On the integration of a microdialysis-based microTAS with calibration facility on a silicon-glass sandwich

The integration is discussed of all parts of a microdialysis-based micro Total Analysis System or ¿TAS. In particular a microdialysis probe, a potentiometric and amperometric ion- and enzyme sensor and a calibration dosing pump have been developed separately using different precision machining techniques. By modifying and adapting these parts they can be realized in one generic technology consisting of a stack of a silicon and a glass wafer. The silicon wafer contains the double lumen microdialysis probe connections, a dosing pump chamber with meander formed cavities containing the calibration solutions and small cavities for both the potentiometric and amperometric sensor. The glass wafer contains all the electrical contacts and wires for the sensors, the pump and Interconnections. Both wafers are anodically bonded to each other, yielding a hermetically sealed liquid handling syste

On-Chip Detection of Beads with a New Electrical Impedance Sensor

Electrical impedance measurements in microfluidic chips are used for single cell analysis. Parallel electrodes are more suited than planar ones since the electrical field distribution is more homogenous. Previous studies showed methods to make parallel electrodes by incorporating an additional layer between two glass wafers, making electrical connections to both sides needed. Also alignment of electrodes is necessary, making the fabrication of parallel electrodes more elaborate. Therefore a new, simpler fabrication method is developed for the fabrication of parallel electrode chips by incorporating a floating electrode in the microchannel just by adding one step in the fabrication process. In this way, only one side of the chip contains electrical connections. Finally, electrical impedance measurements with 3 and 6 µm polystyrene beads were done. All beads were detected and we have shown that it is possible to distinguish the two beads sizes from each other with a confidence level of 95%, based on the relative change in the electrical impedance

On Chip Spermatozoa and Leucocytes Counter

In this project we aim to develop a semen quality test system based on a lab-on-a-chip. Since an important quality parameter of semen is the concentration of spermatozoa, we focus on counting the spermatozoa by using impedance measurements in a microchannel. However, semen contains also an interfering concentration of leucocytes that should be excluded from the cell count. By a proper chip design and a sensitive measurement set-up, it was possibl

A new floating electrode structure for generating homogeneous electrical fields in microfluidic channels

In this article a new parallel electrode structure in a microfluidic channel is described that makes use of a floating electrode to get a homogeneous electrical field. Compared to existing parallel electrode structures, the new structure has an easier production process and there is no need for an electrical connection to both sides of the microfluidic chip. With the new chip design, polystyrene beads suspended in background electrolyte have been detected using electrical impedance measurements. The results of electrical impedance changes caused by beads passing the electrodes are compared with results in a similar planar electrode configuration. It is shown that in the new configuration the coefficient of variation of the impedance changes is lower compared to the planar configuration (0.39 versus 0.56) and less dependent on the position of the beads passage in the channel as a result of the homogeneous electrical field. To our knowledge this is the first time that a floating electrode is used for the realization of a parallel electrode structure. The proposed production method for parallel electrodes in microfluidic channels can easily be applied to other application

A cheap 2D fluorescence detection system for μM-sized beads on-chip

In this paper a compact fluorescence detection system for on-chip analysis of μm-sized beads is presented. The system comprises a cheap optical pickup with integrated functionalities that are used for the detection. Furthermore some other optical components are added for the fluorescence detection. Another part of the system is the microfluidic chip which contains liquid channels and optical markers used for the autofocus and channel find algorithms. Within one minute the channel of interest is found and fluorescent beads are detected in the microchannel without the need for dynamic focusing, since a two-dimensional scan across the channel width is performed

High-resolution microcontact printing and transfer of massive arrays of microorganisms on planar and compartmentalized nanoporous aluminium oxide

Handling microorganisms in high throughput and their deployment into miniaturized platforms presents significant challenges. Contact printing can be used to create dense arrays of viable microorganisms. Such "living arrays'', potentially with multiple identical replicates, are useful in the selection of improved industrial microorganisms, screening antimicrobials, clinical diagnostics, strain storage, and for research into microbial genetics. A high throughput method to print microorganisms at high density was devised, employing a microscope and a stamp with a massive array of PDMS pins. Viable bacteria (Lactobacillus plantarum, Esherichia coli), yeast (Candida albicans) and fungal spores (Aspergillus fumigatus) were deposited onto porous aluminium oxide (PAO) using arrays of pins with areas from 5 x 5 to 20 x 20 mu m. Printing onto PAO with up to 8100 pins of 20 x 20 mu m area with 3 replicates was achieved. Printing with up to 200 pins onto PAO culture chips (divided into 40 x 40 mu m culture areas) allowed inoculation followed by effective segregation of microcolonies during outgrowth. Additionally, it was possible to print mixtures of C. albicans and spores of A. fumigatus with a degree of selectivity by capture onto a chemically modified PAO surface. High resolution printing of microorganisms within segregated compartments and on functionalized PAO surfaces has significant advantages over what is possible on semi-solid surfaces such as agar

Pressure-driven ballistic Kelvin's water dropper for energy harvesting

In this paper, we introduce a microfluidic-based self-excited energy conversion system inspired by Kelvin's water dropper but driven by inertia instead of gravity. Two micro water jets are produced by forcing water through two micropores by overpressure. The jets break up into microdroplets which are inductively charged by electrostatic gates. The droplets land on metal targets which are gradually charged up to high voltages. Targets and electrostatic gates are cross-connected in a way similar to Kelvin's water dropper. Application of pressure as driving force instead of gravity as in Kelvin's dropper allows for much higher energy densities. To prevent overcharging of the droplets by the inductive mechanism and consequent droplet loss by repulsion from the target as in Kelvin's water dropper, a voltage divider using inversely connected diodes was introduced in our system to control the charge induction providing self-limiting positive feedback by the diode characteristics. A maximal 18% energy conversion efficiency was obtained with the diode-gated system

High throughput screening method for assessing heterogeneity of microorganisms

The invention relates to the field of microbiology. Provided is a method which is particularly powerful for High Throughput Screening (HTS) purposes. More specific a high throughput method for determining heterogeneity or interactions of microorganisms is provided