Showing papers by "Gerald Urban published in 2013"

Microfluidic chip with integrated electrical cell-impedance sensing for monitoring single cancer cell migration in three-dimensional matrixes.

Abstract: Cell migration has been recognized as one hallmark of malignant tumor progression. By integrating the method of electrical cell-substrate impedance sensing (ECIS) with the Boyden chamber design, the state-of-the-art techniques provide kinetic information about cell migration and invasion processes in three-dimensional (3D) extracellular matrixes. However, the information related to the initial stage of cell migration with single-cell resolution, which plays a unique role in the metastasis-invasion cascade of cancer, is not yet available. In this paper, we present a microfluidic device integrated with ECIS for investigating single cancer cell migration in 3D matrixes. Using microfluidics techniques without the requirement of physical connections to off-chip pneumatics, the proposed sensor chip can efficiently capture single cells on microelectrode arrays for sequential on-chip 2D or 3D cell culture and impedance measurement. An on-chip single-cell migration assay was successfully demonstrated within several minutes. Migration of single metastatic MDA-MB-231 cells in their initial stage can be monitored in real time; it shows a rapid change in impedance magnitude of approximately 10 Ω/s, whereas no prominent impedance change is observed for less-metastasis MCF-7 cells. The proposed sensor chip, allowing for a rapid and selective detection of the migratory properties of cancer cells at the single-cell level, could be applied as a new tool for cancer research.

Simultaneous flow and thermal conductivity measurement of gases utilizing a calorimetric flow sensor

Abstract: This contribution presents a calorimetric flow sensor that is capable of determining the thermal conductivity of gases (k) under flow conditions. The measuring principle relies on using high frequency heat generation at 200 Hz in order to confine the AC heat transfer into a thin region over the surface of the channel wall, where the flow velocity profile is always close to zero. The thermal conductivity of several common gases and their mixtures is measured for flow rates up to 750 sccm. The sensor takes advantage of DC excitation to measure the flow rate (Q) provided that the volumetric heat capacity (ρcp) or the thermal diffusivity (α = k/(ρcp)) of the gas is known. This paper also presents two analytical models that qualitatively describe the measuring principles. Theoretically predicted functions fit well the experimental results.

Bioluminescence assay for the highly sensitive detection of botulinum neurotoxin A activity.

Abstract: This article describes a novel bioluminescence assay for detecting the proteolytic activity of Botulinum NeuroToxins (BoNT) in complex matrices. The assay is capable of detecting traces of BoNT in blood samples as well as in food drinks. The assay was responsive to BoNT/A subtypes 1 to 5, and serotype E3 in buffered solutions. It was responsive to filtered Clostridium botulinum supernatants and BoNT/A1 in complex with neurotoxin associated proteins in bouillon and milk (3.8% fat) down to 400 fM after 4 h RT incubation and in bouillon at concentrations down to 120 fM after 21 h RT incubation. In combination with an immunocapture/enrichment step it could detect BoNT/A1 in citrated plasma at concentrations down to 30 fM (1.2 mouse LD50 per mL). The simplicity of the assay, combined with a demonstrated ability to lyophilize the reagents, demonstrates its usefulness for detection of BoNT in non-specialised analytical laboratories.

A micro-cantilever sensor chip based on contact angle analysis for a label-free troponin I immunoassay.

Abstract: Cantilever sensors have been extensively explored as a promising technique for real-time and label-free analyses in biological systems. A major sensing principle utilized by state-of-the-art cantilever sensors is based on analyte-induced surface stress changes, which result in static bending of a cantilever. The sensor performance, however, suffers from the intrinsically small change in surface stress induced by analytes, especially for molecular recognition such as antigen–antibody binding. Through the contact angle change on a tailored solid surface, it is possible to convert a tiny surface stress into a capillary force—a much larger physical quantity needed for a practical sensor application. In this work, a micro-cantilever sensor based on contact angle analysis (CAMCS) was proposed to effectively enhance the sensitivity of a sensor in proportion to the square of the length to thickness ratio of the cantilever structure. CAMCS chips were fabricated using a standard complementary-metal-oxide-semiconductor (CMOS) process to demonstrate a 1250-fold enhancement in the sensitivity of surface stress to bioanalyte adsorption using a piezoresistive sensing method. A real-time and label-free troponin I (cTnI) immunoassay, which is now widely used in clinics and considered a gold standard for the early diagnosis and prognosis of cardiovascular disease, was performed to demonstrate cTnI detection levels as low as 1 pg mL−1. The short detection time of this assay was within several minutes, which matches the detection time of commercially available instruments that are based on fluorescence-labeling techniques.

Effect of Plasma Treatments and Plasma-Polymerized Films on the Adhesion of Parylene-C to Substrates

Abstract: This work deals with the most severe limitations of Parylene-C coatings, namely their poor adhesion to the substrate and barrier properties. To address these limitations, the surface properties of the substrate are modified prior to the Parylene deposition step by depositing a nano-film interfacial layer by means of a plasma polymerization process. The multilayer coating was realized using a newly designed, innovative multi-chamber system. Tests of dry adhesion (at 90° and 180°) and electrochemical impedance spectroscopic (EIS) measurements were performed to evaluate the effect of the plasma pre-processing. Adhesion strength of 3 and 6.8 N cm−1 were recorded for the 90° and 180° tape tests, respectively, while an impedance level of 107 Ω cm−2 at 100 Hz was registered by EIS measurement.

Bubble-free electrode actuation for micro-preparative scale electrophoresis of RNA

Abstract: A microfluidic chip is presented for lysis and one-step RNA purification from bacteria. Bacteria are lysed by joule-heating followed by a gel electrophoresis step for clean-up and subsequent elution of small RNA. Bubble formation during electrophoresis at constant current is suppressed through the use of a silver chloride cathode and a silver anode. To prevent silver chloride sediment in the bulk solution, the anode was immersed in a saturated chloride solution. Salt bridges in the form of polyacrylamide gels are used that could be precisely patterned with the help of phaseguides. Bubble-free actuation could be performed for more than 20 min under a constant current. For longer actuation times, cathodic silver-chloride became depleted and a silver-chloride sediment formed in the anodic microchamber at increasing distance from the anode with time. The chip functioning was verified by extraction of transfer-messenger RNA from Escherichia coli and subsequent amplification using reverse transcription real-time PCR. Incorporation of salt bridges enables effective bubble free actuation of Ag/AgCl electrodes in a microfluidic chip. This opens up new possibilities in a surge towards fully integrated diagnostic cartridges that are miniaturized and disposable.

Nanofilms Produced by Magnetron Enhanced Plasma Polymerization from Methane and Oxygen for Coating of Rigid Contact Lenses

Abstract: Although soft contact lenses are more widespread, rigid contact lenses have been around for decades and their materials have been greatly improved, especially in terms of oxygen permeability. Protein adsorption and wettability are, however, complex challenges still faced by both soft and rigid contact lenses (CLs). This study aims at improving these two major attributes by means of a low-pressure magnetron enhanced 15 kHz plasma polymerization process. The wide parameter range of the process allowed the tailoring of the surface properties and delivered stable, reproducible plasma coatings. The XPS, FT-IR, WCA, and QCM surface analysis methods were used to study the nanofilms. A contact angle of down to 18° and a protein (lysozyme) adsorption of only 0.2 µg cm−2 were achieved. Some correlations with the more commonly used “PEO-like” coatings helped to explain the measurement results.

Measurement and simulation of the frequency response of a thermal flow sensor at different flow speeds

Abstract: This contribution presents the complete (amplitude and phase) frequency response of a calorimetric flow sensor in a free, laminar air stream at different flow speeds ranging from 0 to 5 m/s. Given the geometry of the sensor, which features a central thermistor closely surrounded by a heater element, the complexity of the resulting frequency response is reduced by applying a simple transformation. This transformation involves taking the ratio between the temperature oscillations at the surrounding thermistors and the central thermistor. The resulting frequency response shows a second order transfer function of real poles. The parameters of this transfer function are used to analyze the effect of the flow speed on the frequency response. Results show that for air, the position of the first characteristic pole remains constant at the downstream thermistor for flow speeds up to 1 m/s. Experimental and simulated results are consistent, which allows the further study of the sensor's response by means of numerical simulations in order to determine the effect of the thermal properties of the fluids on the frequency response. The ultimately goal is to achieve fluid independent flow measurement.

Nanophase separated amphiphilic polymer co-networks as efficient matrices for optical sensors: Rapid and sensitive detection of NO2

Abstract: A disposable and irreversible sensor for nitrogen dioxide detection, based on the reaction of NO2 with N,N′-diphenyl-1,4-phenylenediamine (DPPD) is described. This work focuses on the application of silicone-containing amphiphilic co-networks (APCNs) as immobilisation matrices for UV/VIS transmission spectroscopy for gas sensors. The developed flow-through gas sensor is based on a DPPD doped APCN, for real-time spectrophotometric detection of the oxidation product, and is formed in a 34 μm thin film. The measurement principle presented here describes the NO2 concentration as a function of the temporal development of absorption at 450 nm. A linear relationship between the change of absorption and the concentration of NO2 at different humidity is obtained in the range from 0.1 to 5.0 ppm at ambient temperatures. As a consequence, the sensor response is reproducible with a very low detection threshold (20 ppb) and detection times within seconds.

Gas concentration and flow speed measurements using a polymer-based membrane sensor

Abstract: This contribution presents a polymer-based membrane sensor that is capable of determining simultaneously flow speed and gas concentration of binary gas mixtures. The sensor therefore combines two excitation modes. It consists of an unsymmetrical 1D-resistor array made of platinum. The well defined temperature coefficient of resistance enables to switch between constant temperature and constant power excitation modes of the heating element. The response signal of the downstream temperature sensor allows the gas concentration measurement of a binary gas mixture using constant power excitation mode. A switch to constant temperature excitation allows flow speed measurements. A sinusoidal AC-excitation with a frequency of 1 Hz is chosen to carry out the proof-of-concept.

Swelling and Water Uptake Behavior of Nanofilms Obtained by a Magnetron Enhanced Plasma‐Polymerization Process

Abstract: This work deals with the water uptake and swelling behavior of magnetron-enhanced plasma-polymerized nanofilms in an aqueous medium. Those coatings are used in biomedical applications such as implants or contact lenses. The role of water in biomaterial surface science is considered to be of great importance. Water is not only the major molecule in most living organisms (70%) and the carrier of cells but it is also the medium in which biochemical processes take place. Because of its small size and mobility, water is the first molecule to come in contact with a biomaterial in any clinical application.[1] It is believed, that the degree of polymer swelling strongly affects the interaction of proteins with the surface of the polymer, which determines its biocompatibility. Polymers with a high swelling degree show weak enthalpic interactions with proteins, resulting in a protein-repellency.[2] A new approach is applied, which combines three characterization techniques: dynamic contact angle measurements, optical waveguide spectroscopy, and electrochemical impedance spectroscopy. A relation between the composition of the films and the water and salt transport phenomena through the nanofilm was observed. A higher amount of oxygen in the precursor gas ratio in the polymerization process leads to a higher wettability as well as a higher water and salt intrusion. Based on this observation an electrical model was introduced and helped to interpret the experimental results.

A novel, multiparametric, flexible microsensor for metabolic monitoring in vivo

Abstract: We present a new, multiparametric microsensor for metabolic monitoring in vivo. In contrast to silicon or ceramic based systems, the flexible, implantable, polymer sensor strip is manufactured in a cost-effective hybrid of thin-film and laminate technology in a wafer-level process. Flexibility allows easy handling and placement in soft tissue. It comprises electrochemical, amperometric micro-(bio)sensors for the energy metabolism parameters lactate and oxygen, the neurotransmitter glutamate as well as an integrated reference electrode. This allows dynamic, highly sensitive, localized, long-term online measurement of multiple metabolic parameters with a single device. The reliable analytical performance of the sensors has been proven. The sensor can be inserted directly into the tissue in clinical applications.

A cell impedance sensor chip for cancer cells detection with single cell resolution

Abstract: In this study, we present a new cell-based impedance sensor chip with integrated microfluidics for cancer cells detection with single cell resolution. To overcome the limitation of cell resolution posed by conventional approaches, a simple but effective cell-trapping method was proposed to position single cells on top of microelectrodes for sequential measurement. Impedance spectra change induced by single cells on microelectrode arrays was successfully recorded and modeled by using an electrical equivalent circuit. The preliminary measurement reveals a high sensitivity of sensor demonstrated by monitoring single cancer cells adhered on microelectrodes with different surface properties. The impedance magnitudes were also recorded to monitor the activities of single cell on microelectrode in real time. The proposed sensor chip has the potential for further detection and quantification of cancer cells from various tumor stages.

Integrated microfluidic component for enriching and extracting biological cell components

Abstract: The invention relates to a microfluidic component, such as those which can be used in particular in the identification of bacteria on the basis of genetic information of the bacteria in the field of molecular diagnostics. An integrated microfluidic component comprises at least one depletion chamber (105) with at least one inlet (108) for introducing a fluid to be processed and at least one outlet (110) for discharging the depleted fluid, said inlet (108) and outlet (110) being arranged such that the fluid can flow between the inlet (108) and the outlet (110); at least one separating element (101), at least one surface of which delimits the depletion chamber (105); and at least one collection chamber (106) for receiving the enriched components of the fluid to be processed, said components having been purified by the separating element (101), wherein the collection chamber (106) is connected to the depletion chamber (105) via the separating element (101) such that a transportation between the depletion chamber (105) and the collection chamber (106) can be carried out through the separating element (101).

Determination of the thermal conductivity of gases under flow conditions

Abstract: This contribution presents a calorimetric flow sensor that is capable of determining the thermal conductivity (k) regardless of the flow conditions. The sensor can also measure the flow rate (Q) provided that the volumetric heat capacity (ρcp) or the thermal diffusivity (α=k/(ρcp)) of the flowing gas is known. No additional sensors or bypass channels are needed. The measuring principle relies on using high frequency heat generation (200 Hz). The thermal conductivity of several common gases is measured.

D3.3 - Cell Culture Monitoring System Comprising Superoxide Sensors for Tumour Cell Analysis

Abstract: A sensor for the selective and sensitive measurement of reactive oxygen species (ROS) candidate superoxide was developed using direct electrochemical oxidation of superoxide radical on gold electrodes at low operation potential. Sensor performance regarding sensitivity and selectivity was investigated and optimised by integration of polymer based cut-off membranes. Sensor calibration was done utilising the artificial enzymatic based production of short-lived superoxide radicals by xanthine/xanthine oxidase system. The reaction kinetics of superoxide production was investigated with electrochemical, optical and magneto-spectroscopic measurement methods. Sensor design and fabrication process allow a full integration of superoxide sensor in existing multiparameter measurement platform SCCF for in vitro cell culture monitoring.

P2.6 - Evaluation of Heater Temperature to Detect Gases in a Flowing Fluid

Abstract: In this contribution the behavior of a calorimetric flow sensor was investigated, at which only the temperature of the heater is evaluated. A time-dependent excitation (f = 1 Hz) was applied to the heating element with a constant power amplitude. The influence of different gases and flow velocities on the heater temperature were observed. Measurements and simulations were carried out in no-flow condition and in flowing fluids in order to obtain the restrictions regarding to a simultaneous detection of flow speed and gas type. A simultaneous measurement of flow velocity and gas type was possible, however certain conditions had to be respected, e.g. a high difference in thermal conductivity which is predetermined by the flow speed range.

Work function based gas sensing with benzene tricarboxylate linked metal organic frameworks — A comparison study

Abstract: Metal Organic Frameworks (MOFs) are porous crystalline materials that can be synthesized using various metal ions and organic linkers. Due to their great physical, chemical and geometrical variety, MOFs are very attractive for the potential application as selective gas sensing materials. In this study we examine work function based gas sensing properties of MOFs, consisting of the same organic linker, benzene tricarboxylate (BTC) and different metal ions (Co, Ni, Cd, Al), towards different linear alkanes and linear monohydric alcohols. The influence of size and polarity of the target gases, as well as the influence of oxygen and humidity on sensing performance is discussed.

Phase guide pattern for liquid operation

Abstract: PROBLEM TO BE SOLVED: To perform overflow control of a phase guide to effectively control filling and/or discharge of a fluid chamber and a channel.SOLUTION: A square chamber 120 has a filling port 122 and a discharge channel 124. A dead angle 126, from which a phase guide is to be generated, is determined. Subsequently, a phase guide pattern serving as a dead angle phase guide and as a delay phase guide for blocking the discharge channel is applied. The filling port and the discharge channel 124 can be positioned in arbitrary locations of the chamber.

Phaseguide-chip for point-of-care diagnostic of bacteria with integrated enrichment, lysis, and nucleic acid purification

Abstract: We report the development and proof-of-concept of a microfluidic chip, that provides a full range of pretreatment steps for the point-of-care detection of bacteria with a total process time of less than 15 minutes It integrates enrichment, lysis and nucleic acid purification Enrichment is achieved through free-flow electrophoresis The enriched cells are lysed by thermoelectrical means Nucleic acids can immediately be purified by electrophoresis through a hydrogel The system uses phaseguides for complete, bubble-free priming and emptying, offering optional reusability

Plasma Nanofilms as Biocompatible and Antibacterial Coatings for Biosensors.

Abstract: In the development of biocompatible materials for biomedical applications and biosensors the foreign body response is an important issue [1]. The healing of surrounding tissue often interferes with the function of an implanted biosensor [2]. Events like protein deposition, hemostasis, inflammation, tissue repair, infections and the encapsulation of the functional part of the sensor are the main cause of failure of the implanted device [3]. In this study biocompatible nanofilms are produced by means of a plasma polymerization process using a lowpressure magnetron-enhanced 15 kHz glow discharge.