Conically tapered fibers with dielectric or metalized waists or tips of a sub-wavelength diameter have the potential of
a range of applications, from optical probes for near-field detection to (bio)chemical sensing in extremely small volumes
of analytes.
For successful design, a robust modeling tool is a prerequisite. In such structures, strongly lossy modes with complex
propagation constants with large imaginary parts may be excited. In this paper, a reliable eigenmode solver for
cylindrical structures containing metal layers is described. An analytical function whose roots correspond to propagation
constants of waveguide eigenmodes is formulated. Its roots are found with a help of Argument Principal Method. Due to
the analyticity limitation, the waveguide structure has to be of a finite diameter with either electrically or magnetically
conductive walls. The approach is implemented within the well-known modeling tool CAMFR. The feasibility of the
method is demonstrated using the example of light propagation in the metalized fiber taper dipped in the surrounding
medium.
The paper shows an approach to the determination of pH changes of solutions with a fine spatial resolution by means of
fiber-optic tapers and fluorescence detection. This approach can be adopted for the determination of auxin flow through
celluar membranes. Spectral absorption and fluorescence of pH transducers, namely of fluorescein, carboxyfluorescein,
6,8-dihydroxy-1,3-pyrenedisulfonic acid disodium salt and 2',7'-bis(2-carbonylethyl)-5(6)-carboxyfluorescein, were
tested. The approach, based on the determination of a shift of the maxima of their fluorescence peaks, was employed for
processing the measured fluorescence data in bulk solutions. Suitable tapered fiber probes were prepared and in vitro
demonstrated for pH monitoring in a pH range from 6 to 7.
The control of chlorine content in water is an important issue in water treatment. This paper presents an opto-electrochemical
approach to the detection of chlorine in water. In this approach, optical changes of a sensing layer
caused by its interaction with chlorine are electrically reversed by using a thin conductive and transparent layer of
Indium-Tin-Oxide (ITO) deposited in between an optical substrate and the sensing layer acting as an electrode. The
paper deals with the preparation and characterization of sensing layers based on commercially available transducers
suitable for the detection of chlorine in water and applicable on
ITO-coated planar substrates and/or silica optical fibers.
Sensing layers of several absorption and luminescent transducers were applied onto ITO layers deposited on planar glass
or fiber-optic substrates by electropolymerization or by the sol-gel method. The best response was observed from o-phenylenediamine
and polyluminol layers prepared by electropolymerization. The sensitivity and limit of detection of a
polyluminol layers are comparable to hygienic limits for the chlorination of water. The parameters of o-phenylenediamine
layers obtained up to now are close to these values. A damaging effect of chlorine in higher concentrations on the sensing layers was observed.
We present a surface plasmon resonance sensor base on prism excitation of surface plasmons and spectral interrogation. For specific detection of biomolecular analytes, multilayers of monoclonal antibodies are immobilized on the surface of the sensor. Detection of biomolecular analytes such as human (beta) -2)-microglobulin, choriogonadotropin, hepatitis B surface antigen, salmonella enteritidis is demonstrated.
The exploitation of surface plasmon resonance optical sensor for the study of the interaction of immobilized fibrinogen and fibrin monomer with soluble fibrinogen and thrombin is reported. Soluble fibrinogen was mostly reversible, the bound thrombin could be inhibited by milimolar concentration of phenylmethylsulphonyl fluoride (PMSF). At lease three sets of different thrombin binding sites were found. There was a residual fraction of thrombin bound to washed fibrin (ogin) (to about a five to ten percent of fibron monomer units) suggesting that a known naturally occurring fibrinogen variant differing in the gamma chain was the target. Surface bound fibrinogen was converted by thrombin to fibrin monomer that interacted with fibrinogen in solution. At low fibrin monomer surface density the second layer was formed that contained about the same amount of protein as the first layer, at higher fibrin monomer concentration less than one molecule of fibrinogen per molecule of fibrin monomer was captured. Starting with surface-bound fibrinogen and alternating addition of thrombin and fibrinogen a fibrin network of predetermined composition, size, and arrangement could be formed.
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