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Riboflavin (RF) is an important vitamin necessary for human living activities. It is a crucial component of the body’s critical enzymes, contributing to energy production, development, and metabolism. Low-cost RF sensors are one of the most essential research objectives for today’s development. In this work, the authors developed a highly sensitive optical platform for real-time detection of RF concentration, with the goal of developing and testing a novel RF sensor based on localized surface plasmon resonance (LSPR) with a tri-tapered-in-tapered (TTIT) seven-core fiber with multimode structure for fast and selective RF concentration measurement in solution. In this work, a TTIT fiber-based RF sensor was developed using a fusion splicer and tapered fiber optic fabrication techniques, in which gold nanoparticles (AuNPs), zinc oxide nanowires (ZnO-NWs), and molybdenum disulfide nanosheets (MoS2-NSs) were uniformly coated on the surface of the optical fiber to enhance the evanescent field in the sensing region, reducing optical signal loss and increasing the sensing area. To detect changes in RF concentration, the evanescent field can stimulate the LSPR of AuNPs immobilized on the probe surfaces. Furthermore, the sensor has great repeatability and stability, and the RF fiber-optic sensor developed in this experiment is an efficient, sensitive, and cost-effective mode of detection for rapid monitoring of RF levels in a wide range of practical applications. The sensor’s sensitivity was 2.14 nm/mM, with a limit of detection (LOD) of $86.86~\mu $ M. The success of the technique will encourage the development of RF detection technologies for food safety and clinical diagnosis.

Alpha-fetoprotein (AFP), a biomarker for liver cancer detection, has important clinical significance. Here, an S-tapered WaveFlex fiber biosensor is developed that is based on the structure of multimode fiber (MMF)–multicore fiber (MCF)–MMF and leaks more energy when excited by light. ZnO nanowires (ZnO-NWs)/WS2 nanosheets (WS2-NSs) and gold nanoparticles (AuNPs) are functionalized on the probe surface to further enhance the sensing performance. 1-D ZnO-NWs possess a larger specific surface area and can provide more sites for antibodies. The fold structure of WS2-NSs provides ample space for functionalization. The combination of the above two nanomaterials is conducive to the immobilization of AuNPs and AFP antibodies and improves the performance of the developed biosensor. AuNPs and AFP antibodies are used to generate localized surface plasmon resonance (LSPR) and enhance the specificity of the probe, respectively. The developed probe is employed to detect AFP solution in the range of 0–1000 ng/mL, and the sensitivity and limit of detection (LoD) are obtained as 1.32 nm/log(ng/mL) and 84 pg/mL, respectively. Moreover, the practical application capability of the probe is verified by the selectivity test, pH test, reproducibility, and reusability experiments. The results demonstrate the potential application of the developed S-tapered WaveFlex AFP sensor in the detection of liver cancer markers.

In this work, we develop a portable, sensitive waveflex biosensor that could be used for glycosylated hemoglobin A1c (HbA1c) detection. The probe consists of multimode fiber (MMF) and multicore fiber (MCF)-based W-shaped innovative sensing structures. Localized surface plasmon resonance (LSPR) is induced by modifying the optical fiber surface with gold nanoparticles. The functionalization of zinc oxide nanowires (ZnO-NWs), tungsten disulfide quantum dots (WS2-QDs), and HbA1c antibodies on the probe surface increases the specific surface area of the fiber probe and enhances the biological specificity of the sensor, respectively. Finally, the linear range, sensitivity, and limit of detection (LoD) of the sensor probe are tested, and the results are as follows: 30– $1500~\mu $ g/mL (2.7–577 mmol/mol), 0.005 nm/( $\mu $ g/mL), and $61.8~\mu $ g/mL, respectively. The repeatability, reusability, stability, selectivity, and pH test of the probe are also evaluated to showcase its sensing performance. In addition, to verify the usefulness of the sensor, HbA1c concentrations in serum samples were tested using the sensor and the D-10 Hemoglobin Testing System. The results of the sensor are consistent with those of the D-10 Hemoglobin Testing System. Therefore, the sensor can be used to detect HbA1c concentration in human serum samples.

Silicon carbide (β-SiC) was synthesized through an improved sol–gel method, then Ni/SiC catalysts were prepared using a hydrothermal method. The catalysts were characterized using TEM, H2-TPR, CO2-TPD and N2-TPD, etc. The results showed that the synthesized β-SiC had a large specific surface area, promoting the dispersion of Ni species and thus exposing more active sites. The interaction between Ni species and β-SiC contributed significantly to catalytic performance. Furthermore, the strong alkalinity of catalyst could adjust the bond energy of the active metal and N (M–N), which were conducive to desorption of the recombinant N2from the metal surface, promoting to ammonia decomposition. Among the Ni/SiC catalysts, 30Ni/SiC-700 synthesized with the Ni loading of 30 wt% and calcination temperature of 700 °C, exhibited the optimal ammonia conversion rate of 93.4% at 600 °C under the space speed of 30,000 mL∙gcat−1∙h−1, and demonstrated a long-term stability, suggesting a very promising catalyst in ammonia decomposition.

Shigella, a highly infectious and pathogenic Gram-negative bacterium, is widely prevalent in everyday food items, prompting significant research due to its potential hazards. Addressing the need for Shigella detection, this study introduces a WaveFlex biosensor based on localized surface plasmon resonance (LSPR) using fiber optics. The sensor is tailored to detect a specific subspecies of Shigella, specifically Shigella sonnei (S. sonnei). It is fabricated using a combination of multimode fiber (MMF) and four-core fiber (FCF), creating a core-mismatched W-type fiber structure designed for efficient mode coupling. Furthermore, this sensor is enhanced with the utilization of nanomaterials, including cerium oxide nanorods (CeO2-NRs), zinc oxide nanowires (ZnO-NWs), and copper selenide@gold nanocomposites (Cu3Se2@Au-NCs). CeO2-NRs and ZnO-NWs contribute to improve biocompatibility and increase surface area for antibody functionalization, while Cu3Se2@Au-NCs promote the LSPR effect and enhance sensing performance. To enhance specificity, the optical fiber coated with these engineered nanomaterials is functionalized with S. sonnei antibody. The results of this work showcase the effective detection of Shigella bacteria by the proposed WaveFlex sensor, offering exceptional sensitivity (0.28 nm/(CFU/mL)), a low limit of detection (LoD) of 0.96 CFU/mL, and a swift detection time of 10 minutes. These findings underscore the sensor's potential for widespread applications in areas such as food safety, medical diagnostics, and environmental monitoring. This study significantly advances bacterial detection technology and contributes to the assurance of public health and food safety.

Aflatoxins are a kind of fungal toxin that causes great damage to humans and animals due to its wide distribution, secretive nature, and high toxicity. For the purpose of achieving qualitative and quantitative detection of aflatoxin B1 (AFB1), a novel tri-taper-in-taper fiber-optic structure based on core mismatch of four-core fiber with a multimode fiber-based WaveFlex biosensor is developed and tested. The sensor probe's surface is coated with gold nanoparticles (AuNPs). Multi-walled carbon nanotubes and zinc oxide nanoparticles are sequentially immobilized on the sensing probe surface to enhance the sensor's sensing capabilities. Then, the AFB1 antibody is utilized to functionalize the sensor to possess specific selectivity. After the modification of nanomaterials and the corresponding bioreceptors, the final sensor structure is formed. By stimulating the localized surface plasmon resonance phenomenon of AuNPs, different concentrations of AFB1 can be detected. The sensor demonstrates high sensitivity (38.29 nm/μM) as well as low LOD (7.12 nM) within the range of 0–100 nM for detection. The sensor is also found to be stable and reproducible in repeated measurements, indicating its potential for practical application. Additionally, it exhibits satisfactory specific recognition of AFB1. These results show that AFB1 can be detected in food and agricultural products using LSPR-based optical fiber sensors, which could have significant ramifications for public health and food safety.

[] In this study, we present a novel optical sensing system for the real-time detection of ascorbic acid (AA), also known as vitamin C, a vital water-soluble vitamin with significant clinical relevance. AA serves not only as a biomarker for various diseases but also as a treatment for conditions such as scurvy, anemia, and cardiovascular disease. Our approach involves the development of a highly sensitive fiber optic sensor tailored for AA detection, utilizing a multimode fiber-four-core fiber (MMF-FCF) configuration. Fabrication involved advanced techniques, including fusion splicing and hydrofluoric (HF) acid etching, which created a core-mismatch structure generating sufficient evanescent waves (EWs). We immobilized tungsten disulfide (WS2) thin-film and cerium dioxide nanorods (CeO2-NRs) onto the probe’s surface to enhance the sensor’s performance. Thereafter, EWs excited the localized surface plasmon resonance (LSPR) phenomenon of gold nanoparticles (AuNPs) immobilized on the probe’s surface, facilitating AA detection. To enhance AA sensor selectivity, the probe’s surface was functionalized with the ascorbate oxidase (AOx) enzyme. The experiments utilized a laser source and an erbium-doped fiber amplifier (EDFA) to achieve precise excitation and signal amplification, enhancing the sensor’s overall performance. Experimental results demonstrated a sensor sensitivity of 0.796 nm/mM and a limit of detection (LoD) of $167.71 \mu \text{M}$ within the 0– $500 \mu \text{M}$ concentration range. These findings emphasize the sensor’s potential value in clinical applications for AA detection.

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A series of ZIF-67-C-IL catalysts were prepared using ZIF-67 and 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([BMIM]NTf2) ionic liquid as precursors. The structure of the catalysts was characterized by XRD, TEM, SEM and XPS. The catalytic performance of the catalysts for the oxygen reduction reaction (ORR) was evaluated in a three-electrode system. The results confirmed that the high-temperature treatment of the precursors resulted in the formation of N, S co-doped carbon-encapsulated Co9S8nanoparticles. To create N, S co-doped carbon coated Co9S8nanoparticle catalysts, ionic liquids are used as sulfur and nitrogen sources. The catalytic activity of ORR can be improved using N, S co-doped carbon to prevent the aggregation of Co9S8nanoparticles. Graphitized and N, S co-doped carbon shells are optimal for achieving high activity stability. Optimal 600-ZIF-67-C(1:1.5)-30IL catalytic activity was observed for ORR. The half-wave potential of ORR was 0.88 V vs. RHE in 0.1 mol L−1KOH, with a limit current density of 4.70 mA cm−2. Similar ORR electrocatalytic activity was observed between this catalyst and commercial Pt/C (20 wt%).

The paper discusses the application of single-mode fiber (SMF) and multimode fiber (MMF) to the fabrication of a sensor structure based on the hetero-core optical fiber structure. The proposed structures are SMF-MMF-SMF (SMS), MMF-SMF-MMF (MSM), and SMF-MMF-SMF-MMF-SMF (SMSMS). The transmitted intensity of the probe is used to estimate the strength of the evanescent field. The results indicate that the SMSMS structure generates more evanescent waves that penetrate deeper into the sensing probe, increasing its sensitivity. As a result, the SMSMS structure has enormous development potential in the field of sensing.

This paper primarily discusses the structural performance analysis of a single/double/quadruple tapered optical fiber (TOF) structure based on single-mode fiber (SMF) and multi-mode fiber (MMF). Furthermore, the TOF’s performance, including its diameter distribution, transmitted intensity, and reproducibility, is also evaluated. According to the experimental results, it can be concluded that the quadruple TOF structure based on SMF has a higher density of evanescent waves (EWs) on the surface of the tapered area, which is essential for the fabrication of high-sensitivity optical fiber sensors. The structure proposed in this article is feasible, and it can be used for optical fiber sensing while offering significant practical and promising applications as well.

Two-dimensional (2D) mono-elemental materials (Xenes) show remarkable potential in the fields of fundamental science and technology, have been regarded as a wide range of building blocks for electronic technologies due to their unique chemical, physical, electrical, and optical properties. Here, 2D tellurene/black phosphorus (Te/BP) heterojunctions are successfully fabricated through liquid-phase exfoliation (LPE) method. Their nonlinear optical absorption properties at 1.0, 2.0, and 2.8 μm have been studied by an open-aperture Z-scan method. The results revealed the excellent broadband saturable absorption responses of the prepared BP/Te heterojunctions, which are further confirmed by using them as saturable absorbers (SAs) for passively Q-switched all-solid-state lasers operating at 1.0, 2.0, and 2.8 μm, respectively. In particular, 1.04 μm continuous-wave (CW) mode-locked lasers with a pulse width of 404 fs is realized for the first time, to our best knowledge. Our work indicates that 2D Xenes especially 2D Xenes based heterojunctions have great potential in the fields of pulsed laser generation/modulation and other optoelectronic and photonic devices.

The nitrogen reduction reaction (NRR) for ammonia synthesis is hindered by weak N2adsorption/activation abilities and the hydrogen evolution reaction (HER). In this study, αBi2O3(monoclinic) and βBi2O3(tetragonal) were first synthesized by calcination at different temperatures. Experiments and calculations revealed the effects of Bi2O3with different crystal phases on N2adsorption/activation abilities and HER. Then, αBi2O3-xand βBi2O3-xseries catalysts with surface oxygen vacancies (OVs) and Bi0active sites were synthesized through the partial in situ reduction method. The results demonstrate the following: (I) Tetragonal βBi2O3can better adsorb N2and cleave the N≡N bond, thereby obtaining a lower NRR rate-limiting energy barrier (*N≡N → *N≡N–H, 0.51 eV). Meanwhile, βBi2O3can effectively suppress HER by limiting proton adsorption (H++ e–→ *H, 0.54 eV). Therefore, βBi2O3-xseries catalysts exhibit higher NH3yield and FE than αBi2O3-x. Meanwhile, in situ FTIR further confirms that βBi2O3could better adsorb/activate N2, and the NRR distal mechanism occurs on the Bi2O3surface. (II) The introduction of NaBH4promotes the conversion of part of Bi3+on the Bi2O3surface into Bi0and releases OVs. The additional active sites (OVs and Bi0) enhance the overall catalyst’s adsorption/activation capacity for N2, further increasing the NH3yield and FE. Meanwhile, semimetal Bi0can effectively limit electron accessibility, thereby inhibiting the combination of charges and adsorbed protons, reducing the HER reaction and improving the FE of NRR. Therefore, the introduction of NaBH4effectively improved the NH3yield and FE of the αBi2O3-xand βBi2O3-xseries catalysts. After optimization, the βBi2O3-0.6 catalyst has the best NRR performance (NH3yield: 51.36 μg h–1mg–1cat.; FE: 38.67%), which is superior to the majority of bismuth-based NRR catalysts. This work not only studies the effects of Bi2O3with different crystal phases on N2and HER reaction but also effectively regulates the active components of Bi2O3surface, thereby realizing efficient NRR to NH3reaction, which provide valuable insights for the rational design of Bi-based NRR electrocatalysts.

In this Letter, a high-quality saturable absorber (SA) based on a multilayered two-dimensional ternary chalcogenide Ta_2NiS_5 with a narrow bandgap, has been successfully fabricated and used as a SA in a 1.9 μm spectral region. The nonlinear saturable absorption properties of the as-prepared SA have been investigated by using an open-aperture Z-scan method. A passively Q-switched all-solid-state laser operating at 1.9 μm has been realized with the Ta_2NiS_5 SA. The maximum average output power, shortest pulse width, pulse energy, and pulse peak power from the passively Q-switched (PQS) laser are 1.1 W, 313 ns, 22.0 μJ, and 71.0 W, respectively. This is the first demonstration of the saturable absorption property of Ta_2NiS_5, to the best of our knowledge. The results indicate well the promising potential of Ta_2NiS_5 as a broadband SA in realizing pulsed mid-infrared lasers with high performance.

For van der Waals (vdW) heterostructures, optical and electrical properties (e.g., saturable absorption and carrier dynamics) are strongly modulated by interlayer coupling, which may be due to effective charge transfer and band structure recombination. General theoretical studies have shown that the complementary properties of graphene and MoS2enable the graphene/MoS2(G/MoS2) heterostructure to be used as an important building block for various optoelectronic devices. Here, density functional theory was used to calculate the work function values of G/MoS2with different thicknesses of MoS2, and its relaxation dynamic mechanism was illustrated. The results reveal that the G/MoS2heterostructure interlayer coupling can be tuned by changing the thickness of MoS2, furthering the understanding of the fundamental charge-transfer mechanism in few-layer G/MoS2heterostructures. The tunable carrier dynamics and saturable absorption were investigated by pump–probe spectroscopy and open-aperture Z-scan technique, respectively. In the experiments, we compared the performances of Q-switched lasers based on G/MoS2heterostructures with different MoS2layers. Taking advantage of ultrafast recovery time and good saturable absorption properties, a femtosecond solid-state laser at 1.0 μm with G/MoS2heterostructure saturable absorber was successfully achieved. This study on interlayer coupling in G/MoS2may allow various vdW heterostructures with controllable stacking to be fabricated and shows the promising applications of vdW heterostructures for ultrafast photonic devices.

Few-layered titanium carbide (Ti_3C_2T_x), a novel two-dimensional (2D) Van der Waals material in the MXene family, was fabricated with a liquid-phase method and applied as a saturable absorber for a continuous-wave mode-locked femtosecond bulk laser. Pulses as short as 316 fs with a repetition rate of 64.06 MHz and maximum output power of 0.77 W were achieved at the central wavelength of 1053.2 nm, demonstrating the first known, to the best of our knowledge, application of MXene in an all-solid-state laser. Considering the flexible band gap for different surface functional groups of Ti_3C_2T_x, these results may promote the development of ultrafast photonics and further applications of 2D optoelectronic layered materials in the infrared and mid-infrared regions.

1T-phase titanium diselenide (1T-TiSe_2), a model two-dimensional (2D) transition metal dichalcogenide, has attracted much attention due to its intriguing electrical and optical properties. In this work, a 1T-TiSe_2-based high-quality large-area saturable absorber (SA) (1T-TiSe_2-SA) was successfully fabricated with the liquid-phase exfoliation method. With the as-prepared 1T-TiSe_2-SA, a stable, passively Q-switched laser operating at 2.95 μm was first realized. Under an absorbed pump power of 3.35 W, the maximum average output power was 130 mW with a slope efficiency of 5%. A pulse width of 160.5 ns was obtained, which is the shortest among 3.0 μm passively Q-switched lasers ever achieved with 2D materials as SAs, to the best of our knowledge. The results indicate that 1T-TiSe_2 is a promising alternative as a nonlinear optical modulator for short-pulse laser generation near the 3.0 μm mid-infrared region.

Metal-organic frameworks (MOFs) are a series of highly porous crystalline materials, which are built from inorganic metal nodes and organic linkers through coordination bonds. Their unique porous structural features (such as high porosity, high surface areas, and highly ordered nanoporous structures) and designable structures and compositions have facilitated their use in gas capture, separation, catalysis, and energy storage and conversion. Recently, the design and synthesis of pure MOFs and their derivatives have opened new routes to develop highly efficient electrocatalysts toward oxygen reduction reactions (ORR) and oxygen evolution reactions (OER), which are the core electrode reactions in many energy storage and conversion techniques, such as metal-air batteries and fuel cells. This review first discusses recent progress in the synthesis and the electrocatalytic applications of pure MOF-based electrocatalysts toward ORR or OER, including pure MOFs, MOFs decorated with active species, and MOFs incorporated with conductive materials. The following section focuses on the advancements of the design and preparation of various MOF-derived materials—such as inorganic nano- (or micro-) structures/porous carbon composites, pure porous carbons, pure inorganic nano- (or micro-) structured materials, and single-atom electrocatalysts—and their applications in oxygen electrocatalysis. Finally, we present a conclusion and an outlook for some general design strategies and future research directions of MOF-based oxygen electrocatalysts.

This article implements the intelligent elderly disease prediction system in order to solve the problem that the existing disease prediction systems lack pertinence for the elderly. The elderly disease prediction model is optimised by adding specific attributes of the elderly based on the attributes selected by automatic attribute selection methods. We use accuracy, sensitivity and specificity to evaluate models' comprehensive performance. The results show that naive Bayes is better than logistic regression, which is more suitable for the intelligent elderly disease prediction system. The structure and class diagram of the system is designed. The intelligent elderly disease prediction system is implemented using the elderly disease prediction model based on naive Bayes.

A novel two-dimensional (2D) material member in the transition metal dichalcogenides family, few-layered rhenium disulfide (ReS_2) was prepared by liquid phase method successfully. By using the open-aperture Z-scan method, the saturable absorption properties at 2.8 μm were characterized with a saturable fluence of 22.6  μJ/cm^2 and a modulation depth of 9.7%. A passively Q-switched solid-state laser at 2.8 μm was demonstrated by using the as-prepared ReS_2 saturable absorber successfully. Under an absorbed pump power of 920 mW, a maximum output power of 104 mW was obtained with a pulse width of 324 ns and a repetition rate of 126 kHz. To the best of our knowledge, this is the first demonstration of applying ReS_2 in an all-solid-state laser. Moreover, this represents the shortest pulses in Q-switched MIR lasers based on a 2D material as the saturable absorber, which demonstrated the superiority of ReS_2 acting as an optical modulator for generating short-pulsed lasers. The results well prove that 2D ReS_2 is a reliable optical modulator for MIR solid-state lasers.

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Terahertz parametric oscillator (TPO) with a rhombic ring-cavity is demonstrated. The oscillating cavity is composed of three mirrors and the terahertz emitting-surface. Terahertz frequency can be tuned from 0.9 THz to 2.9 THz just by shifting the position of a cavity mirror. Under a certain round-trip optical length of the Stokes beam, the pump beam size can be larger in the rhombic ring-cavity TPO than that in the conventional resonant-cavity TPO. The maximum terahertz pulse energy in the rhombic ring-cavity TPO is 3.21 μJ, which is about 3 times higher than that in the conventional resonant-cavity TPO.

The electrocatalytic nitrogen reduction reaction (NRR) to NH3is limited by low Faradaic efficiency (FE). Herein, defective UiO-66-NH2functionalized with quite stable superoxide radicals (O2•) is developed as a highly active NRR catalyst. The experimental and computational results show that one linker per Zr6node is missed and two Zr atoms are exposed in the defective UiO-66-NH2. One of the two exposed Zr atoms can stably adsorb O2•, and thus, a Zr-OO•site forms during the preparations without light excitation or postoxidation, while the other Zr atom is activated as an active site. The synergistic effects of the two Zr sites in the defective UiO-66-NH2suppress hydrogen and hydrazine evolutions considerably. They are as follows: (i) due to repulsion of the proton on the active Zr site and stabilization of the proton on the Zr-OO•site, the active Zr site is unfavorable for the adsorption of the proton with a high energy barrier, which is the HER rate-determining step (RDS); (ii) under the assistance of the OO•of the Zr-OO•site, the first hydrogenation step of *N2(i.e., NRR RDS) on the active Zr site is promoted; and (iii) relying on the assistance of the OO•of the Zr-OO•site, the continuous hydrogenation of *NH2NH2to produce NH3on the active Zr site is spontaneously exothermic, whereas its desorption to hydrazine is blocked. Accordingly, an extremely high FE of ∼85.21% has been realized along with a high yield rate of NH3(∼52.81 μg h–1mgcat–1). To the best of our knowledge, it is the highest FE that has been achieved in recent years. Radical scavenging treatment of the defective UiO-66-NH2and detailed investigations of two categories of control samples further verify the favorable effects of the O2•that closely correlates with the missed linkers on the performance of the NRR to NH3. This work opens a new way toward highly efficient NRR catalysts, i.e., stable radical-activating defective metal–organic frameworks.

We demonstrated a passively Q-switched mode-locked 2.9 µm Ho,Pr:LiLuF4bulk laser based on a semiconductor saturable absorber mirror for the first time, to the best of our knowledge. A stable pulse train with a modulation depth of nearly 100% was obtained. The mode-locked pulse width inside the Q-switched pulse envelope was estimated to be approximately 800 ps with a repetition rate of 47.27 MHz. The maximum average output power was determined to be 146 mW with a Q-switched pulse repetition rate of 18.2 kHz at a center wavelength of 2883 nm.