S. Lettieri

Marine Diatoms as Optical Biosensors

We have chemically modified the frustules of the marine diatom Coscinodiscus concinnus Wm. Smith to properly bind a highly selective bioprobe such as an antibody. By measuring the changes in the photoluminescence emission of diatoms frustules, we have monitored the molecular recognition event between the antibody and its ligand: the dissociation constant estimated is of the same order of that measured by standard Biacore. The nanostructured silica frustules, a low-cost and natural available material, have shown high sensitivity, equal to 1.2+/-0.2 nm microM(-1), and a detection limit of 100 nM, and thus are quite ideal candidates for lab-on-particle applications.

Highly sensitive optochemical gas detection by luminescent marine diatoms

The modifications of photoluminescence properties of silica frustules of different marine diatoms induced by adsorption of nitrogen dioxide, methane, and carbon monoxide are reported. Different species of diatoms were found to exhibit different relative responses and different gas concentration ranges of sensitivity, depending on the morphology and porosity of their frustules. The photoluminescence quenching shows surface signature, exhibiting a coverage-limited kinetics according to a Langmuir mechanism. Due to the large variety of dimensions, porosities, and surface morphologies available in nature, these materials appear to be promising to improve the selectivity of gas sensing based on photoluminescence optochemical transduction.

Hydrogenated amorphous silicon carbon alloys for solar cells

Hydrogenated amorphous silicon carbon films were grown by PECVD from silane/methane gas mixtures by fixing the methane ratio in the gas phase and by changing the rf power and pressure. The effects of the discharge parameters on the optical, electrical and structural properties were investigated. These effects were attributed to the variation of carbon content in the film. The analyses enabled us to determine the optimal growth conditions to produce a-SiC:H materials, suitable in solar cell applications, with a good photosensitivity and low defect density of states.

Optical, structural and electrical properties of μc-Si:H films deposited by SiH4+H2

Abstract Hydrogenated microcrystalline silicon (μc-Si:H) films were prepared by Plasma Enhanced Chemical Vapor Deposition from a mixture of silane highly diluted in hydrogen. The effect of the silane concentration on the deposition rate and on the optical, electrical and structural properties were investigated. The silane concentration appears to control orientation and grain size. Highly conductive μc-Si:H films were grown with high deposition rate at silane concentration of 3%. These films show an enhancement of the optical absorption in the near infrared region. In the visible region the absorption is lower than a-Si:H, however the transient PC signal, induced by 532 nm laser pulses (6 ns time duration), shows an high amplitude and a width comparable with the optical pulse one. μc-Si:H materials can be used for fast photodetectors of pulsed visible light.

Unconventional ratiometric-enhanced optical sensing of oxygen by mixed-phase TiO2

We show that mixed-phase titanium dioxide (TiO2) can be effectively employed as an unconventional, inorganic, dual-emitting, and ratiometric optical sensor of O2. Simultaneous availability of rutile and anatase TiO2 photoluminescence (PL) and their peculiar “anti-correlated” PL responses to O2 allow using their ratio as a measurement parameter associated with the O2 concentration, leading to an experimental responsivity being by construction larger than the one obtainable for single-phase PL detection. A proof of this concept is given, showing a two-fold enhancement of the optical responsivity provided by the ratiometric approach. Besides the peculiar ratiometric-enhanced responsivity, other characteristics of mixed phase TiO2 can be envisaged as favorable for O2 optical probing, namely (a) low production costs, (b) absence of heterogeneous components, and (c) self-supporting properties. These characteristics encourage experimenting with its use for applications requiring high indicator quantities at a co...

Giant O2-Induced Photoluminescence Modulation in Hierarchical Titanium Dioxide Nanostructures

We demonstrate exceptionally large modulation of PL intensity in hierarchical titanium dioxide (TiO2) nanostructures exposed to molecular oxygen (O2). Optical responsivities up to about 1100% at 20% O2 concentrations are observed in hyperbranched anatase-phase hierarchical structures, outperforming those obtainable by commercial TiO2 nanopowders (up to a factor of ∼7 for response to synthetic air) and significantly improving the ones typically reported in PL-based opto-chemical gas sensing using MOXs. The improved PL response is discussed in terms of the specific morphology of hierarchical structures, characterized by simultaneous presence of small nanoparticles, large surface areas, and large voids. These characteristics guarantee an optimal interplay between photogenerated charges, PL-active centers, and adsorbed gas molecules. The results highlight the potentialities offered by hierarchical structures based on TiO2 or other MOXs and open interesting scenarios toward the development of all-optical and/or hybrid (opto/electrical) chemical sensors with improved sensitivity.

Influence of molecule dwell time on μc-Si:H properties

Hydrogenated microcrystalline silicon (μc-Si:H) films have been prepared by plasma-enhanced chemical vapour deposition (PECVD) from a mixture of silane highly diluted in hydrogen. The effect of the molecule dwell time on the deposition rate and on the electrical and structural properties has been investigated. The molecule dwell time appears to control orientation and grain size. Highly conductive μc-Si:H films with a rough surface have been grown at a high deposition rate at higher molecule dwell time in an appropriate silane concentration. These films show an enhancement of the optical absorption in the near-infrared region suitable for photovoltaic applications.

Effective Antibody Anchoring on Gold Plate by Ultra-short UV Pulses

One of the main issues in biosensor research concerns the control of both the amount and the orientation of the bioreceptors. The so-called photonic induced immobilization can be very effective in anchoring antibodies with the variable part preferentially exposed, thus increasing the sensitivity of a Quartz Crystal Microbalance (QCM) immunosensor. In the present paper such a technique is applied to the detection of parathion, a relatively light analyte, demonstrating that the QCM is able to provide a detectable signal only if the photonic induced immobilization is applied, being completely insensitive to parathion when the bioreceptors are left to adhere randomly.

UV-light-assisted functionalization for sensing of light molecules

An antibody immobilization technique based on the formation of thiol groups after UV irradiation of the proteins is shown to be able to orient upside antibodies on a gold electrode of a Quartz Crystal Microbalance (QCM). This greatly affects the aptitude of antibodies in recognizing small antigens thereby increasing the sensitivity of the QCM. The capability of such a procedure to orient antibodies is confirmed by the Atomic Force Microscopy (AFM) of the surface that shows different statistical distributions for the height of the detected peaks, whether the irradiation is performed or not. In particular, the distributions are Gaussian with a standard deviation smaller when irradiated antibodies are used compared to that obtained with no treated antibodies. The standard deviation reduction is explained in terms of higher order induced on the host surface resulting from the trend of irradiated antibodies to be anchored upside on the surface with their antigen binding sites free to catch recognized analytes. As a result the sensitivity of the realized biosensor is increased by even more than one order of magnitude.