97 research outputs found
Whispering gallery mode aptasensors for detection of blood proteins
No full textWhispering gallery mode resonators (WGMR), as silica microspheres, have been recently proposed as an efficient tool for the realisation of optical biosensors. In this work we present a functionalization procedure based on the DNA-aptamer sequence immobilization on WGMR, able to recognize specifically thrombin or VEGF protein, preserving a high Q factor. The protein binding was optically characterized in terms of specificity in buffer solution or in 10% diluted human serum. Simulation of the protein flow was found in good agreement with experimental data. The aptasensor was also chemically regenerated and tested again, demonstrating the reusability of our system
Whispering Gallery Mode Aptasensors for Detection of Blood Proteins
No full textWhispering gallery mode resonators (WGMR), as silica microspheres, have been recently proposed as an efficient tool for the realisation of optical biosensors. In this work we present a functionalization procedure based on the DNA-aptamer sequence immobilization on WGMR, able to recognize specifically thrombin or VEGF protein, preserving a high Q factor. The protein binding was numerically modelled and optically characterized in terms of specificity in buffer solution or in 10% diluted human serum. The aptasensor was also chemically regenerated and tested again, demonstrating the reusability of our system
Ion-exchanged glass microrods as hybrid SERS/fluorescence substrates for molecular beacon-based DNA detection
No full textIon-exchange in molten nitrate salts containing metal ions (i.e. silver, copper, etc.) represents a well-established technique able to modify the chemical-physical properties of glassmaterials. It iswidely used not only in the field of integrated optics (IO) but also, more recently, in plasmonics due to the possibility to induce the formation of metal nanoparticles in the glass matrix by an ad hoc thermal post-process. In this work, the application of this technology for the realisation of low-cost and stable surface-enhanced Raman scattering (SERS) active substrates, based on soda-lime glass microrods, is reported. The microrods, with a radius of a few tens of microns, were obtained by cutting the end of an ion-exchanged soda-lime fibre for a length less than 1 cm. As ion source, silver nitrate was selected due to the outstanding SERS properties of silver. The ion-exchange and thermal annealing postprocess parameters were tuned to expose the embedded silver nanoparticles on the surface of the glass microrods, avoiding the use of any further chemical etching step. In order to test the combined SERS/fluorescence response of these substrates, labelled molecular beacons (MBs) were immobilised on their surface for deoxyribonucleic acid (DNA) detection. Our experiments confirm that target DNA is attached on the silver nanoparticles and its presence is revealed by both SERS and fluorescence measurements. These results pave the way towards the development of low-cost and stable hybrid fibres, in which SERS and fluorescence interrogation techniques are combined in the same optical device
Wavelength-selective robust fiber coupler for high-Q micro-resonators
No full textWe present results on the implementation of a robust fiber based system able to efficiently and selectively couple light to high-Q whispering gallery mode optical micro-resonators
Non-linear fluorescence excitation of Rhodamine 6G and TRITC labeled IgG in whispering gallery mode microresonators
No full textTwo photon versus one photon fluorescence excitation in whispering gallery mode microresonators
No full textWe investigate the feasibility of both one photon and two photon fluorescence excitation using whispering gallery mode microresonators. We report the linear and non linear fluorescence real-time detection of labeled IgG covalently bonded to the surface of a silica whispering gallery mode resonator (WGMR). The immunoreagents have been immobilized onto the surface of the WGMR sensor after being activated with an epoxy silane and an orienting layer. The developed immunosensor presents great potential as a robust sensing device for fast and early detection of immunoreactions. We also investigate the potential of microbubbles as nonlinear enhancement platform. The dyes used in these studies are dylight800, tetramethyl rhodamine isothiocyanate, rhodamine 6G and fluorescein. All measurements were performed in a modified confocal microscope.Preprin
SiO<sub>2-</sub>SnO<sub>2</sub>:Er<sup>3+</sup> planar waveguides: highly photorefractive glass-ceramics
No full textFor different applications in laser photonics and integrated optics, photorefractive materials are surely of great interest and play an important role in miniaturization of devices and fabrication of functional photonic structures such as gratings and waveguides. In this work, high photorefractivity of sol-gel derived SiO2-SnO2:Er3+ glass-ceramic planar waveguides, with negative effective refractive index change, is demonstrated. Through the photorefractivity investigation employing the UV pulsed KrF excimer laser (λ = 248 nm), the glass-ceramic planar waveguides show fast photorefractive response after a cumulative dose of only 0.3 kJ/cm2. A higher SnO2 content in the glass-ceramics leads to a greater change of saturated effective refractive index: Δneff = - (2.60 ± 0.20) x 10-3 at 1550 nm on the TE0 mode, for the 30 mol% SnO2 planar waveguides and Δneff = - (2.00 ± 0.20) x 10-3 on the 1550 nm TE0 mode, for the 20 mol% SnO2 ones. To investigate the structural modifications involved in the photorefractivity of the SiO2-SnO2:Er3+ glass-ceramics, XRD and Raman characterizations are employed. The grating fabrication by direct UV writing on the SiO2-SnO2:Er3+ glass-ceramic planar waveguide as well as an important reduction in the employed energy is demonstrated
A SERS affinity bioassay based on ion-exchanged glass microrods
No full textThe well-known enhancement effect of surface-enhanced Raman spectroscopy (SERS) is associated with the presence of metallic nanostructures at the substrate surface. Different bottom-up and top-down processes have been proposed to impart the substrate with such a nanostructured layer. The former approaches are low cost but may suffer from reusability and stability. The latter strategies are expensive, time consuming and require special equipment that complicate the fabrication process. Here, we present the possibility to obtain stable and reusable SERS substrates by a low-cost silver-sodium ion-exchange process in soda-lime glass microrods. The microrods were obtained by cutting the tip of the ion-exchanged soda-lime fiber, resulting in disks of about few millimeters in length and one hundred microns in diameter. A thermal annealing post-process was applied to trigger the reduction of Ag+ ions into nanoparticles (AgNPs) within the ion-exchanged glass microrods. Afterwards, ion-exchange and thermal treatments were carefully tuned to assure the presence of silver NPs exposed on the surface of the microrods, without using any chemical etching. An AFM analysis confirmed the presence of AgNPs with size of tens of nm on the surface of the fiber probe. A SERS affinity bioassay was developed on the probe with the final aim of detecting microRNA fragments acting as biomarkers of different diseases. Specifically a DNA hybridization assay was built up by anchoring a molecular beacon containing a Raman tag on the Ag surface via thiol chemistry. Initial SERS experiments confirmed the presence of the beacon on the NPs embedded on the microrods surface, as monitored by detecting main spectral bands ascribed to the oligonucleotide chain. Finally, the ability of the platform to interact with the target microRNA sequence was assessed. The analysis was repeated on a number of miRNA sequences differing from the target to evaluate the specificity of the proposed assay
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