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De Marcellis A.,University of L'Aquila | Cubells-Beltran M.-D.,University of Valencia | Reig C.,University of Valencia | Madrenas J.,Polytechnic University of Catalonia | And 4 more authors.
IET Circuits, Devices and Systems | Year: 2014

In this study, the authors report on two different electronic interfaces for low-power integrated circuits electric current monitoring through current-to-frequency (I-f) conversion schemes. This proposal displays the intrinsic advantages of the quasidigital systems regarding direct interfacing and self-calibrating capabilities. In addition, as current-sensing devices, they have made use of the giant magnetoresistance (GMR) technology because of its high sensitivity and compatibility with standard complementary metal oxide semiconductor processes. Single elements and Wheatstone bridges based on spin-valves and magnetic tunnel junctions have been considered. In this sense, schematic-level simulations for integration in Austria Microsystems 0.35 μm technology have been corroborated by means of experimental measurements with the help of printed circuit board prototypes and real GMR devices. Tables with relevant parameters (silicon area, power consumption, sensitivity etc.) have been constructed as practical tools for designers. Electric currents down to 2 μA have been resolved in this way. © The Institution of Engineering and Technology 2014.


Fonseca L.P.,University of Lisbon | Martins V.C.B.,Institute Engineering Of Sistemas E Computadores Microsistemas E Nanotecnologias | Freitas P.P.,Institute Engineering Of Sistemas E Computadores Microsistemas E Nanotecnologias
1st Portuguese Meeting in Biomedical Engineering, ENBENG 2011 | Year: 2011

It is thought that worldwide more than 109 analyses are now performed every day with a double-digit growth rate. Microreactors and analytical microdevices and biosensors can provide important role on the control of environment, bioprocesses, processed food, biomedical analysis, among others due to rapid analysis and high sensitivity. This work envisages showing the potential of microreactors and biosensors on two mainly applications: i) The development of enzyme-base analytical microreactors for detection of multi-analyte compounds (e.g. sugars, alcohols, aminoacids, organic acids, among others) based on enzyme immobilization carried out on CPG beads integrated in FIA/SIA systems and sol-gel matrix integrated in glass capillary and microchannels. ii) The manipulation of individual microbial cells and single strand DNA molecules with functional paramagnetic nano-and micro-beads and their detection with magneto-resistive sensors demonstrates the applicability of these biosensors for the detection of pathogen microorganisms (e.g. Salmonella) through two different strategies: hybridization of DNA molecules (DNA-chips) and antibody-antigen biorecognition (immuno-chips). © 2011 IEEE.


Roldn A.M.,University of Granada | Roldn J.B.,University of Granada | Reig C.,University of Valencia | Cubells-Beltrn M.-D.,University of Valencia | And 3 more authors.
Microelectronics Journal | Year: 2011

An advanced model for quasi-linear spin-valve (SV) structures is presented for circuit simulation purposes. The model takes into account electrical and thermal effects in a coupled way in order to allow a coherent representation of the sensor physics for design purposes of electronics applications based on these sensor devices. The model was implemented in Verilog-A and used in a commercial circuit simulator. For testing the model, different SV structures have been specifically fabricated and measured. The characterization included DC measurements as well as steady-state and transient thermal analysis. From the experimental data, the parameters of the model have been extracted. The model reproduces correctly the experimental measurements obtained for devices with diverse sizes in different electrical and thermal operation regimes. © 2010 Elsevier Ltd.


Duarte C.M.,Institute Engineering Of Sistemas E Computadores Microsistemas E Nanotecnologias | Duarte C.M.,The Interdisciplinary Center | Fernandes A.C.,Institute Engineering Of Sistemas E Computadores Microsistemas E Nanotecnologias | Cardoso F.A.,Institute Engineering Of Sistemas E Computadores Microsistemas E Nanotecnologias | And 5 more authors.
IEEE Transactions on Magnetics | Year: 2015

Identification of bovine mastitis pathogens is necessary to control the disease, reduce the risk of chronic infections, and target the antimicrobial therapy to be prescribed. Development prospects for new bovine mastitis diagnosis methodologies go also through rapid and efficient devices that can offer a 'cow-side' use, meaning that raw milk collected for analysis should have limited pretreatment. This paper aims at developing a magnetic counter that identifies the presence of Streptococcus agalactiae (a Group B Streptococci) in raw milk. The detection is done with an integrated microfluidic platform, where 50 nm magnetic beads attached to Streptococcus agalactiae are dynamically detected by magnetoresistive sensors. This device allows the analysis of raw milk without bridging the microfluidic channels, making this integrated platform very attractive for fast bacteriological contamination screening. © 1965-2012 IEEE.


Valadeiro J.P.,Institute Engineering Of Sistemas E Computadores Microsistemas E Nanotecnologias | Valadeiro J.P.,University of Lisbon | Amaral J.,Institute Engineering Of Sistemas E Computadores Microsistemas E Nanotecnologias | Amaral J.,University of Lisbon | And 7 more authors.
IEEE Transactions on Magnetics | Year: 2015

The detection of low-intensity and low-frequency signals requires magnetic sensors with enhanced sensitivity, low noise levels, and improved field detection at low operating frequencies. Two strategies to improve the detectivity levels of devices based on tunnel magnetoresistive sensors are demonstrated: 1) a large number of sensors connected in series or 2) an individual sensor with a large sensing area and integrated magnetic flux guides. State-of-the-art MgO-based magnetic tunnel junctions with a soft pinned sensing layer were used in this paper. For 952 sensors in series a sensitivity of 29.3%/mT and a detection level of 455 pT/Hz1/2 were obtained at 100 Hz, whereas the integration of magnetic flux guides in a single sensor yielded a sensitivity of 138.3%/mT and a detection level of 576 pT/1/2 at the same frequency. These two strategies imply a large device footprint, being suitable when a high spatial resolution is not an application requirement. © 1965-2012 IEEE.


Silva A.V.,Institute Engineering Of Sistemas E Computadores Microsistemas E Nanotecnologias | Silva A.V.,University of Lisbon | Leitao D.C.,Institute Engineering Of Sistemas E Computadores Microsistemas E Nanotecnologias | Leitao D.C.,University of Lisbon | And 6 more authors.
EPJ Applied Physics | Year: 2015

Ultrasensitive magnetic field sensors envisaged for applications on biomedical imaging require the detection of low-intensity and low-frequency signals. Therefore linear magnetic sensors with enhanced sensitivity low noise levels and improved field detection at low operating frequencies are necessary. Suitable devices can be designed using magnetoresistive sensors, with room temperature operation, adjustable detected field range, CMOS compatibility and cost-effective production. The advent of spintronics set the path to the technological revolution boosted by the storage industry, in particular by the development of read heads using magnetoresistive devices. New multilayered structures were engineered to yield devices with linear output. We present a detailed study of the key factors influencing MR sensor performance (materials, geometries and layout strategies) with focus on different linearization strategies available. Furthermore strategies to improve sensor detection levels are also addressed with best reported values of ∼40 pT/√Hz at 30 Hz, representing a step forward the low field detection at room temperature. © EDP Sciences, 2015.


Roldan A.,University of Granada | Reig C.,University of Valencia | Cubells-Beltran M.D.,University of Valencia | Roldan J.B.,University of Granada | And 3 more authors.
Solid-State Electronics | Year: 2010

An analytical compact model for giant magnetoresistance (GMR) based current sensors has been developed. Different spin-valve based full Wheatstone bridge sensors, with the current straps integrated in the chip, have been considered. These devices have been experimentally characterized in order to extract the model parameters. In this respect, we have focused on the sensors linear operation regime. The model, which allows the individual description of the magnetoresistive elements, has been implemented in a circuit simulator by means of a behavioral description language: Verilog-A. We also propose the use of the devices in a direct power measurement application at the integrated circuit (IC) level, by taking advantage of their multiplicative properties. A simple circuit is suggested, and analyzed in depth by means of the tested model, showing promising results regarding the application range. © 2010 Elsevier Ltd. All rights reserved.


Pinto I.F.,Institute Engineering Of Sistemas E Computadores Microsistemas E Nanotecnologias | Pinto I.F.,University of Lisbon | Soares R.R.G.,Institute Engineering Of Sistemas E Computadores Microsistemas E Nanotecnologias | Soares R.R.G.,University of Lisbon | And 6 more authors.
Analytical Chemistry | Year: 2016

Multimodal ligands are synthetic molecules comprising multiple types of interactions that have been increasingly used for the capture of different biopharmaceutical compounds within complex biological mixtures. For monoclonal antibodies (mAbs) in particular, these ligands have shown the possibility of direct capture from cell culture supernatants in native conditions, as well as enhanced selectivity and affinity compared to traditional single-mode ligands. However, performing the capture of a target mAb using multimodal chromatography comes with the need for extensive optimization of the operating conditions, due to the multitude of interactions that can be promoted in parallel. In this work, a high-throughput microfluidic platform was developed for the optimization of chromatographic conditions regarding the capture of an anti-interleukin 8 mAb, using a multimodal ligand (2-benzamido-4-mercaptobutanoic acid), under a wide range of buffer pH and conductivities. The interaction of the ligand with the fluorescently labeled target mAb was also analyzed with respect to the individual contribution of the hydrophobic (phenyl) and electrostatic (carboxyl) moieties using fluorescence microscopy. The results were further validated at the macroscale using prepacked columns in standard chromatography assays, and recovery yield values of 94.6% ± 5.2% and 97.7% ± 1.5% were obtained under optimal conditions for the miniaturized and conventional approaches, respectively. In summary, this study highlights that a microfluidic-based approach is a powerful analytical tool to expedite the optimization process while using reduced reagent volumes (<50 μL), less resin (∼70 nL), and delivering results in less than 1 min per assay condition. © 2016 American Chemical Society.


Mouro J.,Institute Engineering Of Sistemas E Computadores Microsistemas E Nanotecnologias | Gualdino A.,Institute Engineering Of Sistemas E Computadores Microsistemas E Nanotecnologias | Teagno L.,Institute Engineering Of Sistemas E Computadores Microsistemas E Nanotecnologias | Chu V.,Institute Engineering Of Sistemas E Computadores Microsistemas E Nanotecnologias | And 2 more authors.
Procedia Engineering | Year: 2014

Flexural and in-plane vibrating thin-film resonators fabricated on glass substrates using low temperature surface micromachining and hydrogenated silicon structural layers with sub-micron gaps are demonstrated. Using hydrogenated silicon thin-films with distinct types of mechanical stress as the resonator structural layer allows controlling the quality factor and resonance frequencies. Sub-micron actuation gaps are a key feature to optimize the electromechanical coupling between the actuation/ capacitive sensing schemes and the resonating mechanical structure. Modeling the resonant system as a RLC circuit with parasitic parallel capacitances allows extracting the motional parameters. Strategies for reducing the influence of the parasitic parallel capacitance are shown. © 2014 The Authors. Published by Elsevier Ltd.


Chicharo A.,Institute Engineering Of Sistemas E Computadores Microsistemas E Nanotecnologias | Cardoso F.,Institute Engineering Of Sistemas E Computadores Microsistemas E Nanotecnologias | Cardoso S.,Institute Engineering Of Sistemas E Computadores Microsistemas E Nanotecnologias | Freitas P.J.P.,Institute Engineering Of Sistemas E Computadores Microsistemas E Nanotecnologias | Freitas P.J.P.,International Iberian Nanotechnology Laboratory
IEEE Transactions on Magnetics | Year: 2015

This paper investigates real-time monitoring and detection of 10.5 nm magnetic nanoparticles (MNPs) (Fe3O4) flowing in a nitrocellulose (NC) membrane over two spin valve sensors. The fabricated device gives information on the concentration of MNP flowing through the NC membrane of a typical lateral flow test, and gives relevant dynamic characteristics, such as flow rate and MNP distribution on capillary-driven systems. Sensor output varies linearly with MNP concentration. Experiments show average flow rates varying from 0.2 to 0.3 mm/s depending on MNP concentration. Signal shape [V(t)] gives information on MNP spatial distribution at the particle front flowing over the sensor. © 2015 IEEE.

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