J. Loureiro

Toward a magnetoresistive chip cytometer: Integrated detection of magnetic beads flowing at cm/s velocities in microfluidic channels

This work describes an integrated device comprising microfluidic channels and incorporated spin-valve sensors sensitive enough to count, determine the magnetic orientation, flowing height, and speed of single micron-sized magnetic beads moving with velocities of 8–35 mm/s. Sensor signals of 3–100 μVp-p correspond to bead moments at different directions indicating a physical rotation of the beads and a slow response (seconds) of the bead moment to magnetizing field changes.

Transparent aluminium zinc oxide thin films with enhanced thermoelectric properties

Improved thermoelectric properties of Aluminum Zinc Oxide (AZO) thin films deposited by radio frequency (RF) and pulsed Direct Current (DC) magnetron sputtering at room temperature are reported. In both techniques films were deposited using sintered and non-sintered targets produced from nano-powders. It is confirmed that both the Al doping concentration and film thickness control the thermoelectric, optical and structural properties of these films. Seebeck coefficients up to −134 μV K−1 and electrical conductivities up to 4 × 104 (Ω m)−1 lead to power factors up to 4 × 10−4 W mK−2, which is above the state-of-the-art for similar materials, almost by a factor of three. The thermoelectric I–V response of an optimized AZO element with a planar geometry was measured and a maximum power output of 2.3 nW, for a temperature gradient of 20 K near room temperature, was obtained. Moreover, the low thermal conductivity (<1.19 W mK−1) yields a ZT value above 0.1. This is an important result as it is at least three times higher than the ZT found in the literature for AZO, at room temperature, opening new doors for applications of this inexpensive, abundant and environmental friendly material, in a new era of thermoelectric devices.

Experimental and theoretical study of dissociation in the positive column of a hydrogen glow discharge

The positive column of a hydrogen glow discharge was studied under typical operating conditions: gas pressure from 0.3 up to 5.0 Torr and discharge current from 1 up to 50 mA. Optical emission spectroscopy, optical absorption spectroscopy, and laser induced fluorescence have been employed in order to determine the gas temperature (300<Tg<600 K), the density of ground state hydrogen atoms (1012<[H(1s)]<1013 cm−3), and the kinetic temperature of H atoms (336<Ta<1600 K), respectively. Langmuir probes were utilized to measure the electric field (8<E<61 V cm−1) in the positive column. A kinetic model based on the solutions to the homogeneous electron Boltzmann equation coupled to a set of rate balance equations for the vibrational levels H2(X 1Σg+,v), H atoms, and H− ions was developed in order to predict the concentrations of these species. From a comparison between the measured and calculated concentrations of H atoms, the reassociation probability on the wall, in Pyrex glass, is estimated to be ≅10−2.

OPTIMIZATION AND INTEGRATION OF MAGNETORESISTIVE SENSORS

This paper addresses challenging issues related to the integration of magnetoresistive (MR) sensors in applications such as magnetic field mapping, magnetic bead detection in microfluidic channels, or biochips. Although sharing the same technological principle for detection (magnetoresistance effect), each application has unique specifications in terms of noise, sensitivity, spatial resolution, electrical robustness or geometric constraints. These differences are of high impact for manufacturing, because some strategies used for sensor optimization compromise the freedom for device architecture.

Magnetoresistive Detection of Magnetic Beads Flowing at High Speed in Microfluidic Channels

An integrated device including microfluidic channels and incorporated magnetoresistive spin valve sensors has been developed and used to detect single magnetic bead motion at cm/s velocities. The sensitivity of the system is high enough to determine the magnetic orientation, the flowing height and the speed of each particle for velocities between 10-23 mm/s and the counting capability of the device is fully working for this range of velocities and below this limit. Sensor signals (between 3-100 muVp-p) correspond to bead moments at different directions indicating a physical rotation of the beads, and a slow response (seconds) of the bead moment to magnetizing field changes. Subsequent magnetic characterization of the micron-sized beads indicates that they are composed of strongly interacting magnetic nanoparticles.

Nanostructured p-type Cr/V2O5 thin films with boosted thermoelectric properties

The urgent need for non-toxic and abundant thermoelectric materials has become a significant motivation to improve the figures of merit of metal oxides in order to remove the barrier towards their widespread use for thermoelectric applications. Here we show the influence of a Cr layer in boosting the thermoelectric properties of vanadium pentoxide (V2O5) thin films, deposited by thermal evaporation and annealed at 500 °C. The Cr to V2O5 thickness ratio controls the morphological and thermoelectric properties of the thin films produced. The optimized Seebeck coefficient and power factor values at room temperature are +50 μV K−1 and 7.9 × 10−4 W m−1 K−2, respectively. The nanograin structure of the films is responsible for an improvement in the electrical conductivity up to 3 × 105 (Ω m)−1 with a typical thermal conductivity of 1.5 W m−1 K−1. These results combine to yield promising p-type thermoeletric CrV2O5 thin films with a ZT of 0.16 at room temperature.

Integrated Spintronic Platforms for Biomolecular Recognition Detection

This paper covers recent developments in magnetoresistive based biochip platforms fabricated at INESC‐MN, and their application to the detection and quantification of pathogenic waterborn microorganisms in water samples for human consumption. Such platforms are intended to give response to the increasing concern related to microbial contaminated water sources. The presented results concern the development of biological active DNA chips and protein chips and the demonstration of the detection capability of the present platforms. Two platforms are described, one including spintronic sensors only (spin‐valve based or magnetic tunnel junction based), and the other, a fully scalable platform where each probe site consists of a MTJ in series with a thin film diode (TFD). Two microfluidic systems are described, for cell separation and concentration, and finally, the read out and control integrated electronics are described, allowing the realization of bioassays with a portable point of care unit. The present pla...

Optimization of Cuprous Oxides Thin Films to be used as Thermoelectric Touch Detectors

The electronic and optical properties of p-type copper oxides (CO) strongly depend on the production technique as it influences the obtained phases: cuprous oxide (Cu2O) or cupric oxide (CuO), the most common ones. Cu films deposited by thermal evaporation have been annealed in air atmosphere, with temperature between 225 and 375 °C and time between 1 and 4 h. The resultant CO films have been studied to understand the influence of processing parameters in the thermoelectric, electrical, optical, morphological, and structural properties. Films with a Cu2O single phase are formed when annealing at 225 °C, while CuO single phase films can be obtained at 375 °C. In between, both phases are obtained in proportions that depend on the film thickness and annealing time. The positive sign of the Seebeck coefficient (S), measured at room temperature (RT), confirms the p-type behavior of both oxides, showing values up to 1.2 mV·°C-1 and conductivity up to 2.9 (Ω·m)-1. A simple detector using Cu2O have been fabricated and tested with fast finger touch events.

Spintronic chip cytometer

Modern flow cytometers are being developed with enhanced portability for on-site measurements, and by integrating magnetoresistive sensors within microfluidic channels (to detect magnetically labeled cells), external and expensive equipment can be avoided. This work describes the real-time detection of Kg1-a cells magnetically labeled with 50 nm magnetic particles using a magnetoresistive based cell cytometer. When flowing through a microchannel 150 μm wide and 14 μm high, with speeds around 1 cm/s, the average observed signals were bipolar with an amplitude of 10 to 20 μV (0-p) corresponding to cell events. The number of cells counted by the SV cytometer has been compared with that obtained with a hemocytometer, and both methods agree within the respective error bars.

Magnetic separation of undifferentiated mouse Embryonic Stem (ES) cells from neural progenitor cultures using a microfluidic device

Embryonic Stem (ES) cells are cell lines derived directly from the pre-implantation embryo. The generation of pure populations of neural progenitors from ES cells and their further differentiation into neurons, astrocytes and oligodendrocytes allows the potential use of these cells for the cure of neurodegenerative diseases and for neural drugs testing. An integrated device based on magnetophoresis, including microfluidic channels and incorporated high magnetic field gradients, was used to control the motion of cells, labeled with magnetic particles (MPs), through a biochip. In this work, the magnetophoretic device has been used for depletion of tumorogenic pluripotent stem cells from 46C mouse ES cell cultures by the specific recognition and labeling of the stage specific embryonic antigen 1 (SSEA-1). Purity degrees ranging from 95% to 99,5% were obtained and determined by flow cytometry analysis