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 <i>Eurotium amstelodami, Aspergillus penicillioides and Aspergillus restrictus </i>have been successfully analyzed on-chip. Growth of <i>Eurotium amstelodami </i>shows a proportional impedance change of 10 % (12 chips tested) per day, with a sensitivity of 0.6 kΩ/pH unit.
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 CH<sub>2</sub>-stretch ratio by infrared absorbance measurements of skin biopsies. Investigations conducted with the biopsymeter shows that malignant melanomas and melanoma metastases have higher CH<sub>2</sub>-stretch ratio values compared to healthy skin tissues.
In this contribution we present a sensor system to measure the CH<sub>2</sub>-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.
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 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 (CH<sub>3</sub>-antisymmetric stretch), 3.42 μm (CH<sub>2</sub>-
antisymmetric stretch), 3.48 μm (CH<sub>3</sub>-symmetric stretch) and 3.51 μm (CH<sub>2</sub>-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 (CH<sub>2</sub>-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 CH<sub>2</sub> 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 CH<sub>2</sub>
stretch ratio with the IR spectroscope measurement. This confirms the usability of the sensor to measure the CH<sub>2</sub> stretch
ratio and its potential for fast, label-free and low cost screening of cell samples.