In this work, polymeric coated Long Period Gratings (LPGs) working in transition mode have been used to
monitor the coordination and self assembling of water nano layers providing new scenarios in chemical sensing
applications. In particular, nano-scale layers of syndiotactic and atactic polystyrene (sPS and aPS) have been deposited
by dip - coating onto LPGs to tune the devices at the transition point. Experimental results demonstrate
the polymers capability to orient water molecules in proximity of their surfaces. The sPS and aPS interactions
with water have been compared. Moreover, the high sensitivity of the coated LPGs was used to monitor the
effect of disorder induced by different cations depending on their size and electrical charge. Experimental results
show for the first time that, thanks to the water - polymer interaction, sPS coated LPGs could be successfully
employed as high sensitivity cation sensors.
We report preliminary results on the development of multilayer coated long period gratings (LPGs) for life science
applications. The dip-coating technique and a solvent/nonsolvent strategy were exploited to deposit double-layer
polymeric film onto a LPG. A primary coating of atactic polystyrene was used as high refractive index layer to tune the
working point of the device in the so-called transition region thus achieving remarkable surrounding medium refractive
index sensitivity. A secondary layer of atactic poly(methyl methacrylate-co-methacrylic acid) containing functional
carboxyl groups, characterized by a lower refractive index, was deposited onto the primary coating in order to have the
desired functional groups on the surface of the device. Commonly used covalent immobilization procedure, NHS/EDC
coupling method, was exploited to link streptavidin on the surface of the functionalized coated device. Finally, real-time
detection of biotinylated bovine serum albumin affinity binding on immobilized streptavidin was performed by
monitoring the shift of the LPG attenuation bands.
We present real-time monitoring of multiple biomolecular interactions by means of high refractive index (HRI) coated
long period grating (LPG) working in transition region. The coating was deposited by dip-coating as a thin layer of few
hundreds nanometers of atactic polystyrene (PS). The HRI coating was used to enhance the LPG sensitivity to refractive
index changes of the surrounding medium and its thickness was determined in order to tune the coated device at the
desired working point. To allow immobilization of specific biomolecules, the PS overlay surface was functionalized
through bovine serum albumin (BSA) and glutaraldehyde. In particular, BSA was directly adsorbed on PS through strong
hydrophobic interactions, then glutaraldehyde was linked atop exploiting the lysines side chains. This intermediate layer
allowed to covalently immobilize human IgG (antibody) on the device surface. To prove the immobilization method, the
interaction between IgG and its proper anti-human IgG (antigen) was studied. The four binding interactions were on-line
monitored following the shift of the LPG attenuation band. The experiment also suggests a novel and interesting
biofunctionalization approach of unreactive synthetic polymers with applications in immunosensing.
In this work, we present preliminary results concerning the development of a platform for biochemical sensing based on
overlayered Long Period Gratings (LPGs) working in transition mode. The surrounding medium refractive index (SRI)
sensitivity of the bare device was greatly enhanced by means of the modal transition phenomenon which is enabled in
LPGs with a nanoscale polymer overlay of higher refractive index than the cladding. This strategy was pursued to
develop a sensitive tool for biochemical detection in aqueous solutions. Dip-coating was used to deposit thin layers of
Polystyrene (PS) with different thicknesses on the same LPG to test the performances of the device in different working
points of its modified sensitivity characteristic. The PS overlay surface was modified through adsorption of biotinylated
bovin serum albumin (BBSA). Adsorption dynamic of BBSA was observed by on-line monitoring the shift of the LPGs
attenuation bands. In the same way also a subsequent steptavidin (SA) binding dynamic on the byotinilated sites of the
adsorbed proteins was recorded. Several washing cycles between the steps showed a rather stable immobilization of the
protein monolayers. Experimental results show that overlayered LPGs are among the most sensitive refractive index
transducers to be employed in biochemical detection and that wide margins of further optimization exist.
In this work, nano-sized polymeric coatings with higher refractive index than the cladding one were used to induce the
modal transition in tapered long period gratings in a cascaded configuration. The aim of this experimental investigation
was to increase the sensitivity of the bare device to surrounding refractive index changes while preserving a good fringes
visibility. An original configuration of the device in terms of coated/not coated area was identified that best achieve the
aforementioned target.
In this work, an experimental analysis on the spectral effects induced by depositing a uniform high refractive index
(HRI) thin coating on weakly tilted fiber Bragg gratings (TFBGs) is carried out. First, two weakly TFBGs presenting
different tilt angles were fabricated. Successively, by using dip-coating technique, two different coating thicknesses were
deposited on each of them. The transmission spectra of the obtained structures were collected as the surrounding
refractive index (SRI) changed in the range 1÷1.47. The coated gratings present some differences in their spectral
evolution, that can be opportunely exploited. The coated configuration could improve some aspects of previous
demodulation techniques exploited in the case of bare TFBGs. Moreover, an important effect of HRI coatings is to
enhance the SRI sensitivity of the spectral position of the dips corresponding to cladding modes coupling, leading to a
different interrogation method for sensing applications.
In this work, the experimental analysis of the response of nanocoated Tapered Long Period Gratings (TLPGs) to
Surrounding Refractive Index (SRI) changes is presented. The modal transition is demonstrated to take place in this kind
of devices and to be an effective method to improve their SRI sensitivity. The dip-coating method was carried out by an
automated system and showed to be a reliable technique for the deposition of conformal coatings. A comparison with
traditional UV-written LPGs revealed that a thicker overlay is necessary for the TLPG to tune the transition region in the
same SRI range.
KEYWORDS: Near field, Sensors, Near field optics, Particles, Tin, Fiber optics sensors, Near field scanning optical microscopy, Optical fibers, Annealing, Metals
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, we report the experimental investigation of the sensitivity characteristics to the surrounding refractive index
(SRI) in thinned long period gratings for a wide range of fiber diameters and different low orders cladding modes. Wet
chemical etching combined with microscopic analysis allow us to identify the experimental dependence of the SRI
sensitivity on the cladding radius.
In this work, the experimental analysis of the sensitivity characteristics to the surrounding refractive index in nanoscale coated long period gratings (LPGs) is presented. Polymeric coatings of refractive index higher than the cladding one have been considered with thickness values ranging in hundreds of nanometers. The presence of the high refractive index coating induces the cladding to overlay mode transition depending on the overlay features (thickness and index) and the surrounding refractive index. The immediate consequence is a drastic enhancement in the sensitivity to surrounding refractive index due to a large shift of all the attenuation bands in the refractive index range where the modal transition occurs. As matter of fact the sensitivity characteristics changes from the sub-linear monotone behaviour to a resonant like shape. Here, a complete experimental analysis combined with an analytical fitting has been investigated to outline the new SRI sensitivity profile and its dependence on the overlay thickness and order mode.
In this work, the numerical and experimental analysis of coated Long Period Gratings (LPGs) as high sensitivity optochemical sensor is presented. The proposed structure relies on LPGs coated with nanoscale high refractive index (HRI) overlays. When azimuthally symmetric nano-scale HRI coatings are deposited along LPGs devices, a significant modification of the cladding modes distribution occurs, depending on the layer features (refractive index and thickness)
and on the external refractive index. If these parameters are properly chosen, a strong field enhancement within the overlay occurs, leading to an excellent sensitivity to the coating properties. Here, the effects of the overlay thickness and the cladding mode order on sensor sensitivity and response time have been numerically and experimentally investigated. In order to provide a high sensitivity and species specific opto-chemical sensor, the LPGs were coated with nanoscale overlays of Syndiotactic Polystyrene (sPS) in the nanoporous crystalline δ form. The sensitive material was chosen in light of its selectivity and high sorption properties towards chlorinated and aromatic compounds. Sensor probes were prepared by using dip coating technique and a proprietary procedure to obtain the form sPS. Experimental demonstration of the sensor capability to perform sub ppm detection of chloroform in water at room temperature is also reported.
In this work, a novel fiber optic sensor able to measure the concentration of organic analytes, in aqueous environment is presented. Long period gratings were selected as high sensitive refractive index transducers and syndiotactic polystyrene in the nanoporous crystalline form was used as sensitive polymeric layer due to its high sorption properties towards chlorinated and aromatic compounds. In particular, a thin semi-crystalline syndiotactic polystyrene film with crystalline nanoporous form was deposited along the sensing element by using dip-coating technique. Chemical detection has been carried out by measuring the wavelength shift and the amplitude change in the attenuation bands of the long period grating due to analytes sorption. Experimental results demonstrate the capability of the proposed sensor to detect very low concentrations (in the range of few ppm) of chloroform in water.
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