Development of a biophotonic fiber sensor using direct-taper and anti-taper techniques with seven-core and four-core fiber for the detection of doxorubicin in cancer treatment.

Doxorubicin (DOX) is an important drug for cancer treatment, but its clinical application is limited due to its toxicity and side effects. Therefore, detecting the concentration of DOX during treatment is crucial for enhancing efficacy and reducing side effects. In this study, the authors developed a biophotonic fiber sensor based on localized surface plasmon resonance (LSPR) with the multimode fiber (MMF)-four core fiber (FCF)-seven core fiber (SCF)-MMF-based direct-taper and anti-taper structures for the specific detection of DOX. Compared to other detection methods, it has the advantages of high sensitivity, low cost, and strong anti-interference ability. In this experiment, multi-walled carbon nanotubes (MWCNTs), cerium-oxide nanorods (CeO2-NRs), and gold nanoparticles (AuNPs) were immobilized on the probe surface to enhance the sensor's biocompatibility. MWCNTs and CeO2-NRs provided more binding sites for the fixation of AuNPs. By immobilizing AuNPs on the surface, the LSPR was stimulated by the evanescent field to detect DOX. The sensor surface was functionalized with DOX aptamers for specific detection, enhancing its specificity. The experiments demonstrated that within a linear detection range of 0-10 µM, the sensitivity of the sensor is 0.77 nm/µM, and the limit of detection (LoD) is 0.42 µM. Additionally, the probe's repeatability, reproducibility, stability, and selectivity were evaluated, indicating that the probe has high potential for detecting DOX during cancer treatment.

Boosting Electrocatalytic N2 Reduction to NH3 by Enhancing N2 Activation via Interaction between Au Nanoparticles and MIL-101(Fe) in Neutral Electrolytes.

Electrocatalytic nitrogen reduction reaction (NRR) has attracted much attention as a sustainable ammonia production technology, but it needs further exploration due to its slow kinetics and the existence of competitive side reactions. In this research, xAu/MIL-101(Fe) catalysts were obtained by loading gold nanoparticles (Au NPs) onto MIL-101(Fe) using a one-step reduction strategy. Herein, MIL-101(Fe), with high specific surface area and strong N2 adsorption capacity, is used as a support to disperse Au NPs to increase the electrochemical active surface area. Au NPs, with a high NRR activity, is introduced as the active site to promote charge transfer and intermediate formation rates. More importantly, the strong interaction between Au NPs and MIL-101(Fe) enhances the electron transfer between Au NPs and MIL-101(Fe), thereby enhancing the activation of N2 and achieving efficient NRR. Among the prepared catalysts, 15 %Au/MIL-101(Fe) has the highest NH3 yield of 46.37 µg h-1 mg-1 cat and a Faraday efficiency of 39.38 % at -0.4 V (vs. RHE). In-situ FTIR reveals that the NRR mechanism of 15 %Au/MIL-101(Fe) follows the binding alternating pathway and also indicates that the interaction between Au NPs and MIL-101(Fe) strengthens the activation of the N≡N bond in the rate-limiting process, thereby accelerating the NRR process.

Plasmonic sensor based on offset-splicing and waist-expanded taper using multicore fiber for detection of Aflatoxins B1 in critical sectors.

In this work, authors have developed a portable, sensitive, and quick-response fiber optic sensor that is capable of detection of Aflatoxins B1 (AFB1) quantitatively and qualitatively. Using multi-mode fiber (MMF) and multi-core fiber (MCF), the MMF-MCF-MCF-MMF fiber structure based on symmetric transverse offset splicing and waist-expanded taper is fabricated. The evanescent waves are enhanced to form a strong evanescent field by etching the fiber surface with hydrofluoric acid. To successfully excite the localized surface plasmon resonance phenomenon, gold nanoparticles are deposited on the optical fiber probe's surface. Further, to modify the fiber optic probes, Niobium carbide (Nb2CTx) MXene and AFB1 antibodies are functionalized. Nb2CTx MXene is employed to strengthen the biocompatibility of the sensor and increase the specific surface area of the fiber probe, while AFB1 antibody is used to identify AFB1 micro-biomolecules in a specific manner. The reproducibility, reusability, stability, and selectivity of the proposed fiber probe are tested and validated using various concentration of AFB1 solutions. Finally, the linear range, sensitivity, and limit of detection of the sensing probe are determined as 0 - 1000 nM, 11.7 nm/µM, and 26.41 nM, respectively. The sensor offers an indispensable technique, low-cost solution and portability for AFB1-specific detection in agricultural products and their byproducts with its novel optical fiber structure and superior detecting capability. It is also useful for marine species like fish and consequently affecting health of human body.

Humanoid shaped optical fiber plasmon biosensor functionalized with graphene oxide/multi-walled carbon nanotubes for histamine detection.

Histamine is a biologically active molecule that serves as a reliable predictor of the quality of fish. In this work, authors have developed a novel humanoid-shaped tapered optical fiber (HTOF) biosensor based on the localized surface plasmon resonance (LSPR) phenomenon to detect varying histamine concentrations. In this experiment, a novel and distinctive tapering structure has been developed using a combiner manufacturing system and contemporary processing technologies. Graphene oxide (GO)/multi-walled carbon nanotubes (MWCNTs) are immobilized on the HTOF probe surface to increase the biocompatibility of biosensor. In this instance, GO/MWCNTs are deployed first, then gold nanoparticles (AuNPs). Consequently, the GO/MWCNTs help to give abundant space for the immobilization of nanoparticles (AuNPs in this case) as well as increase surface area for the attachment of biomolecules to the fiber surface. By immobilizing AuNPs on the surface of the probe, the evanescent field can stimulate the AuNPs and excite the LSPR phenomena for sensing the histamine. The surface of the sensing probe is functionalized with diamine oxidase enzyme in order to enhance the histamine sensor's particular selectivity. The proposed sensor is demonstrated experimentally to have a sensitivity of 5.5 nm/mM and a detection limit of 59.45 µM in the linear detection range of 0-1000 µM. In addition, the probe's reusability, reproducibility, stability, and selectivity are tested; the results of these indices show that the probe has a high application potential for detecting histamine levels in marine products.

Slide-type waveflex biosensor based on signal enhancement technology for alpha-fetoprotein detection.

The development of signal enhancement technology in optical fiber biosensors is beneficial for the accurate measurement of low-concentration samples. Here, a localized surface plasmon resonance (LSPR)-based fiber biosensor combining a slide-type fiber structure (thus named WaveFlex Biosensor) and low-dimensional materials is proposed for alpha-fetoprotein (AFP) detection. A symmetric transverse offset splicing technology was used to fabricate the multi-mode fiber (MMF-multi-core fiber (MCF)-MMF structure. Furthermore, the MMF on one side was prepared into an S-taper, forming a slide-type fiber structure to generate more energy leakage. The LSPR signal generated by gold nanoparticles (AuNPs) was enhanced by the CeO2 NPs and C3N quantum dots functionalized on the fiber probe. The excellent performance of NPs was conducive to improving the sensitivity of the WaveFlex biosensor and enabling the rapid detection of samples. An AFP antibody was used to identify AFP micro-biomolecules in a specific manner. Based on the combination of the above two methods, the developed fiber probe was applied to detect AFP, and the sensitivity and limit of detection were 32 pm/(ng/mL) and 6.65 ng/mL, respectively. The experimental results demonstrate that the signal-enhanced AFP WaveFlex biosensor has great potential for the rapid and accurate detection of AFP.

Homemade low-cost fabrication technique and stability analysis of a U-shaped fiber sensor structure.

In this work, the fabrication method of a U-shaped optical fiber (UOF) structure using single-mode fiber is proposed. Few UOF sensors have been developed to date, but the fabrication process has not been described in detail. Here, its subsequent homemade fabrication, optimization strategies, and analysis are thoroughly explored. Further, the influence of transmission on U-shaped diameter is explored. The transmitted intensity is mainly used to assess the strength of the evanescent field. For this purpose, three different diameters of 2 mm, 4 mm, and 6 mm UOFs are fabricated. The results show that the transmission of the U-shaped structure is dependent on the diameter of the UOF. Thereafter, different concentrations of glucose solutions are detected using the optimized stable UOF structure to showcase the sensing properties. Overall, this work is essential for beginners who want to conduct research on optical fiber sensors with a curved shape.

Development of a core-offset-based SMS fiber structure for detection of various biomolecules.

This paper discusses the details about the fabrication of single-mode fiber (SMF)- and multi-mode fiber (MMF)-based core-offset sensor structures for biomolecules detection. SMF-MMF-SMF (SMS) and SMF-core-offset MMF-SMF (SMS structure with core-offset) are proposed in this paper. In the conventional SMS structure the incident light is introduced from the SMF to the MMF and then passes through the MMF to the SMF. However, in the SMS-based core offset structure (COS) the incident light is introduced from the SMF to the core offset MMF and then passes through the MMF to the SMF, and more incident light leaks at the fusion point between the SMF and the MMF. This structure causes more incident light to leak out from the sensor probe, forming evanescent waves. By analyzing the transmitted intensity, the performance of COS can be improved. The results show that the structure of the core offset has great potential for the development of fiber-optic sensors.

Effective splicing technique of different cladding diameter-based optical fibers and performance evaluation.

In this work, the fabrication and sensing performance of fusion structures based on single-mode fiber (SMF) and multimode fiber (MMF) with different cladding diameters are discussed, and the effects of different lengths of MMF and fiber etching on sensing performance are analyzed. First, the transmitted intensity measurement experiment is performed, and the results indicate that the performance of the SMF-MMF-SMF(SMS)-based structure is better for sensing purposes. In addition, the results demonstrate that the performance of etched fiber is better than that of non-etched fiber. The etched fiber structure with lower fiber diameters produces more evanescent waves and is better for sensing purposes. Therefore, the proposed structure has certain development potential as an application of future optical fiber sensors.

Development and stability analysis of an S-tapered optical fiber-based sensor structure.

In this paper, three S-tapered fiber (STF) structures with different diameters (40, 60, and 80 µm) are fabricated using conventional single-mode fiber. First, the reproducibility of the proposed S-tapered structure is confirmed through an analysis of the diameter distribution. Considering the transmitted intensities of the three various diameter, S-tapered structures reveal that the STF with a 40 µm diameter produces more evanescent waves and is more sensitive to external refractive index variations. Therefore, the STF structure with a 40 µm diameter was evaluated for the detection of different concentration of glucose solutions, demonstrating that the structure has the potential to be utilized to develop a highly sensitive fiber sensor.

Sub-60-fs ultralow threshold and efficient Kerr-lens mode-locked Yb,Gd:CaSrF2 laser.

In this Letter, using a Yb,Gd:CaSrF2 co-doping mixed crystal, an ultra-low threshold and efficient Kerr-lens mode-locked femtosecond oscillator is realized with a mode-locking threshold as low as 150 mW. With a 200-mW pump power, the shortest pulses are obtained with a pulse duration of 57 fs. A maximum mode-locked output power of 185 mW is observed under a 500-mW pump power, corresponding to an optical-to-optical efficiency of up to 37%. To the best of our knowledge, the 150-mW threshold is the lowest pump power to realize Kerr-lens mode-locking operation in Yb-doped bulk lasers. Furthermore, an optical efficiency of 37% is the highest efficiency in Yb-doped fluoride bulk lasers to date. Our results provide a new basis for high-efficiency and low-threshold Yb-doped ultrafast bulk lasers.

Feasibility analysis of an SMS-/MSM-/SMSMS-based optical fiber sensor structure.

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.

Performance analysis of an SMF-/MMF-based single/double/quadruple tapered optical fiber structure.

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.

Generation of a square-shaped pulse in mode-locked fiber lasers with a microfiber-based few-layer Nb2C saturable absorber.

Niobium carbide (Nb2C), a novel two-dimensional MXene material, has attracted much attention due to its outstanding electronic and optical properties. In this work, a microfiber-based few-layer Nb2C saturable absorber (SA) is fabricated by the magnetron sputtering deposition technique. The reverse saturable absorption (RSA) response of few-layer Nb2C nanosheets is observed with I-scan measurements. The square-wave pulses (SWPs) are generated by using the as-prepared microfiber-based few-layer Nb2C SA in an erbium-doped fiber laser. The SWP width increases from 0.33 to 2.061 ns with the single pulse energy increases linearly up to 0.89 nJ while the amplitude remains as a constant. In addition, nonlinear polarization rotation mode-locking fiber lasers with different cavity lengths are constructed to explore the formation conditions of SWP. Our results indicate that the RSA effect of the few-layer Nb2C nanosheets plays a decisive role in the formation of the SWP.

Ternary chalcogenide Ta2NiS5 as a saturable absorber for a 1.9 µm passively Q-switched bulk laser.

In this Letter, a high-quality saturable absorber (SA) based on a multilayered two-dimensional ternary chalcogenide Ta2NiS5 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 Ta2NiS5 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 Ta2NiS5, to the best of our knowledge. The results indicate well the promising potential of Ta2NiS5 as a broadband SA in realizing pulsed mid-infrared lasers with high performance.

Multi-wavelength bright-dark pulse pair fiber laser based on rhenium disulfide.

As a new member of transition metal dichalcogenides (TMDs), rhenium disulfide (ReS2), with a nearly unchanged direct bandgap from bulk to monolayer form, is attractive in physics and material fields. By using the optically driving deposition method, the ReS2 saturable absorber (SA) has been fabricated with a modulation depth and saturation fluence of 6.9% and 27.5 µJ/cm2, respectively. Based on the ReS2-SA, a multi-wavelength bright-dark pulse pair from a mode-locked fiber laser has been observed experimentally for the first time, to the best of our knowledge. The saturable absorbing ability of the ReS2 is attributed to the formation of the bright pulses and the dark pulses. The cross-phase modulation (XPM) caused by different wavebands of bright pulse and dark pulse support the coexisting of the bright-dark pulse pair.

High-power passively Q-switched 2.0 µm all-solid-state laser based on a MoTe2 saturable absorber.

In this article, a high-power diode-end-pumped passively Q-switched (PQS) Tm:YAP laser is reported with novel two-dimension (2D) molybdenum ditelluride (MoTe2) as a saturable absorber (SA). By using the open-aperture Z-scan method, the saturable absorption properties around 2.0 µm was characterized with a saturable fluence of 2.26 µJ∕cm2 and a modulation depth of 6.0% for the as-prepared MoTe2 SA. The band structure of MoTe2 with the introduction of Te vacancies is simulated by the DFT method, and the results indicate that the bandgap can be reduced with the vacancies in a suitable range. The shortest pulse width of 380 ns was obtained with an average output power of 1.21 W at a repetition rate of 144 kHz, corresponding to a maximum single pulse energy of 8.4 µJ and peak power of 22.2 W. It is the first presentation of MoTe2 as the saturable absorber in 2.0 µm solid-state pulse laser generation and the pulse width is the shortest among 2.0 µm solid-state lasers passive Q-switched with transitional metal dichalcogenides (TMDs) SAs to the best of our knowledge. The results indicated that MoTe2 should be an excellent optical modulator for high repetition rate and short pulsed laser generation in a broadband spectral range.

Bilayer platinum diselenide saturable absorber for 2.0 µm passively Q-switched bulk lasers.

A noble transition metal dichalcogenide, bilayers platinum diselenide (PtSe2), has a narrow bandgap (0.21 eV) and high charge carrier mobility. This metal was manufactured for use as a saturable absorber via the chemical vapor deposition method. The saturable absorption properties of samples, at a wavelength of 2.0 µm, were characterized by the open aperture Z-scan method. An all-solid-state 2.0 µm passively Q-switched laser was achieved experimentally based on the as-prepared bilayers PtSe2 saturable absorber. The maximum average output power, shortest pulse width, highest single-pulse energy, and highest pulse peak power of this laser were 1.41 W, 244 ns, 24.3 µJ, and 99.6 W, respectively.

Few-layer TiSe2 as a saturable absorber for nanosecond pulse generation in 2.95 µm bulk laser.

1T-phase titanium diselenide (1T-TiSe2), 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-TiSe2-based high-quality large-area saturable absorber (SA) (1T-TiSe2-SA) was successfully fabricated with the liquid-phase exfoliation method. With the as-prepared 1T-TiSe2-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-TiSe2 is a promising alternative as a nonlinear optical modulator for short-pulse laser generation near the 3.0 µm mid-infrared region.

Few-layer Ti3C2Tx (T = O, OH, or F) saturable absorber for a femtosecond bulk laser.

Few-layered titanium carbide (Ti3C2Tx), 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 Ti3C2Tx, these results may promote the development of ultrafast photonics and further applications of 2D optoelectronic layered materials in the infrared and mid-infrared regions.

Biaxial crystal ß-BaTeMo2O9: theoretical analysis and the feasibility as high-efficiency acousto-optic Q-switch.

The high efficiency acousto-optic modulators become indispensable in photonics and optoelectronics for the pulse generation and signal modulation in optical display and telecommunications. In this paper, the validity and feasibility of the biaxial crystals as acousto-optic mediums have been theoretically analyzed and confirmed by experiments using a biaxial crystal of ß-BaTeMo2O9. The diffraction angle and diffraction efficiency of the ß-BaTeMo2O9 acousto-optic Q-switch are determined to be 1.420° and 78.1%, which are comparable with that of TeO2 acousto-optic modulator at the identical operating wavelength of 1064 nm and 100 MHz, respectively. The minimum of the modulated pulse width can be achieved to be 6 ns at 5 kHz with Nd:YVO4 as the gain medium. The results not only provide an excellent acousto-optic medium, but also explore the field of biaxial acousto-optic medium for device fabrications.