Rui Igreja

Analysis of the thermally stimulated discharge current around glass-rubber transition temperature in polyethylene terephthalate

The nature of the thermally stimulated discharge current (TSDC) for polyethylene terephthalate samples in the temperature range from room temperature to above glass-rubber transition temperature of the amorphous phase is analyzed. The well conditioning of the sample is strictly necessary in order to have a good reproducibility and accuracy of results. A main peak was observed whose maximum temperature moves towards a lower value with the decreasing of the amount of charge that flows through the sample during polarization. The peak position changes as well, if the sample is polarized in air or in oxygen and the nature of change is more important in the case of oxygen. The shape of the peak is complex and at least four shoulders have been identified around 85, 90, 105, and 125 °C using the cleaning technique. The activation energy tends to increase with repetition of the TSDC runs, in the glass-rubber transition temperature range, in the case when the cleaning technique is used for the peaks separation. For...

Application of Hyperthermia for Cancer Treatment: Recent Patents Review

Cancer is one of the main causes of death in the world and its incidence increases every day. Current treatments are insufficient and present many breaches. Hyperthermia is an old concept and since early it was established as a cancer treatment option, mainly in superficial cancers. More recently the concept of intracellular hyperthermia emerged wherein magnetic particles are concentrated at the tumor site and remotely heated using an applied magnetic field to achieve hyperthermic temperatures (42-45°C). Many patents have been registered in this area since the year 2000. This review presents the most relevant information, organizing them according to the hyperthermic method used: 1) external Radio-Frequency devices; 2) hyperthermic perfusion; 3) frequency enhancers; 4) apply heating to the target site using a catheter; 5) injection of magnetic and ferroelectric particles; 6) injection of magnetic nanoparticles that may carry a pharmacological active drug. The use of magnetic nanoparticles is a very promising treatment approach since it may be used for diagnostic and treatment. An ideal magnetic nanoparticle would be able to detect and diagnose the tumor, carry a pharmacological active drug to be delivered in the tumor site, apply hyperthermia through an external magnetic field and allow treatment monitoring by magnetic resonance imaging.

Recent advances in ceramic-polymer composite electrets

Recent work on ceramic-polymer composites for piezoelectric and pyroelectric applications is presented with special regard to the production and characterisation of new composite materials as well as two new applications of these composite materials. One of these composites is made using ceramic powders obtained using the sol-gel technique. This technique allows a better control of the stoichiometry as well as a lower temperature of crystallisation as compared with the conventional mixed oxides route. A better control of powder morphology also produces ceramic grains in the submicron range enabling the production of nanocomposites with electroactive properties. A second type of composite is reported using high temperature polymer PEEK, thus extending the temperature range of common electroactive composite materials. Finally the use of these materials is demonstrated in two piezoelectric applications, an angular acceleration accelerometer and an acoustic emission sensor.

Processing and characterization of sol-gel derived modified PbTiO3 for ferroelectric composite applications

Powders of (Pb0.8Ca0.2)(Ti0.99Mn0.01)O3 have been prepared by sol-gel processing. A tetragonal phase is formed after heat treatment at as low as 800°C. The tetragonality was found to be 1.053±0.005 and Curie temperature 315°C. Composite films with 0–3 connectivity were prepared from 800°C heat treated powders and P(VDF-TrFE) by the solvent casting technique. Composites poled at 20 MV/m, exhibited a pyroelectric coefficient of 17.4 μC/m2K and a pyroelectric figure of merit (FOMp=p/ε) of 0.51 μC/m2K.

Single nucleotide polymorphism detection using gold nanoprobes and bio‐microfluidic platform with embedded microlenses

The use of microfluidics platforms combined with the optimal optical properties of gold nanoparticles has found plenty of application in molecular biosensing. This paper describes a bio‐microfluidic platform coupled to a non‐cross‐linking colorimetric gold nanoprobe assay to detect a single nucleotide polymorphism associated with increased risk of obesity fat‐mass and obesity‐associated (FTO) rs9939609 (Carlos et al., 2014). The system enabled significant discrimination between positive and negative assays using a target DNA concentration of 5 ng/µL below the limit of detection of the conventionally used microplate reader (i.e., 15 ng/µL) with 10 times lower solution volume (i.e., 3 µL). A set of optimization of our previously reported bio‐microfluidic platform (Bernacka‐Wojcik et al., 2013) resulted in a 160% improvement of colorimetric analysis results. Incorporation of planar microlenses increased 6 times signal‐to‐loss ratio reaching the output optical fiber improving by 34% the colorimetric analysis of gold nanoparticles, while the implementation of an optoelectronic acquisition system yielded increased accuracy and reduced noise. The microfluidic chip was also integrated with a miniature fiber spectrometer to analyze the assays’ colorimetric changes and also the LEDs transmission spectra when illuminating through various solutions. Furthermore, by coupling an optical microscope to a digital camera with a long exposure time (30 s), we could visualise the different scatter intensities of gold nanoparticles within channels following salt addition. These intensities correlate well to the expected difference in aggregation between FTO positive (none to small aggregates) and negative samples (large aggregates). Biotechnol. Bioeng. 2015;112: 1210–1219.

Organic Vapour Discrimination Using Sorption Sensitive Chemocapacitor Arrays

An interdigital chemocapacitor (IDC) sensor array has been developed to discriminate organic vapour samples with pure organics and mixtures. Sensors were coated with diverse polymers (PEUT, PDMS and modified PDMS). Dedicated signal conditioning circuits were developed with a reduced S/N ratio enabling measurement of capacitance changes as low as 0.07 fF. A new sampling technique was also developed to improve isobaric sampling conditions on the sensors chamber. Linear techniques such as Principal Component Analysis (PCA) for discrimination between the different samples were sucessfully applied. As far as we know, this is the first time that an array of interdigital chemocapacitors is used for organic vapour discrimination.

Digital Microfluidics for Nucleic Acid Amplification

Digital Microfluidics (DMF) has emerged as a disruptive methodology for the control and manipulation of low volume droplets. In DMF, each droplet acts as a single reactor, which allows for extensive multiparallelization of biological and chemical reactions at a much smaller scale. DMF devices open entirely new and promising pathways for multiplex analysis and reaction occurring in a miniaturized format, thus allowing for healthcare decentralization from major laboratories to point-of-care with accurate, robust and inexpensive molecular diagnostics. Here, we shall focus on DMF platforms specifically designed for nucleic acid amplification, which is key for molecular diagnostics of several diseases and conditions, from pathogen identification to cancer mutations detection. Particular attention will be given to the device architecture, materials and nucleic acid amplification applications in validated settings.

Stress Induced Mechano-electrical Writing-Reading of Polymer Film Powered by Contact Electrification Mechanism

Mechano-electrical writing and reading in polyaniline (PANI) thin film are demonstrated via metal-polymer contact electrification mechanism (CEM). An innovative conception for a non-destructive self-powered writable-readable data sheet is presented which can pave the way towards new type of stress induced current harvesting devices. A localized forced deformation of the interface has been enacted by pressing the atomic force microscopic probe against the polymer surface, allowing charge transfer between materials interfaces. The process yields a well-defined charge pattern by transmuting mechanical stress in to readable information. The average of output current increment has been influenced from 0.5 nA to 15 nA for the applied force of 2 nN to 14 nN instead of electrical bias. These results underscore the importance of stress-induced current harvesting mechanism and could be scaled up for charge patterning of polymer surface to writable-readable data sheet. Time evolutional current distribution (TECD) study of the stress-induced patterned PANI surface shows the response of readability of the recorded data with time.

Interdigitated Capacitive Immunosensors With PVDF Immobilization Layers

We have explored for the first time PVDF Immobilon-P membranes, attached to interdigitated capacitor microelectrodes, as 3-D matrixes for the immobilization of antibodies in an interdigitated capacitive immunosensor format. The thick membranes allow distribution of antibodies across the entire region probed by the measuring electric field applied to the microelectrodes. This new approach is an alternative to the use of nanometer electrodes necessary to detect smaller layers of antibodies. As a proof-of-concept, a horseradish peroxidase (HRP) antibody/antigen affinity pair allowed for specific detection of the antigen in blocked membranes containing the antibody. Immobilization of antibody and penetration of antigen inside the PVDF membrane was assessed by fluorescence measurements and by an HRP enzymatic assay, respectively. The new interdigitated capacitive immunosensor was able to discriminate between buffer alone and HRP antigen in buffer, as proven by capacitance measurements.

Dielectric characterization of PEBA and PDMS for capacitive interdigital vapour sensors

During the wine fermentation process the aroma profile produced is very complex and changes notably due to the yeast metabolism, while ethanol is produced simultaneously in much higher concentrations (up to 10 wt.%) relatively to aroma compounds (in the ppm range), making very difficult to follow the aroma profile with the conventional sensors. An automated aroma sensing system for the wine-must fermentation may render possible to detect and correct undesired off-flavors, representing major losses for the wine-industry. We are developing an Interdigital Capacitor (IDC) sensor array to be part of an electronic nose for on-line and real-time monitoring of wine fermentation process. The basic transducer has an interdigital electrode configuration (typical gap and finger of 100 /spl mu/m) made on a glass substrate coated with a polymer sensitive layer. We had developed an analytical model for the interdigital geometries to predict the capacitance in accordance with the geometry of the electrodes and the change of capacitance with the change of permittivity and thickness of the sensitive layer. Numerical simulation of the sensors geometry has been made for the validation of the analytical model. The capacitance measured for the sensors are in good agreement with our analytical model. Polydimethylsiloxane (PDMS) and polyetherblockamide (PEBA) have been chosen for the sensitive layer and are characterized.