In this contribution, we present travelling-wave based dielectrophoretic (twDEP) microfluidic devices for the handling of suspended grown cells. Travelling-wave based dielectrophoretic devices rely on a moving electric field gradient, which can be realised by applying phase-shifted AC-voltages between sets of parallel electrodes. The distance between these electrodes can be reduced to a few micrometres. In optimised conditions, channels with a height of even hundreds of micrometres are applicable. Two microfluidic devices have been realised to investigate the advantages of travellingwave dielectrophoresis for cell handling.
We present a microfluidic chip for an easy setup of a 3D-culture of mammalian cells. The chip contains feeding structures and gas supply for long-term cultivation of mammalian cells. The device is fabricated out of hard materials like silicon and glass that are all highly biocompatible. The chip uses the concept of surficial phaseguides that allows the partial filling of a microfluidic chip with liquids based on hydrophobic and hydrophilic surfaces. Here, a suspension of mammalian cells and melted agarose is filled into the chip and is pulled by the capillary pressure on the hydrophilic areas but not on the hydrophobic phaseguides. Consequently, only a part of the chip is filled with the agarose which gels by cooling a form the 3D-cell culture. The unfilled areas are used as supply structures for nutrition and gases. So the supply is based on diffusion and the supply of nutrition and gases is controlled independently. We cultured HaCaT-cells over 24 hours in our device and achieve a good viability.
We present a method to graft a layer of poly-ethylene-glycol (PEG) to the surface of stereo-lithography fabricated or 3D-printed microfluidic devices rendering it hydrophilic and repellent to the adhesion of proteins. The PEG forms a rigid bond with the surface that is more stable than many coatings or surface treatments. This makes stereolithography much more attractive as a prototyping platform for microfluidics. The method has been proven with two different resins by different manufacturers, showing the universality of said treatment.
In this work, we present a new miniaturized culture medium based sensor system where we apply an optical reference in an impedance measurement approach for the detection of mold in archives. The designed sensor comprises a chamber with pre-loaded culture medium which promotes the growth of archive mold species. Growth of mold is detected by measuring changes in the impedance of the culture medium caused due to increase in the pH (from 5.5 to 8) with integrated electrodes. Integration of the reference measurement helps in determining the sensitivity of the sensor. The colorimetric principle serves as a reference measurement that indicates a pH change after which further pH shifts can be determined using impedance measurement. In this context, some of the major archive mold species Eurotium amstelodami, Aspergillus penicillioides and Aspergillus restrictus have been successfully analyzed on-chip. Growth of Eurotium amstelodami shows a proportional impedance change of 10 % (12 chips tested) per day, with a sensitivity of 0.6 kΩ/pH unit.
We present a microfluidic chip where droplets of different liquids and sizes can be generated and merged independent of the droplets size and inter-droplet separation. The designed chip consists of two T-junctions located at each side of the long channel and a droplet merging area located at the center of the channel. Our system uses an extra outlet placed before the merging area, which allow the control of the travel time, hitting speed, and merging location of the droplets. From one side of the channel droplets can be generated and stored for several hours. At the other side of the channel droplets containing reagents can be made. Individual droplets generated at each side of the channel can be selected, transferred to the centre location of the channel, and merged with each other. Due to simplicity and efficiency of this droplet merging method, the system can be easily used for on-chip cell analysis.
We present an infrared biopsymeter to assist pathologists in the diagnosis of melanoma presence in skin biopsies. The designed and realized system combines the features of visual inspection and physical sensing to reduce false positives and false negatives occurring during standard histopathological analyses. The biopsymeter determines the CH2-stretch ratio by infrared absorbance measurements of skin biopsies. Investigations conducted with the biopsymeter shows that malignant melanomas and melanoma metastases have higher CH2-stretch ratio values compared to healthy skin tissues.
In-situ integration of microfluidic channels into the microfabrication process flow of implantable microsystems is desirable, for example to enable efficient drug delivery. We propose a fabrication method for such microfluidic channels using parylene C, a biocompatible material whose inert nature favours water flow. A single deposition of parylene C enabled monolithical integration of fully-sealed micro-channels in a silicon substrate. The channel geometry was predefined by etching 100 μm-deep grooves into a silicon substrate. A PVC foil was fixed manually on the wafer and served as a top-cover for the grooves. The wafers were coated with the adhesion promoter AdPro Poly® and a 15 μm-thick parylene C film was deposited conformally into the grooves-foil enclosed space. The outgasing nature of the PVC foil hindered the adhesion of parylene C, allowing the foil to be peeled off easily from the parylene surface. The functionality of the fully-sealed parylene channels, embedded in the silicon wafer, was verified by injecting DI water with dispersed polystyrene microbeads (diameter 6 μm): the polystyrene beads were successfully transported along the channel. Further, a fully-sealed parylene chamber remained leak-tight throughout a stepwise application of hydrostatic pressures from 0.2 to 3.0 bar (15 s step-interval). In short, our parylene channels are: (1) suitable for microsystem drug-delivery; (2) in-situ enclosed hollow spaces embedded in the silicon substrate, realized with a single parylene deposition; (3) intact at hydrostatic pressures up to 3 bar.
In microchip capillary electrophoresis most frequently electrokinetic sample injection is utilized, which does not allow
pressure driven sample handling and is sensitive for pressure drops due to different reservoir levels. For efficient field
tests a multitude of samples have to be processed with the least amount of external equipment. We present the use of a
hydrogel plug to separate the sample from clean buffer to enable independent sample change and buffer refreshment. In-situ
polymerization of the gel does away with complex membrane fabrication techniques. The sample is
electrokinetically injected through the gel and subsequently separated by a voltage between the second gel inlet and the
buffer outlet. By blocking of disturbing flows by the gel barrier a well-defined ion plug is obtained. After each
experiment, the sample and the separation channel can be flushed independently, allowing for a continuous operation
mode in order to process multiple samples.
We present a new method for the direct injection of liquid sample into a capillary electrophoresis (CE) device. Instead of
a double-T injection mechanism, a single inlet provided with a membrane filter is used. From a reservoir on top of this
inlet, the liquid directly enters the separation channel through the membrane. The driving force is a short electrical pulse.
This avoids an additional sample channel, so that the chip needs only three microfluidic connects and no mechanical
sample pumping is demanded. The high injection reproducibility and the comparatively simple setup open up the way for
mobile application of soil analysis.
Grinding processes causes the formation of a characteristic surface structure, known as chatter
marks. In this work, an angle-resolved light scattering technique is used to characterise them.
In order to identify the chatter marks in a measured profile, the fast Fourier transform (FFT) is
usually applied to the measured data. The FFT, however only for strictly periodic data yields
unambiguous results. To overcome this, the multiresolution analysis (MRA) is also applied by
means of the lifting scheme. In this manner, it is shown that chatter marks, for example, can be
uniquely identified by applying the multiresolution analysis to the angle-resolved light scattering
data, even when FFT fails to do this. Thus MRA alone or alternatively in combination with
FFT, opens new opportunities for optical online control in case of industrial surface finishing
Non-contacting characterisation of finished surface is commonly done by means of optical systems, e.g., 3D
microscopy. In case of the confocal white light microscope the topography of the tribological surface is determined
by measuring the intensity distribution of the reflected light. In this work the inter- and intra-layer contributions
to the complex optical conductivity tensor are quantum mechanically (ab initio) calculated on the microscopic
scale. Based on these complex optical layer-resolved conductivity tensors, the Maxwell equations are solved for
a proper modeling of the visible light propagation trough and from a layered sample. Applied to semi-infinite
bcc Fe/Fe(100), among others, the incidence dependence of the scattered light is also discussed for variously
With respect to varying operation conditions, only sensors directly installed in the engine can detect the current oil
condition hence enabling to get the right time for the oil change. Usually, only one parameter is not sufficient to obtain
reliable information about the current oil condition. For this reason, appropriate sensor principles were evaluated for the
design of sensor arrays for the measurement of critical lubricant parameters. In this contribution, we report on the
development of a sensor array for engine oils using laboratory analyses of used engine oils for the correlation with sensor
signals. The sensor array comprises the measurement of conductivity, permittivity, viscosity and temperature as well as
oil corrosiveness as a consequence of acidification of the lubricant. As a key method, rapid evaluation of the sensors was
done by short term simulation of entire oil change intervals based on artificial oil alteration. Thereby, the compatibility
of the sensor array to the lubricant and the oil deterioration during the artificial alteration process was observed by the
sensors and confirmed by additional laboratory analyses of oil samples take.
In this contribution we present an imaging platform that operates in standard incubators, allowing the investigation of
multiple cell cultures at the same time. Also, the sensor platform operates with disposable multi-well plates. The system
consists of four image sensors (Charge-Coupled Devices) built into a custom made holder, in which a multi-well plate
can be positioned without the need of further alignment. The focal points of the image sensors are fixed at the bottom of
the wells of interest. Above the multi-well plate, white light emitting LEDs with an aperture are mounted to provide
orthogonal illumination over the sensors. For the observation and understanding of tumour progression, cell proliferation
and cell motility studies are of great importance. For such studies, a sensor system that monitors cell motility in four
wells simultaneously (of a 24-well plate) has been designed and realized. In the present work we focus on measuring the
motility of adherently grown mammalian epithelial cells. Simultaneous, real-time observation of stimulated (with
hepatocyte growth factor) and control samples of MDCK (Madin-Darby Canine Kidney) cells has been carried out.
The presented imaging platform is an attractive and versatile alternative to conventional time-lapse microscopy to
monitor the motility of individual cells. Furthermore, the high-throughput feature makes its use advantageous for the
simultaneous tracking of biological samples under different conditions.
In this contribution we present a sensor system to measure the CH2-stretch ratio of suspended mammalian cells. To
overcome the strong infrared absorbance of water our sensor system comprises a sample chip with three equal chambers
with an inner height of only 20 μm.
DNA microarrays can provide bacterial identification, which is crucial for targeted therapy. However they lack
rapidness, because of multiple analysis steps. Therefore a fast one-step method for synthesising a hybridisation-ready
reagent out of initial bacterial DNA is required.
This work presents the combination and acceleration of PCR and fluorescent labelling within a disposable microfluidic
chip, fabricated by injection moulding. The utilised geometry consists of a spiral meander with 40 turns, representing a
cyclic-flow PCR system. The used reaction chemistry includes Cy3-conjugated primers and a high-yield polymerase
leading to a one-step process accelerated by cyclic-flow PCR.
Three different bacterial samples (Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa) were
processed and the bacterial DNA was successfully amplified and labelled with detection limits down to 102 cells per
reaction. The specificity of species identification was comparable to the approach of separate PCR and labelling.
Furthermore the overall processing time was decreased from 6 hours to 1.5 hours.
We showed that a disposable polycarbonate chip, fabricated by injection moulding is suitable for the significant
acceleration of DNA microarray assays. The reaction output lead to high-sensitivity bacterial identification in a short
time, which is crucial for an early and targeted therapy against infectious diseases.
Grinding processes often underlie chattering which results in a wavy surface of the ground metal sheet. In this
work it will be shown that the angle resolved light scattering method is not only suitable to monitor industrial
grinding processes, in both waviness and roughness modes, but also enables the determination of the waviness
of a ground surface.
Furthermore it is demonstrated that the roughness, e.g. the average roughness Ra and roughness depth Rz,
of a ground surface directly depends on the grinding pressure. The light scattering value Aq correlates with the
roughness values obtained with a stylus probe system. In this way it is proven that the light scattering system
unambiguously determines chatter marks and the roughness of a metal sheet during a grinding process.
In this contribution we present a novel LED-photodiode based infrared absorbance sensor in the wavelength range of
3.0 - 3.7 μm for cell analysis. Instead of using time consuming and expensive labelling and staining techniques to
distinguish healthy from malignant cell types, this IR sensor system can perform faster, cheaper and without the need of
additional chemicals. Depending on the used narrow bandpass filters, absorbance due to specific molecular vibration can
be measured, such as the functional absorbance peaks at 3.38 μm (CH3-antisymmetric stretch), 3.42 μm (CH2-
antisymmetric stretch), 3.48 μm (CH3-symmetric stretch) and 3.51 μm (CH2-symmetric stretch). For normalization and
baseline correction the absorbance at wavelengths 3.33 and 3.57 μm are used. By recording the IR absorbance spectra of
healthy and malignant epithelial kidney cell lines with an IR spectroscope, we found significant differences in the
absorbance ratio 3.51 μm / 3.42 μm (CH2-symmetric/antisymmetric stretch). This result has led us to a sensor concept
where only four wavelengths are being measured. In the 3.0 - 3.7 μm wavelength region a low cost LED-photodiode
system can be used instead of a spectroscope. Yeast cells, which also contain the CH2 symmetric and antisymmetric
stretch bands, are used to validate this sensor system and to make a first comparison of the system to spectroscopic
recordings. Sensor experiments on dried spots of baker's yeast on calcium-fluoride slides yielded a comparable CH2
stretch ratio with the IR spectroscope measurement. This confirms the usability of the sensor to measure the CH2 stretch
ratio and its potential for fast, label-free and low cost screening of cell samples.
This paper explores the use of photo patternable polymers for integrated high-speed screening arrays, where enzyme reactions are monitored in nano liter volume reactors using fluorescence of NADH and photodiode detection. Implementing the array of nano liter volume wells using a low-temperature CMOS-compatible process allows wells to be patterned after the photodiode array and electronics fabrication is completed. We demonstrate filling of 400 X 400 micron square, 25 micron deep photoresist-on-silicon wells with liquid samples by electro spray and wetting. We also demonstrate usability of the wells on NADH samples by measuring the fluorescence of 0.1, 0.5 and 1 millimolar NADH solutions using external optics.
We are developing a method for high-throughput screening using arrays of `nanowells' built into a silicon substrate. These wells can serve as bioreactors for studying a variety of biochemical reactions such as the enzymatic activity that occurs in yeast metabolism. For a variety of studies it is important to know the volume of liquid that has been deposited in a given well and/or to monitor the evaporation of the liquid. Using silicon as our substrate means that we can take advantage of the ability to build microelectronics into the wells in order to develop `smart' wells.
Intelligent Molecular Diagnostic Systems (IMDS)- The objective of this multidisciplinary research program is to design and develop an analytical system that is able to measure and interpret concentrations of various analytes which are dispensed on a micro-array. The analytes are detected by means of fluorescence or (chemi)luminescence measurement. Furthermore, the collected data are combined and interpreted using modern reasoning techniques. Micro-injection- Dispensing picoliters (pl) of reagents (enzymes, antibodies, etc.) and liquid samples on a micro-array requires special techniques. At the moment we are working on a technique which will allow for accurately dispensing liquid volumes less than 100 pl on a micro-array. Detection of (beta) -D-glucose- (beta) -D-glucose standards are dispensed on a micro-array, after which a solution of Amplex Red reagent, horse radish peroxidase (HARP), and glucose oxidase in a mixture of ethylene glycol and water is added. Ethylene glycol is added to prevent evaporation. The (beta) -D-glucose reacts with glucose oxidase to D-gluconolactone and H2O2. The H2O2 reacts with 10-acetyl-3,7-dihydroxyphenoxazine (Amplex Red) with a 1:1 stoichiometry to produce highly fluorescent resorufin. The formation of resorufin with time is followed with a Zeiss Axioskop microscope equipped with a KAF Photometrics CCD camera, in order to determine the sensitivity, concentrations, and volumes associated with the dispensed fluids.
The goal of our TU Delft interfaculty research program is to develop intelligent molecular diagnostic systems (IMDS) that can analyze liquid samples that contain a variety of biochemical compounds such as those associated with fermentation processes. One specific project within the IMDS program focuses on photon sensors. In order to analyze the liquid samples we use dedicated microarrays. At this stage, these are basically miniaturized micro titre plates. Typical dimensions of a vial are 200 X 200 X 20 micrometer3. These dimensions may be varied and the shape of the vials can be modified with a result that the volume of the vials varies from 0.5 to 1.6 nl. For all experiments, we have used vials with the shape of a truncated pyramid. These vials are fabricated in silicon by a wet etching process. For testing purposes the vials are filled with rhodamine solutions of various concentrations. To avoid evaporation glycerol-water (1:1, v/v) with a viscosity of 8.3 times the viscosity of water is used as solvent. We aim at wide field-of-view imaging at the expense of absolute sensitivity: the field-of-view increases quadratically with decreasing magnification. Small magnification, however, implies low Numerical Aperture (NA). The ability of a microscope objective to collect photons is proportional to the square of the NA. To image the entire microarray we have used an epi-illumination fluorescence microscope equipped with a low magnification (2.5 X/0.075) objective and a scientific CCD camera to integrate the photons emitted from the fluorescing particles in the solutions in the vials. From these experiments we found that for this setup the detection limit is on the order of micromolar concentrations of fluorescing particles. This translates to 108 molecules per vial.
A new process for the fabrication of piezoelectric quartz thin films on silicon is investigated. With this process, new silicon-implemented acoustic wave delay lines for sensor applications can be realized. An acoustic-wave delay-line consists of two interdigital thin film metal transducers fabricated on a piezoelectric crystal. In order to realize acoustic-wave devices on (non-piezoelectric) silicon, the use of piezoelectric thin films such as zinc oxide, aluminum nitride or PZT has been reported. However, these films often exhibit stress, aging, pinholes, or poor reproducibility which affects the performance of the device. The bonding of piezoelectric quartz (with its known and fixed mechanical and piezoelectric properties) to silicon improves the performance of silicon-implemented acoustic-wave devices. The process used, consists of a wet chemical treatment after which the wafers are prebonded at room temperature. Annealing at 140 degree(s)C for 3 hours yields a sufficient high bond strength.
Every oscillator contains an element which determines the frequency of the oscillator. A delay-line can be such an element. An oscillator which uses a delay-line puts specific demands on the electrical circuits needed in this oscillator. In this paper we look systematically at the parameters involved in the design of the electronic circuitry. In order to be able to do this properly we first determine the electrical behavior of an acoustical delay- line with the help of an equivalent circuit. Consequently we look at the parameters of the electronic circuit which are important for realization of a highly stable oscillator with special attention for the fact that the frequency determining element is a delay-line. With the help of this analysis we were able to find design criteria. According to this criteria we built actual circuits by using monolithic integration and measured them. The result of these measurements are given.
This work describes the determination of mechanical properties of sputtered piezoelectric zinc oxide (ZnO) films. The residual stress of the thin ZnO films was measured using the wafer curvature and the sputter parameters for growth of films with low tensile stress determined. Tensile films are often preferred in membrane structures because, e.g. buckling is avoided. A membrane deflection method was applied to measure the plane-strain modulus of ZnO films on SiNx. A new model which includes the flexural rigidity of a multilayered membrane was used to calculate the residual stress and plane-strain modulus of the membrane layers. The measured plane-strain modulus for ZnO on SiNx is 115 GPa. Nano indenter experiments on a ZnO film deposited on a Al-SiO2-Si substrate revealed a similar value of 122 GPa for the plane-strain modulus. These results can be used for more accurate modeling of ZnO based microsensors and actuators, such as Lamb wave sensors.
In this paper we present a silicon micromachined wet cell for use with a Love-wave liquid sensor. The Love-wave sensor is composed of an electronic amplifier and an acoustic Love- wave delay-line on a piezoelectric substrate. Together they form an oscillator. Liquid is placed in intimate contact with the Love-wave sensor; corresponding to its viscosity the acoustic wave velocity changes, which is observed through a change in the oscillation frequency. An issue that arises in a sensor of this type is that the input impedance of the interdigital transducers (IDTs) of the delay-line changes dramatically due to the dielectric properties of the liquid above them. This adds electrical load to the amplifier and affects the oscillator's performance by reducing its resolution and sensitivity. The electric loading of the IDTs by the liquid also leads to unwanted sensitivity with respect to the electrical properties of the liquid. The wet cell was designed to overcome this disadvantage. By virtue of this cell the liquid is directed only over the wave propagation path, and so the transducers are protected from the liquid's influence. In designing the cell, bubble formation in the liquid, chemical inertness, bonding aspects and temperature effects were all considered. The design utilizes a silicon micromachined channel that guides the liquid between the transducers. Furthermore a heater for controlling the temperature of the liquid has been incorporated. Experiments have shown that placing thin side walls of a silicon micromachined channel in the propagation path of the wave adds little to the insertion loss. Losses of only 6 dB or less were recorded, which confirms the suitability of this configuration. In addition to viscosity sensors this design can be applied to a broad range of Love-wave liquid sensors, including those in the biochemical area.
Microacoustic sensors feature a number of benefits like real-time electronic readout, small size, robustness, high sensitivity, and cost-effective fabrication. For liquid sensing applications Love wave devices utilizing a surface bound shear mode are particularly well-suited. In this paper we discuss the crucial issues in the design of a Love wave device for the utilization in a smart liquid-sensor system, where special attention is paid to the interaction of the sensing device with the associated electronics and the influence of the adsorbing film used for biosensing applications.
The demand for small, low-cost, and reproducible sensors and actuators has lead to the use of the silicon IC-technology for the realization of these devices. To include the required function of the sensor or actuator in the silicon, special processing is often required. Micromachining, thin film deposition and wafer-to-wafer bonding processes have been developed for the realization of sensor and actuator systems. By making these processes compatible to silicon integrated circuit (IC) processing, an additional advantage is obtained: the possibility of integrating electronic circuitry with the sensor or actuator on one silicon chip which allows the development of smart sensors. In this paper some special technologies for integrated sensors and actuators are reviewed. Special attention is given to the newly developed IC-compatible wafer-to-wafer silicon fusion bonding, because this process is expected to accelerate the commercial realization and application of smart sensor and actuator systems.
This paper deals with the technology of acoustic-wave sensor devices. The use of planar technologies for their fabrication gives them advantageous properties such as high reproducibility, small size and low production costs. Most acoustic-wave sensors are made of piezoelectric-crystal wafers. They are highly stable and reproducible and low-cost device fabrication is possible because the wafers are suited to be used in standard integrated circuit (IC) equipment such as metal-evaporation depositors and photo-lithographic machinery. The silicon-implementation of acoustic devices gives the possibility of making use of the best-developed technology every: the silicon IC-technology. Additional features are the possibility of integration of electronic circuitry on the acoustic device and the development of new types of devices. However, the silicon implementation is hampered by difficulties in the development of reproducible piezoelectric quartz and silicon wafers are combined could increase the performance of silicon integrated acoustic-wave devices.
The influences of surface characteristics, including adsorptive states led by different chemical treatments and surface roughness, on direct bonding between dissimilar CVD materials were investigated. The bonding procedures were carried out at temperature lower than 400 degrees Celsius. In this temperature range, LPCVD poly-silicon, PECVD oxide, and LPCVD silicon-nitride showed highly process dependent bonding behaviors, i.e., bondable or not bondable to another material under certain experimental conditions. Based on these facts, a selective bonding conception for Si-based CVD material is proposed and applied to fabricate new fluid structures and devices.