Microfabricated biochips are developed to continuously monitor cell population dynamics in a non-invasive manner. In the presented work we describe the novel combination of contact-less dielectric microsensors and microfluidics to promote biofilm formation for quantitative cell analysis. The cell chip consists of a polymeric fluidic (PDMS) system bonded to a glass wafer containing the electrodes while temperature and fluid flow are controlled by external heating and pumping stations. The high-density interdigitated capacitors (microIDES) are isolated by a 550 nm multi-passivation layer of defined dielectric property and provide stable, robust and non-drifting measurement conditions. The performance of this detector is evaluated using various bacterial and yeast strains. The high sensitivity of the developed dielectric microsensors allows direct identification of microbial strains based on morphological differences and biological composition. The novel biofilm analysis platform is used to continuously monitor the dynamic responses of C. albicans and P. pastoris biofilms to increased shear stress and antimicrobial agent concentration. While the presence of shear stress triggers significant changes in yeast growth profiles, the addition of 0.5 microg mL(-1) amphotericin B revealed two distinct dynamic behaviors of the C. albicans biofilm. Initially, impedance spectra increased linearly at 30 Omega h(-1) for two hours followed by 10 Omega h(-1) (at 50 kHz) over 10 hours while cell viability remained above 95% during fungicide administration. These results demonstrate the ability to directly monitor dielectric changes of sub-cellular components within a living cell population.

We present an analytical derivation of the switching field distribution (SFD) at finite temperature for a single domain particle from the Néel-Brown model in the presence of a linearly swept magnetic field. By considering the field dependence of the attempt frequency f0 in the rate equation, we find enhancement of coercivity compared to models using constant f0. The contribution of thermal fluctuations to the standard deviation of the switching field HC derived here reaches values of 10% HC. Considering this contribution, which has been neglected in previous work, is important for the correct interpretation of measurements of switching field distributions.

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Articles you may be interested inSpin transfer switching characteristics in a [Pd/Co]m/Cu/[Co/Pd]n pseudo spin-valve nanopillar with perpendicular anisotropy

In the presented work we describe the novel combination of contact-less dielectric microsensors and microfluidics for quantitative cell analysis. The lab-on-a-chip system consists of microfluidic channels and chambers together with integrated and passivated interdigitated electrode structures. In contrast to existing bioimpedance methods implemented for cell analysis, the dielectric microsensors are completely insulated and physically removed from the liquid sensing environment using defined multi-passivation layer of distinct size and composition. Consequently, these structures act as contact-less microsensors for the characterization of in vitro cultivated cells. The overall performance of the system is demonstrated on various bacterial and yeast strains. Due to the high sensitivity of the contact-less dielectric microsensors it is possible to directly identify microbial strains, based on morphological differences and biological composition in the absence of any indicators or labels. Additionally, dielectric changes occurring in sub-cellular structures such as membranes can be directly monitored over a wide frequency range. As a result, microfluidic biochips are developed to continuously monitor cell morphology changes in a non-invasive manner over long periods of time.Mikrofluidische Lab-on-a-Chip-Systeme zur Analyse biologischer Zellen mittels integrierter planarer Impedanzsensoren.Ein neuartiges miniaturisiertes Analysesystem zur quantitativen Zellanalyse, auf Basis dielektrischer Mikrosensoren und Mikrofluidik, wird in dieser Arbeit vorgestellt. Das realisierte Lab-on-a-Chip beinhaltet in Kammern eingebettete, passivierte interdigitale Elektrodensysteme. Die Einfü hrung einer Multilagen-Passivierung ermö glicht, im Gegensatz zu herkö mmlichen Bioimpedanz-Systemen, die Isolation und somit die rä umliche Trennung der dielektrischen Mikrosensoren von der Flü ssigkeitsumgebung in den Analysekammern. Anhand von unterschiedlichen, in vitro kultivierten, Bakterien und Hefezellen wird das Lab-on-a-Chip charakterisiert. Es zeigt sich, dass mikrobiologische Substanzen aufgrund morphologischer Unterschiede bzw. ihrer biologischen Zusammensetzung ohne Verwendung von Markern oder Indikatoren identifiziert werden kö nnen. Dielektrische Variationen in subzellularen Strukturen, wie beispielsweise der Membranen, sind ü ber einen weiten Messfrequenzbereich beobachtbar. Der prä sentierte mikrofluidische Biochip wurde speziell fü r die kontinuierliche und nicht-invasive Beobachtung der Zellmorphologie ü ber lange Zeiträ ume entwickelt.Schlü sselwö rter: Lab-on-a- IntroductionThe application of impedance techniques for cell analysis is a well established and widely used non-destructive methodology. Interdigitated electrode structures (IDES) have long been employed, in addition to two and three electrode systems, to monitor impedance changes (Giaever, Keese 1984) of biological samples. A comprehensive introduction into the theory and applications of IDES can be found e.g. in a review of (Mamishev et al., 2004). In brief, impedan...