Near-Field Opto-Chemical Sensors

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Near field behavior of SnO 2 particle-layer deposited on standard optical fiber by electrostatic spray pyrolysis method

We report the emergent optical near field profiles from standard single mode optical fibers on the cleaved end of which were deposited particle layers of SnO(2). The layers, composed of micron and sub-micron sized particles, were deposited by means of Electrostatic Spray Pyrolysis (ESP) technique. Powerful analytical tools such as Atomic Force Microscopy (AFM) and Scanning Near-field Optical Microscopy (SNOM) were used to obtain simultaneously the SnO(2) layers topography and the related optical near field intensity distribution, when the fiber-substrate is illuminated by a light radiation in NIR range. We show that isolated microstructures, positioned in correspondence of the fiber core, reveal highly unusual capability of locally enhancing the collected optical near field. The observed phenomenon leads to new concepts of fiber optic chemical sensors and in fiber microsystems as well

Transition mode long period grating biosensor with functional multilayer coatings

We report our latest research results concerning the development of a platform for label-free biosensing based on overlayered Long Period Gratings (LPGs) working in transition mode. The main novelty of this work lies in a multilayer design that allows to decouple the problem of an efficient surface functionalization from that of the tuning in transition region of the cladding modes. An innovative solvent/nonsolvent strategy for the dip-coating technique was developed in order to deposit on the LPG multiple layers of transparent polymers. In particular, 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. In this way, state-of-the-art-competitive sensitivity to surrounding medium refractive index changes was achieved. An extremely thin secondary functional layer of poly(methyl methacrylate-co-methacrylic acid) was deposited onto the primary coating by means of an original identification of selective solvents. This approach allowed to obtain desired functional groups (carboxyls) on the surface of the device for a stable covalent attachment of bioreceptors and minimal perturbation of the optical design. Standard 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide / N-hydrosuccinimide (EDC / NHS) coupling chemistry was used to link streptavidin on the surface of the coated LPG. Highly sensitive real-time monitoring of multiple affinity assays between streptavidin and biotinylated bovine serum albumin was performed by following the shift of the LPGs attenuation bands

Optical trap stiffness in the presence and absence of spherical aberrations

Optical traps are commonly constructed with high-numerical-aperture objectives. Oil-immersion objectives suffer from spherical aberrations when used for imaging in aqueous solutions. The effect of spherical aberrations on trapping strength has been modeled by approximation, and only a few experimental results are available in the case of micrometer-sized particles. We present an experimental study of the dependence of lateral and axial optical-trap stiffness on focusing depth for polystyrene and silica beads of 2 μm diameter by using oil- and water-immersion objectives. We demonstrate a strong depth dependence of trap stiffness with the oil-immersion objective, whereas no depth dependence was observed with the water-immersion objective. © 2006 Optical Society of America

Optoelectronic Capillary Sensors in Microfluidic and Point-of-Care Instrumentation

This paper presents a review, based on the published literature and on the authors’ own research, of the current state of the art of fiber-optic capillary sensors and related instrumentation as well as their applications, with special emphasis on point-of-care chemical and biochemical sensors, systematizing the various types of sensors from the point of view of the principles of their construction and operation. Unlike classical fiber-optic sensors which rely on changes in light propagation inside the fiber as affected by outside conditions, optical capillary sensors rely on changes of light transmission in capillaries filled with the analyzed liquid, which opens the possibility of interesting new applications, while raising specific issues relating to the construction, materials and instrumentation of those sensors

Bone marrow mesenchymal stem cell functions are stimulated by oxidized titanium surfaces

The aim of this study was to analyze the features of a novel oxidized titanium implant surface and to evaluate its effect on the response of human bone marrow mesenchymal stem cells (BM-MSC). 10x10x1 mm turned (control) and oxidized (test) titanium samples (P.H.I. s.r.l., San Vittore Olona, Milano, Italy) were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM) and characterized by height, spatial and hybrid roughness parameters. Primary cultures of BM-MSC were seeded on titanium samples and cell morphology, adhesion, proliferation and osteogenic differentiation, in terms of alkaline phosphatase activity, osteocalcin synthesis and extracellular matrix mineralization, were evaluated At SEM and AFM analyses, control and test surfaces appeared considerably different: turned samples were grooved, whereas oxidized surfaces showed a more complex micro- and nano-scaled texture, as evidenced by roughness parameters. At 6 hours from the plating, cell adhesion and osteogenic parameters were greater on oxidized (p<0.05 at least) vs turned surfaces, whereas the 7-d cell proliferation rate was similar on both samples. Although both control and test samples were in the range of average roughness proper of smooth surfaces, they exhibited significantly different topographic properties in terms of height, spatial and, mostly, of hybrid parameters. Furthermore, oxidized surfaces enhanced BM-MSC adhesion and differentiation, and this could be due to the different structure at micro and nano-scale levels