Whispering Gallery Mode (WGM) resonators are very sensitive to nanoparticles attaching to the surface. We simulate this process using COMSOL Wave Optics module. Our spherical WGM resonators are produced by melting a tip of an optical fiber and we measure optical Q factors in the 105 range. Molecular oxygen lines of the air in the 760 nm region are used as reference markers when looking for the shifts of the WGM resonance lines. We demonstrate WGM microresonator surface coating with a layer of ZnO nanorods as well as with polystyrene microspheres. Coatings produce increased contact surface. Additional layer of antigens/antibodies will be coated to make high-specificity biosensors.
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<sup>-3</sup> to 10<sup>2</sup> ng/ml.
Structural and optical properties of Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> nanolaminates fabricated by atomic layer deposition (ALD) were
investigated. We performed Raman spectroscopy, transmission electron microscopy (TEM), X-Ray reflectivity (XRR),
UV-Vis spectroscopy, and photoluminescence (PL) spectroscopy to characterize the Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> nanolaminates. The
main structural and optical parameters of Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> nanolaminates were calculated. It was established that with
decreasing of the layer thickness, the value of band gap energy increases due to the quantum size effect related to the
reduction of the nanograins size. It was also shown that there is an interdiffusion layer at the Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> interface which
plays a crucial role in explaining the optical properties of Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> nanolaminates. Correlation between structural and
optical parameters was discussed.
A novel optical sensor based on TiO<sub>2</sub> nanoparticles for Valine detection has been developed. In the presented work, commercial TiO<sub>2</sub> nanoparticles (Sigma Aldrich, particle size 32 nm) were used as sensor templates. The sensitive layer was formed by a porphyrin coating on a TiO<sub>2</sub> nanostructured surface. As a result, an amorphous layer between the TiO<sub>2</sub> 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 TiO<sub>2</sub> 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 TiO<sub>2</sub> 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.
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 SnO<sub>2</sub> 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 SnO<sub>2</sub> 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 SnO<sub>2</sub>-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 SnO<sub>2</sub>-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 SnO<sub>2</sub>-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 SnO<sub>2</sub>-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 SnO<sub>2</sub> 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.