Our researchers

Fernando José Arizti Urquijo

Most recent scientific publications (since 2010)

Authors: Oblak, E.; Riego, P. ; Fallarino, L.; et al.
ISSN 0022-3727  Vol. 50  Nº 23  2017 
We perform a detailed comparative study of conventional transverse magneto-optical Kerr effect (T-MOKE) measurements and a methodology that utilizes an effective polarization detection scheme for mixed s- and p-polarized incoming light. To test the ultimate sensitivity of both methods, we also design a series of specialized samples in which the T-MOKE signal of a Co-film is artificially reduced by means of a Ag overcoat of varying thickness. We find that the effective polarization detection scheme leads to a more than 30-fold increase of the T-MOKE signal and signal-to-noise ratio, even under general operation conditions which were not individually optimized. This allowed for the observation of T-MOKE hysteresis loops of Co-films that were buried under 80 nm of Ag, for which the MOKE signal was only 1/600 of that for an uncoated Co-film. In comparison, conventional T-MOKE measurements did not succeed for Ag overcoats thicker than 40 nm.
Authors: Gurruchaga, Kizkitza; Arizti, Fernando José; et al.
ISSN 0195-9298  Vol. 36  Nº 2  2017 
The quality of the ball screw shafts used in the aeronautical sector has to be controlled and certified with the most advanced non-destructive techniques. The capacity of magnetic Barkhausen noise(MBN) as a non-destructive technique to control the quality of ball screw shafts by assuring the appropriate induction hardened layer depth and detecting local overheated regions, known as grinding burns, which may occur during grinding processes is shown in the present work. Magnetic Barkhausen noise measurements were made with a system designed and implemented by the authors and the derived parameters were compared with microhardness measurements made at various depths after the different induction hardening treatments and the grinding processes were applied. A multiparametric study of the MBN signal as a function of the magnetic field in the surface of the sample is done in order to estimate the thickness of the hardened layer and to detect the grinding burns produced during grinding processes. The hardened layer thickness can be characterized with an error of +/- 200 mu m in the range between 150 and 2500 mu m by the position of the first peak of the MBN envelope in terms of the tangential magnetic field measured at the surface and the grinding burns can be detected with the position of the second peak of the MBN envelope in terms of the tangential magnetic field measured at the surface.
Authors: Zuzuarregui, A.; Souto, D.; Pérez-Lorenzo, E.; et al.
Journal: ANALYST
ISSN 0003-2654  Vol. 140  Nº 2  2015  pp. 654 - 660
This paper describes the design, implementation and validation of a sensitive and integral technology solution for endotoxin detection. The unified and portable platform is based on the electrochemical detection of endotoxins using a synthetic peptide immobilized on a thin-film biosensor. The work covers the fabrication of an optimized sensor, the biofunctionalization protocol and the design and implementation of the measuring and signalling elements (a microfluidic chamber and a portable potentiostat-galvanostat), framed ad hoc for this specific application. The use of thin-film technologies to fabricate the biosensing device and the application of simple immobilization and detection methods enable a rapid, easy and sensitive technique for in situ and real time LPS detection.
Authors: Paredes, J; Alonso-Arce, Maykel; Schmidt, C.; et al.
ISSN 1387-2176  Vol. 16  Nº 3  2014  pp. 365 - 374
Central venous catheters (CVC) are commonly used in clinical practice to improve a patient's quality of life. Unfortunately, there is an intrinsic risk of acquiring an infection related to microbial biofilm formation inside the catheter lumen. It has been estimated that 80 % of all human bacterial infections are biofilm-associated. Additionally, 50 % of all nosocomial infections are associated with indwelling devices. Bloodstream infections account for 30-40 % of all cases of severe sepsis and septic shock, and are major causes of morbidity and mortality. Diagnosis of bloodstream infections must be performed promptly so that adequate antimicrobial therapy can be started and patient outcome improved. An ideal diagnostic technology would identify the infecting organism(s) in a timely manner, so that appropriate pathogen-driven therapy could begin promptly. Unfortunately, despite the essential information it provides, blood culture, the gold standard, largely fails in this purpose because time is lost waiting for bacterial or fungal growth. This work presents a new design of a venous access port that allows the monitoring of the inner reservoir surface by means of an impedimetric biosensor. An ad-hoc electronic system was designed to manage the sensor and to allow communication with the external receiver. Historic data recorded and stored in the device was used as the reference value for the detection of bacterial biofilm. The RF communication system sends an alarm signal to the external receiver when a microbial colonization of the port occurs. The successful in vitro analysis of the biosensor, the electronics and the antenna of the new indwelling device prototype are shown. The experimental conditions were selected in each case as the closest to the clinical working conditions for the smart central venous catheter (SCVC) testing. The results of this work allow a new generation of this kind of device that could potentially provide more efficient treatments for catheter-related infections.
Authors: Sevillano, Juan Francisco; Arizti, Fernando José; et al.
ISSN 0026-2692  Vol. 44  Nº 10  2013  pp. 912 - 919
This paper presents a comparative study on time-to-digital converters (TDC) for their use as part of an RFID tag sensor. TDCs can digitize any physical magnitude previously converted to time delay and exploit the benefits of time domain conversion: high resolution with reduced power consumption and low voltage operation. Three different TDC architectures are analyzed and a calibration strategy tailored for RFID sensing applications is proposed in order to account for process variations. Converters implemented using a 0.18 mu m CMOS standard process have been analyzed at transistor level for human body temperature sensing applications. An accuracy of 0.011 degrees C is achieved in the range from 35 degrees C to 43 degrees C for the nonius TDC with a power consumption of only 4.1 nW at 10 samples per second from a 1.8 V voltage supply. (C) 2012 Elsevier Ltd. All rights reserved.
Authors: Paredes, J; Becerro, S.; Arizti, Fernando José; et al.
ISSN 0925-4005  Vol. 178  2013  pp. 663 - 670
Bacterial biofilms are a common cause of persistent and chronic infections, mostly related to implantable devices. In this context, Staphylococcus species are the most relevant microorganisms involved in causing high costs for the healthcare system. New diagnostic and/or therapeutic tools should be developed by providing in vivo analysis of the specific physiological parameters directly related to the status of the indwelling device. Monitoring the biofilm's biological evolution will allow an earlier diagnostic. Impedance microbiology is suggested as a proper technique for directly measuring the development of bacterial biofilms generated inside intravascular catheters. In this study we propose interdigitated microelectrode biosensors be integrated within those implantable devices. In vitro assays have been carried out in order to characterize this methodology as a detection and monitoring tool for bacterial biofilm development. Impedance spectroscopy (IS) was implemented in 96-well microtiter plates, leading to positive results in detecting and monitoring bacterial biofilm development. Two Staphylococcus aureus and two Staphylococcus epidermidis strains were successfully monitored during a 20-h culture, and results show that the low range of the frequency is the most suitable setting for measuring the maximum relative changes. (c) 2013 Elsevier B.V. All rights reserved.
Authors: Gonzalez-Diaz, J.B.; Arregi, J.A.; Martínez de Guereñu, Ane; et al.
ISSN 0021-8979  Vol. 113  Nº 15  2013 
We obtain angular-resolved quantitative magneto-optical measurements with good signal-to-noise ratio from very diffusive reflection patterns of industrial steel samples, which are a consequence of their large surface roughness. For the diffuse spots generated by these samples, we observe that while the overall shape of the magnetic hysteresis loop is nearly independent, a monotonous increase of the magneto-optical polarization change occurs as a function of the scattering angle. We demonstrate that this observation can be explained by considering the diffuse spot as a superposition of independent reflections from planar surfaces with varying incidence angles. This main finding can be ultimately used to facilitate an efficient non-invasive analysis of industrial magnetic samples by means of magneto-optical methods despite their elevated level of roughness. (C) 2013 AIP Publishing LLC
Authors: Paredes, J; Becerro, S.; Arizti, Fernando José; et al.
ISSN 0956-5663  Vol. 38  Nº 1  2012  pp. 226 - 232
Detection of device-associated infectious processes is still an important clinical challenge. Bacteria grow adhered to the device surfaces creating biofilms that are resistant to antimicrobial agents, increasing mortality and morbidity. Thus there is need of a surgical procedure to remove the indwelling infected device. The elevated cost of these procedures, besides patients discomfort and increased risks, highlights the need to develop more efficient, accurate and rapid detection methods. Biosensors integrated with implantable devices will provide an effective diagnostic tool. In vivo, rapid and sensitive detection of bacteria attached to the device surfaces will allow efficient treatments. Impedance spectroscopy technique would be an adequate tool to detect the adherence and the growth of the microorganism by monitoring the impedance characteristics. In this work a label-free interdigitated microelectrode (IDAM) biosensor has been developed to be integrated with implantable devices. Impedance characterization of Staphylococcus epidermidis biofilms has been performed achieving electrical monitoring of the bacterial growths in a few hours from the onset of the infection. This pathogen represents the most common microorganism related to intravascular catheters associated infections. The experimental setup presented in this work, a modified CDC biofilm reactor, simulates the natural environment conditions for bacterial biofilm development. The results prove that the low range of frequency is the most suitable setting for monitoring biofilm development. Our findings prove the effectiveness of this technique which shows variations of 59% in the equivalent serial capacitance component of the impedance. (C) 2012 Elsevier B.V. All rights reserved.
Authors: Gurruchaga, Kizkitza; Martínez de Guereñu, Ane; Soto, M.; et al.
ISSN 0018-9464  Vol. 46  Nº 2  2010  pp. 513 - 516
The capacity of magnetic Barkhausen noise (MBN) measurements to characterize recovery and the onset and evolution of recrystallization processes occurring during the annealing of cold rolled low carbon steel is analyzed. Cold rolled low carbon steel samples were isothermally annealed at laboratory under different conditions in order to promote various degrees of recovery or recrystallization. The effect of recovery and recrystallization processes on the MBN envelope, the amplitude of the peak of the MBN envelope, the time integral of the MBN envelope and the MBN energy is discussed and related to the microstructural changes produced by these softening processes. The obtained results prove that several parameters derived from the MBN are able to follow the progress of recovery and recrystallization.