Michele Sozzi

Toward A Highly Specific DNA Biosensor: PNA-Modified Suspended-Core Photonic Crystal Fibers

The feasibility of a biosensor for DNA detection based on suspended-core photonic crystal fibers is investigated. The possibility of functionalization of the hole surface, which allows DNA strand binding, is demonstrated, along with the selective detection of DNA through hybridization of immobilized peptide nucleic acid probes with their full-complementary and mismatched DNA segments.

Optical Fiber Ring Cavity Sensor for Label-Free DNA Detection

An outcladding sensitized label-free DNA biosensor is developed based on tilted fiber Bragg gratings. The biosensor, functionalized with peptide nucleic acid (PNA) probes, is based on a double tilted fiber Bragg grating that forms a modified Fabry-Perot core-cladding closed-loop cavity. Interference is set up between an injected guided mode and the reflected core mode and cladding modes created by the light scattered by the tilted gratings, leading to the generation of interference fringes within both these spectral notches. When the DNA binds to the PNA probes attached onto the fiber cladding, a refractive index change occurs at the cladding-PNA interface and the fringe visibility changes accordingly. Real-time spectral measurement results are reported, showing that a 10-nM DNA solution induces a 10% modulation of the corresponding fringes visibility. Cycling tests are performed for measuring and checking the repeatability of the sensor.

Optical Fiber Sensors for Label-Free DNA Detection

Optical fiber-based biosensors are an emerging field of research with an extremely broad area of possible applications and a disruptive potential to turn the paradigm known as lab-on-fiber into reality. In the past few years, a variety of system choices has been explored, ranging from the type of sensing fiber, to the optical transducing element, to possible sensing amplification strategies. We revise some of the possible approaches to the design of a biosensor, highlighting their advantages and disadvantages, based on previous literature and on the experience of our research groups. The discussion is focused onto DNA sensing systems, especially in a label-free format, where the hybridization and recognition of the sought DNA sequence is translated directly into a modification of the optical fiber properties.

Modification of a long period grating-based fiber optic for DNA biosensing

The feasibility of a biosensor for DNA label-free detection, based on long period fiber gratings, has been investigated. The surface of the grating has been functionalized with Peptide Nucleic Acid (PNA) probes. DNA strands, matched with the PNA probes, have been immobilized on the surface itself. The possibility of a resonant wavelength shift in the transmission spectrum due to the DNA capture will be discussed. The problem of reusing the sensor for multiple measurements will also be addressed.

Non-monotonous refractive index changes recorded in a phosphate glass optical fibre using 248nm, 500fs laser radiation

Results are presented on the photosensitivity behavior of a phosphate glass optical fibre using 248nm, 500fs laser radiation. Bragg grating exposures performed using a double phase mask interferometer and peak intensities of 0.37TW/cm2, revealed that grating growth becomes non-monotonic in terms of average and modulated refractive index changes, resembling the Type IIA photosensitivity behavior. Average refractive index changes greater than 10−3 were measured after accumulated energy density doses of 6.5KJ/cm2. The Bragg gratings inscribed maintained significant part of their strength up to 377°C. Exposed and side-polished fibre samples were subjected to Knoop micro-hardness measurements for revealing that the irradiated glass undergoes significant volume dilation.

Thermal effect-resilient design of large mode area double-cladding Yb-doped photonic crystal fibers

The effects of thermally-induced refractive index change on the guiding properties of different large mode area fibers have been numerically analyzed. A simple but accurate model has been applied to obtain the refractive index change in the fiber cross-section, and a full-vector modal solver based on the finite-element method has been used to calculate the guided modes of the fibers operating at high power levels. The results demonstrate that resonant structures added to the fiber cross-section can be exploited to provide efficient suppression of high-order modes with a good resilience to thermal effects.

Air-suspended solid-core fibers for sensing

Microstructured optical fibers have the potential to provide improved performance relative to more traditional spectroscopic fiber sensors. In fact the manipulation of the geometry of the fiber cross section can allow to maximize the interaction of light and sample. Recently, solid air-suspended core fibers have been appointed as the most promising design for evanescent field sensing. In this kind of device, sensing is carried out through the interaction between evanescent tails of index-guided modes and sample, which fills cladding holes. Suspended core fibers are made by three silica webs joining in the fiber center and forming the core. This design can provide an evanescent field power fraction greater than any other structure previously proposed, together with a wide transmission band. In this paper, the electromagnetic field behaviour of the guided modes of a range of suspended-core fibers is investigated, using a full-vectorial finite element based modal solver. The impact of different design parameters and materials on guidance, the amount of power in the cladding and the possibility of obtaining effective single-mode guidance are also investigated.

Photodynamic therapy: a synergy between light and colors

In this work the application of different laser wavelengths, in combination with different photosensitizing dyes, to bacterial cultures, in liquid or solid mean, has been investigated. Two types of Streptococcus mutans cultures have been used for the experiments, inside agar and saline solution. Three different laser wavelengths have been applied to the bacterial cultures together with a photosensitizing dye: red diode (650 nm) on cultures stained with Toluidine Blue, blueviolet diode (450 nm) on cultures stained with Curcumin and KTP laser (532 nm) on cultures stained with Erythrosine. The choice of the dye has been made considering the color affinity with the used wavelength. Tests without dyes have also been performed. Experimental results show that the maximum inhibition of bacterial growth with the blue laser has been obtained in a saline solution with a growth of 40.77%. While the combination with Curcumin lead to an inhibition growth of about 99.1%, for a laser fluence of 30J/cm2. No inhibition has been observed using the red laser in saline solution without dye, while the combination with Toluidine Blue resulted in a 100% inhibition growth for 20 and 30 J/cm2 fluences. An inhibition growth of just 16.26% has been obtained with the use of KTP laser in saline solution without dye. The use of Erythrosine had the effect of a complete inhibition growth. From the obtained results it is possible to observe that the combination of laser wavelength with a particular photosensitizing dye can dramatically increase the bacterial growth.

Optimization of pulsed fiber laser scribing for CdTe and CIGS solar cells

The FP7 EU funded ALPINE project is focused on the processing of new type of thin film CdTe and CIGS photovoltaic modules by means of pulsed fiber laser scribing. The latest results of scribing tests performed for different laser parameters for P1, P2 and P3 steps in both CdTe and CIGS solar cells are discussed showing examples for CdTe module processing.

Long period grating-based fiber optic sensor for label-free DNA detection

The feasibility of a DNA biosensor based on a long period grating inscribed in an optical fiber has been investigated. The sensor can perform a label-free detection, due to the functionalization of the optical fiber external surface with peptide nucleic acid probes matched with the DNA target strands. A wavelength shift of 1.2 nm for a 120 nM DNA solution has been measured. Fluorescence measurements have been also taken, in order to give a further proof of the fiber functionalization and hybridization.