher spatial resolution and lower temperature sensing uncertainty (0.25 °C) benefiting from the periodically enhanced Rayleigh backscattering. Furthermore, the experiments also confirm that the ultra-weak FPA can be applied for absolute temperature field profile sensing with large temperature gradient, which is particularly suitable for high-resolution temperature measurement of miniature devices.

Dual-fiber optic bioprobe system for triglyceride detection using surface plasmon resonance sensing and lipase-immobilized magnetic bead hydrolysis.

The rapid and accurate detection of triglyceride (TG) plays a valuable role in the prevention and control of dyslipidemia. In this paper, a novel method for TG detection using a dual-fiber optic bioprobe system, which can accurately detect different levels of TG concentration in serum, is proposed. The system employs disposable microprobe-type fiber optic surface plasmon resonance (SPR) biosensors for signal acquisition, providing high stability and portability while avoiding cross-contamination caused by repeated use. The proposed biosensor with a high sensitivity of 1.25 nm/(mg/mL) for TG detection in serum and a tiny diameter of 125 µm, was fabricated using a novel multimode fiber-single-mode fiber-reflector (MSR) structure, which has been scarcely ever reported to the best of our knowledge. In the process of TG detection, lipase-immobilized magnetic beads were introduced to specifically hydrolyze TG, and the relationship between the TG content and the SPR differential signal was obtained from dual-fiber optic bioprobe measurements of the TG sample before and after hydrolysis. The proposed method achieved TG detection in the concentration range of 0-8 mg/mL (including healthy and unhealthy levels of TG concentration in the human body). Additionally, the miniaturized fiber optic biosensors used in this work have the advantages of low sample consumption, high sensitivity, simple operation, label-free measurement, high selectivity, and low cost. This method provides a new pathway for rapid and reliable TG detection and has potential applications in medical research and clinical diagnosis.

Plasmonic tapered-fiber interference sensor for simultaneously detecting refractive index and temperature.

A single-optic-fiber sensor is proposed to simultaneously detect the refractive index (RI) and temperature (T) at a single wavelength band. This sensor is based on the mixed effects of Mach-Zehnder interference (MZI) and surface plasmon resonance (SPR), where MZI is excited by a tapered-fiber structure, and SPR is stimulated by a 45 nm gold film on the tapered-fiber surface. The detection signal of an SPR spectrum superimposed on interference stripes was obtained. After fast Fourier transform and filter processing, the MZI and SPR signals were separated. Experimental results indicate that our sensor can improve the RI sensitivity to 2021.07 nm/RIU (21-fold greater than that of the original tapered-fiber MZI sensor) and detect T simultaneously. Additionally, this highly integrated sensor simplifies the detection system, with potential applications in portable biochemical sensing.

Multiplexed Weak Waist-Enlarged Fiber Taper Curvature Sensor and Its Rapid Inline Fabrication.

This study proposes a multiplexed weak waist-enlarged fiber taper (WWFT) curvature sensor and its rapid fabrication method. Compared with other types of fiber taper, the proposed WWFT has no difference in appearance with the single mode fiber and has ultralow insertion loss. The fabrication of WWFT also does not need the repeated cleaving and splicing process, and thereby could be rapidly embedded into the inline sensing fiber without splicing point, which greatly enhances the sensor solidity. Owing to the ultralow insertion loss (as low as 0.15 dB), the WWFT-based interferometer is further used for multiplexed curvature sensing. The results show that the different curvatures can be individually detected by the multiplexed interferometers. Furthermore, it also shows that diverse responses for the curvature changes exist in two orthogonal directions, and the corresponding sensitivities are determined to be 79.1°/m-1 and -48.0°/m-1 respectively. This feature can be potentially applied for vector curvature sensing.

High-sensitivity and large-range fiber optic temperature sensor based on PDMS-coated Mach-Zehnder interferometer combined with FBG.

Although numerous efforts have been dedicated towards developing fiber sensors with high performances, challenges still remain in achieving high-quality temperature sensors with high sensitivity, large measurement range and high stability. This study proposes a compact fiber optic temperature sensor based on PDMS-coated Mach-Zehnder interferometer (MZI) combined with FBG, and it can realize both high-sensitivity and large-range temperature measurement. The MZI is based on Thin No-Core Fiber (TNCF) with lateral-offset. Owing to the high refractive index sensitivity of MZI and the high thermo-optic coefficient of PDMS, the sensor can achieve a high temperature sensitivity (>10 nm/°C). Besides, by optimizing the TNCF length, the cascaded FBG can be used to locate different temperature intervals in units of approximately 10 °C, and therefore the detectable temperature range is largely extended. The experimental test demonstrates that the average sensitivities of 11.19 nm/°C, 8.53 nm/°C, 7.76 nm/°C, 7.27 nm/°C are achieved at the temperature around 30 °C, 40 °C, 50 °C and 60 °C, and it shows excellent consistency and repeatability during the thermal cycle tests.

Optimized localization algorithm of dual-Sagnac structure-based fiber optic distributed vibration sensing system.

In this study, an optimized localization algorithm is proposed for a dual-Sagnac structure-based fiber optic distributed vibration sensing (DVS) system. Different from the previous localization algorithms, the spectrum peak ratio of the interference signals in the frequency domain is applied for localization calculation, and the localization accuracy is effectively improved for the interference signal with low Signal-Noise-Ratio (SNR). Besides, the proposed optimized algorithm can solve the difficult problem of multi-point vibration localization by employing a continuous low-coherence light source, which largely reduces the system cost. Meanwhile, multi-parameter including the frequency and amplitude of the vibration signal can be retrieved simultaneously except for the vibration position, which is not available for the traditional localization algorithm of the interferometric DVS system. Experimental results verify that the system with the proposed optimized algorithm can realize high-accuracy localization of single-point vibration, multi-point with single-frequency vibration, multi-point with multi-frequency vibration. The corresponding maximum localization errors are only 0.18%, 0.22%, and 0.36% respectively.

Four-wave mixing-based photonic crystal fiber microfluid sensor with embedded U-shape microslits.

In this paper, we propose a four-wave mixing-based photonic crystal fiber (PCF) microfluid sensor, and two U-shape microslits fabricated by a femtosecond laser are embedded into the sensor for real-time microfluid measurement. Theoretical and experimental results prove that the signal wavelength is sensitive to both the refractive index (RI) and the material dispersion property of the liquid sample filled into the air channels. For different aqueous target samples at low concentrations, the responses of signal wavelength are consistent with each other. The obtained RI sensitivity is approximately 881.36 nm/RIU, and the sensing resolution is around 1.6 × 10-4 RIU. The proposed sensor also shows a better figure of merit (FOM) as high as 313.65 RIU-1 when compared with the fiber SPR sensors. Besides, the signal wavelengths present different responses with the increasing aqueous concentration due to the separated dispersion characteristics of the filled liquid samples, which can be potentially applied for the discrimination of liquid samples with a well-designed wavelength-coded sensor array in the future.

Interrogation technique analyses of a hybrid fiber optic sensor based on SPR and MMI.

This study evaluates the interrogation techniques of a hybrid fiber optic sensor based on surface plasmon resonance (SPR) and multimode interference (MMI). The sensor is based on a single mode, fiber-no core, fiber-single mode fiber (SMF-NCF-SMF) structure with a deposited gold film layer. Both SPR and MMI effects are excited in a single sensor structure without enlarging the device size. However, at the same time, the interference fringe patterns are also mixed with the SPR transmission spectra, and the traditional SPR interrogation technique becomes unavailable since the resonant wavelength is hard to be located. In this study, the fast Fourier transform and different filtering algorithms are applied, both SPR signal and interference signal with different orders are separated effectively due to their different spatial frequency distributions, and they are processed individually for refractive index (RI) sensing. The experimental results verify that the overall RI sensitivity of the hybrid sensor is significantly enhanced. This study provides an important supplement to the traditional SPR and MMI functions.

High-performance fiber sensor via Mach-Zehnder interferometer based on immersing exposed-core microstructure fiber in oriented liquid crystals.

Rapid technology development and various applications show great demands for high-quality temperature sensors with super-sensitivity, broad working temperature ranges, excellent linearity and high stability. Although tremendous efforts have been dedicated towards developing fiber sensors with high performance, challenges still remain in achieving all of the four parameters. Herein, we fabricate a fiber sensor via a Mach-Zehnder interferometer (MZI) combined with a liquid crystal (LC)-filled microtube, where the LC in the microtube is uniformly orientated. The LCs with uniform orientation treatment play a vital role in the fiber sensor. The feasibility of this sensor was verified by theoretical simulation and demonstrated through experiments. The fabricated LC fiber sensor has super temperature sensitivity of -21.6 nm/°C with a good linearity of 0.976 from 22°C to 31°C, -558.5 nm/°C from 31°C to 32°C, -37.3 nm/°C with a good linearity of 0.999 from 32°C to 34°C and -6.7 nm/°C with a good linearity of 0.999 from 34°C to 110°C, respectively. The sensitivity of the fiber sensor is increased by up to 155 times, compared to the previously reported fiber sensor filled with LC based on the MZI without LC orientation treatment. The fiber sensor with super-sensitivity, broad working temperature range, excellent linearity and high stability provides great potential applications in such as environment monitoring, food detection, medicine, and chemical industry.

Distributed fiber optics disturbance sensor using a dual-Sagnac interferometer.

We demonstrate a distributed fiber optics disturbance sensing system based on a dual-Sagnac interferometer that uses one broadband light source and works at the same wavelength. This proposed sensing system is able to reduce the coherent noise and avoid the influence of polarization crosstalk effectively. Experimental results show that, for the presented prototype system with the fiber loop of 1.3 Km, when the sampling rate is set as 32.8 kHz, the maximum detectable frequency reaches the system theoretical limit of 8.18 kHz, and the spatial resolution is less than 15 m with a frequency range of 50-4000 Hz.

A disposable fiber optic SPR probe for immunoassay.

Immunoassay can be divided into two aspects, one is immobilization of antibodies for the efficient detection of corresponding antigens, and the other is immobilization of antigens to search for antibodies which work against them. In this paper, we demonstrated these two aspects of immunoassay by using the disposable fiber optic biosensors based on surface plasmon resonance (SPR) through surface decoration with half-antibody fragments, which has been scarcely ever reported to the best of our knowledge. We first fabricated the fiber optic SPR biosensor which consists of one gold film coated single-mode fiber sandwiched by two multimode fibers. Then, we decorated the fiber optic SPR biosensors with antibody fragments and antigen fragments, respectively, and compared the specific detection performances of these two kinds of sensors. After surface decoration with half-antibody fragments, the antigen-decorated fiber probe has a demonstrated sensitivity and limit of detection of 0.9771nm/(µg/mL) and 0.1 µg/mL, respectively, which improves by 10 times compared with the performance of the antibody-decorated fiber probe. Additionally, the selective detection results indicate that our proposed biosensor can be employed as a reliable antigen detector or an effective antibody filter. Our proposed sensor has the advantages of miniaturization, low cost, simple usage, label-free detection, high efficiency and sensitivity, and can effectively avoid cross-contamination caused by reuse. Given the reliable and clean detection method for immunoassay, our work should open a new window for the utilization of miniaturized fiber optic sensors in biochemical sensing.

A Simplified Hollow-Core Photonic Crystal Fiber SERS Probe with a Fully Filled Photoreduction Silver Nanoprism.

In this paper, a simplified hollow-core photonic crystal fiber surface-enhanced Raman scattering (SERS) probe is presented. Silver nanoprisms are grown with a photoreduction method and account for the SERS, which have better electromagnetic enhancement than spherical silver nanoparticles at 785 nm. Due to the antiresonant reflecting guidance mechanism, the excited laser and SERS signal are effectively guided in such a fully filled hollow-core photonic crystal fiber SERS probe and complicated selective filling with target sample is avoided. Rhodamine 6G molecules are used as probe molecules and the simplified hollow-core photonic crystal fiber SERS probe is test. Detection of low concentration Rhodamine 6G down to 10-8 M is achieved with a short integration time of 300 ms.

A label-free fiber optic SPR biosensor for specific detection of C-reactive protein.

A highly sensitive and label-free fiber optic surface plasmon resonance (SPR) biosensor for specific detection of C-reactive protein (CRP) is proposed and demonstrated. We take dopamine as a cross-linking agent to immobilize the anti-CRP monoclonal antibody, which is an efficient and simple method for specific modification of the fiber optic SPR sensor. The modified sensor can successfully detect CRP specifically. We realize the fabrication of a disposable fiber optic SPR sensor for the CRP specific detection. Through optimizing the immobilization time of anti-CRP monoclonal antibody and the reaction time of antigen and antibody experimentally, the sensor shows a satisfactory linear response (R2 = 0.97) to CRP concentration within the range from 0.01 to 20 µg/ml. Moreover, the highest CRP sensitivity is obtained at 1.17 nm per lg (µg/ml). With the advantages of simple structure and easy fabrication, our sensor is convenient to be batch produced and controlled with good consistency, which is especially suitable for the fabrication of disposable biosensor. It makes sense that our detection can effectively avoid the cross pollution caused by repeated use of the sensor.

Photoreduced silver nanoparticles grown on femtosecond laser ablated, D-shaped fiber probe for surface-enhanced Raman scattering.

Surface-enhanced Raman scattering (SERS) probes are made by facile photochemical deposition of silver nanoparticles on a femtosecond (fs) laser ablated, D-shaped fiber. The structure and surface morphology of the probe are investigated by scanning electron microscopy. High-quality SERS signals are detected using Rhodamine 6G molecules via an in situ sensing mode. Experimental results show that the SERS signals increase with the increase of the length of fs laser ablated, D-shaped zone. Our D-shaped fiber SERS probe shows a feasible method for a large active area, high performance, and real-time and remote measurement of SERS signals in biochemical analysis.

All-fiber reflecting temperature probe based on the simplified hollow-core photonic crystal fiber filled with aqueous quantum dot solution.

An all-fiber reflecting fluorescent temperature probe is proposed based on the simplified hollow-core photonic crystal fiber (SHC-PCF) filled with an aqueous CdSe/ZnS quantum dot solution. SHC-PCF is an excellent PCF used to fill liquid materials, which has low loss transmission bands in the visible wavelength range and enlarged core sizes. Both end faces of the SHC-PCF were spliced with multimode fiber after filling in order to generate a more stable and robust waveguide structure. The obtained temperature sensitivity dependence of the emission wavelength and the self-referenced intensity are 126.23 pm/°C and -0.007/°C in the temperature range of -10°C-120°C, respectively.

Charge transfer from cobaltammine complex cations to metal fluoride anions in molecular solids with novel photoelectronic effects (metal: zirconium, titanium).

[Co(en)3](Ti2F11) containing H-bonded assembly of a discrete cobaltammine complex cation and titanium fluoride anion was successfully synthesized under solvothermal conditions. A novel photoelectronic effect was observed in the near-UV region. By extending our understanding of this compound, taking into account our previously reported three cobalt complex-containing zirconium fluorides, the mechanism of photoelectronic effects from these molecular solids was determined by investigating the relative work function for their component species with the help of a Scanning Kelvin probe. The results suggest that the charge transfer from the excited cobaltammine complex cations to the metal fluoride anions as a result of the cooperative behaviors might occur upon illumination, which is responsible for these novel photoelectronic effects.

Some features of the photonic crystal fiber temperature sensor with liquid ethanol filling.

We introduce a novel photonic crystal fiber (PCF) temperature sensor that is based on intensity modulation and liquid ethanol filling of air holes with index-guiding PCF. The mode field, the effective refractive index and the confinement loss of PCF were all found to become highly temperature-dependent when the thermo-optic coefficient of the liquid ethanol used is higher than that of silicon dioxide and this temperature dependence is an increasing function of the d/Lambda ratio and the input wavelength. All the experiments and simulations are discussed in this paper and the temperature sensitivity of transmission power was experimentally determined to be 0.315 dB/ degrees C for a 10-cm long PCF.