S. van den Driesche

Guided Dielectrophoresis: A Robust Method for Continuous Particle and Cell Separation

In this paper, we report on an on-chip separation device that is based on guided dielectrophoresis (DEP). The simple design comprises a pair of electrodes and a microfluidic channel for sample delivery. Continuous separation into two distinct populations (corresponding to positive and negative DEP, respectively) in the microchannel was achieved without the need of accurate hydrodynamic focusing or multiple excitation frequencies. In this device, the sample position after separation is only determined by the geometry of the channel and the electrodes, which results in a separation process that is robust against fluctuations in separation voltage and flow caused by vibrations in the setup. The separation principle has been simulated and proven by measurements comprising polystyrene beads and two human cell lines: Jurkat (T-cell leukemia) and HeLa (cervical cancer). Automatic image processing was used to detect the particle positions at the separation channel outlet.

D 2 O based microfluidics for in vitro ir cell analysis

We present the use of D2O (deuterium oxide) as a liquid medium for infrared analysis of biological cells in microfluidic devices. In contradiction to standard buffer liquids, D2O shows a low infrared absorption in the range of 3.3 to 3.6 μm wavelength, which makes it suitable for infrared analysis methods in that range. We illustrate the performance by the measurement of CH2 and CH3 stretch vibrations of phospholipid bilayer of the cell membrane of yeast, in a microfluidic chip.

Impedance spectroscopy for detection of mold in archives with an integrated reference measurement

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.

CH2-Symmetric/CH2-Antisymmetric Stretch Ratio Sensor for Cell Analysis

Here we report on a novel infrared sensor system for measuring the CH2-symmetric/CH2-antisymmetric stretch ratio of cell samples. Based on IR absorbance spectra of healthy and malignant breast [1], blood [2] and brain [3] cells found in literature we hypothesized the possibility of disease stage cell discrimination by only comparing a few absorbance peaks in the lipid absorbance wavelength region between 3 and 4 μm. By comparing the lipid CH2-symmetric and CH2-antisymmetric stretch ratios (with baseline correction and normalization) of three defined epithelial kidney cell lines, healthy MDCK and carcinoma A-498 and Caki-1 with the developed sensor, significant stretch ratio differences have been found between healthy and tumor cell types (and even between the two tumor types). The developed LED-photodiode based infrared absorbance sensor could be used for quick pre-screening of biopsy samples which, compared to labeling and staining techniques, does not require highly trained personnel and is much cheaper than liquid nitrogen cooled FTIR spectroscopes.