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Sensor Letters 01/2011; 9(2):925-928. · 0.82 Impact Factor
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Sensor Letters 01/2011; 9(2):920-924. · 0.82 Impact Factor
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ABSTRACT: In this paper we report on Surface Acoustic Wave (SAW) gas sensors based on quartz two-port resonators configured as oscillators at resonant frequency of 915 MHz. Nanowires (NW) of semiconducting tin dioxide (SnO<sub>2</sub>) have been grown by Vapor Phase (VP) process and used as filler in a nanocomposite layer to fabricate a highly-sensitive nanomaterial for gas detection, at room temperature. The nanocomposite layer consisting of an organic host-matrix of cadmium arachidate (CdA) and a weight-tailored filler of SnO<sub>2</sub> NW has been deposited as thin film onto SAW resonators by means of the molecular engineering Langmuir-Blodgett (LB) technique. SAW gas sensors performance was investigated in presence of ppm-level of ethanol, methanol, ethylacetate, toluene, at room temperature. The results demonstrate good sensitivity to vapors under test at ppm-level and a SAW gas response tuned by the weight-content of filler of SnO<sub>2</sub> NW in the LB nanocomposite layer.
Sensors, 2008 IEEE; 11/2008
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ABSTRACT: A thin-film bulk acoustic resonator (TFBAR) based on a vibrating membrane of AlN/Si<sub>3</sub>N<sub>4</sub> has been fabricated onto a silicon substrate and functionally characterized as gas sensor at a resonating frequency of 1.045 GHz. This novel TFBAR-based gas sensor has been functionalized by a sensing nanocomposite layer, prepared by a Langmuir-Blodgett (LB) technique, of single-walled carbon nanotubes (SWCNTs) embedded in a host matrix of organic material of cadmium arachidate. High-performance gas detection at room temperature of a SWCNT-coated TFBAR sensor has been reported. The sensing device exhibits high sensitivity (e.g., acetone: 12 kHz/ppm; ethylacetate: 17.3 kHz/ppm), fast response (within 2-3 min), slow reversibility (within 1 h), and good repeatability (les 5% variation) of response toward tested organic vapors of acetone, ethylacetate, and toluene.
IEEE Transactions on Electron Devices 06/2008; · 2.32 Impact Factor
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ABSTRACT: Recent preliminary studies have demonstrated the feasibility of using Single-Walled Carbon Nanotubes (SWCNTs) as sensitive coatings of optical fiber sensors for the detection of chemical traces in water at room temperature. A low-finesse extrinsic Fabry-Perot configuration was adopted as sensing scheme and Langmuir-Blodgett thin SWCNT films have been integrated to form the sensing optical cavity. This contribution reports on the improvement of the per-formance of such SWCNTs-based chemo-optic transducers based on a proper choice of the number of carbon nanotube monolayers. The results here shown reveal a strong enhancement in term of sensor sensitivity of more than one order of magnitude, combined with a significant reduction of the response times. The achieved sub-ppm resolution, the response rapidity, and the complete and fast recovery of the initial output signal corresponding to the condition of uncontaminated water reveal the potentiality of the improved version of the sensor to be applied for water monitoring applications.
The Open Environmental & Biological Monitoring Journal 01/2008; 1:26-32.
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ABSTRACT: This work is focused on the room temperature sensitivities and response times analysis against aromatic volatile organic compounds of both silica optical fiber and quartz crystal microbalance sensors, coated by single-walled carbon nanotubes (SWCNTs) Langmuir-Blodgett multilayers as highly sensitive nanomaterials. The fabricated samples have been characterized by means of X-ray diffraction, high-resolution transmission electron microscopy and scanning electron microscopy, silica optical fiber, and quartz crystal microbalance transducers have been simultaneously exposed at room temperature to toluene and xylene individual vapors in the ppm range. For each transducer type, a time division multiplexing approach has been exploited, enabling the simultaneous interrogation of up to 8 optical and 6 acoustic probes, respectively. The results obtained indicate that both optical and acoustic sensors provide very high reproducibility and sensitivity either towards toluene or xylene, with a resolution of few hundreds of ppb. Furthermore, sensitivities and response times turned out to be dependent on the particular analytes used for the vapors testing. Both transducer types demonstrate a similar response time, while with regard the recovery time, the optical detection seems to be significantly faster than the electrical counterpart. The effect of the SWCNTs monolayers number on sensors sensitivity and response time has also been investigated, demonstrating the possibility to enhance the performances of the proposed transducers by tailoring the geometric properties of the sensitive nanomaterial.
IEEE Transactions on Nanotechnology 12/2007; · 2.29 Impact Factor
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ABSTRACT: We demonstrate the successful operation of a chemical microsensor based on thin film bulk acoustic resonator (TFBAR) for organic vapor detection at room temperature. The TFBAR consists of a vibrating membrane of AlN/Si<sub>3</sub>N<sub>4</sub> fabricated on silicon substrate and resonating at the frequency of 1.045 GHz. Using a nanocomposite layer based on Single-Walled Carbon Nanotubes (SWCNTs) and prepared by the Langmuir-Blodgett technique onto the TFBAR device as highly-sensitive nanomaterial, the sensing performance of TFBAR sensor has been evaluated both as a passive device by a network analyzer with phase and insertion loss responses, and as oscillator with frequency response. The vapor sensing characteristics of SWCNTs-based TFBAR sensor are presented illustrating interesting results.
Sensors, 2007 IEEE; 11/2007
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ABSTRACT: In this letter, the possibility to use single-walled carbon nanotubes (SWCNTs) as sensitive nanostructured material for the development of an optoelectronic sensor that can perform chemical detection in water has been investigated and demonstrated for the first time. The fabricated sensor has been employed in a reflectometric system involving single wavelength reflectance measurements. The good stability of the steady-state signal, the high sensitivity, as well as the good response dynamics obtained in the case of toluene detection confirm the potentiality of SWCNTs to be employed in a water environment.
IEEE Sensors Journal 08/2007; · 1.52 Impact Factor
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ABSTRACT: HiPco (high-pressure CO dissociation process) single-walled carbon nanotube (SWCNT) bundles containing Fe particles were purified in a two-step purification process by thermal annealing in oxygen and post-treatment in HCl. Nanocomposite films of pristine and purified SWCNTs embedded in an organic matrix of cadmium arachidate (CdA) were prepared by a Langmuir–Blodgett (LB) molecular engineering technique with a fixed weight filler content of 75 wt% onto a surface acoustic wave (SAW) transducer operating as an oscillator at a frequency of 433 MHz. The raw and purified samples were characterized at various stages of the purification process using thermogravimetric analysis (TGA), high-resolution transmission electron microscopy (HR-TEM), along with energy-dispersive x-ray spectroscopy (EDS), field emission scanning electron microscopy (FE-SEM) and x-ray diffraction (XRD). Functional characterizations of the SWCNT–nanocomposite-based SAW sensors were investigated towards methanol, isopropanol and ethanol, and demonstrated high sensitivity, reversibility, fast response and ppm level detection at room temperature. Results indicate that the sensitivity of the SAW sensors based on a nanocomposite film of oxygen-annealed SWCNTs is enhanced to the alcohols tested at room temperature. Purification of the SWCNTs in the nanocomposite film affects the SAW sensitivity to alcohol by modulating the sensing properties. The sensing mechanisms are analysed and discussed.
Nanotechnology 04/2007; 18(18):185502. · 3.98 Impact Factor
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ABSTRACT: In this letter, the feasibility of using hollow-core optical fibers (HOFs) integrated with carbon nanotubes for volatile organic compound (VOC) detection applications has been investigated. The Langmuir-Blodgett technique has been used in order to transfer single walled carbon nanotubes (SWCNTs) onto HOFs. Reflectance characterization of the obtained sensing probes has been carried out in the range 1520-1620 nm. Finally, the sensing capability of the HOF sensors has been investigated by exposure in a test chamber to traces of tetrahydrofuran. The preliminary results obtained demonstrate the capability of the novel HOF sensor to perform chemical detection of VOCs showing a good sensitivity and fast response times
IEEE Photonics Technology Letters 12/2006; · 2.19 Impact Factor
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ABSTRACT: In this letter, preliminary results on the feasibility to use optical fiber sensors coated by single-walled carbon nanotubes (SWCNTs)-based sensitive materials for hydrogen detection at cryogenic temperatures are presented. The optical probes have been realized by the Langmuir-Blodgett deposition of close-end and open-end SWCNTs on the distal end of standard optical fibers. The results obtained from hydrogen detection testing, carried out at a temperature as low as 113 K, demonstrate the excellent potentiality of the proposed configuration to sense very low percentages of gaseous hydrogen (<5%), with good recovery and reversibility features as well as fast response times.
Applied Physics Letters 11/2006; 89(20):201106-201106-3. · 3.84 Impact Factor
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ABSTRACT: The authors investigate the sensing properties of single-walled carbon nanotubes (SWCNTs) films, which are used as nanostructured materials for chemical sensors onto three types of transducers using different principles of operation as surface acoustic waves (SAWs), quartz-crystal microbalance (QCM), and a standard silica optical fiber (SOF) for detection of volatile organic compounds at a room temperature. The sensing probes have been configured as 315- and 433-MHz SAW two-port resonator-based oscillator, 10-MHz QCM resonator, and SOF light-reflectometry-based system at a wavelength of 1310 nm. A nanocomposite film of SWCNTs embedded in a cadmium-arachidate matrix was deposited by Langmuir-Blodgett (LB) technique onto the SAW sensors. An LB multilayer of SWCNTs-onto-CdA buffer material was also deposited onto the QCM and SOF sensors. The experiments demonstrate that carbon-nanotubes acoustic and optical sensors are highly sensitive to a wide range of polar and nonpolar organic solvents up to a sub-ppm detection limit at a room temperature
IEEE Sensors Journal 09/2006; · 1.52 Impact Factor
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ABSTRACT: The incorporation of single-wall carbon nanotubes (SWCNTs) in cadmium arachidate film by means of the Langmuir-Blodgett (LB) technique was investigated as a function of arachidic acid/SWCNT mass ratio at the air/water interface and in Langmuir-Blodgett films. The behaviour at the air/water interface shows that SWCNTs act as an independent phase with respect to the cadmium arachidate. Deposition conditions are optimized when the weight ratio between the arachidic acid (AA) and SWCNTs is in the range 0.018:1 to 1:1. The general order of the LB multilayered structure was destroyed by the progressive density increase in SWCNT quantity as evidenced by X-ray reflectivity (XRR) analysis. Scanning electron microscopy images indicated that when a multilayered structure was formed its layers consisted of SWCNT bundles stacked one over the other. Copyright © 2006 John Wiley & Sons, Ltd.
Surface and Interface Analysis 08/2006; 38(9):1285 - 1290. · 1.18 Impact Factor
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ABSTRACT: Single-walled carbon nanotubes (SWCNTs) are advanced nanostructured materials with promising sensing properties in terms of sensitivity, low sub-ppm limit of detection, on-line and real-time vapour detection, at room temperature. This work is focused on the study of the sensitivity to aromatic volatile organic compounds (VOCs) of standard silica optical fibre (SOF) and quartz crystal microbalance (QCM) sensors incorporating Langmuir–Blodgett multilayers of SWCNTs. Multilayers of SWCNTs with different thicknesses and successfully transferred directly onto the sensors' surface were tested for the detection of toluene and xylene at room temperature and compared with the sensing performances of SWCNT multilayers buffered by a linker multilayer of cadmium arachidate. The optical and acoustic sensors' principle of operation relies respectively on the complex dielectric function and mass change induced by target analyte molecules adsorbed into the sensitive nanomaterials. A time division multiplexing approach for both optical and acoustic chemical sensors has been exploited in order to simultaneously test up to eight SOF and six QCM sensors. The results obtained demonstrate that the sensors based on SWCNTs provide high sensitivity, very low limits of VOC detection and fast response, at room temperature, with a clear dependence of the sensors' sensitivities on the nanomaterial thickness. Furthermore, higher sensitivity was observed in the case of optical fibre sensors exposed to xylene; in addition, behaviour with the opposite sign in the optical response occured between buffered and not buffered SWCNTs overlayers. Also, effects of humidity have been investigated in the case of optical fibre sensors demonstrating a linear dependence of the response at a constant temperature of 28 °C.
Measurement Science and Technology 04/2006; 17(5):1220. · 1.49 Impact Factor
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ABSTRACT: Carbon nanotube coated acoustic and optical sensors have been successfully studied for volatile organic compound (VOC) sensing applications, at room temperature. Here, Langmuir–Blodgett (LB) films consisting of tangled bundles of single-walled carbon nanotubes (SWCNTs) have been transferred onto different transducing sensors by using a linker–buffer LB multilayered material of cadmium arachidate pre-deposited on the sensor surface to promote adhesion of SWCNTs. Two different kinds of sensors have been designed, fabricated and utilized: quartz crystal microbalance 10 MHz AT-cut quartz resonators and standard silica optical fibre sensors based on light reflectometry at a wavelength of 1310 nm. The proposed detection techniques are focused on two key parameters in gas sensing applications: mass and refractive index, and their changes induced by gas molecule absorption. The results indicate high sensitivity, good repeatability and reversibility. Signals from each sensor type have been analysed and processed by using pattern recognition techniques such as principal component analysis and use of artificial neural networks. The recognition of the hybrid system is successfully performed, improving the data fusion from acoustic and optical sensors with SWCNT-functionalized sensors that are highly discriminating. To our knowledge, this is the first reported study of combined hybrid integration of acoustic sensors with optical fibre sensors using nanostructured materials as single-walled carbon nanotubes for VOC detection, at room temperature.
Nanotechnology 09/2005; 16(11):2536. · 3.98 Impact Factor
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ABSTRACT: We investigate the sensing properties of single-walled carbon nanotube (SWCNTs) films used as nanostructured materials for chemical sensors onto three types of transducers using different principles of operation. These are surface acoustic waves (SAWs), quartz crystal microbalance (QCM) and standard silica optical fiber (SOF) for detection of organic solvents, at room temperature. The sensing probes have been configured as a 315- and 433-MHz SAW two-port resonator based oscillator, 10 MHz QCM resonator, and SOF light-reflectometry based system at a wavelength of 1310 nm. A nanocomposite film of SWCNTs embedded in a cadmium arachidate (CdA) matrix was deposited by an LB technique onto SAW sensors. An LB multilayer of SWCNTs-onto-CdA buffer material was also deposited onto QCM and SOF sensors. Our experiments demonstrate that carbon nanotube acoustic and optical sensors are highly sensitive to a wide range of polar and non-polar organic solvents up to a sub-ppm detection limit.
Sensors, 2004. Proceedings of IEEE; 11/2004
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ABSTRACT: We demonstrate the integration of single-walled carbon nanotubes (SWCNTs) onto quartz crystal microbalance (QCM) and standard silica optical fiber (SOF) sensor for alcohol detection at room temperature. Different transducing mechanisms have been used in order to outline the sensing properties of this class of nanomaterials, in particular the attention has been focused on two key parameters in sensing applications: mass and refractive index changes due to gas absorption. Here, Langmuir–Blodgett (LB) films consisting of tangled bundles of SWCNTs without surfactant molecules have been successfully transferred onto QCM and SOF. Mass-sensitive 10 MHz QCM SWCNTs sensor exhibited a resonant frequency decreasing upon tested alcohols exposure; also the normalized optoelectronic signal (λ=1310 nm) of the refractive index-sensitive SOF SWCNTs sensor was found to decrease upon alcohols ambient. Highly sensitive, repeatable and reversible responses of the QCM and SOF SWCNTs sensors indicate that the detection, at room temperature, in a wide mmHg vapor pressures range of alcohols and potentially other volatile organic compounds is feasible.
Applied Physics Letters 09/2004; 85(12):2379-2381. · 3.84 Impact Factor
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ABSTRACT: The goal of our work has been the incorporation of single wall carbon nanotubes (SWCNTs) in Langmuir-Blodgett organic multilayers. We deposited multilayers consisting of six cadmium behenate (CdBe) layers alternated with one layer of SWCNTs. SWCNTs and CdBe molecules were spread at the air/water interface and deposited at a fixed compression pressure for CdBe (27mN/m) and two different compression pressures for the nanotubes, 15 and 45mN/m, respectively. Low angle X-ray measurements exhibited distinct satellite peaks in all the samples demonstrating that the periodicity of the LB CdBe reference sample was conserved when SWCNTs were inserted in the structure. In agreement with the observations at optical and electronic microscopes, the samples deposited at the higher compression pressure (45mN/m) presented more densely-packed and more uniform coverage of nanotubes.
01/2004;
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ABSTRACT: The development of biocompatible materials which can be processed into three-dimensional scaffolds and the design of appropriate configurations in order to enable the cellular infiltration and proliferation is a major issue in the tissue engineering. The hyaluronan total benzyl ester (Hyaff 11) has been found to be suitable substrate to grow a variety of cell types. Since structural, physical, chemical and biological data can help for tailoring appropriate scaffold for tissue engineering, information on chemicophysical properties on degradability of hyaluronan total benzyl ester non-woven has been obtained. The thermal analysis, the evaluation of the surface chemical composition, the morphology, the mechanical behaviour and the swelling tests were carried out on these materials. The hyaluronan total benzyl ester non-woven showed a thermal stability up to 220 degrees C and the surface composition differed from that of the bulk for C-O and C-C contribution. No contaminant were detected. The non-woven swelled in culture medium. Moreover the mechanical tests showed that when submitted to a press treatment, the samples have best mechanical properties. The pressed Hyaff 11 non-woven undergoes degradation when exposed to DMEM. The frying and breaking of the fibres, a decrease of the mechanical properties and a molecular weight loss have been observed. First, the ester bond of the Hyaff 11 non-woven is hydrolysed and the benzylic alcohol is released and the low molecular weight values indicate that a cleavage of the polymer is promoted by the components of the culture medium. After 11 days, some fragments, constituted by hyaluronic acid with a molecular weight of 23,000 Da became soluble in the medium. No oligomer was detected.
Biomaterials 03/2002; 23(4):1053-63. · 7.40 Impact Factor
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ABSTRACT: The barrier membranes for guided tissue regeneration (GTR) to treat bone defects have to satisfy the criteria of biocompatibility, cell-occlusiveness, space-making, tissue integration and clinical manageability. In this study a system constituted of a poly(L-lactide) acid (PLLA) asymmetric membrane combined with an alginate film was prepared. The PLLA membrane functions to both support the alginate film and separate the soft tissue; the alginate film is intended to act as potential vehicle for the growth factors to promote osteogenesis. The structural, morphological, and mechanical properties of the bilamellar membrane and its stability in culture medium were evaluated. Moreover, the feasibility of using the alginate membranes as controlled-release delivery vehicles of TGF-beta was monitored. Finally, the bacterial adhesion and permeability of Streptococcus mutans, selected for the high adhesive affinity, were monitored. The results showed that the surfaces of the alginate side, to be used in contact with the bone defect, were rougher than PLLA ones. When in contact with complete culture medium, the PLLA-alginate membrane retained its mechanical and structural properties for more than 100 days. Then, the degradation processes occurred but the membrane continued to be stable and manageable for 6 months. Growth factors such as TGF-beta can be incorporated into alginate membranes functioning as drug delivery vehicle, and retain the biological activity when tested in an in vitro model system. The obtained membrane acted as a barrier to the passage of S. mutans bacteria and showed to promote a lower bacterial adhesion with respect to commercial GTR membranes.
Journal of Biomedical Materials Research 12/2001; 57(2):248-57.
