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.
We present a new methodology that enables a significant sensitivity improvement for transverse magneto-optical Kerr effect (T-MOKE) detection. For this purpose, we developed a novel measurement ...scheme, in which the polarization detection conditions are changed during the measurement sequence in a pre-defined way. An analytical expression of the associated T-MOKE signal pattern was derived, which allowed us to analyze and classify our experimental data in a straightforward way. Furthermore, this new measurement approach enables the identification of noise and false background signals that might be generated by the sample under investigation, the environment or the detection system itself and it provides a pathway to unambiguously separate all these effects from true T-MOKE signals. These capabilities significantly increase the sensitivity and robustness of T-MOKE detection. The method enabled us to measure magneto-optical signals for samples that are paramagnetic at room temperature or exhibit really small magneto-optical responses, even in the presence of false signals that were far larger in size. Our new methodology was integrated into a scanning wafer tool, which allows for nondestructive, laterally resolved surface characterization measurements and even has the capability of measuring optical and magneto-optical properties simultaneously.
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.
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.
► New CDC biofilm reactor system based method for bacterial growth monitoring has been developed. ► Reliable and repeatable environment was created to monitor the bacterial biofilm development. ► Label-free IDAM biosensors were used for monitoring the S. epidermidis biofilm development. ► Impedance spectroscopy was tested as an effective technique for tracking of bacterial growth. ► Low frequency range provides the highest sensitivity for the analysis of biofilm attachment.
How structure sensitive parameters derived from hysteresis loops can provide nondestructive information about the evolution of the microstructure of cold rolled low carbon steel as a result of ...recovery and recrystallization processes during the annealing is shown. The coercive field, remanent induction and hysteresis losses can be used to monitor the decrease in the dislocation density during recovery. These parameters are also influenced by the average grain refinement that takes place during recrystallization, which compensates the variation produced by the annihilation of dislocations during recrystallization. The maximum of the induction and of the relative differential permeability are shown to be very sensitive to the onset and to the monitoring of the recrystallization, respectively. The correlations between coercive field and remanent induction and hysteresis losses can also be used to distinguish between recovery and recrystallization.
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.
A cold rolled low carbon steel has been annealed at low temperatures (300–500 °C) in order to promote recovery without interaction with recrystallization. It has been shown that the recovery process ...can be monitored by means of non-destructive magnetic techniques using coercive field (
H
c) measurements. Transmission electron microscopy and electron backscattering diffraction (EBSD) observations were carried out in order to investigate the microstructural changes associated with the measured decrease in
H
c produced by the recovery. The EBSD image quality maps show that on a microstructural scale, the cold work stored energy is distributed heterogeneously among different texture components, in agreement with previous studies. Recovery mainly affects the {1
1
1} γ-fibre orientations, leading to the formation of well defined subgrains.
This paper describes a new accurate completely digital configurable computer-aided system for the simultaneous measurements of magnetic hysteresis loops and Barkhausen noise in a wide range of ...excitation frequencies (from 0.01 to 80 Hz) for the purposes of inspection of material properties and microstructure characterization. The importance of the correct choice of the data-acquisition (DAQ) card to have enough resolution in both hysteresis loop and magnetic Barkhausen noise (MBN) measurements is emphasized. Both the magnetic induction signal to construct the magnetic hysteresis loop and the Barkhausen noise are computed by the digital processing (numerical integration and digital filtering, respectively) of the induced electromotive force (EMF) signal. The accuracy of the hysteresis loop measurements is improved by using additional digital filters. The resolution of MBN results in simultaneous measurements is tested. Finally, some results of hysteresis loops and root-mean-square (RMS) envelopes of the MBN signal are presented to show the capability of the system to work at different excitation frequencies without changing any hardware.
Macroporous silicon is developed in p-type substrates in order to extend the active surface area of the electrodes in a silicon integrated capacitive element. Some laboratory prototypes with a 3D ...architecture and Si/SiO
2/PolySi layers have been developed. The contribution of the surface enlargement to the final capacitance is analyzed by comparing it with a 2D planar reference capacitive device. By this method, a capacitance gain of 2400% has been obtained at low frequencies with a capacitance density of 180
nF/cm
2. Based on the physical microstructure, an equivalent electrical circuit of the porous capacitive element is proposed and its electrical behavior discussed.
The recovery kinetics of a cold-rolled (84% cold reduction) extra-low carbon steel were studied during isothermal annealing at low temperatures (300–500 °C). The recovery process has been monitored ...by magnetic coercive field measurements. The experimental data were satisfactorily modelled using a logarithmic time dependence law. The activation energy for the recovery process has been found to increase with the fraction of recovery. The existing relationship between the coercive field and the internal stress was obtained experimentally as both variables are directly related to the total dislocation density. By applying this correlation the kinetics of the dislocation hardening part of the yield stress was derived from the kinetics of the coercive field.
