Lab-on-Fiber Operando Deciphering of a MOF Electrocatalyst.

Despite the great success in deploying metal-organic frameworks (MOFs) as efficient electrocatalysts, the low adoption of operando methods hinders the understanding of underlying mechanism. By leveraging the subtle refractive index evolution, including both the real and the imaginary parts, an entirely new concept of a lab-on-fiber operando method and its feasibility for "pristine-immersion-operando-post analysis" of electrocatalyts are demonstrated. Concurrent collection of absorption spectra and surface plasmon resonance is achieved by engineering fiber-optic waveguides to simultaneously induce guided light attenuation and plasmonic coupling.

Multifocal meta-fiber based on the fractional Talbot effect.

Multi-focusing of light is a crucial capability for photonic devices that can be effectively achieved by precisely modulating the phase delay on the incident wavefront. However, integrating functional structures into optical fibers for remote light focusing remains challenging due to the complex device design and limited fabrication approaches. Here, we present the design and fabrication of metalens array on the end-face of a tailored single-mode step-index fiber for focusing light field into closely packed focal spot array.

Sensing characteristics of structural microfiber long-period gratings.

We present a detailed investigation into the sensing characteristics of a structural microfiber long-period grating (mLPG) sensor. By spirally winding a thinner microfiber to another thicker microfiber, periodic refractive index modulation is formed while the optical signal transmitted in the thicker microfiber is resonantly coupled out to the thinner microfiber, and then a 5-period four-port mLPG can be obtained with a device length of only ∼570 µm demonstrated a strong resonant dip of 25 dB. We studied the sensitivity characteristics of the four-port mLPG with surrounding strain, force, temperature and refractive index, and the obtained sensitivities were -6.

ZIF-90-Derived Porous ZnO Coated Optical Microfiber Interferometer Sensor for Enhanced Humidity Sensing and Breath Monitoring.

Humidity plays an important role in many fields, and the realization of high sensitivity and fast response simultaneously for humidity detection is a great challenge in practical application. In this work, we demonstrated a high-performance relative humidity (RH) sensor made by supporting zeolitic imidazolate framework-90 (ZIF-90)-derived porous zinc oxide (ZnO) onto an optical microfiber Sagnac interferometer (OMSI). The ZIF-90-modified OMSI (ZIF-90-OMSI) sensor was in situ heated at different temperatures to obtain porous ZnO, and their humidity-sensing properties were investigated ranging from 25 to 80% RH.

Nanoscale Adsorption, Assembly, and Deionization Dynamics Recorded by Optical Fiber Sensors.

Capacitive deionization in environmental decontamination has been widely studied and now requires intensive development to support large-scale deployment. Porous nanomaterials have been demonstrated to play pivotal roles in determining decontamination efficiency and manipulating nanomaterials to form functional architecture has been one of the most exciting challenges. Such nanostructure engineering and environmental applications highlight the importance of observing, recording, and studying basically electrical-assisted charge/ion/particle adsorption and assembly behaviors localized at charged interfaces.

Transparent microfiber Fabry-Perot ultrasound sensor with needle-shaped focus for multiscale photoacoustic imaging.

Photoacoustic tomography emerged as a promising tool for noninvasive biomedical imaging and diseases diagnosis. However, most of the current piezoelectric ultrasound transducers suffer optical opacity and tissue-mismatched acoustic impedance, hindering the miniaturization and integration of the system for multiscale and multimodal imaging. Here, a transparent polydimethylsiloxane (PDMS) encapsulated optical microfiber ultrasound sensor was demonstrated for photoacoustic imaging with scalable spatial resolution and penetration depth.

Au-NPs signal amplification ultra-sensitivity optical microfiber interferometric biosensor.

An optical microfiber interferometric biosensor for the low concentration detection of sequence-specific deoxyribonucleic acid (DNA) based on signal amplification technology via oligonucleotides linked to gold nanoparticles (Au-NPs) is proposed and experimentally analyzed. The sensor uses a "sandwich" detection strategy, in which capture probe DNA (DNA-c) is immobilized on the surface of the optical microfiber interferometer, the reporter probe DNA (DNA-r) is immobilized on the surface of Au-NPs, and the DNA-c and DNA-r are hybridized to the target probe DNA (DNA-t) in a sandwich arrangement. The dynamic detection of the DNA-t was found to range from 1.

Sensitivity enhancement of a fiber-based interferometric optofluidic sensor.

Optofluidic sensors, which tightly bridge photonics and micro/nanofluidics, are superior candidates in point-of-care testing. A fiber-based interferometric optofluidic (FIO) sensor can detect molecular biomarkers by fusing an optical microfiber and a microfluidic tube in parallel. Light from the microfiber side coupled to the microtube leads to lateral localized light-fluid evanescent interaction with analytes, facilitating sensitive detection of biomolecules with good stability and excellent portability.

A universal strategy: Rational construction of noble metal nanoparticle-shell/conducting polymer nanofiber-core electrodes with enhanced electrochemical performances.

To address a challenge for decoration of noble metal nanoparticles (NMNPs)-shell on conducting polymer nanofiber (CPNF) electrodes (i.e. NMNP-shell/CPNF-core electrodes) for boosting electrochemical performances, a two-step strategy comprising chemical pre-deposition and electrochemical deposition is designed.

Development of an optical microfiber immunosensor for prostate specific antigen analysis using a high-order-diffraction long period grating.

Fiber-optic biosensors are of great interest to many bio/chemical sensing applications. In this study, we demonstrate a high-order-diffraction long period grating (HOD-LPG) for the detection of prostate specific antigen (PSA). A HOD-LPG with a period number of less than ten and an elongated grating pitch could realize a temperature-insensitive and bending-independent biosensor.

Ultrasensitive sensing in air based on Sagnac interferometer working at group birefringence turning point.

In this paper, a gas refractometer based on microfiber Sagnac interferometer is demonstrated, which can achieve an ultrahigh sensitivity when operating at the group birefringence turning point. We undertake a theoretical analysis and a simulated calculation to study the device characteristics and obtain the specific parameters of ellipticity and long axis of the elliptic microfiber for the group birefringence turning point. In the experiment, we obtain a positive sensitivity of 0.

Optical Microfiber Reader for Enzyme-Linked Immunosorbent Assay.

In clinical diagnosis, accurate and reliable measurement technologies for the detection of disease biomarkers at ultralow concentrations can provide guidance for the initiation of treatment and potentially improve survival for patients. Here, we demonstrate an optical microfiber reader for enhanced analytical sensitivity in enzyme-linked immunosorbent assays (ELISA) that enables the detection of tiny changes of the refractive index (RI) induced by the catalyzed oxidation of substrate, owing to the strong interaction between the evanescent field and surrounding medium. By employing the microfiber reader for the C-reaction protein (CRP) and interleukin-6 (IL-6) assays after the enzymatic signal amplification in ELISA, we experimentally investigate the biosensing capacity of the device.

Ultra-high sensitivity of dual dispersion turning point taper-based Mach-Zehnder interferometer.

We present here a detailed investigation into the sensitivity of the taper-based Mach-Zehnder interferometer as a function of external refractive index, with particular attention to the dispersion turning point (DTP) and possibilities for ultra-sensitive sensors. Our numerical simulation revealed that two DTPs exist with a decrease in the microfiber waist diameter; given this relationship, it is possible to obtain an ultra-sensitive operation. We then conducted experiments with fabricated devices with different waist diameters to achieve both positive and negative sensitivities at two DTPs.

Fiber Light-Coupled Optofluidic Waveguide (FLOW) Immunosensor for Highly Sensitive Detection of p53 Protein.

Highly sensitive detection of molecular tumor markers is essential for biomarker-based cancer diagnostics. In this work, we showcase the implementation of fiber light-coupled optofluidic waveguide (FLOW) immunosensor for the detection of p53 protein, a typical tumor marker. The FLOW consists of a liquid-core capillary and an accompanying optical fiber, which allows evanescent interaction between light and microfluidic sample.

Sampled Bragg gratings formed in helically twisted fibers and their potential application for the simultaneous measurement of mechanical torsion and temperature.

We propose and demonstrate a novel type of sampled Bragg gratings by combining a helically twisted fiber and a Bragg grating. A comb-like spectrum with a series of harmonic narrow resonances is observed, and the influence of geometrical parameters on the resonances is studied. As a special application, the intrinsic nature of the device that contains the Bragg grating and helical fiber spectral responses permits the temperature to be detected from the former, whereas the mechanical torsion is extracted from the latter, suggesting a potential for the simultaneous measurement of these two parameters.

Few-period helically twisted all-solid photonic bandgap fibers.

We present a type of few-period helically twisted all-solid photonic bandgap fiber (AS-PBGFs). The helical structure leads to orbital resonance of a cladding rod light, which couples with the core mode. A two-period twist structure exhibits an extremely strong resonant dip of up to 30 dB.

A label-free cardiac biomarker immunosensor based on phase-shifted microfiber Bragg grating.

Fiber optics evanescent field based biosensor is an excellent candidate for label-free detection of cardiac biomarkers which is of great importance in rapid, early, and accurate diagnosis of acute myocardial infarction (AMI). In this paper, we report a compact and sensitive cardiac troponin I (cTn-I) immunosensor based on the phase-shifted microfiber Bragg grating probe which is functionalized. The fine reflective signal induced by the phase shift in modulation significantly improves the spectral resolution, enabling the ability of the sensor in perceiving an ultra-small refractive index change due to the specific capture of the cTn-I antigens.

High-sensitivity DNA biosensor based on microfiber Sagnac interferometer.

Nucleic acid detection with label-free biosensors circumvents the need for costly fluorophore functionalization steps associated with conventional assays by utilizing optical fiber transducers. In spite of their technological prowess, however, these biosensors' sensitivity is limited by the design/configuration of their transducers. Therefore, it is imperative to integrate novel optical fiber transducers with existing label-free approaches to overcome those limitations.

Spectral tuning of the diameter-dependent-chirped Bragg gratings written in microfibers.

Chirped fiber Bragg gratings can straightforwardly and efficiently be fabricated onto microfibers with a uniform phase mask. Due to the variation of the propagating constant, which depends on the fiber diameter, the broadband spectrum of the grating can be formed. Depending on the different responses to the ambient refractive index in different parts of the grating, the bandwidth of the grating can be tuned by changing the surrounding solution.

Mesoporous nanospheres functionalized optical microfiber biosensor for low concentration neurotransmitter detection.

A label-free and ultrasensitive microfiber interferometer biosensor has been demonstrated for detection of neurotransmitter molecule (5-HT). The surface morphology of the silicon dioxide nanospheres acting as molecule sieve provides an effective mean of gathering 5-HT molecules by designed mesoporous structure. The slight concentration change of 5-HT molecules is translated into a dramatic wavelength shift of the interferometric fringe pattern.

Higher-order diffraction of long-period microfiber gratings realized by arc discharge method.

We report novel microfiber long period gratings (MF-LPGs) characterized by higher-order diffraction, which are fabricated using an arc discharge method. It is shown that an 11-period MF-LPG can exhibit an extremely high resonant dip (>30 dB) and a low transmission loss (<1.0 dB).

Micrometer-resolution in-fiber OCT probe with tunable working distance.

Optical coherence tomography (OCT) is an attractive modality in biomedical imaging systems due to its non-invasive imaging character. Since the image quality of OCT may be limited by the decrease of transverse resolution away from the focus spot, working distance tunable probe can be a strategy to overcome such limitation and maintain high transverse resolution at different imaging depths. In this paper, a miniature, working distance-tunable in-fiber OCT probe is demonstrated.

Study of lateral-drilled DBR fiber laser and its responsivity to external refractive index.

We report a lateral-drilled DBR fiber laser which contains a defective parabola-like opening inside the cavity fabricated by the CO-laser exposure and study the laser responsivity to external refractive index (RI). Surrounding materials can readily reach the vicinity of the fiber core via the opening and interact with the laser mode. Research shows that the laser emission power mainly relies on changes of external RI while the lasing wavelength on temperature.

Investigation on single taper-based all-solid photonic bandgap fiber modal interferometers.

We demonstrate a single taper-based all-solid photonic bandgap (AS-PBG) fiber modal interferometer that consists of a central tapered fiber region connected to the untapered via two abrupt transitions. Modal interference is given by superimposing the bandgap-guided fundamental core mode with a lower effective index and a specific index-guided cladding supermode with a higher effective index. A series of interferometers with taper diameter of 50μm ~60μm and device length of ~3mm are fabricated and studied in contrast to the conventional counterparts.

[Changes of soil microbial biomass carbon and their impact factors for Pinus tabuliformis plantations at different development stages on the Loess Plateau, China.].

By taking an abandoned land as control and the young (13-15 year-old), middle-age (25-27 year-old) and mature (41-43 year-old) plantations of Pinus tabuliformis as research objects, the variation characteristics and impact factors of soil microbial biomass carbon (MBC) for the P. tabuliformis plantations in 0-60 cm soil layer were studied. Results showed that the average MBC at the young, middle-age and mature plantations was 93.