Bent Optical Fiber Probe Research Articles

An optical fiber chlorogenic acid sensor using a Chitosan membrane coated bent optical fiber probe

Hydrogel polymers have hydrophilic function groups bonded on the polymer's backbone network. Water molecules and compounds soluble in aqueous solution can permeate into hydrogel's network. This property was employed in this work in developing an optical fiber chemical sensor for detecting chlorogenic acid (CGA). A Chitosan membrane was coated on a bent optical fiber probe (BOFP) by simply dipping the BOFP into a Chitosan solution, which was made by dissolving solid Chitosan in a 2 % acetic acid solution, and pulling out. When such a Chitosan-coated BOFP was exposed to CGA in an aqueous sample solution, CGA molecules permeate into the Chitosan membrane, and were detected through monitoring the compound's intrinsic optical absorption signal at 400 nm. Chitosan has one amine group on each of its glucose rings, which helps the membrane concentrating CGA (a weak acid) from aqueous sample solution. Therefore, the sensor shows high sensitivity in detecting CGA with a detection limit of 0.018 μg/mL. The sensor's response to CGA is reversible, because CGA permeation into/out of the polymer network is a reversible process. The effectiveness of the developed sensor for detecting CGA was verified though analyzing CGA in green coffee extract products. The analytical results obtained with the developed sensor agree well with results obtained with a traditional UV/Vis optical absorption spectrometric method. The effectiveness of the sensor for analyzing CGA in green coffee extract samples was also verified through standard addition and recovery experiment with obtained recovery rate ranging from 97 % to 100 %.

An Optical Fiber ${\rm H}_{2}{\rm O}_{2}$-Sensing Probe Using a Titanium(IV) Oxyacetylacetonate Immobilized Nafion Coating on an Bent Optical Fiber Probe

An optical fiber sensor technique has been developed for monitoring trace H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> in aqueous solutions. A titanium(IV) oxyacetylacetonate doped Nafion coating on the surface of a bent optical fiber probe was used as a transducer. Trace H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> in an aqueous solution diffused into the polymer coating reacts with the sensing agent. The resulted product absorbs light with peak absorption wavelength at 360 nm, which is detected by using optical fiber evanescent wave absorption spectrometry. This sensor reversibly responses to trace H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> in water, and has a detection limit (3σ) of 7.4 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">*</sub> 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> mole H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /L. This fiber-optic sensor is immune of interferences from electromagnetic field which makes it useful in proton exchange membrane fuel cell researches.

Kelvin probe force microscope with near-field photoexcitation

We developed a combined probe microscope—a scanning probe near-field optical microscope (SNOM) combined with Kelvin probe force microscope (KFM) that uses a slim and bent optical fiber probe (S/B fiber probe). The developed SNOM-KFM system enables near-field photoexcitation through an apex of the S/B fiber probe during KFM measurement, so that the photoexcitation effects on surface potential (SP) can be measured with submicron spatial resolution. By measuring the SP of tris(8-hydroxyquinolinato) aluminum(III) (Alq3) thin films, we found that the S/B fiber probes have large negative values in the KFM transfer function. Near-field photoexcitation was performed on Alq3 thin films through the S/B fiber probes, and the spatial pattern of photoinduced reduction in SP was visualized by KFM measurement with the same probe.

Silver nanoparticles doped silica nanocomposites coated on an optical fiber for ammonia sensing

Silver doped silica nanocomposite was synthesized via a sol–gel technique combined with a nanoparticle preparing method using a thiol stabilizer ((3-mercaptopropyl)trimethoxysilane). The freshly prepared sol sample of Ag-doped silica nanocomposite was investigated by transmission electron microscope (TEM). Determined from the TEM image, the sizes of the Ag nanoparticles are around 25 nm. The Ag-doped silica nanocomposite was coated as a membrane on the surface of a bent silica optical fiber by using a dip-coating technique. The response of this coated bent optical fiber probe to trace ammonia in a gas sample was investigated by using a fiber optic spectrometric method. It was found that the exposure of the nanocomposite coated bent optical fiber probe to an ammonia containing gas sample enhances the attenuation of light power guided through the fiber probe. This response is reversible. Ammonia in a gas sample down to sub-ppm level can be continuously monitored with this sensing technique.

Optical fiber ammonia sensing probes using reagent immobilized porous silica coating as transducers

Optical fiber probes for sensing ammonia vapor in gas samples and trace ammonia dissolved in water were developed. An organic dye was immobilized in a porous silica membrane with a sol–gel process as an ammonia indicator. The organic dye immobilized porous silica membrane was coated on the surface of a bent optical fiber core. The coated optical fiber probe was tested for sensing ammonia vapor in gas samples using fiber optic UV–vis absorption spectrometry. An optical fiber ammonia vapor probe with a PDMS protection coating was tested for sensing trace ammonia in water samples. The characteristics of the bent optical fiber probes for sensing ammonia vapor in gas samples and trace ammonia in water samples were studied. Test results indicate that the optical fiber ammonia vapor probe can detect ammonia vapor in a gas sample down to 13ppb, and the PDMS protection coated optical fiber ammonia probe can detect ammonia in a water sample down to 5ppb. Low cost, simple structured fiber optic sensors for detecting ammonia vapor in gas samples and trace ammonia dissolved in water can be developed based on the result reported in this paper.

Phase Separation in Supported Phospholipid Bilayers Visualized by Near-Field Scanning Optical Microscopy in Aqueous Solution

An experimental approach for near-field scanning optical microscopy (NSOM) of biological samples in an aqueous environment with a resolution of <100 nm has been developed. This was accomplished by using high-throughput bent optical fiber probes prepared by a two-step chemical etching method followed by focused ion beam milling to fabricate a reproducible aperture. The utility of the method for high-resolution fluorescence imaging of biological samples in liquid was demonstrated using phase separated, supported phospholipid bilayers as models for natural membranes. Bilayers with a phase separated dipalmitoyl−phosphatidylcholine/dilauroyl−phosphatidylcholine (DPPC/DLPC) mixture in one or both leaflets were imaged by both atomic force microscopy and NSOM. The addition of dihexadecanoyl-sn-glycero-3-phosphoethanolamine−Texas Red (DHPE−TR) was used to visualize fluid and gel phases for the NSOM fluorescence measurements. Hybrid bilayers with 7:3 DLPC/DPPC in the bottom leaflet and DPPC on top showed phase sepa...

Nanostructure patterns written in polycarbonate by a bent optical fiber probe

An atomic force microscope operated in tapping mode using a homemade bent optical fiber probe was used to pattern nanometer-scale features. Trenches of different dimensions were written on polycarbonate that was pre-exposed to an excimer laser. Lines with widths varying from 260 to 600 nm and depths ranging from 30 to 120 nm have been made. The present technique as a complementary tool to other lithographic processes has been demonstrated to be potentially suitable for low-cost and high-precision applications.

Imaging of DNA molecules by scanning near-field microscope

We utilized a novel scanning near-field optical microscope (SNOM) for imaging DNA molecules. The microscope system was constructed with a commercial inverse microscope and a newly developed scanning unit. In the system, a bent optical fiber probe is used to operate in a dynamic mode atomic-force microscope (AFM). A λDNA solution of 5 μM (base) with 5 μM and 500 nM YOYO-1 was prepared and cast on a γ-APTES treated cover slip. The λDNA was aggregated in line and immobilized on the cover slip. The percentage of fluorescence intensity of λDNA with 5 μM YOYO-1 showed integers at almost each point on the DNA. As the fluorescence intensity correlated with the areas of a cross-section of the DNA topography, it appeared that YOYO-1 intercalated in the DNA homogeneously. The fluorescence images of λDNA with 500 nM YOYO-1, however, were irregular and did not correlate with the area of the topographic cross-section, suggesting that YOYO-1 did not intercalate in the λDNA uniformly in this concentration and intercalated cooperatively.

Application to dielectric, metallic, and magnetic samples of a transmission mode scanning near field optical microscope with normal force distance regulation on bent optical fibers

We have developed a scanning near field optical microscope (SNOM) based on bent optical fiber probes with a normal force atomic force microscopies (AFM) regulation. The optical fibers are used both as optical probes and AFM cantilevers. This SNOM was especially developed for transmission mode SNOM and it offers the possibility to realize simultaneously all AFM modes imaging and optical analysis. The fiber is used to illuminate the sample and the detection is performed through an inverted optical microscope. This article presents results obtained on dielectric, metallic, and magnetic samples with submicronic features. We have resolved the object of 80 nm in size, separated by 40 nm, and we illustrate the capabilities of our SNOM in investigating, locally, the variation of the optical properties of periodic samples, even though contaminant, and for a large variety of samples.

近接場磁気光学顕微鏡用プローブの偏光特性と磁気光学像

The scanning near-field optical microscope (SNOM) is well known as a tool for observing nano-structures. On that account, a SNOM to which a certain magneto-optical (MO) measurement technique is applied, or MO-SNOM, is likely to become a powerful tool for nanometric studies on magnetism. In our study, a transmission-illumination mode SNOM with a bent optical fiber probe, which operates as a cantilever in atomic force microscopy (AFM), was employed. Incorporation of the polarization modulation technique into this system has made it possible to resolve magnetic structures with a high sensitivity of up to 1 mrad and a resolution of approximately 1/5 times the wave-length of the light source (argon ion laser: 488 nm). The behavior of polarized light in the probes, however, prevents quantitative analysis of MO effects. This paper describes an investigation into the polarization properties of the bent optical fiber probes, based on their Stokes parameters. A method for acquiring pure signals dependent on ellipticity or rotation in MO imaging is presented.

Scanning probe optical microscopy of evanescent fields

Two new methods for probing evanescent fields using a Dimension™ 3000 atomic force microscope (AFM) from Digital Instruments are described. The first method uses a fiber-optic pickup probe to collect light generated by a commercial silicon AFM probe, which perturbs the evanescent field. The pickup probe is mounted directly onto the AFM cantilever probe holder so that it tracks with the AFM probe tip as it scans a sample but is positioned in such a manner as to permit the use of conventional laser deflection distance regulation. The second method uses a novel bent optical fiber probe with a chemically etched conical quartz tip to perturb the evanescent field together with a metallized cladding to collect the scattered light.

Polarization properties of light emitted by a bent optical fiber probe and polarization contrast in scanning near-field optical microscopy

This article describes the polarization properties of light emitted by a bent optical fiber probe which is used for scanning near-field optical microscopy operated in atomic force mode (SNOM/AFM). SNOM/AFM can be applied to the observation of magnetic domains by imaging polarization contrast in transmission mode. A bent optical fiber probe with a subwavelength aperture is vibrated vertically as a cantilever for atomic force microscopy. Plane polarized light with an extinction ratio of better than 70:1 was emitted by the aperture by controlling the polarization state of incident light to the probe. A particular transverse polarization component of light transmitting a sample is selected by a polarization analyzer and detected. We obtained clear polarization contrast images of 0.7 μm length bits written with a conventional method using a focused laser beam on a bismuth-substituted dysprosium-iron-garnet film.

Polarization effect in scanning near-field optic/atomic-force microscopy (SNOM/AFM)

The polarization effect is reported using a bent optical fiber probe for a scanning near-field optic/atomic-force microscope (SNOM/AFM). We have demonstrated that the SNOM/AFM could be applied to the observation of magnetic domains by imaging polarization contrast in transmission mode. An optical fiber probe with a subwavelength aperture is bent and vibrated vertically as a cantilever for an atomic-force microscope (AFM) for atomic-force regulation. Plane polarized light with an extinction ratio of better than 70 : 1 was emitted by the aperture of the bent probe by controlling the polarization properties of incident light to the probe. By detecting a particular transverse polarization component of light transmitting a sample selected by a polarization analyzer, we obtained clear polarization contrast images of 0.7 μm length bits written on a bismuth-substituted dysprosium-iron-garnet film.

Optical fiber structures studied by a tapping-mode scanning near-field optical microscope

A tapping-mode scanning near-field optical microscope system with a bent optical fiber probe has been successfully developed to study the near-field optics at fiber end faces. Topographic and near-field intensity images of fiber end faces were obtained simultaneously. A brief and gentle etching process on fiber end faces in a saturated solution of ammonium bifluoride was able to reveal the structures of fibers. The topographic features generated by different local chemistry is closely related to the local doping concentration and the distribution of refractive index. The correlation between fiber structures and their near-field intensity profiles of propagating modes can be acquired directly by this novel method. Fibers of step-index, graded-index, single-mode, multimode, and circular, or noncircular geometry were imaged with a near-field resolution.

Near-field optical recording on the cyanine dye layer of a commercial compact disk-recordable

A tapping-mode near-field scanning optical microscope system with a bent optical fiber probe has been successfully developed to deliver the optical energy to the surface of cyanine dye layer of a commercial compact disk-recordable. The interference and damage result from the force-sensing laser beam can be avoided by using a bent fiber probe. Results of our optical writing showed the size of writing bits can be &amp;lt;40 nm. The estimated writing density may be 400 times higher than available commercially. We have also found the heating of metal coating at the end of fiber probe can perform thermal writing. Atomic force microscope images showed the raised edge of writing bits caused by this thermal writing effect. For the pure optical writing, we found the depth of writing bits should be controlled in a range less than the probe height maintained by the feedback electronics.

Resolution of an optical image of a scanning near-field optical/atomic force microscope as a function of sample-probe distance during synchronized irradiation

We examined the resolution of optical images of scanning near-field optical/atomic force microscope (SNOAM) by synchronizing the modulated light to be probe vibration. The system examined in this paper, which we have developed previously, uses a sharpened and bent optical fiber probe. The probe was vibrated vertically toward the specimen stage by dynamic-mode atomic force microscopy function. We controlled the phase and the range of the modulated light using a phase shifter to change the irradiation position. The resolution of optical images showed remarkable change over a 40 rm vertical range of the irradiation position from the sample surface. We obtained the best resolution of the optical image by optimizing the phase and the range of the irradiation. The aperture size was estimated to be 55 nm by comparing the best optical image and topography of our standard pattern.