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ABSTRACT: A sensitive optical method of total internal reflection ellipsometry (TIRE) in conjunction with immune assay approach was exploited for the registration of T-2 mycotoxin in a wide range of concentrations from 100 microg/ml down to 0.15 ng/ml. Association constants of 1.4x10(6) and 1.9x10(7)mol(-1)s for poly- and monoclonal T-2 antibodies, respectively, were evaluated from TIRE kinetic measurements. According to TIRE data fitting, binding of T-2 molecules to antibodies (at saturation) has resulted in the increase in adsorbed layer thickness of 4-5 nm. The QCM impedance measurements data showed anomalously large mass increase and film softening, most likely, due to the binding of large T-2 aggregates to antibodies.
Biosensors and Bioelectronics 02/2007; 22(6):885-90. · 5.60 Impact Factor
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ABSTRACT: The emission and conductivity characteristics of oxide cathodes depend largely on the activation process. In this paper, the electrical properties of new type of oxide cathodes for cathode ray tube (CRT) application, supplied by LG Philips Displays, have been investigated in relation to different cathode activation regimes. The influence of the activation process over different durations has been investigated. A temperature of T=1425 K was chosen to be higher than the optimum cathode activation temperature (T=1200 K), and the other temperature of T=1125 K was lower than that. The electron activation energy (E) was found to vary in the range from 0.58 to 2.28 eV for cathodes activated at the higher temperature regime, and from 1.08 to 1.9 eV for those activated at the lower temperature regime. Scanning electron microscopy (SEM) and electron diffraction X-ray (EDX) analyses show a structural phase transformation in the oxide material that was activated at 1125 K for a period of 1-12 hours. The SEM mapping shows a large contamination of Ba in the top layer of oxide material. The activator agents tungsten and aluminum are found to penetrate into the BaO/SrO layer in two different ways.
Journal of Display Technology 04/2006; · 2.28 Impact Factor
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ABSTRACT: The use of Staphylococcal protein A and lectins as intermediate immobilising agents allows operators to orient antibodies (Ab) towards the solution due to the presence of a specific binding sites of immunoglobulin (Ig) molecules. Antibodies of different species of animals have unequal affinities to individual lectins. The effective thickness of immobilised Ab's depends on the type of substrates used and increases in the following sequence: bare gold or silicon surface, the surface treated with self-assembled polyelectrolytes (PESA) or with protein A or some lectins deposited on the preliminary formed polyelectrolyte layer. The glycolysated protein of jp51 may be selectively immobilised from the mixture of retroviral proteins (p24 and jp51), if it is necessary to distinguish infected animals from preliminarily immunised ones by means of a vaccine based on p24 protein. It was shown that the use of Staphylococcal protein A, instead of some lectins as intermediate layer for the Ab immobilisation, does not lead to a more sensitive determination of such low-weight toxins as 2,4-dichlorophenoxyacetic acid (2,4-D). The above-mentioned results were obtained with surface plasmon resonance (SPR) technique.
Bioelectrochemistry 05/2005; 66(1-2):111-5. · 3.76 Impact Factor
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ABSTRACT: A very sensitive optical method of total internal reflection ellipsometry (TIRE) in conjunction with an immune assay approach were exploited for the registration of low molecular weight environmental toxins, such as simazine, atrazine and T2 mycotoxin in a wide range of concentrations down to 0.1 ng/ml. QCM impedance measurements provided additional information on the mechanism of T2 binding.
Sensors, 2004. Proceedings of IEEE; 11/2004
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ABSTRACT: A non-destructive technique employing a mercury probe as a counter electrode was successfully developed in order to study the mechanism of charge transport through thin polymer films on silicon and aluminum substrates. The polyelectrolyte self-assembly technique was employed to form the organic films. Both DC and AC current-voltage characteristics were measured at room temperature. An exponential dependence of the tunnelling current on the film thickness was found, and a tunnelling coefficient of 3.3×10<sup>-9</sup> m<sup>-1</sup> was calculated. The observed voltage dependence was interpreted in terms of the model of a trapezoidal-triangular barrier. The peak in current-voltage characteristics of polymer films on aluminum substrates may be attributed to resonance tunnelling via surface states on the alumina/polymer film interface.
IEE Proceedings - Circuits Devices and Systems 11/2004; · 0.36 Impact Factor
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ABSTRACT: Composite lead sulphide/phthalocyanine thin films were produced for the first time by exposure of thin spun films of a lipophilic lead phthalocyanine derivative to H<sub>2</sub>S gas. The formation of lead sulphide was confirmed by Raman and X-ray photoelectron spectroscopy measurements. UV-visible absorption and photoluminescence spectral measurements as well as a film morphology study using atomic force microscopy indicate the formation of lead sulphide clusters. From the blue spectral shift of the fundamental adsorption band, the size of the PbS clusters was estimated to be 2.24 nm.
IEEE Transactions on Nanotechnology 10/2004; · 2.29 Impact Factor
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ABSTRACT: The method of spectroscopic ellipsometry has been applied to study in situ the adsorption of bovine serum albumin (BSA). The porosity and amount of adsorbed BSA were determined by fitting the ellipsometric data to the Bruggeman effective medium approximation model. The presence of intermediate adsorbed layers of polyelectrolytes was found to increase protein adsorption.
Nanotechnology 03/2004; 15(5):703. · 3.98 Impact Factor
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ABSTRACT: Metal-insulator-semiconductor structures were fabricated using 40-layers-thick Langmuir-Blodgett (LB) films of stearic acid (SA) on hydrophobic n-type silicon (n-Si) substrates. Cadmium sulphide (CdS) nanoparticles were introduced by exposure to H<sub>2</sub>S gas for a period of 12 h. Samples containing CdS nanoparticles exhibit lower dc leakage current but higher effective dielectric constant. The effective dielectric constant of the CdS embedded SA matrix is found to be 5.1. The Poole-Frenkel effect is prevalent for charge transport in the LB films containing CdS nanoparticles at the field higher than 10<sup>7</sup>· Vm<sup>-1</sup>. The effect becomes saturated at higher fields.
IEEE Transactions on Nanotechnology 10/2003; · 2.29 Impact Factor
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ABSTRACT: Composite phthalocyanine thin films were produced for the first time by exposure of thin films of an organic solvent soluble lead phthalocyanine derivative to H<sub>2</sub>S gas. UV-visible absorption and photoluminescence spectral measurements indicate the probable formation of lead sulfide clusters, while the film structure and morphology were studied with atomic force microscopy.
Nanotechnology, 2003. IEEE-NANO 2003. 2003 Third IEEE Conference on; 09/2003
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ABSTRACT: Non-centrosymmetric alternate-layer Langmuir-Blodgett (LB) films of stearic acid and eicosylamine molecules were treated with a twelve-hour-long exposure of hydrogen sulphide (H<sub>2</sub>S) gas. Surface plasmon resonance (SPR) experiments are carried out to monitor the change in optical properties of composite films. Structural analysis using atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy give a positive identification of the presence of cadmium sulphide (CdS) nanoparticles after the treatment. Quasistatic measurements give smaller pyroelectric activity in H<sub>2</sub>S-gas-treated LB films than untreated ones
IEE Proceedings - Circuits Devices and Systems 09/2003; · 0.36 Impact Factor
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ABSTRACT: Surface plasmon resonance experiments were successfully employed to investigate the mechanisms of interaction of spun thin films of polyphenylsulfide polymer with ozone at ppb levels. Oxidation of the polymer by ozone exposure results in an irreversible increase in the index of refraction of the polymer. The detection sensitivity is enhanced with the improved surface coverage of the film.
Journal of Physics D Applied Physics 08/2003; 36(17):2130. · 2.54 Impact Factor
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ABSTRACT: The principles of attenuation of the light intensity due to multiple reflections are realised in a planar silicon oxide (SiO(2))silicon nitride (Si(3)N(4)) waveguiding structure for the purpose of developing optical biosensors with improved sensitivity. The analysis of the experimental data shows that the large difference in refractive indices of core and cladding layers gives rise to an increase in sensitivity by a factor of 3 over previously reported structures. Composite polyelectrolyte self-assembled thin films containing cyclo-tetra-chromotropylene as an indicator and enzymes glucose oxidase or urease were employed in the superstrate as a sensing membrane. Individual enzyme reactions as well as their inhibition by pesticides were studied by monitoring the intensity of light output from the planar waveguide. The results were compatible with those obtained by conventional ultraviolet-visible absorption spectroscopy. The instrument detection limit for Imidacloprid pesticide was found to be as low as 10 ppb in concentration.
IEE Proceedings - Nanobiotechnology 07/2003; 150(1):25-30. · 1.82 Impact Factor
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ABSTRACT: Titanium dioxide thin films were prepared by spin coating of sol precursor onto microscopic glass slides, silicon and indium tin oxide (ITO) coated glass substrates. Spin speed was varied between 1000 and 6000 rpm. From the morphological analysis, it is found that thin films spun with speed ω≤4000 rpm assume higher ordered structure than those spun at a speed higher than 4000 rpm. Conduction at low voltages is believed to be variable range hopping at temperatures T<220 K while the ionization of donors situated at Ea = 0.46 eV below the conduction band edge becomes dominant at temperatures higher than 220 K. At high field charge transport is due to trap-controlled space charge limited mechanism. Traps with a density Nt≈1×1022 m−3 are thought to be situated at energy level Et = 0.3 eV below the conduction band and are associated with film nonstoichiometry and interface states.
Journal of Physics D Applied Physics 04/2003; 36(9):1120. · 2.54 Impact Factor
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ABSTRACT: Metal-insulator-semiconductor structures were fabricated using 40 layers thick Langmuir-Blodgett (LB) films of stearic acid (SA) on hydrophobic n-type silicon (n-Si) substrates. Samples containing cadmium sulphide (CdS) nanoparticles exhibit higher rectification than untreated ones by two orders of magnitudes. The flat band voltage was found to be 0.5 V from the capacitance measurement. The effective dielectric constant of the CdS embedded SA matrix was estimated to be 5.2.
Nanotechnology, 2002. IEEE-NANO 2002. Proceedings of the 2002 2nd IEEE Conference on; 02/2002
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ABSTRACT: The most sensitive optical method of interferometry was exploited for determination of changes in the refractive index following the adsorption of biological molecules onto the solid surface. Instead of having two waveguiding arms (the main and the reference) in traditional Mach-Zhender interferometer, two ortogonal TM and TE modes propagating through the SiO(2)-Si(3)N(4)-SiO(2) waveguide structure were employed in planar polarization interferometer (PPI). Multiperiodic PPI response was, therefore, formed due to the phase shift between TM and TE modes. A matrix simulation procedure was developed in order to investigate the influence of both the refractive index and molecular layer thickness on the PPI response. Nonspecifical binding of fibrinogen to silicon nitride surface was studied as a model object for PPI testing. The results obtained are in good agreement with the known information about fibrinogen adsorption on the different surfaces. An attempt to introduce the concept of 'surface molecular concentration and molecular polariziability' instead of 'molecular layer thickness and refractivity' was undertaken.
Biosensors and Bioelectronics 09/2001; 16(6):381-90. · 5.60 Impact Factor
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ABSTRACT: Films of polyallylamine hydrochloride (PAA) and polysteresulfonate
sodium salt (PSS) were formulated using the polyelectrolyte
self-assembly technique. Electrical measurements show that there is no
presence of counter ions and films are electrically stable. Responses of
composite films of PAA/(indicator/PAA)<sub>n</sub>(Enzyme/PAA)<sub>m
</sub> deposited on suitably treated glass substrates to heavy metals
and pesticides are found to be selective from their optical absorption
spectra
Nanotechnology, 2001. IEEE-NANO 2001. Proceedings of the 2001 1st IEEE Conference on; 02/2001
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ABSTRACT: Composite Langmuir-Blodgett films of
polyphenylsulphide/calix-4-resorcinarene (PPS/C-4-RA) with different
molar ratios were deposited on quartz crystals and silicon wafers. Using
ellipsometric and quartz-crystal microbalance methods, the thickness and
mass of the film were found to increase linearly with the number of
deposited layers. An optimal molar ratio for the deposition of
C-4-RA/PPS films was found to be about 1/3, yielding a thickness of 9.25
nm/layer and frequency changes of 1.5 kHz/layer corresponding to surface
concentration of PPS of 2·10<sup>22</sup> m<sup>-2</sup>. The
frequency of C-4-RA/PSS-coated quartz crystals decreases with time on
exposure to ozone. Both the mass gain and concentration of oxygen
appearing in the film during oxidation were calculated. The highest
response was observed for LB films with the C-4-RA/PPS molar ratio of
1/3. An average ozone concentration of O.5 ppm was recorded by QCM
transducers near a standard photocopier
IEE Proceedings - Science Measurement and Technology 08/2000; · 0.49 Impact Factor
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ABSTRACT: Two possible types of cadmium sulphide (CdS) nanostructures can be formed within Langmuir–Blodgett (LB) films of calixarene Cd salt as a result of exposure to H2S gas: nanoclusters with the size of about 1.5 nm or two-dimensional planes with the thickness of about 1.7 nm. Transmission electron microscopy and electron diffraction studies on calixarene/CdS LB films show that CdS particles are not present in the fresh samples at the beginning, but they are gradually formed under exposure to a high energy electron beam. A blueshift of the first exciton absorption band and an increase of the extinction coefficient, caused by exposure to H2S gas, were found with UV-visible optical spectroscopy and surface plasmon resonance, respectively. © 2000 American Institute of Physics.
Journal of Applied Physics 07/2000; 88(3):1333-1338. · 2.17 Impact Factor
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ABSTRACT: Thin films of
tetra-undecyl-tetra-p-nitrophenylazocalix(4)resorcinarene (Azol)
molecules were deposited on different substrates by the spin coating
method. The refractive index of the spun films is found to be 1.494 from
surface plasmon resonance (SPR) experiments on the sample in contact
with two different dielectric media: air and high purity water. The
thickness of films decreases with the increase in the spin speed as a
-2/3 power law but rises linearly with the concentration. These
observations are in agreement with hydrodynamic theory for spinning of a
low-viscosity and highly volatile liquid
IEE Proceedings - Science Measurement and Technology 06/2000; · 0.49 Impact Factor
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Philosophical Magazine B. 07/1999; 79(7):1005-1019.
