In this work, the performance of five different fiber optic sensors at cryogenic temperatures has been analyzed. A photonic crystal fiber Fabry-Pérot interferometer, two Sagnac interferometers, a commercial fiber Bragg grating (FBG), and a π-phase shifted fiber Bragg grating interrogated in a random distributed feedback fiber laser have been studied. Their sensitivities and resolutions as sensors for cryogenic temperatures have been compared regarding their advantages and disadvantages. Additionally, the results have been compared with the given by a commercial optical backscatter reflectometer that allowed for distributed temperature measurements of a single mode fiber.

An energy harvesting device combined with a giant magnetoimpedance (GMI) sensor is presented to analyze low frequency vibrating systems. An electromagnetic harvester based on magnetic levitation is proposed for the electric power generation. The device is composed of two fixed permanent magnets at both ends of a cylindrical frame, a levitating magnet acting as inertial mass and a pick-up coil to collect the induced electromotive force. At the resonance frequency (10 Hz) a maximum electrical power of 1.4 mW at 0.5 g is generated. Moreover, an amorphous wire was employed as sensor nucleus for the design of a linear accelerometer prototype. The sensor is based on the GMI effect where the impedance changes occur as a consequence of the variations of the effective magnetic field due to an oscillating magnetic element. As a result of the magnet’s periodic motion, an amplitude modulated signal (AM) was obtained, its amplitude being proportional to mechanical vibration amplitude (or acceleration). The sensor’s response was examined for a simple ferrite magnet under vibration and compared with that obtained for the vibrational energy harvester. As a result of the small amplitudes of vibration, a linear sensor response was obtained that could be employed in the design of low cost and simple accelerometers.

The capacity to detect magnetic nanoparticles (MNPs) of a sensor based on non-linear giant magnetoimpedance effect has been addressed. A meander type sensor was designed with four nearly zero magnetostrictive ribbons connected in series. Different amounts of MNPs, in aqueous solutions, were cumulatively added to the sensor surface. The associated evolution of magnetoinductive voltage of first ( $V_{Z}$ ) and second harmonic ( $V_{2f}$ ) was analyzed as a function of external magnetic field $H $ (maximum value, $H_{\text {MAX}} = 4.4$ kA/m) and as a function of exciting frequency, $f $ (100 kHz–3 MHz). Both harmonics exhibited optimal detection ratios at $H_{\text {MAX}}$ due to the effect of MNPs stray fields on the transverse permeability of the sensing ribbons. Further analysis with frequency was performed to quantify the amount of MNPs. Different parameters were respectively defined, $m_{\text {LF}} $ and ${m}_{\text {HF}}^{2}$ (proportional to permeability) and $R_{0}$ revealing the highest sensitivity of second harmonic for the detection of MNPs. In order to further confirm the role of stray fields in MNPs detection, a comparative study was performed employing diamagnetic gold nanoparticles.

In this work a one-pot synthesis of water soluble glutathione capped magnetite nanoparticles is reported. The magnetic characterization of the samples shows the expected superparamagnetic behavior, but a wide range of blocking temperatures is found, since the size and interparticle interactions are very sensitive to preparation conditions. These properties are correlated with the glutathione-iron ratio and oxidant dose, in order to optimize the aqueous colloidal stability and magnetic properties of the superparamagnetic iron oxide nanoparticles for Magnetic Resonance Imaging applications. The efficiency of the glutathione coated nanoparticles as contrast agent is then evaluated by means of the determination of the relaxation times T1 and T2 in ¹H Nuclear Magnetic Resonance experiments. Moreover, the influence of the thickness of the glutathione capping layer on the colloidal stability and, thus, on relaxation times has been studied. Finally, the relaxitivity of the sample that shows the best performance has been determined. Graphic abstract A novel one-pot synthesis for “in situ” functionalized hydrophilic magnetite nanoparticles at atmospheric pressure and a temperature lower than 200 °C for Magnetic Resonance Imaging applications is reported. Their properties are analyzed in terms of the synthesis process: glutathione-iron ratio and oxidant dose.

Soft magnetic amorphous alloys obtained via rapid quenching techniques are widely employed in different technological fields such as magnetic field detection, bio labeling, non-contact positioning, etc. Among them, magnetoelastic applications stand out due to excellent mechanical properties exhibited by these alloys, resulting from their amorphous structure, namely, their high Young modulus and high tensile strength. In particular, the giant stress impedance (GSI) effect represents a powerful tool to develop highly sensitive magnetoelastic sensors. This effect is based on the changes in the high-frequency electric impedance as the result of the variation in magnetic permeability of the sample under the action of mechanical stresses. In this work, the GSI effect is analyzed in two soft magnetic ribbons ((Co_0.93 Fe_0.07)₇₅ Si_12.5 B_12.5 and (Co_0.95 Fe_0.05)₇₅ Si_12.5 B_12.5) for the subsequent development of two practical devices: (i) the characterization of the variations in the cross-section dimensions of irregularly shaped elements, and (ii) the design of a flow meter for measuring the rate of flow of water through a pipe.

An optimal design of nanoparticles suitable for biomedical applications requires proper functionalization, a key step in the synthesis of such nanoparticles, not only for subsequent crosslinking to biological targets and to avoid cytotoxicity, but also to endow these materials with colloidal stability. In this sense, a reliable characterization of the effectiveness of the functionalization process would, therefore, be crucial for subsequent bioconjugations. In this work, we have analyzed glutathione as a means to functionalize four of the most widely used nanoparticles in biomedicine, one of which is a hybrid gold-magnetic-iron-oxide nanoparticle synthetized by a simple and novel method that we propose in this article. We have analyzed the colloidal characteristics that the glutathione capping provides to the different nanoparticles and, using information on the Z-potential, we have deduced the chemical group used by glutathione to link to the nanoparticle core. We have used electron microscopy for further structural and chemical characterization of the nanoparticles. Finally, we have evaluated nanoparticle cytotoxicity, studying cell viability after incubation with different concentrations of nanoparticles, showing their suitability for biomedical applications.