120 research outputs found
Mechanical properties and strain monitoring of glass-epoxy composites with graphene-coated fibers
An engineered interphase can improve the mechanical properties of epoxy/glass composites simultaneously inducing a piezoresistive response. To prove this concept, E-glass fibers were coated with graphene oxide (GO) by electrophoretic deposition, while reduced graphene oxide (rGO) coated fibers were obtained by subsequent chemical reduction. The fiber-matrix interfacial shear strength (measured by the single-fiber fragmentation test) increased for both GO and rGO coated fibers. Unidirectional composites with a high content of both uncoated and coated fibers were produced and mechanically tested under various configurations (three-point bending, short beam shear and mode-I fracture toughness, creep). Composites with coated fibers performed similarly or better than composites prepared with uncoated fibers. Finally, composites with rGO coated fibers were tested for their piezoresistive response under both static and dynamic conditions. The electrical resistance changed proportionally to applied strain thus confirming the possibility of using composites with rGO coated fibers as strain sensors in load-bearing components
Sub-ppm NO2 Detection through Chipless RFID Sensor Functionalized with Reduced SnO2
NO2 is an important environmental pollutant and is harmful to human health even at very low concentrations. In this paper, we propose a novel chipless RFID sensor able to work at room temperature and to detect sub-ppm concentration of NO2 in the environment. The sensor is made of a metallic resonator covered with NO2-sensitive tin oxide and works by monitoring both the frequency and the intensity of the output signal. The experimental measurements show a fast response (a few minutes) but a very slow recovery. The sensor could therefore be used for non-continuous threshold monitoring. However, we also demonstrated that the recovery can be strongly accelerated upon exposure to a UV source. This opens the way to the reuse of the sensor, which can be easily regenerated after prolonged exposure and recycled several times
A Surface Plasmon Resonance Plastic Optical Fiber Biosensor for the Detection of Pancreatic Amylase in Surgically-Placed Drain Effluent
Postoperative pancreatic fistula (POPF), the major driver of morbidity and mortality following pancreatectomy, is caused by an abnormal communication between the pancreatic ductal epithelium and another epithelial surface containing pancreas-derived, enzyme-rich fluid. There is a strong correlation between the amylase content in surgically-placed drains early in the postoperative course and the development of POPF. A simple and cheap method to determine the amylase content from the drain effluent has been eagerly advocated. Here, we developed an amylase optical biosensor, based on a surface plasmon resonance (SPR) plastic optical fiber (POF), metallized with a 60 nm layer of gold and interrogated with white light. The sensor was made specific by coupling it with an anti-amylase antibody. Each surface derivatization step was optimized and studied by XPS, contact angle, and fluorescence. The POF-biosensor was tested for its response to amylase in diluted drain effluents. The volume of sample required was 50 \ub5L and the measurement time was 8 min. The POF-biosensor showed selectivity for amylase, a calibration curve log-linear in the range of 0.8\u201325.8 U/L and a limit of detection (LOD) of ~0.5 U/L. In preliminary tests, the POF-biosensor allowed for the measurement of the amylase content of diluted surgically-placed drain effluents with an accuracy of >92% with respect to the gold standard. The POF-biosensor allows for reliable measurement and could be implemented to allow for a rapid bedside assessment of amylase value in drains following pancreatectomy
Fabrication of a Highly NO2-Sensitive Gas Sensor Based on a Defective ZnO Nanofilm and Using Electron Beam Lithography
Hazardous substances produced by anthropic activities threaten human health and the green environment. Gas sensors, especially those based on metal oxides, are widely used to monitor toxic gases with low cost and efficient performance. In this study, electron beam lithography with two-step exposure was used to minimize the geometries of the gas sensor hotplate to a submicron size in order to reduce the power consumption, reaching 100 °C with 0.09 W. The sensing capabilities of the ZnO nanofilm against NO2 were optimized by introducing an enrichment of oxygen vacancies through N2 calcination at 650 °C. The presence of oxygen vacancies was proven using EDX and XPS. It was found that oxygen vacancies did not significantly change the crystallographic structure of ZnO, but they significantly improved the electrical conductivity and sensing behaviors of ZnO film toward 5 ppm of dry air
PDMS-Based Microdevices for the Capture of MicroRNA Biomarkers
The isolation and analysis of circulating biomarkers, the main concern of liquid biopsy,
could greatly benefit from microfluidics. Microfluidics has indeed the huge potentiality to bring liquid
biopsy into the clinical practice. Here, two polydimethylsiloxane (PDMS)-based microdevices are
presented as valid tools for capturing microRNAs biomarkers from clinically-relevant samples. After
an extensive study of functionalized polydimethylsiloxane (PDMS) properties in adsorbing/eluting
microRNAs, the best conditions were transferred to the microdevices, which were thoroughly
characterized. The channels morphology and chemical composition were measured, and parameters
for the automation of measures were setup. The best working conditions were then used with
microdevices, which were proven to capture microRNAs on all channel surfaces. Finally, microfluidic
devices were successfully validated via real-time PCR for the detection of a pool of microRNAs related
to non-small cell lung cancer, selected as proof-of-principle. The microfluidic approach described
here will allow a step forward towards the realization of an ecient microdevice, possibly automated
and integrated into a microfluidic lab-on-a-chip with high analytical potentialities
Investigation on oxygen vacancies influence on reduced WO3 sensing properties
Nowadays, the development of innovative and low-cost smart gas sensors is required in many applications,
including medical screening, environmental monitoring and precision farming. Chemoresistive gas sensors are
the most widely studied solid state gas sensors in this perspective, due to their small size, low production cost and
high sensitivity [1]. However, the lack of selectivity of the nanostructured metal oxides (MOX), i.e. the most
widely used class of sensing material so far, limited the effective and widespread adoption of these devices in
many applications. In the last few years, great attention has been paid on the development of innovative sensing
materials with advanced chemoresistive properties, able to overcome the shortcomings of the typical MOX,
seeking the optimization of the sensing performance. Modified MOX (doped or functionalised) proved to be good
candidates, owing to the right combination of typical MOX stability and improved selectivity due to surface
sensitisation [2]. Considering doping, the investigation of the influence of intrinsic dopants on the MOX sensing
properties has attracted considerable attention recently, particularly with regard to oxygen vacancies (Ov), which
have shown to have huge impact on the MOX electrical properties and surface reactivity.
In this work, a specific reducing treatment at high temperature has been investigated in order to develop reduced
WO3 with controlled Ov concentration. Nanostructured WO3 has been synthesised by using a simple sol gel
method. Then, a calcination treatment at 650ÂșC in air has been carried out in order to obtain a nanocrystalline and
stoichiometric WO3. A rapid thermal annealer (RTP) has been employed for the controlled reduction of the WO3
nanoparticles, by using H2 (4% in N2) as reducing agent. Different times (15 and 30 minutes) and temperatures
(from 300 to 800ÂșC) were investigated, in order to study their impact on the Ov formation. The Ov in the reduced
samples were characterized by using SEM-EDX, XRD and XPS. The XPS characterization has revealed a strong
increase in the 5+, 4+ and 3+ oxidation states of W as the treatment temperature rises, due to a strong increase in
the surface concentration of Ov. Both in-plane and bridging Ov were formed. An increase of the bulk Ov has been
observed as well by XRD analysis. On the other hand, the concentration of Ov did not change significantly with
treatment time. The reduced powders were deposited on silicon substrates and their sensing performances were
investigated vs. NH3. WO3 reduced at 700ÂșC showed the best sensing performance towards NH3 at near room
working temperature, showing an impressive increase of the sensitivity and selectivity compared to stoichiometric
WO3. The role of surface Ov in the sensing mechanism is under investigation
Different Strategies for the MicroïŹuidic PuriïŹcation of Antibiotics from Food: A Comparative Study
The presence of residual antibiotics in food is increasingly emerging as a worrying risk for human health both for the possible direct toxicity and for the development of antibiotic-resistant bacteria. In the context of food safety, new methods based on microfluidics could offer better performance, providing improved rapidity, portability and sustainability, being more cost effective and easy to use. Here, a microfluidic method based on the use of magnetic microbeads specifically functionalized and inserted in polymeric microchambers is proposed. The microbeads are functionalized either with aptamers, antibodies or small functional groups able to interact with specific antibiotics. The setup of these different strategies as well as the performance of the different functionalizations are carefully evaluated and compared. The most promising results are obtained employing the functionalization with aptamers, which are able not only to capture and release almost all tetracycline present in the initial sample but also to deliver an enriched and simplified solution of antibiotic. These solutions of purified antibiotics are particularly suitable for further analyses, for example, with innovative methods, such as label-free detection. On the contrary, the on-chip process based on antibodies could capture only partially the antibiotics, as well as the protocol based on beads functionalized with small groups specific for sulfonamides. Therefore, the on-chip purification with aptamers combined with new portable detection systems opens new possibilities for the development of sensors in the field of food safety
Onâchip purification of tetracycline from food matrices
Antibiotics are widespread both to treat human and animal diseases and to improve growth in food animals. However, their overuse in food-producing animals has led to critical issues for human health, such as the direct toxicity and the development of antibiotic-resistant bacterial strains. Therefore, the identification of traces of antibiotic in food before entering the market has became extremely important and brought out the need for novel bioanalytical methods and protocols. To meet this need, here, a microfluidic system was set up for the purification of tetracycline (TC) from raw milk, honey, and eggs. The system is based on the use of magnetic beads exposing copper ions, which are loaded in a microfluidic chamber and actuated by a ready-made device. Tetracycline is captured by copper ions present on the microbeads, purified from the unwanted raw material present in the initial sample and recovered by a suitable elution solution. Different elution solutions were tested and results were evaluated by X-ray photoelectron spectroscopy (XPS) and visible spectrometry. The microfluidic system was successfully employed for the purification of TC from raw milk, honey, and eggs after an initial dilution in buffer. The overall protocol was, therefore, demonstrated to efficiently purify tetracycline, laying the bases for a future implementation of in-field on-chip tests
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