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Zhang Z.H.,University of Manitoba | Gui Y.S.,University of Manitoba | Fu L.,University of Manitoba | Fan X.L.,Lanzhou University | And 7 more authors.
Physical Review Letters | Year: 2012

An intrinsic thermoelectric coupling effect in the linear response regime of magnetic tunneling junctions (MTJ) is reported. In the dc response, it leads to a nonlinear correction to Ohm's law. Dynamically, it enables a novel Seebeck rectification and second harmonic generation, which apply for a broad frequency range and can be magnetically controlled. A phenomenological model on the footing of the Onsager reciprocal relation and the principle of energy conservation explains very well the experimental results obtained from both dc and frequency-dependent transport measurements performed up to GHz frequencies. Our work refines previous understanding of magnetotransport and microwave rectification in MTJs. It forms a new foundation for utilizing spin caloritronics in high-frequency applications. © 2012 American Physical Society. Source

Pimenta S.,University of Minho | Cardoso S.,INESC Microsistemas e Nanotecnologias INESC MN | Miranda A.,International Iberian Nanotechnology Laboratory | De Beule P.,International Iberian Nanotechnology Laboratory | And 2 more authors.
Biomedical Optics Express | Year: 2015

This paper presents the design, optimization and fabrication of 16 MgO/TiO2 and SiO2/TiO2 based high selective narrow bandpass optical filters. Their performance to extract diffuse reflectance and fluorescence signals from gastrointestinal tissue phantoms was successfully evaluated. The obtained results prove their feasibility to correctly extract those spectroscopic signals, through a Spearman’s rank correlation test (Spearman’s correlation coefficient higher than 0.981) performed between the original spectra and the ones obtained using those 16 fabricated optical filters. These results are an important step for the implementation of a miniaturized, low-cost and minimal invasive microsystem that could help in the detection of gastrointestinal dysplasia. © 2015 Optical Society of America. Source

Bi H.,International Iberian Nanotechnology Laboratory | Duarte C.M.,INESC Microsistemas e Nanotecnologias INESC MN | Duarte C.M.,University of Lisbon | Brito M.,International Iberian Nanotechnology Laboratory | And 5 more authors.
Biosensors and Bioelectronics | Year: 2016

Quantitative analysis of antioxidants in a fast, simple and accurate manner is of great importance in the view of real-time monitoring the health of individuals. Recently, we have developed a UV/vis spectroscopic microfluidic sensor to specifically quantify ascorbic acid based on the immobilization of ascorbate oxidase, a relatively unstable enzyme. In this work, three different strategies for the immobilization of the unstable enzyme, including alumina sol-gel encapsulation, physisorption to PDMS channels with, and without alumina xerogel modification, were compared to build a microsensor. We found that the loading amount of the enzyme is not the determinative factor for the performance of the microfluidic biosensor but the retained activity of the enzyme and diffusion in the microfluidic channel. Taking into account of the two factors, the protocol of adsorbing enzymes to alumina (Al2O3) xerogel modified PDMS surface was demonstrated to be the best for preparing the microfluidic sensor among the utilized protocols. The microsensor prepared under the optimized protocol was further used to quantify ascorbic acid in human blood, where only dozens of microliters of blood (few drops) was required, demonstrating its potential application in clinical diagnosis. The developed strategy is featured with optimized enzymatic activity, simple process of microfluidic platform, low sample consumption, and straightforward spectrophotometry based detection. © 2016 Elsevier B.V. Source

Serrate D.,University of Zaragoza | De Teresa J.M.,University of Zaragoza | Marquina C.,University of Zaragoza | Marzo J.,University of Zaragoza | And 5 more authors.
Biosensors and Bioelectronics | Year: 2012

The combination of magnetoresistive sensors and magnetic labeling of bioanalytes, which are selectively captured by their complementary antibody in the proximity of the sensor is a powerful method in order to attain truly quantitative immunological assays. In this paper we present a technical solution to exploit the existing spin valve technology to readout magnetic signals of bio-functionalized magnetic nanoparticles. The method is simple and reliable, and it is based on a discrete scan of lateral flow strips with a precise control of the contact force between sensor and sample. It is shown that the signal of the sensor is proportional to the local magnetization produced by the nanoparticles in a wide range of concentrations, and the sensitivity thresholds in both calibration samples and real immunorecognition assays of human chorionic gonadotropin hormone are well below the visual inspection limit (5.5. ng/ml). Furthermore the sample scanning approach and the reduced dimensions of the sensors provide unprecedented spatial resolution of the nanoparticle distribution across the supporting nitrocellulose strip, therefore enabling on-stick control references and multi-analyte capability. © 2012 Elsevier B.V. Source

Cardoso F.A.,INESC Microsistemas e Nanotecnologias INESC MN | Costa T.,INESC Investigacao e Desenvolvimento INESC ID | Costa T.,University of Lisbon | Germano J.,INESC Investigacao e Desenvolvimento INESC ID | And 10 more authors.
IEEE Transactions on Magnetics | Year: 2012

Since 2006, fully scalable matrix-based magnetoresistive biochips have been proposed. This integration was initially achieved with thin film switching devices and moved to complementary metal-oxide-semiconductor (CMOS) switching devices and electronics. In this paper, a new microfabrication process is proposed to integrate magnetoresistive sensors on a small CMOS chip (4 mm 2). This chip includes a current generator, multiplexers, and a diode in series with a spin valve as matrix element. In this configuration, it is shown that the fabricated spin-valves have similar magnetic characteristics when compared to standalone spin valves. This validates the successfulness of the developed microfabrication process. The noise of each matrix element is further characterized and compared to the noise of a standalone spin valve and a portable electronic platform designed to perform biological assays. Although the noise is still higher, the spin valve integrated on the CMOS chip enables an increase in density and compactness of the measuring electronics. © 1965-2012 IEEE. Source

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