Quantitative high-resolution sensing of DNA hybridization using magnetic tweezers with evanescent illumination

We applied the combined approach of evanescent nanometry and force spectroscopy using magnetic tweezers to quantify the degree of hybridization of a single synthetic single-stranded DNA oligomer to a resolution approaching a single-base. In this setup, the 200 nucleotide long DNA was covalently attached to the surface of an optically transparent solid support at one end and to the surface of a superparamagnetic fluorescent microsphere (force probe) at the other end. The force was applied to the probes using an electromagnet. The end-to-end molecular distance (i.e. out-of-image-plane position of the force probe) was determined from the intensity of the probe fluorescence image observed with total-internal reflectance microscopy. An equation of state for single stranded DNA molecules under tension (extensible freely jointed chain) was used to derive the penetration depth of the evanescent field and to calibrate the magnetic properties of the force probes. The parameters of the magnetic response of the force probes obtained from the equation of state remained constant when changing the penetration depth, indicating a robust calibration procedure. The results of such a calibration were also confirmed using independently measured probe-surface distances for probes mounted onto cantilevers of an atomic force microscope. Upon hybridization of the complementary 50 nucleotide-long oligomer to the surface-bound 200-mer, the changes in the force-distance curves were consistent with the quantitative conversion of 25% of the original single-stranded DNA to its double-stranded form, which was modeled as an elastic rod. The method presented here for quantifying the hybridization state of the single DNA molecules has potential for determining the degree of hybridization of individual molecules in a single molecule array with high accuracy.     

Optical fiber chemical sensors utilizing dye-doped silicone polymer claddings

Transparent dimethyl siloxane network polymers with refractive indices near 1.40 may be applied to fused silica fibers (n = 1.458) as they are drawn to produce plastic-clad silica (PCS) optical fibers. The evanescent tail of the light energy propagating in the core of such fibers extends into the silicone cladding, where it interacts with chemical species present in the polymer. If the silicone is doped with a dye, the absorption spectrum or fluorescence spectrum of the dye is reflected in the transmission spectrum of the fiber. Further, if the dye changes its absorption spectrum or fluorescence spectrum as a result of diffusion of a chemical species into the silicone, the change is detectable in the fiber output. The polymer material properties which determine the performance of these sensors are described, along with examples of sensors for ammonia and oxygen which utilize either color changing or fluorescent dyes.     

Cure monitoring of the liquid composite molding process using fiber optic sensors

Fluorescence has been demonstrated to be an accurate tool for monitoring resin cure. It is measured using an evanescent wave fiber-optic sensor. An economical optical fiber sensor has been developed with a refractive index greater than 1.6, permitting evanescent wave monitoring of epoxy resins. The fluorescence wave-length-shift, which has been correlated with monomer conversion, is monitored during the liquid molding process. Unidirectional glass fabrics with volume fractions from 40% to 60% were injected with epoxy resin at a variety of driving pressures and cured at several temperatures. Several composite parts were fabricated to test the effects of vacuum pressure, injection rate, cure temperature, and fiber fraction on the performance of the sensor. The sensitivity of the evanescent wave fluorescence sensor to the condition of the resin system was also examined. The sets of resin/hardener samples were subjected to rigorous chemical analysis to determine the extent of their differences.     

In-situ monitoring of product shrinkage during injection molding using an optical sensor

We have used an optical fiber sensor for in-situ monitoring of product shrinkage during injection molding. The sensor, consisting of a bundle of optical fibers with a sapphire window at its end, is positioned in the ejector pin channel of the mold so that the sapphire window sits flush with the inside wall of the mold cavity. The optical view with this sensor is through the thickness (3.175 mm) of the molded product. The fiber bundle is divided into light excitation fibers and light collection fibers. Light from a helium neon laser is transmitted to the resin via the excitation fibers and the detected response is light that reflects from any interface at which there is a difference of index of refraction. When the molded product shrinks, it separates from the wall and sapphire window, and establishes the geometry of a Fabry-Perot interferometer. During the molding of polystyrene, polypropylene and polyethylene, we observed optical interference fringes that were generated by the movement of the molded product away from the mold wall and window. By counting fringes, a measurement of shrinkage was made. Sensor behavior is described by a model that takes into account the reflection coefficient at each surface, the change in index of refraction of the resin and the coherence of the excitation light. The model has been used to describe asymmetric product shrinkage.     

La2O3-Al2O3-SiO2 Glasses for High-Power, Yb3+-Doped, 980-nm Fiber Lasers

Single-mode semiconductor pumps have failed to keep pace with the increasing power requirements of Er-doped fiber amplifiers (EDFAs), so there is a need for high-powered 980-nm sources. Yb³⁺-doped tapered fiber lasers can provide high-power output by conversion of a low-brightness, high-powered, 920-nm, multimode broad stripe laser diode to a high-brightness, 980-nm, single-mode output. The tapered fiber laser requires a fiber with high numerical aperture (NA) (>0.4), a rectangular core, and good Yb³⁺ spectroscopy for efficient operation. CVD-based fiber fabrication methods are incapable of delivering fibers with an NA > ∼0.3 or with good efficiency at 980 nm so a new method of high-NA fiber fabrication was developed. The core glass composition is critical for maintaining a high-NA fiber with good power extraction while avoiding phase separation, loss, and clustering. The SiO₂ level controlled the NA and interdiffusion between core and clad, while the Al₂O₃/La₂O₃ ratio controlled phase separation. A La₂O₃-Al₂O₃-SiO₂ glass was developed that is compatible with a pure SiO₂ cladding glass and has a laser slope efficiency of 70% at 980 nm. The optimized fiber composition yielded 450 mW of 980-nm power in a single-mode fiber.     

The influence of surface modifications of glass on glass fiber/polyester interphase properties

Unsized glass fibers and planar glass substrates were subjected to low temperature plasma or wet-chemical process to modify the fiber or substrate surface and thus influence the interphase properties of the glass/polyester system. Plasma-polymerized thin films (interlayers) of organosilicon monomers (hexamethyldisiloxane and vinyltriethoxysilane) were deposited in an RF helical coupling plasma system on the glass surface. Commercial silane coupling agent (vinyltriethoxysilane) was coated onto an unmodified glass surface from an aqueous solution. Bonding at the glass/interlayer interface was analyzed by employing a micro-scratch tester together with an optical polarizing microscope for the planar samples. The results revealed that the adhesion bonding could be controlled by plasma process parameters. Scanning electron and atomic force microscopies enabled characterization of the film surface morphology. Chemical composition and chemical structure of prepared interlayers were characterized using X-ray photoelectron and infrared spectroscopies. Microcomposites (macrocomposites) were tested to evaluate the interfacial shear strength (short-beam strength) of the glass fiber/polyester interphase using the microbond test (short-beam shear). Our study indicated that the most efficient interphase could be prepared by plasma polymerization or wet-chemical process using the vinyltriethoxysilane monomer. The short-beam strength was 110% higher than that for untreated fibers in both cases.     

Conjugated polyelectrolytes--conformation-sensitive optical probes for staining and characterization of amyloid deposits

Specific markers for diseases associated with protein aggregate depositions are of great interest. Here we report the use of conjugated polyelectrolytes as conformation-sensitive optical probes for histological labeling of amyloid deposits in ex vivo tissue samples-amyloid light chains in primary systemic amyloidosis, islet amyloid polypeptide in human pancreas, and Abeta amyloid in Alzheimer's disease. Under suitable conditions, these probes bind specifically to amyloid deposits, and this is seen as an orange-red emission from the polyelectrolyte. Furthermore, the probes emit light of different colors when bound to different amyloid deposits or other intracellular structures. This phenomenon is most probably due to differences in the protein conformation in these structures. Hence, different protein conformations will generate geometric alterations of the bound polyelectrolyte backbone, affording different emissions from the bound probe. Conformation-sensitive probes thus provide a direct link between spectral signal and protein conformation. Finally, the probes also proved useful for ex vivo fluorescence imaging by multiphoton excitation.     

Influence of chemical polishing on fluorophosphate fiber preform

Surface treatment of optical glass fibers is an effective method to clean the impurities and remove the damage layer, such as scratches caused by the cold processing. Optical losses at the fiber core/cladding interface can thereby be decreased. Using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), we studied the surface composition and morphology of fluorophosphate (FP) glass after polishing and chemical etching. In addition, we investigated the etching mechanism and the optimal concentration of etching solution. Results show that the surface composition is very close to that of the bulk glass for some elements, and the root-mean-square (RMS) roughness is approximately 0.821 nm. A method including acid–alkali pretreatment and a second polishing step is a novel way to improve the smoothness of surface and to eliminate defects such as contaminants and scratches.     

Upconversion nanoparticles for sensitive and in-depth detection of Cu(2+) ions

Detection of Cu(2+) ions and study of their subcellular distribution in physiological processes are of considerable significance because of their potential environmental and biological applications. Some fluorescence based sensors have been developed for selective detection of Cu(2+) ions, based on organic fluorescent probes that specifically bind to Cu(2+) ions. However, these sensors are not suitable for detection in biological samples due to the short penetration depth of UV/visible light used to excite the fluorescent probes. The use of near-infrared (NIR) light can afford penetration depths of an order of magnitude greater than that of visible light, however, a material that can convert NIR light to visible light is required. A facile method has been developed for in-depth detection of Cu(2+) ions based on fluorescence upconversion. A mesoporous silica shell is coated on upconversion nanoparticles (UCNPs) and a Cu(2+) ion sensitive fluorescent probe, rhodamine B hydrazide, is incorporated into the mesoporous silica. Upon excitation by a NIR light, the UCNPs emit visible light to excite the Cu(2+)-sensitive fluorescent probe. Because of the unique optical properties of UCNPs and their ability to convert NIR light to visible light, this is a feasible method for sensitive and in-depth detection of Cu(2+) ions in a complex biological or environmental sample due to the low autofluorescence and the high penetration depth of NIR light.     

Chemical applications of near-field scanning optical microscopy: Surface and near-surface chemical imaging with conventional near-field optical probes and externally illuminated chemically active ion sensors

Near-field optics using force sensing cantilevered optical fibers and micropipettes is used to investigate the chemical distribution of protein complexing dyes in chromosomes and the sensing and chemical imaging of surfaces and nearsurface regions. These results are put in the context of what presently can be considered as a broad picture of near-field optical chemical applications.     

Friction and wear bahavior of short fiber-reinforced poly(amide-imide) composites

Tribological behavior of short fiber-reinforced thermoplastic composites was investigated experimentally and theoretically. Short carbon fiber and glass fiber reinforced poly(amide-imide) composites were tested. Titanium oxide powder-filled composite was also tested for comparison with the fiber composites. Block-on-ring type wear testing was performed for 24 h at three different sliding conditions. Frictional force was measured and stored by a data acquisition system and wear was measured as weight loss after the test. Wear tracks on the specimen and the counterface were examined with an optical microscope to observe fiber damage and formation of wear film. The equivalent stress distribution around each fiber at the sliding surface was calculated by employing a finite element program. The lowest friction and wear was obtained for the carbon fiber composite, the highest friction for the glass fiber composite, and the highest wear for TiO₂-filled one. It was observed that the glass fibers are damaged and removed from the surface more easily than the carbon fibers, and the finite element analysis also suggests easier debonding of glass fibers.     

Er~(3+)-Tm~(3+)共掺碲酸盐玻璃中近红外超宽带发光性质

研究了Er~(3+)-Tm~(3+)共掺TeO_2O-Nb_2O_5-Ln_2O_3(TKNL)碲酸盐玻璃的近红外发光光谱以及上转换光谱性质,该碲酸盐玻璃的起始析晶温度与玻璃转变温度之差△T为136℃,表明此玻璃具有良好的热稳定性,有利于拉制光纤。在808 nm半导体激光器的激发下在近红外波段观察到半高宽为185 nm的宽带近红外发光。通过对不同Tm~(3+)浓度以及不同激发波长下TKNL玻璃的近红外发光以及上转换发光的研究,探讨了Er~(3+)m~(3+)之间的能量传递机理。上述玻璃材料有望用作S和C波段光纤放大器的增益介质。     

Design and fabrication of SCPOF preform doped with rare earth complexes

Segmented‐cladding fibers (SCF) consist of a uniform core of high refractive index and a cladding with regions of high and low refractive index alternating angularly, which can effectively realize single mode with a large core diameter. Because polymer optical fibers are usually of large diameter, theoretical model for SCF was further extended to segmented‐cladding polymer optical fibers (SCPOF) doped with rare earth complex in this article. On the basis of the physical principle, a material model for SCPOF was established, from which refractive index and glass transition temperature of polymer materials was predetermined for the core and cladding of SCPOF, respectively. According to the model, a preform for SCPOF was fabricated with the core doped with Eu(DBM)₃Phen that has characteristic emission at 613 nm under excitation at 365 nm. From results of fluorescence photograph, it is clearly seen that the expected preform has been obtained by a two‐step method developed in this work. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Rethinking Optical Fiber: New Demands,Old Glasses

From a materials perspective optical fibers are victims of their own success. The advent of the laser, 50 yr ago, coupled with an insatiable demand for information enabled by light‐based communications, ushered in a golden age of glass science and engineering. It is somewhat ironic that the staggering ubiquity of information today, which is carried globally and almost instantaneously via optical fibers, is enabled largely by one material—silica—into which only a few components are added. The richness of the Periodic Table has largely been forgotten. The purpose of this study was to rethink the materials that can be used to make commercially relevant optical fibers and describe the extraordinary properties, with stimulated Brillouin scattering being the primary exemplar, of fibers made from otherwise ordinary materials. In particular, this study focuses on the use of the molten core approach to optical fiber fabrication and the novel yet practical fibers that can be produced. This study is purposely provocative and aims to reassert the centrality (and simplicity and beauty) of glass science as the best approach to meet future challenges for high‐performance optical fibers.     

Theoretical analysis of the thermally induced delamination of polymeric coatings in double-coated optical fibers

To maintain its mechanical strength, the glass fiber of optical fibers is coated by polymeric materials during the fabrication process, However, when the thermally induced shear stress at the interface of the glass fiber and primary coating is larger that its adhesive stress, the adhesive bond between the glass fiber and primary coating will be broken. When the polymeric coatings are delaminated from the glass fiber, the optical fiber will lose its mechanical strength. In this article, the thermally induced delamination of polymeric coatings in double-coated optical fibers is investigated. To minimize the coating's delamination, the thermally induced shear stress at the interface of the glass fiber and primary coating should be reduced. The method to minimize such a shear stress is to select suitable polymeric coatings as follows: The thickness and Poissòn's ratio of the primary coating should be increased, but the Young's modulus of the primary coating and the thickness, Young's modulus, and thermal expansion coefficient of the secondary coating should be decreased. Finally, the optimal design of commercialized double-coated optical fibers to minimize the thermally induced coating's delamination is also discussed.     

LTCC Microfluidic System

A simple and inexpensive low-temperature cofired ceramic (LTCC) microfluidic device with integrated optical fibers is designed, manufactured, and tested with positive results. Fluidic channels, mixer, detector, optical fiber, light source, light detector, heater, and temperature sensor are integrated in one LTCC module. The optical system in the LTCC microsystem permits measurements of light transmittance and fluorescence. The design, technology, and results of the module's evaluation are presented.     

Tribological analysis of glass fibers using atomic force microscopy (AFM)/lateral force microscopy (LFM)

By using atomic force microscopy (AFM)/lateral force microscopy (LFM), a comparative study of the topography as well as the tribological properties (at a micrometer scale) of sized E‐glass fibers was done. Normal and lateral deflection signals are recorded when an AFM tip scans a fiber surface. Friction force data were obtained from the forward and backward scans of lateral force images whose contrasts reveal differences in friction coefficient values and, hence, surface chemical heterogeneity of certain‐sized glass fibers. Sizes having an epoxy film former lead to a higher friction coefficient value than those containing a starch film former. Moreover, the epoxy‐containing size is more readily plowed by the AFM tip. Annealing of this size lowers its friction coefficient. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1013–1025, 2000     

Surface Analysis and Treatment of Extruded Fluoride Phosphate Glass Preforms for Optical Fiber Fabrication

Fabrication of fluoride phosphate glass optical fibers using the extrusion method for preform fabrication has been studied using the commercial Schott N‐FK51A glass. The extrusion step was found to create a surface layer of differing composition from the bulk glass material, leading to defects drawn down onto the optical fiber surface during fiber fabrication, resulting in high loss and fragile fibers. Similar phenomena have also been observed in other fluoride‐based glasses. Removal of this surface layer from preforms prior to fiber drawing was shown to improve optical fiber loss from >5 dB/m to 0.5–1.0 dB/m. The removal of this surface layer is therefore necessary to produce low‐loss fluoride phosphate optical fibers.     

Fluorescence monitoring of twin screw extrusion

An optical fiber probe has been constructed in order to obtain real-time measurements of fluorescence radiation during twin screw mixing and extrusion of plasticized polybutadiene and calcium carbonate particulate. The probe consists of an optical fiber bundle which was inserted along the axis of a half-inch sensor bolt, and it was used to transmit optical excitation energy to the processed material and to detect the subsequent fluorescence. The source of fluorescence radiation was a fluorescent dye which was doped into the processed ingredients at very low concentrations. Although most of our measurements were taken with the probe positioned close to the exit die, the sensor bolt can be placed in any instrumentation port along the extruder line. Experiments were carried out to measure residence time distribution, quality-of-mix, and mix concentrations as a function of processing conditions. Product mix changes in response to variations in material feed rates and screw RPM were also observed. Values of residence time were obtained by measuring the transit times for the dye to travel from an upstream injection port to the measurement probe, a distance of 63 cm. Flow instabilities, such as mat formation of the solids, were observed by noting the abrupt changes and discontinuities in the fluorescence signal.     

玻璃光纤制品医用消毒试验分析

通过对玻璃光纤制品进行常规的4种医用消毒试验，发现干热法和湿热法医用消毒对玻璃光纤制品基本无影响，但药物法和辐射法消毒则对玻璃光纤制品产生出不同程度损伤。试验发现，可以通过改变光学玻璃材料或增加表面增强技术等方法适应不同医用消毒方法，并提出了制造适合医用消毒的化学稳定性强的环保型光学玻璃、耐辐射光学玻璃、可拓宽玻璃光纤光传输波段光学玻璃以及研究玻璃光纤束表面增强技术的必要性和时代性。