On‐chip technology for single‐cell arraying, electrorotation‐based analysis and selective release

This paper reports a method for label-free single-cell biophysical analysis of multiple cells trapped in suspension by electrokinetic forces. Tri-dimensional pillar electrodes arranged along the width of a microfluidic chamber define actuators for single cell trapping and selective release by electrokinetic force. Moreover, a rotation can be induced on the cell in combination with a negative DEP force to retain the cell against the flow. The measurement of the rotation speed of the cell as a function of the electric field frequency define an electrorotation spectrum that allows to study the dielectric properties of the cell. The system presented here shows for the first time the simultaneous electrorotation analysis of multiple single cells in separate micro cages that can be selectively addressed to trap and/or release the cells. Chips with 39 micro-actuators of different interelectrode distance were fabricated to study cells with different sizes. The extracted dielectric properties of HeLa, HEK 293, and human immortalized T lymphocytes cells were found in agreements with previous findings. Moreover, the membrane capacitance of M17 neuroblastoma cells was investigated and found to fall in in the range of 7.49 ± 0.39 mF/m2.

Three-dimensional electrodes for dielectrophoretic applications

Kevin Keim

This thesis reports the use of metal-coated three-dimensional SU-8 electrodes for dielectrophoretic bio sensing and particle manipulation applications. Placing free standing three-dimensional electrodes in microfluidic channels, electric fields can be applied homogeneously over the complete height of the device. Due to this at any vertical position in the channel an equal dielectrophoretic force is created. These electrodes have been used to parallelize individual single-cell analysis by the mean of electrorotation and to tune the sorting size of deterministic lateral displacement devices by adding dielectrophoretic forces. Electrorotation uses rotating electric fields to make cells spin and determine their dielectric properties from their speed of rotation at different electric excitation frequencies. Using a double array of individual connected three-dimensional electrodes placed in a wide microfluidic channel, individual cells can be selectively trapped and released in single-cell dielectrophoretic micro cages and analyzed in parallel by electrorotation. The parallel analysis of cells in individual electrorotation cages is demonstrated for the first time and the membrane capacitance of Henrietta Lacks, human embryonic kidney 293, and human T lymphocytes are found in agreement with literature. The membrane capacitance of M17 neuroblastoma is investigated and found to be 7.49 ± 0.39 mF/m2. Additionally membrane capacitance changes within a human embryonic kidney 293 cell population are observed with the system based on an osmolarity study and the viability is assured by monitoring the membrane functionality using an erythrosin B dye. Failure of the membrane sealing function is observed in real-time by a shift of the electrorotation spectrum and a drop in the membrane capacitance. Deterministic lateral displacement uses shifted rows of posts in a microfluidic labyrinth to sort particles based on their size. The principle uses the deterministic behavior of particles in the device, particles below a certain size move straight through the device, while larger particles are displaced to the side. Replacing the passive posts by three-dimensional electrodes allows the creation of local dielectrophoretic forces. Applying voltages of up to 15 Vpp dynamically reduces the sorting size of the device from 6 µm to 250 nm, enabling a device tunable for a specific sorting size. Nanometer sized particles can be separated in within micrometer structures reducing the problem of clogging. Additionally, this device could enable sorting of equal sized nanometer particles based on their dielectric properties. These two examples show the applicability of metal-coated three-dimensional SU-8 electrodes for dielectrophoretic applications. They first enable the design of new devices, which could not be realized previously, as shown by the electrorotation device, and second traditional passive structures can be replaced by electrodes, which can help to improve their performance or enable new functionalities.

EPFL2020

Microelectronics Meets Biology

Emile Dupont

Microfluidics plays a key role in the design of automated platforms for realizing biological assays in a miniaturized format. Several advantages are offered by a microfluidic system, namely, low sample and reagent consumption (typically a few microliters), the possibility to mass-produce and to integrate several analysis modules enabling portable automated applications, fast analysis and low cost. Furthermore, the combination of advanced Complementary Metal-Oxide-Semiconductor (CMOS) technology and microfluidics can result in flexible and easy-to-use hybrid systems that hold large potential for application in an analytical laboratory or at the point-of-care. In this Thesis, two different monolithic silicon CMOS chips were designed, fabricated and tested, demonstrating state-of-the-art performance utilising a novel fluorescence detection principle. They allowed the detection of monoclonal antibodies in a solution or the precise counting of specifically labelled fluorescent cells in a mixed-cell sample. The proposed detection method does not require the utilization of a fluorescence camera and filter set. The first part of this Thesis presents different methods, fabrication processes and materials for microfluidic cartridges that can be integrated in a hybrid way with silicon CMOS chips. Glass and SU-8 capillaries are tested, a novel material (NOA 63) is proposed for fabricating a natively hydrophilic microfluidic cartridge, and the fabrication of custom-designed polydimethyl(-siloxane) (PDMS) cartridges for easy integration on top of a CMOS chip is introduced. The second part of this Thesis presents the combination of microfluidics with a monolithic and fully-integrated CMOS chip for the manipulation and detection of fluorescent magnetic beads, inside a PDMS microchannel that is loosely positioned on top of the chip. Magnetic manipulation is done by current actuation of microcoils on the chip; detection is achieved using single photon avalanche diodes (SPADs), located in the centre of each microcoil, that count the fluorescent photons originating from a single labeled magnetic bead. This approach permits in principle microscope-less fluorescence detection with high sensitivity. Using sandwich immunoassays on the beads' surfaces, the selective detection of the cancer biomarker 5D10 monoclonal antibody (mAb) from a non-purified hybridoma cell-culture medium is demonstrated. In the third part, a CMOS chip comprising a matrix of SPADs is designed, fabricated and tested. The recognition of single fluorescently-labelled cells from the breast cancer cell line MCF-7 in a test solution of mixed MCF-7 and non-fluorescent Jurkat cells is demonstrated, without the need of a bulky and expensive fluorescent microscope setup. Moreover, due to the use of a SPAD matrix spanning the complete width of the microchannel, the system does not require any cell focusing mechanism, needed when using a single detector. This allowed the use of a very simple, easily replicable and disposable plastic microfluidic cartridge.

EPFL2010

Effect of Ca substitution on crystal structure and superconducting properties of ferromagnetic superconductor RuSr2-xCaxGd1.4Ce0.6Cu2O10-delta

Mehdi Mazaheri, Neda Nikseresht Ghanepour, Henrik Moodysson Rønnow

We have investigated the effect of Ca substitution for Sr site on structural, magnetic and superconducting properties of RuSr2-xCaxGd1.4Ce0.6Cu2O10-delta system. In this system, the magnetic coupling of RuO2 and CuO2 plays an important role in magnetic and superconducting states. X-ray diffraction analysis shows that all samples are single phase and the lattice parameters decrease continuously by increasing Ca content. The onset superconducting transition temperature is found to decrease with Ca substitution. As Ca content increases, rotation of the RuO6 octahedron increases and Ru-O(1)-Ru angle decreases. These variations strengthen the magnetic moments in the RuO2 planes. The enhancement of weak ferromagnetic component and hole trapping by Ru magnetic moments in RuO2 planes reduces the electrical conduction, and destroys the superconducting state in the system. Analysis of the resistivity data (rho) based on the hoping conduction mechanism, indicates a variation of the hoping exponent (p) across the magnetic transition at T-m. The hoping exponent p is not affected sharply by Ca concentration. (C) 2011 Elsevier B.V. All rights reserved.