A rapid and low cost photoluminescence (PL) immunosensor for the determination of low concentrations of Ochratoxin A(OTA) and Aflatoxine B1 (AfB1) has been developed. This biosensor was based on porous silicon (PSi) fabricated by metal-assisted chemical etching (MACE) and modified by antibodies against OTA/AfB1 (anti-OTA/anti-AfB1). Biofunctionalization method of the PSi surface by anti-OTA/ anti-AfB1 was developed. The changes of the PL intensity after interaction of the immobilized anti-OTA/anti-AfB1with OTA/AfB1 antigens were used as biosensor signal, allowing sensitive and selective detection of OTA/AfB1 antigens in BSA solution. The sensitivity of the reported optical biosensor towards OTA/AfB1 antigens is in the range from 10-3 to 102 ng/ml.
Structural and optical properties of TiO2 ALD coated silicon nanostructures were investigated. The morphology and
chemical composition of TiO2 coated silicon nanopillars and porous silicon were studied by using methods of scanning
electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Optical characteristics were studied using
measurements of reflectance and luminescence spectra. Detailed analysis of morphological features and
photoluminescence mechanisms were provided. Peculiarities of reflectance spectra were discussed. It was shown the
possible application of these structures as antireflectance coatings.
In this work, we present a detailed experimental Raman investigation of nanostructured silicon films prepared by metalassisted chemical etching with different nanocrystal sizes and structures. Interpretation of observed one and two-phonon Raman peaks are presented. First-order Raman peak has a small redshift and broadening. This phenomenon is analyzed in the framework of the phonon confinement model. Second-order Raman peaks were found to be shifted and broadened in comparison to those in the bulk silicon. The peak shift and broadening of two-phonon Raman scattering relates to phonon confinement and disorder. A broad Raman peak between 900-1100 cm-1 corresponds to superposition of three transverse optical phonons ~2TO (X), 2TO (W) and 2TO (L). Influence of excitation wavelength on intensity redistribution of two-phonon Raman scattering components (2TO) is demonstrated and preliminary theoretical explanation of this observation is presented.
A novel optical sensor based on TiO2 nanoparticles for Valine detection has been developed. In the presented work, commercial TiO2 nanoparticles (Sigma Aldrich, particle size 32 nm) were used as sensor templates. The sensitive layer was formed by a porphyrin coating on a TiO2 nanostructured surface. As a result, an amorphous layer between the TiO2 nanostructure and porphyrin was formed. Photoluminescence (PL) spectra were measured in the range of 370-900 nm before and after porphyrin application. Porphyrin adsorption led to a decrease of the main TiO2 peak at 510 nm and the emergence of an additional peak of high intensity at 700 nm. Absorption spectra (optical density vs. wavelenght, measured from 300 to 1100 nm) showed IR shift Sorret band of prophiryn after deposition on metal oxide. Adsorption of amino acid quenched PL emission, related to porphyrin and increased the intensity of the TiO2 emission. The interaction between the sensor surface and the amino acid leads to the formation of new complexes on the surface and results in a reduction of the optical activity of porphyrin. Sensitivity of the sensor to different concentrations of Valine was calculated. The developed sensor can determine the concentration of Valine in the range of 0.04 to 0.16 mg/ml.
An impact of morphology on reflectance of porous silicon was investigated. Depending on the metal-assisted chemical etching conditions the macro- micro structures could be formed. The reflectance properties of various porous silicon structures after ammonia adsorption were investigated. It was shown that increasing of ammonia concentration in the measurement camber leads to an increase of the reflectance. The most sensitive structures for ammonia detection are porous silicon having approximately size of pores - 10-15 μm. A fast response of porous silicon on the adsorption of ammonia molecules may be used for development of new sensors.
Proc. SPIE. 6619, Third European Workshop on Optical Fibre Sensors
KEYWORDS: Optical fibers, Sensors, Particles, Molecules, Optical coatings, Near field scanning optical microscopy, Near field, Biological and chemical sensing, Molecular interactions, Near field optics
In this work, the surprising sensing performances of opto-chemical sensors based on SnO2 particles layers against
chemical pollutants either in air and water environment, at room temperature, are reported. The Electrostatic Spray
Pyrolysis (ESP) method has been used to deposit the sensing coatings upon the distal end of standard fibers. This
technique allows the fabrication of SnO2 layers composed of micron and sub-micron dimensions able to locally modify
the profile of the optical near-field collected in the close proximity of the fiber tip. Such layers morphology leads to
strong surface interactions between sensing coatings, analyte molecules and the evanescent contribute of the field,
resulting in an excellent sensors sensitivity against chemical pollutants, even at room temperature.
In the last decade a huge number of SnO2-based gas sensors have been proposed for environmental monitoring, automotive applications, air conditioning in houses, airplane and aircrafts. However, most of the proposed sensors work at very high temperatures in order to reach high sensitivities. Here, a SnO2-based optical fiber sensor is proposed for the room temperature detection of chemical pollutants in air. Particles layers composed by tin dioxide grains, with wavelength and subwavelength dimensions, resulted very promising because they are able to significantly modify the optical near field profile emerging from the film surface due to local enhancements of the evanescent wave contribute, and thus to improve the sensitivity to surface effects induced by the analyte interaction. The room temperature sensing performances of SnO2-based particles layers towards environmental pollutants have been investigated by the exposure to different concentrations of toluene and xylene vapors as well as gaseous ammonia. They have also been compared with the performances obtained with other optical fiber sensors in the same configuration, but coated with different sensitive materials, such as Single-Walled carbon nanotubes. The preliminary results obtained evidenced the surprising capability of the SnO2-based optical sensor to detect chemical pollutants at ppm level in air at room temperature. Finally, preliminary results on the effects of the processing parameters and post processing thermal annealing on film morphology and optical near field are presented.
In this work, the possibility to detect ppm ammonia concentrations in water environment, at room temperature, by means of Standard Optical Fibers (SOFs) sensors coated by Metal Oxides (MOXs) films has been demonstrated. Electro-spray pyrolisis technique has been used to deposit SnO2 films onto the distal end of single-mode optical fibers. This deposition technique allows the possibility to tailor the fabricated films properties by varying the deposition parameters, such as the metal chloride concentrations, the solution volume and the substrate temperature. The sensor operating principle relies on the measurement of the light intensity reflected by the fiber-sensitive layer interface: the pollutant molecules adsorption within the MOX film causes a change in its complex dielectric function and thus in the fiber-film reflectance. Spectral characterization of the obtained sensing probes has been carried out in the range 400-1750nm. Single wavelength reflectance measurements have been carried out to test the sensor performances for ppm ammonia detection. High sensitivity to the target analyte, response times of approximately 10-20 minutes and a Limit Of Detection as low as sub-ppm has been observed.
In this work, preliminary experimental results on the capability of a Metal Oxides (MOXs) based optical sensor to perform ammonia detection in water environments, at room temperature, are presented. Electro-spray pyrolisis technique has been used to deposit the SnO2 films on the distal end of standard Silica Optical Fibers (SOFs). Reflection spectra of the sensing probes have been measured in the range 1520-1620nm by using a tunable laser and an optical spectrum analyzer. Single wavelength reflectance measurements have been carried out to test the sensing performances for ammonia detection in the range 4-20 ppm. High sensitivity to the target analyte and fast response times have been observed. From the results obtained, a Limit Of Detection (LOD) as low as sub-ppm has been achieved.
The photoelectronic properties of samples of porous silicon received by method of anodic electrochemical etching of monocrystalline silicon in electrolytes on the base of hydrofluoric acid are investigated. Wide spectral photosensitivity from infra-red to ultraviolet of spectrum area on series of received structures is found out. The physical mechanism of photosensitivity is discussed. The electronic parameters of porous silicon samples under gas adsorption were investigated. It was opend that the ammonia adsorption changes electrical conductivity of porous silicon samples on constant and variable current of measurement. In microporous asymmetrical structures we observed electromotive force on contacts under ammonia adsorption. The physical mechanism of adsorption of ammonia is connected with interaction dipolar molecules ammonia with double electric layer on surface of porous silicon.