Determining the pH values of microscopic plant samples may help to explain complex processes in plants, so it is an area of interest to botanists. Fiber-optic probes with small dimensions can be used for this purpose. This paper deals with the fiber-optic detection of the pH values of droplets of plant xylem exudate based on ratiometric fluorescence intensity measurements with an internal reference. For this purpose, novel V-taper sensing probes with a minimum diameter of around 8 μm were prepared that enable the delivery of fluorescence signal from the detection site on the taper tip to the detector. The taper tips were coated with pH-sensitive transducer (8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt; HPTS) and a reference [dichlorotris-(1,10-phenanthroline) ruthenium (II) hydrate (Ru-phen dichloride)] immobilized in a xerogel layer of propyltriethoxysilane and (3-glycidoxy)propyl trimethoxysilane. The prepared probes were sensitive to pH values mainly in the range from 6.0 to 9.0. In the pH range 6-9, the results were limited by measurement errors of about 0.2 pH units, and in the pH range 5-6 by measurement errors of about 0.5 pH units. Using the developed V-taper sensing probes, the pH values of in vivo and in vitro samples of small volumes (~6 μl) of exudate were measured. The results were validated by comparison with conventional electrochemical pH measurements.
Mammalian bodies are hierarchical systems whose internal cooperation and coherent activity require high capacity information transfer between the central control unit--the brain--and the periphery--the organs. A communication system capable of meeting information capacity requirements should be based on transmission of electromagnetic signals. Structures that fulfill requirements for such information transfer have not yet been analyzed. Acupuncture meridians have been demonstrated experimentally in some animals. They might represent systems of information transfer between the brain and the peripheral organs. The ducts of the meridians may correspond to optical fibers operating from the far infrared to the visible wavelength region. The main features of a model of the duct as an optical fiber are delineated and its properties outlined. However, to analyze essentials of the transmission capabilities, the whole meridian structure should be mapped and a more comprehensive set of physical parameters measured. In particular, experimental data concerning morphological arrangements of ordered water in the ducts and corpuscles, and a complete content of the biological particles in the flowing water and its permittivity are missing.
Suspended core microstructured optical fibers (SC-MOFs) represent a special kind of microstructured fibers which can be employed for optical sensing. In this article one experimental SC-MOF and its tapers were numerically analyzed in order to determine if the overlap of evanescent waves with the fiber cladding holes can be increased by tapering. Power distributions of fundamental modes in the SC-MOF and its tapers were calculated by using a vectorial finite element method. The calculations have shown that the evanescent wave overlap (at a wavelength of 1550 nm) can be increased from 0.75% up to 26% by tapering of a section of the SC-MOF from an original diameter of 125 m down to 31.25 m. Fiber tapers designed on the basis of the numerical analysis were prepared by so-called 'flame brush technique' employing a fiber puller of own construction. Experiments with the prepared tapers have proved that the cladding holes remain sufficiently large for passing liquid and gas analytes through and that the core diameter of the untapered pigtails is large enough for low-loss coupling of optical beams into the tapered fiber.
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