Electrical stimulation induces anti-tumor immunomodulation via a flexible microneedle-array-integrated interdigital electrode

Immunotherapy has revolutionized cancer therapy, using chemical or biological agents to reinvigorate the immune system. However, most of these agents have poor tumor penetration and inevitable side effects that complicate therapeutic outcomes. Electrical stimulation (ES) is a promising alternative therapy against cancers that does not involve chemical or biological agents but is limited in the fabrication and operation of complex micrometer-scale ES devices. Here, we present an optically microprinted flexible interdigital electrode with a gold-plated polymer microneedle array to generate alternating electric fields for cancer treatment. A flexible microneedle-array-integrated interdigital electrode (FMIE) was fabricated by combining optical 3D microprinting and electroless plating processes. FMIE-mediated ES of cancer cells induced necrotic cell death through mitochondrial Ca2+ overload and increased intracellular reactive oxygen species (ROS) production. This led to the release of damage-associated molecular patterns that activated the immune response and potentiated immunogenic cell death (ICD). FMIE-based ES has an excellent safety profile and systemic anti-tumor effects, inhibiting the growth of primary and distant tumors as well as melanoma lung metastasis. FMIE-based ES-driven cancer immunomodulation provides a new pathway for drug-free cancer therapy.

Ultraminiature optical fiber-tip directly-printed plasmonic biosensors for label-free biodetection

Miniaturization of biosensors has become an imperative demand because of its great potential in in vivo biomarker detection and disease diagnostics as well as the point-of-care testing for coping with public health crisis, such as the coronavirus disease 2019 pandemic. Here, we present an ultraminiature optical fiber-tip biosensor based on the plasmonic gold nanoparticles (AuNPs) directly printed upon the end face of a standard multimode optical fiber at visible light range. An in-situ precision photoreduction technology is developed to additively print the micropatterns of size-controlled AuNPs. The AuNPs reveal distinct localized surface plasmon resonance, whose peak wavelength provides an ideal spectral signal for label-free biodetection. The fabricated optical fiber-tip plasmonic biosensor can not only detect antibody, but also test SARS-CoV-2 mimetic DNA sequence at the concentration level of 0.8 pM. Such an ultraminiature fiber-tip plasmonic biosensor offers a cost-effective biodetection technology for a myriad of applications ranging from point-of-care testing to in vivo diagnosis of stubborn diseases.

Ultrasensitive optofluidic enzyme-linked immunosorbent assay by on-chip integrated polymer whispering-gallery-mode microlaser sensors

Optical whispering-gallery-mode (WGM) microcavities offer great promise in ultrasensitive biosensors because of their unique ability to enable resonant recirculation of light to achieve strong light-matter interactions in microscale volumes. However, it remains a challenge to develop cost-effective, high-performance WGM microcavity-based biosensing devices for practical disease diagnosis applications. In this paper, we present an optofluidic chip that is integrated with directly-printed, high-quality-factor (Q) polymer WGM microlaser sensors for ultrasensitive enzyme-linked immunosorbent assay (ELISA). Optical 3D μ-printing technology based on maskless ultraviolet lithography is developed to rapidly fabricate high-Q suspended-disk WGM microcavities. After deposition with a thin layer of optical gain material, low-threshold WGM microlasers are fabricated and then integrated together with optical fibres upon a microfluidic chip to achieve an optofluidic device. With flexible microfluidic technology, on-chip, integrated, WGM microlasers are further modified in situ with biomolecules on surface for highly selective biomarker detection. It is demonstrated that such an optofluidic biochip can measure horseradish peroxidase (HRP)-streptavidin, which is a widely used catalytic molecule in ELISA, via chromogenic reaction at the concentration level of 0.3 ng mL-1. Moreover, it enables on-chip optofluidic ELISA of the disease biomarker vascular endothelial growth factor (VEGF) at the extremely low concentration level of 17.8 fg mL-1, which is over 2 orders of magnitude better than the ability of current commercial ELISA kits.

Ultracompact optical fiber acoustic sensors based on a fiber-top spirally-suspended optomechanical microresonator

Acoustic wave sensors with a high sensitivity and small size are highly desired for a wide variety of important and emerging applications such as photoacoustic gas sensing and bio-imaging. Here we present an ultracompact optical fiber acoustic sensor based on an optomechanical resonator that is directly in situ printed on the end face of a standard single-mode optical fiber by using an optical 3D μ-printing technology. The fiber-top optomechanical microresonator is composed of a microscale suspended polymer micro-disk that forms a Fabry-Perot interferometric cavity, together with the optical fiber end face, and acts as the acoustic wave-sensitive micromechanical resonator simultaneously. The microbeams for suspending the micro-disk are devised with a spiral structure to overcome the small-size imposed low deflection amplitude so as to improve its sensitivity to acoustic waves. The sensor with a high sensitivity of 118.3 mV/Pa and low noise equivalent acoustic signal level of 0.328µPa/Hz^1/2 at audio frequency is experimentally demonstrated. Moreover, with a resonance amplification mechanism, the sensitivity can be enhanced by 40.1 times when the frequency of the acoustic wave matches with the natural resonance frequency of the optomechanical resonator. Such an ultrasmall fiber-tip acoustic sensor has not only a miniaturization-induced broad bandwidth, but also a structure-enhanced ultrahigh sensitivity and thus is very promising in various acoustic wave-based sensing, imaging, and testing applications.

[Application value of sedation in colonoscopy]

Objective: To investigate the value of sedation in colonoscopy. Methods: A retrospective cohort study of colonoscopy procedures was performed in our institution. Inclusion criteria: (1) colonoscopy procedures were performed by well-trained gastrointestinal surgeons our institution; (2) medical records were complete and colonoscopy was documented properly by notes, videos, photographs, and traceable pathological reports. Those with incomplete records or performed in other institution were excluded. According to above criteria, clinical data of 49 057 cases of clinic and hospitalization receiving diagnostic or therapeutic colonoscopyat Department of Gastric and Colorectal Surgery, Daping Hospital from July 2007 to February 2017 were collected. Among them, there were 24 638 (50.2%) males and 24 419 females, with mean age of (50.6±14.1) (4 to 98) years. Based on the application of sedation during colonoscopy, patients were divided into the sedation group (39 412 cases, 80.3%) and the non-sedation group (9 645 cases, 19.7%). Clinical characteristics of two groups were compared. Results: The sedation rate increased from 45.6% (369/810) to 94.8% (917/967) from 2007 to 2017. As compared to non-sedation group, a higher proportion of females [51.0% (20 095/39 412) vs. 44.8% (4 324/9 645), χ(2)=117.422, P<0.001] and younger median age (50.0 years vs. 51.0 years, Z=-4.774, P<0.001) were found in the sedation group, whose differences were statistically significant. In all the 9645 cases in the non-sedation group, about 5.5% (534) of them terminated the examination because of unbearable discomfort, including 244 (4.6%) males and 290 (6.7%) females (χ(2)=20.522, P<0.001). Among all the screening population who were ≥50 years old, there was no significant difference in the polyp detection rate (PDR) between the sedation group and the non-sedation group [26.7% (4 737/17 753) vs. 27.4% (1 093/3 984), χ(2)=0.937, P=0.330]. The cecal intubation rate (CIR) in the sedation group was significantly higher than that in the non-sedation group [(85.2% (14 422/16 933) vs. 76.1% (2 803/3 682), χ(2)=180.032, P<0.001]. Five cases in the sedation group developed iatrogenic colonic perforation (ICP), with none in the non-sedation group. Conclusions: The application of sedation in colonoscopy is increasingly popular. Sedation can significantly improve CIR in colonoscopy, while it has no positive influence on PDR. Meanwhile, sedation increases the medical expense and may result in higher ICP rate.

Rapid optical μ-printing of polymer top-lensed microlens array

Microlenses have wide applications for light beam focusing or shaping in micro-optical systems. However, it remains challenging for conventional microfabrication methods to rapidly fabricate arrays of microlenses with complex profiles like lens-on-lens structures. In this paper, we present the rapid fabrication of polymer microlenses with lens-on-lens structures by using a digital optical μ-printing technology. An improved dynamic optical exposure method is developed to directly and precisely fabricate polymer top-lensed microlenses (TLMLs). Arrays of TLMLs with either elongated focal depth or two separate foci have been numerically investigated and experimentally demonstrated.

Ultrafast Light-Controlled Growth of Silver Nanoparticles for Direct Plasmonic Color Printing

A precision photoreduction technology for the ultrafast high-precision light-controlled growth of silver nanoparticles for printing plasmonic color images is presented. Ultraviolet (UV) patterns with about a million pixels are generated to temporally and spatially regulate the photoreduction of silver salts to precisely create around a million clusters of distinct silver nanoparticles on a titanium dioxide (TiO₂)-capped quartz substrate. The silver nanoparticle-TiO₂-quartz structure exhibits a Fano-like reflection spectrum, whose spectral dip can be tuned by the dimension of the silver nanoparticles for plasmonic color generation. This technology allows the one-step production of multiscale engineered large-area plasmonic substrates without the use of either nanostructured templates or additional nanofabrication processes and thus offers an approach to plasmonic engineering for a myriad of applications ranging from structural color decoration to plasmonic microdevices and biosensors.

Solution-Processed Bilayer Dielectrics for Flexible Low-Voltage Organic Field-Effect Transistors in Pressure-Sensing Applications

Flexible pressure sensors based on organic field-effect transistors (OFETs) have emerged as promising candidates for electronic-skin applications. However, it remains a challenge to achieve low operating voltages of hysteresis-free flexible pressure sensors. Interface engineering of polymer dielectrics is a feasible strategy toward sensitive pressure sensors based on low-voltage OFETs. Here, a novel type of solution-processed bilayer dielectrics is developed by combining a thick polyelectrolyte layer of polyacrylic acid (PAA) with a thin poly(methyl methacrylate) (PMMA) layer. This bilayer dielectric can provide a vertical phase separation structure from hydrophilic interface to hydrophobic interface which adjoins well to organic semiconductors, leading to improved stability and remarkably reduced leakage currents. Consequently, OFETs using the PMMA/PAA dielectrics reveal greatly suppressed hysteresis and improved mobility compared to those with a pure PAA dielectric. Using the optimized PMMA/PAA dielectric, flexible OFET-based pressure sensors that show a record high sensitivity of 56.15 kPa-1 at a low operating voltage of -5 V, a fast response time of less than 20 ms, and good flexibility are further demonstrated. The salient features of high capacitance, good dielectric performance, and excellent reliability of the bilayer dielectrics promise a bright future of flexible sensors based on low-voltage OFETs for wearable electronic applications.

Optical Fiber-Tip Sensors Based on In-Situ µ-Printed Polymer Suspended-Microbeams

Miniature optical fiber-tip sensors based on directly µ-printed polymer suspended-microbeams are presented. With an in-house optical 3D μ-printing technology, SU-8 suspended-microbeams are fabricated in situ to form Fabry–Pérot (FP) micro-interferometers on the end face of standard single-mode optical fiber. Optical reflection spectra of the fabricated FP micro-interferometers are measured and fast Fourier transform is applied to analyze the cavity of micro-interferometers. The applications of the optical fiber-tip sensors for refractive index (RI) sensing and pressure sensing, which showed 917.3 nm/RIU to RI change and 4.29 nm/MPa to pressure change, respectively, are demonstrated in the experiments. The sensors and their optical µ-printing method unveil a new strategy to integrate complicated microcomponents on optical fibers toward ‘lab-on-fiber’ devices and applications.

Optical µ-Printing of Cellular-Scale Microscaffold Arrays for 3D Cell Culture

Guiding cell culture via engineering extracellular microenvironment has attracted tremendous attention due to its appealing potentials in the repair, maintenance, and development of tissues or even whole organs. However, conventional biofabrication technologies are usually less productive in fabricating microscale three-dimensional (3D) constructs because of the strident requirements in processing precision and complexity. Here we present an optical µ-printing technology to rapidly fabricate 3D microscaffold arrays for 3D cell culture and cell-scaffold interaction studies on a single chip. Arrays of 3D cubic microscaffolds with cubical sizes matching the single-cell size were fabricated to facilitate cell spreading on suspended microbeams so as to expose both apical and basal cell membranes. We further showed that the increasing of the cubical size of the microscaffolds led to enhanced spreading of the seeded human mesenchymal stem cells and activation of mechanosensing signaling, thereby promoting osteogenesis. Moreover, we demonstrated that the spatially selective modification of the surfaces of suspended beams with a bioactive coating (gelatin methacrylate) via an in-situ printing process allowed tailorable cell adhesion and spreading on the 3D microscaffolds.

[Expression of NF-κB in a degenerative human intervertebral disc model]

Objective: To investigate the changes in the expression of NF-κB signaling pathway in human degenerative intervertebral discs. Methods: From October 2014 to March 2016, 55 nucleus pulposus of surgical patients with degenerative human intervertebral disc were collected for study in Department of Orthopedic Surgey, Hospital of Zaozhuang Mining Corporation, and Department of Orthopedics, Shanghai General Hospital Affiliated Shanghai Jiaotong University, School of Medicine.The collected nucleus pulposus tissues were divided into two groups: experimental group(30) and control group(25). Cell culture observed normal and degenerative nucleus pulposus cells morphological changes; immunofluorescence observed NF-κB p65 changes in the nucleus of nucleus pulposus cells.Real-time PCR was observed changes in aggregated proteoglycans and matrix metalloproteinase gene mRNA.Finally, the use of blockers of nucleus pulposus cells were treated 24 hours, Western blot analysis the changing of p65, ADAMTS-4, MMP-13, aggregate proteoglycans and collagen Ⅱ protein expression. Results: Compared with the experimental group, the nucleus pulposus cells in the control group had larger cell volume, abundant cytoplasm and faster growth rate.Cell immunofluorescence show Nondegenerative nucleus pulposus cells p65 protein was mainly localized in the cytoplasm, degeneration of nucleus pulposus cells p65 protein was mainly concentrated in the nucleus.RT-PCR showed degenerative group of matrix metalloproteinases (MMP-1, MMP-3, MMP-13), aggrecanase(ADAMTS-4, ADAMTS-5) and IL-6 mRNA expression was significantly higher than Nondegenerative group; aggrecan and type Ⅱ collagen expression than those without degeneration group was significantly lower.Expression of nucleus pulposus degeneration in nuclear protein p65 with the degenerative level increased gradually increased.BAY11-7082 blocked the activity of NF-κB signaling pathway, which could significantly down-regulate the expression of ADAMTS-4 and MMP-13 protein and significantly up-regulate the expression of Agg and COLⅡ protein.With the increase of BAY11-7082 concentration, gradually strengthened. Conclusion: The activation of the NF-κB signaling pathway in a degenerative intervertebral disc is gradually increased, regulating the over-expression of matrix-degrading enzymes.It plays an important role in the degradation of extra-cellular matrix.

Optofluidic tunable mode-locked fiber laser using a long-period grating integrated microfluidic chip

An optofluidic tunable mode-locked fiber laser using a microfluidic chip integrated with long-period grating (LPG) is presented. The microfluidic chip enables ultrafine adjustment of the liquid's refractive index and, thus, LPG's spectrum via tuning the mixing ratio of the microfluidic flows. With such an optofluidic spectrum-tunable filter, the central wavelength of the mode-locked laser can be tuned continuously, while the mode-locking state is steadily maintained. The mode-locked pulses are measured with a pulse duration of 0.9 ps and repetition rate of 12.14 MHz, respectively. Moreover, bound solitons with variable soliton separations are experimentally demonstrated.

Tunable scalar solitons from a polarization-maintaining mode-locked fiber laser using carbon nanotube and chirped fiber Bragg grating

Generation of tunable scalar solitons from a polarization-maintaining (PM) mode-locked fiber laser is presented. A single-walled carbon nanotube (SWCNT) absorber is used for self-started mode locking. A chirped fiber Bragg grating (CFBG) mounted on a cantilever is employed as a tunable all-fiber filter. Mode-locked solitons are obtained with typical pulse duration of ~6.94 ps and repetition rate of 28.94 MHz. Linearly polarized laser emission is characterized with degree of polarization (DOP) of ~99.5%. The wavelength of the emitted scalar soliton can be continuously tuned through adjusting the CFBG, while maintaining the polarization stability.

Optical fiber LPG biosensor integrated microfluidic chip for ultrasensitive glucose detection

An optical fiber sensor integrated microfluidic chip is presented for ultrasensitive detection of glucose. A long-period grating (LPG) inscribed in a small-diameter single-mode fiber (SDSMF) is employed as an optical refractive-index (RI) sensor. With the layer-by-layer (LbL) self-assembly technique, poly (ethylenimine) (PEI) and poly (acrylic acid) (PAA) multilayer film is deposited on the SDSMF-LPG sensor for both supporting and signal enhancement, and then a glucose oxidase (GOD) layer is immobilized on the outer layer for glucose sensing. A microfluidic chip for glucose detection is fabricated after embedding the SDSMF-LPG biosensor into the microchannel of the chip. Experimental results reveal that the SDSMF-LPG biosensor based on such a hybrid sensing film can ultrasensitively detect glucose concentration as low as 1 nM. After integration into the microfluidic chip, the detection range of the sensor is extended from 2 µM to 10 µM, and the response time is remarkablely shortened from 6 minutes to 70 seconds.

Rapid 3D Patterning of Poly(acrylic acid) Ionic Hydrogel for Miniature pH Sensors

Poly(acrylic acid) (PAA), as a highly ionic conductive hydrogel, can reversibly swell/deswell according to the surrounding pH conditions. An optical maskless -stereolithography technology is presented to rapidly 3D pattern PAA for device fabrication. A highly sensitive miniature pH sensor is demonstrated by in situ printing of periodic PAA micropads on a tapered optical microfiber.

Rapid 3D µ-printing of polymer optical whispering-gallery mode resonators

A novel microfabrication method for rapid printing of polymer optical whispering-gallery mode (WGM) resonators is presented. A 3D micro-printing technology based on high-speed optical spatial modulator (SLM) and high-power UV light source is developed to fabricate suspended-disk WGM resonator array using SU-8 photoresist. The optical spectral responses of the fabricated polymer WGM resonators were measured with a biconically tapered optical fiber. Experimental results reveal that the demonstrated method is very flexible and time-saving for rapid fabrication of complex polymer WGM resonators.

Widely tunable mode-locked fiber laser using carbon nanotube and LPG W-shaped filter

A widely tunable mode-locked fiber laser using a carbon nanotube absorber and a fiber-optic W-shaped spectral filter is presented. The W-shaped filter is constructed by sandwiching a phase-shifted long-period grating between two LPGs of different periods. By adjusting the temperature of the W-shaped filter from 23°C to 100°C, the central wavelength of the mode-locked fiber laser can be continuously tuned from 1597 to 1553 nm. The tuning range is further extended to 1531.6 nm when a shorter erbium-doped fiber is used in the fiber oscillator. The experimental results reveal that the large thermal tunability of the proposed LPG filter provides an effective approach to achieve compact widely tunable mode-locked fiber lasers covering both C and L bands.

Integrated microfluidic flowmeter based on a micro-FBG inscribed in Co²⁺-doped optical fiber

A novel microfluidic flowmeter integrated with microfiber Bragg grating (µFBG) is presented. Two glass capillaries and a short length of high-light-absorption Co²⁺-doped optical fiber were stacked inside a larger outer capillary tube. The stack was then drawn into a tapered device. Two microchannels with the diameter of ~50  μm were formed inside the capillaries for flowing of microfluidics. An FBG was inscribed in the tapered Co²⁺-doped fiber with waist diameter of ~70  μm, and acts as a flow-rate sensor. A pump laser with wavelength of 1480 nm was utilized to locally heat the µFBG, rendering the µFBG as miniature "hot-wire" flowmeter. The flow rate of the liquid in the microchannels is determined by the induced wavelength shift of the µFBG. The experimental results achieve a minimum detectable change of ~16  nL/s in flow rate, which is very promising in the use as part of biochips.

In-line open-cavity Fabry-Pérot interferometer formed by C-shaped fiber fortemperature-insensitive refractive index sensing

We report an open-cavity optical fiber Fabry-Pérot interferometer (FPI) capable of measuring refractive index with very low temperature cross-sensitivity. The FPI was constructed by splicing a thin piece of C-shaped fiber between two standard single-mode fibers. The refractive index (RI) response of the FPI was characterized using water-ethanol mixtures with RI in the range of 1.33 to 1.36. The RI sensitivity was measured to be 1368 nm/RIU at the wavelength of 1600 nm with good linearity. Thanks to its all-glass structure, the FPI exhibits very low temperature cross-sensitivity of 3.04 × 10⁻⁷ RIU/°C. The effects of cavity length on the performance of the sensor were also studied. A shorter cavity gives rise to broader measurement range while offering larger detection limit, and vice versa. What's more, the effect of material dispersion of analyte on the sensitivity of open-cavity FPIs was identified for the first time. The sensor is compact in size and easy to fabricate. It is potentially useful for label-free optical sensing of chemical and biological samples.

In-line microfluidic integration of photonic crystal fibres as a highly sensitive refractometer

Photonic crystal fibres appear to be an ideal platform for the realisation of novel optofluidic devices and sensors due to their waveguide nature and microstructured architecture.

Digital microfabrication of user-defined 3D microstructures in cell-laden hydrogels

Complex 3D interfacial arrangements of cells are found in several in vivo biosystems such as blood vasculature, renal glomeruli, and intestinal villi. Current tissue engineering techniques fail to develop suitable 3D microenvironments to evaluate the concurrent effects of complex topography and cell encapsulation. There is a need to develop new fabrication approaches that control cell density and distribution within complex 3D features. In this work, we present a dynamic projection printing process that allows rapid construction of complex 3D structures using custom-defined computer-aided-design (CAD) files. Gelatin-methacrylate (GelMA) constructs featuring user-defined spiral, pyramid, flower, and dome micro-geometries were fabricated with and without encapsulated cells. Encapsulated cells demonstrate good cell viability across all geometries both on the scaffold surface and internal to the structures. Cells respond to geometric cues individually as well as collectively throughout the larger-scale patterns. Time-lapse observations also reveal the dynamic nature of mechanical interactions between cells and micro-geometry. When compared to conventional cell-seeding, cell encapsulation within complex 3D patterned scaffolds provides long-term control over proliferation, cell morphology, and geometric guidance. Overall, this biofabrication technique offers a flexible platform to evaluate cell interactions with complex 3D micro-features, with the ability to scale-up towards high-throughput screening platforms.

Homogeneous acylation of eucalyptus wood at room temperature in dimethyl sulfoxide/N-methylimidazole

Succinoylation and benzoylation of ball-milled eucalyptus wood using succinic anhydride and benzoyl chloride as acylating reagent, respectively, were investigated at room temperature using dimethyl sulfoxide/N-methylimidazole (DMSO/NMI) as reaction medium without additional catalysts. The effects of the corresponding acylating reagent dosage (1-5:1 for succinoylation and 0.5-5:1 for benzoylation) and reaction time (0.35-5h for succinoylation and 0.5-3h for benzoylation) on the extent of acylation, measured by weight percent gain (WPG), were studied. WPG of succinoylation and benzoylation was in the range of 70.8-144.7% and 17.3-43.1%, respectively. The efficiency of acylation at room temperature significantly increased in DMSO/NMI compared with ionic liquid 1-butyl-3-methylimidazolium chloride because of the role of NMI as solvent, base and catalyst. Fourier transform infrared (FT-IR), and solid-state cross-polarization/magic-angle spinning (CP/MAS) (13)C nuclear magnetic resonance (NMR) spectroscopy studies provided evidence for the occurrence of succinoylation and benzoylation reactions and the attachment of functional groups via ester bonds.

Rapid fabrication of complex 3D extracellular microenvironments by dynamic optical projection stereolithography

The topographic features of the extracelluar matrix (ECM) lay the foundation for cellular behavior. A novel biofabrication method using a digital-mirror device (DMD), called dynamic optical projection stereolithography (DOPsL) is demonstrated. This robust and versatile platform can generate complex biomimetic scaffolds within seconds. Such 3D scaffolds have promising potentials for studying cell interactions with microenvironments in vitro and in vivo.

Nonlinear fiber-optic strain sensor based on four-wave mixing in microstructured optical fiber

We demonstrate a nonlinear fiber-optic strain sensor, which uses the shifts of four-wave mixing Stokes and anti-Stokes peaks caused by the strain-induced changes in the structure and refractive index of a microstructured optical fiber. The sensor thus uses the inherent nonlinearity of the fiber and does not require any advanced postprocessing of the fiber. Strain sensitivity of -0.23 pm/με is achieved experimentally and numerical simulations reveal that for the present fiber the sensitivity can be increased to -4.46 pm/με by optimizing the pump wavelength and power.

Selective excitation and coupling of high-order optical modes of a microstructured optical fiber by using a fiber-end microtip

We present the selective excitation and coupling of high-order optical modes in microstructured optical fibers (MOFs) by using a fiber-end microtip. After the self-growing of a microtip on the end face of a standard single-mode fiber, it is demonstrated that a fine tuning of the relative displacement between the microtip and MOF can greatly improve the excitation and coupling efficiency of high-order optical modes of the MOF. A 6.85 dB improvement in coupling efficiency of the second-order mode of a homemade small-hole MOF is experimentally achieved, and a sensitivity-enhanced measurement of the refractive index in MOF microholes is demonstrated.

Compact microfiber Bragg gratings with high-index contrast

We fabricate fiber Bragg grating (FBG) in microfibers (MFs) using focused ion beam milling technique. By periodically etching 100 nm-depth grooves on the surface of silica MFs with diameters less than 2 μm, evident grating features with transmission dip up to 15 dB are obtained. Because of the high-index contrast of the gratings structure, the length of the microfiber Bragg grating (MFBG) can be reduced to 500 μm level. Using a 518 μm-length 1.8 μm-diameter MFBG, we also demonstrate sensitivity up to 660 nm per refractive index unit (RIU) for refractive index (RI) sensing. The highly compact MFBGs demonstrated here may serve as low-dimensional building blocks for miniaturized photonic components and devices.

All-optical fiber anemometer based on laser heated fiber Bragg gratings

A fiber-optic anemometer based on fiber Bragg gratings (FBGs) is presented. A short section of cobalt-doped fiber was utilized to make a fiber-based "hot wire" for wind speed measurement. Fiber Bragg gratings (FBGs) were fabricated in the cobalt-doped fiber using 193 nm laser pulses to serve as localized temperature sensors. A miniature all-optical fiber anemometer is constructed by using two FBGs to determine the dynamic thermal equilibrium between the laser heating and air flow cooling through monitoring the FBGs' central wavelengths. It was demonstrated that the sensitivity of the sensor can be adjusted through the power of pump laser or the coating on the FBG. Experimental results reveal that the proposed FBG-based anemometer exhibits very good performance for wind speed measurement. The resolution of the FBG-based anemometer is about 0.012 m/s for wind speed range between 2.0 m/s and 8.0 m/s.

Optical fiber relative humidity sensor based on FBG incorporated thin-core fiber modal interferometer

A new fiber-optic relative humidity (RH) sensor based on a thin-core fiber modal interferometer (TCFMI) with a fiber Bragg grating (FBG) in between is presented. Poly (N-ethyl-4-vinylpyridinium chloride) (P4VP·HCl) and poly (vinylsulfonic acid, sodium salt) (PVS) are layer-by-layer deposited on the side surface of the sensor for RH sensing. The fabrication of the sensing nanocoating is characterized by using UV-vis absorption spectroscopy, quartz crystal microbalance (QCM) and scanning electron microscopy (SEM). The incorporation of FBG in the middle of TCFMI can compensate the cross sensitivity of the sensor to temperature. The proposed sensor can detect the RH with resolution of 0.78% in a large RH range at different temperatures. A linear, fast and reversible response has been experimentally demonstrated.

Low-cost high-performance fiber-optic pH sensor based on thin-core fiber modal interferometer

A new fiber-optic pH sensor based on a thin-core fiber modal interferometer with electrostatic self-assembled nanocoating is presented. After inserting a segment of thin-core fiber into a standard single-mode fiber, high-order cladding modes are excited and interfere with the core mode to form an in-fiber modal interferometer. The side surface of the sensor is then deposited with poly(allylamine hydrochloride) and poly(acrylic acid) nanocoating by electrostatic self-assembly technique. A fast and linear response is obtained in either acid or alkali solution (in the pH range 2.5 to 10) with resolution of 0.013 pH unit.

Fabrication of a compact reflective long-period grating sensor with a cladding-mode-selective fiber end-face mirror

A long-period grating (LPG) based compact optical fiber sensor working in reflection mode is demonstrated. A technique to make a mirror on the cladding region of a fiber end-face to reflect only the cladding modes was realized by growing a polymeric microtip on the core region of the fiber end-face, by photopolymerization, followed by coating the fiber end-face with an aluminum film. Using the cladding-mode-selective fiber end-face mirror, the transmission spectrum of the LPG was "inverted" and reflected. Preliminary results of using the sensor to measure the refractive index of glycerol/water solutions were successfully demonstrated.

Double-layer fabrication scheme for large-area polymeric photonic crystal membrane on silicon surface by multibeam interference lithography

We report on the fabrication of two-dimensional polymeric photonic crystal membranes on the surface of silicon using visible-light multibeam interference lithography. The structures are created by the interference of three beams of a green laser. A polymer buffer layer doped with a Rhodamine B laser dye, interlaid between the lithography layer and the silicon substrate, suppresses the effects of strong reflection and nonradiative absorption of silicon on the interference pattern. Large-area defect-free photonic crystal membranes are experimentally realized on silicon surface.

Succinoylation of sugarcane bagasse under ultrasound irradiation

The chemical modification of sugarcane bagasse with succinic anhydride using pyridine as solvent after ultrasound irradiation was studied. The optimized parameters included ultrasound irradiating time 0-50 min, reaction time 30-120 min, succinic anhydride concentration by the ratio of dried sugarcane bagasse to succinic anhydride from 1:0.25 to 1:1.50, and reaction temperature 75-115 degrees C are required in the process. The extent of succinoylation was measured by the weight percent gain (WPG), which increased with increments of reaction time, succinic anhydride concentration, and reaction temperature. The ultrasound irradiation has a positive effect on bagasse succinoylation process. On the other hand, the ultrasonic pre-treatment application broke down the cell wall polymers, resulting in, therefore, a negative effect on the WPG. Evidences of succinoylation were also provided by FT-IR and CP MAS (13)C NMR and the results showed that the succinoylation at C-2 and C-3 occurred. The thermal stability of the succinylated bagasse decreased upon chemical modification.

Homogeneous modification of sugarcane bagasse cellulose with succinic anhydride using a ionic liquid as reaction medium

The homogeneous chemical modification of sugarcane bagasse cellulose with succinic anhydride using 1-allyl-3-methylimidazolium chloride (AmimCl) ionic liquid as a reaction medium was studied. Parameters investigated included the molar ratio of succinic anhydride/anhydroglucose units in cellulose in a range from 2:1 to 14:1, reaction time (from 30 to 160min), and reaction temperature (between 60 and 110 degrees C). The succinylated cellulosic derivatives were prepared with a low degree of substitution (DS) ranging from 0.071 to 0.22. The results showed that the increase of reaction temperature, molar ratio of SA/AGU in cellulose, and reaction time led to an increase in DS of cellulose samples. The products were characterized by FT-IR and solid-state CP/MAS (13)C NMR spectroscopy, and thermal analysis. It was found that the crystallinity of the cellulose was completely disrupted in the ionic liquid system under the conditions given. The data also demonstrated that homogeneous modification of cellulose with succinic anhydride in AmimCl resulted in the production of cellulosic monoester. The thermal stability of the succinylated cellulose decreased upon chemical modification.

Optical low-coherence reflectometry based on long-period grating Mach-Zehnder interferometers

The optical low-coherent interferometric technology for long-period grating (LPG) Mach-Zehnder interferometers is described. By including the coupling and recoupling behaviors of a LPG pair, a numerical model is developed to analyze the output reflectogram of the system. The effects of the grating interval, grating length, grating strength, and light source on the output reflectogram have been comprehensively discussed, which reveals that the low-coherence reflectometry offers the capability of interrogating the multiplexed sensors based on LPG pairs. A comparison of the calculated and experimental results is presented, and an excellent agreement between the simulation and the measurement is shown.

Mode recoupling in a novel Bragg grating pair

A new type of mode recoupling in a Bragg grating pair, in which one of the gratings is written in the fiber cladding, is proposed to overcome limitations of concatenated long-period and fiber Bragg gratings reported earlier [Opt. Lett. 27, 1214 (2002)]. Its reflection spectrum is similar to that of the previously reported concatenated grating structure; however, the reflectivity can be much larger than the previous limitation of 50%. Furthermore, avoidance of the loss induced by a long-period grating makes such a Bragg grating pair more attractive for practical applications.