The measurement of pH in small objects (cells, drops of liquid etc.) using optical fluorescence-based sensors on optical
fiber tapers is one of the most widely used optical techniques. In these sensors the diameter of the taper can play
important role for collecting fluorescence from tested samples. This paper presents results of experimental measurements
of fluorescence intensity of dye sensitive to pH in a solution that is excited by a blue laser. The fluorescence of the dye is
collected by a taper tip. The fiber tips were prepared from a graded-index fiber with a core diameter of 50 μm.
Measurements with taper tips of different diameters have allowed us to estimated a limited tip diameter necessary for
collecting any fluorescence form the dye solution on a level of about 5μm.
Local chemical sensing in living cells by fluorescence methods with submicron spatial resolution is in the scope of
biologist because of bringing new information about biochemical processes in living matter [1]. One of the most
important monitored variables is pH. Despite of progress of novel submicron probes suitable for in-situ measurement in
living cells [1] and biological micro samples [2] still there is a lack off suitable opto-chemical transducers sensitive
around pH 5-7 limiting development of novel fluorescence sensors. Moreover, the interaction of the immobilized
transducer with the matrix can strongly affect its fluorescence properties.
In our contributition the 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF) fluorescence pH transducer
was incorporated into organosols based on tetraethylorthosilicate (TEOS), 3-glycidoxypropyltrimethoxysilane (GPTMS)
and 3-aminopropyltriethoxysilane (APTES). Formed organosols were spin-coated onto Pyrex glass substrates and
thermally treated at 140°C for 4 hours. Prepared thin layers were exposed to Britton-Robinson buffers with different pH
ranging from 4 to 8 pH units. Optical properties of immobilized BCECF were investigated by the mean of absorption and
fluorescence spectroscopy Acquired results were compared with the properties of BCECF solutions. It was found that all
matrices reduce the sensitivity of the BCECF transducer comparing to the free solution. GPTMS and APTES contained
layers exhibited better mechanical properties and increase the solubility of BCECF inside prepared layers comparing to
layers prepared from pure TEOS.
A size of tapered silica fibre probes makes them suitable for exploration of small objects, as e.g. cells. Fibre-optic probes
of enhanced mechanical durability can be advantageously used particularly for investigation of plant cells with hard
walls. The paper deals with preparation of suitable optical probes based on coated fibre tapers and their using for local
detection of extracellular pH in samples simulating native conditions of plant cells.
Fibre tapers from single-mode and polymer-clad-silica fibres were prepared by tapering apparatus of own construction.
The drawn tapers were immediately coated with a thin layer of Indium-Tin-Oxide in order to protect them from
embrittlement. A CO2 laser was used for cutting the tapered fibres in narrow taper waist. Opto-chemical transducer 2',7'-
Bis(2-carbonylethyl)-5(6)-carboxyfluorescein was immobilized onto the end-face of cut fibre tapers by a thin TEOS
layer. The pH was determined by fluorescence spectroscopy using excitation wavelength 473 nm.
The fibre taper probes of waist diameter from 80 μm to 2 μm and of suitable optical and mechanical properties were
prepared. Suitability of opto-chemical transducer 2',7'-Bis(2-carbonylethyl)-5(6)-carboxyfluorescein for detection of
samples simulating native conditions of pH ranging from 5.0 to 7.0 was confirmed. This approach has allowed us to
determine extra-cellular pH of in-vitro samples.
In this paper we present a novel method for the measurement of the thickness of the sensing layer applied on the tip
of an optical fiber and fiber tapers. The method is based on analysis of distributions of the fluorescence intensity
over this layer.
In experiments the fluorescence of the sensing layer prepared by the sol-gel method was investigated be means of a
confocal microscope Zeiss LS5 Duo. The fluorescence was excited at 477 nm by an Ar laser and detected in a
spectral range from 518 to 600 nm. The fluorescence distribution was determined by scanning the layer in the
direction of the taper axis (z-direction) with a step of 500 nm in an overall length of 42 μm and 26 μm. The layer
thickness was estimated from the measured distribution of fluorescence intensity. Assumptions of method are that
close to the layer boundary the fluorescence intensity decreases with z2, the concentration of fluorescence centers in
the layer is homogenous and attenuation of excitation wavelength in the sensing layer is neglected. This method has
made possible to investigate sensing layers with thicknesses of about 1 μm.
This paper presents new experimental results on the sensitivity of a microstructure fiber (MSF) to toluene and ethanol
in gaseous mixtures with nitrogen. This sensitivity is compared with that determined with a single-capillary fiber (CF).
The results obtained both with the fibers modified by a porous detection layer prepared by the sol-gel method from
tetraethoxysilane are presented. MSF with air holes arranged in one shell and coated with an UV acrylate jacket was
prepared by using the "stack and draw" technique. CF coated with polydimethylsiloxane optical cladding was prepared.
The segments of the prepared fibers were modified by a porous polysiloxane layer applied onto the hole walls. The
sensitivity of the MSF and SCF to gaseous toluene and ethanol in nitrogen was determined from spectral changes of C-H
and O-H absorption bands in a range of 1300-1800 nm. Limits of detection of 0.008 and 0.02 vol.% have been
determined for toluene and ethanol, respectively.
The paper presents new experimental results on the sensitivity of three types of microstructure fibers (MSFs) modified
by xerogel layers to aromatic hydrocarbons, namely to toluene. MSFs with air holes with diameters in a range 10 - 50
&mgr;m, arranged in one, two or three rings, were prepared and their segments were used in sensing experiments. Capillary
silica fibers (CFs) were also fabricated for reference sensing measurements. Segments of the fabricated MSFs and CFs
were modified by thin xerogel layers applied onto the hole walls by the sol-gel method from sols based on
tetraethoxysilane or methyltriethoxysilane. For sensing experiments, the segments were fixed in a special cell making it
possible to control the excitation of the fiber and flow of gaseous chemicals through the air holes. The sensitivity of the
MSFs and SCFs to gaseous mixtures of toluene in nitrogen was determined from spectral changes of the output light
from the fibers in a range of 1600-1800 nm. Experimental results show that the sensitivity of MSFs depends on their
architecture, particularly on the arrangement, diameters and number of air holes. A detection limit of about 0.007 vol.%
of toluene has been achieved.
The paper examines the fabrication and properties of silica optical fibers suitable for the development of evanescent- wave fiber-optic sensors. Attention is given to factors increasing the fraction of power transmitted in the evanescent wave. The effects of the refractive-index profile and fiber bending in the evanescent-wave area and their relation to the sensor sensitivity are investigated. A simple thermometer is developed on the basis of these effects. Approaches for the modification of optical properties in the evanescent-wave area are examined. In this part, porous layers prepared by the sol-gel method based on the silicon and titanium alkoxides and standard polysiloxane polymer coatings are described. The sol-gel derived layers are investigated from the point of view of preparing an optical core with a porous part. The possibilities of controlling the refractive index, as well as absorption coefficient of the coatings by immobilizing pH indicators and Cu2+-phthalocyanine are shown together with examples of using evanescent-wave sensing structures for the detection of organophosphorous compounds and pH measurements.
Two novel modifications of the MCVD process extended with the 'solution doping' technique are presented and used for reproducible preparation of preforms with a high content of P2O5 (up to 20 mol.%) and rare-earth ions (up to 36000 ppm) in the Al2O3-P2O5-SiO2 core. Erbium-doped and ytterbium-sensitized silica optical fibers have been fabricated by this method and used for the investigation of fiber lasers emitting at 1550 nm when pumped at 1064 nm. The relation between the core composition, conditions during the stages of the preform fabrication and the final fiber properties are discussed resulting in a conclusion that lasing of the fibers is influenced by central perturbations of the refractive- index profile. Fibers which can be characterized by a slope efficiency of up to 20% and laser threshold of 400 - 500 mW measured under Fresnel reflection from the fiber end have been fabricated.
The radiation-induced light absorption in bulk quartz, Polymer Clad Silica (PCS) and Gradient-Index (GI) fibers is studied. The radiation-induced absorption spectra of four kinds of bulk quartz samples in UV wavelength region are measured. The new absorption band around 215 nm is found, the increase of the sample absorption is attributed to the impurity content. Radiation-induced attenuation spectra of PCS fibers drawn from the bulk quartz materials are shown. The dependence the radiation-induced attenuation on the fiber diameter in the PCS fibers is related to the changes in the silicone optical cladding. The radiation- induced light attenuation in GI fibers is studied in the wavelength range of 450 to 1000 nm. The radiation-induced absorption band centered around 560 nm and the shift of the UV absorption edge towards the longer wavelengths are found. Simple experimental schemes are proposed on the base of these results and tested for radiation dosimetry purposes including the measurements in the nuclear power plant Dukovany.
The precise far-field scanning measurement is used for determination of a spot-size wavelength dependence of real single-mode (SM) fibers. Both Gauss's and Petermann's formulas for mode field radius (MFR) calculation are used and compared. The results of spot- size measurement by transverse-offset (TO), knife-edge-scan (KE) in far field, and far-field pattern (FFP) techniques are compared.
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