Three-dimensional electrodes for dielectrophoretic applications

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.

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

Paul Karoly Otto Ery, Carlotta Guiducci, Kevin Keim, Samuel Kilchenmann, Mohamed Zakarya Alsaid Ali Rashed

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.

2019

Nanoscale superparamagnetic composite particles for biomedical applications

Mathieu Chastellain

The present thesis report deals about the material scientists contribution to the interdisciplinary European project "MAGNANOMED" involving people having very different backgrounds (physicist, chemists, biochemists, veterinary surgeons, ...). The work carried out was aimed at the development of iron oxide based nanoscale superparamagnetic composite particles for biomedical applications. Particles showing a superparamagnetic behaviour are of particular interest as they are sensitive to magnetic fields without retaining magnetisation after removal of the latter. Not only superparamagnetic particles can be guided, but they also exhibit heating properties when submitted to appropriate alternating magnetic fields. These characteristics make them promising for targeted applications where they could act as careers as well as activators. The local temperature increase can be used for confined control release of linked entities or to modify specific cells activities in a well defined area. Moreover iron oxide nanoparticles can be used for magnetic resonance imaging enhancement. No single sample could meet the requirements imposed by every application mentioned above, so the chosen strategy was first to synthesize and thoroughly characterize iron oxide nanoparticles. In a second step, the particles would serve as primary building blocks for higher order composite structures or "beads" (with one or more iron oxide cores) to be formed according to the specific needs of every particular application. The surface tailoring, so that to ensure the desired properties in physiological media and allow further functionalisation, consisted in an important part of the work. Despite the many works carried out in the field over the past decades, the needs for well controlled biocompatible superparamagnetic beads are not only important but also growing. A focus was made on three specific applications: hyperthermia (controlled heating in a well defined body area by means of an external alternating magnetic field), drug delivery (magnetic targeted drug release) and DNA purification (magnetically driven separation in vitro). A supplementary application called ferrofluid actuated micro pump is also described as it turned out that a synthesis side product could be judiciously used in this field. The achievements realized allowed to define a reproducible and versatile synthesis route, which fulfils the above mentioned criteria as summarised in the following. Iron oxide particles, which physical properties could be well controlled, were shown to generate heat when submitted to an external magnetic field suitable for medical applications. The measured power dissipated could be successfully related to the particles and field characteristics using a theoretical approach and the tremendous influence of particles size distribution was highlighted. Polyvinyl alcohol coated iron oxide particles were produced for drug delivery. Biocompatibility was asserted based on both in vitro and in vivo experiments. The particles bio-distribution could be influenced by means of a constant magnetic field (magnet) and depending on the coating nature (presence of functional groups), the cellular uptake could be controlled. Silica beads with a homogeneous iron oxide particles space distribution were synthesised in view of DNA separation using a novel approach. The bead size could be adjusted in the 20 nanometres up to several microns range. Preliminary classical plasmid automated purification experiments revealed a competitive separation yield. These results are promising in view of the final targeted application in currently developed quicker automated processes. A highly concentrated iron oxide suspension (ferrofluid) showing suitable colloidal stability was successfully applied in micropumps actuated by means of a magnetically induced ferrofluid motion. The obtained pumping characteristics such as backpressure and flow rate were better then described in literature for similar devices using water based ferrofluids. AFM 3D-view of iron oxide particles coated with polyvinyl alcohol, average height 9 nm (left) and Stonehenge monument in Britain, heaviest stone 50 tons (right). "In its day, the construction of Stonehenge was an impressive engineering feat, requiring commitment, time and vast amounts of manual labour" [http://www.britannia.com/ history/h7.html] (see appendix 12.6). Nowadays, this remark still holds for Nano-stonehenge synthesis ...

EPFL2004

New Capabilities of the FLUKA Multi-Purpose Code

Francesco Cerutti, Nikolaos Charitonidis, André Donadon Servelle, Philippe Jean Schoofs

FLUKA is a general purpose Monte Carlo code able to describe the transport and interaction of any particle and nucleus type in complex geometries over an energy range extending from thermal neutrons to ultrarelativistic hadron collisions. It has many different applications in accelerator design, detector studies, dosimetry, radiation protection, medical physics, and space research. In 2019, CERN and INFN, as FLUKA copyright holders, together decided to end their formal collaboration framework, allowing them henceforth to pursue different pathways aimed at meeting the evolving requirements of the FLUKA user community, and at ensuring the long term sustainability of the code. To this end, CERN set up the FLUKA.CERN Collaboration (1) . This paper illustrates the physics processes that have been newly released or are currently implemented in the code distributed by the FLUKA.CERN Collaboration (2) under new licensing conditions that are meant to further facilitate access to the code, as well as intercomparisons. The description of coherent effects experienced by high energy hadron beams in crystal devices, relevant to promising beam manipulation techniques, and the charged particle tracking in vacuum regions subject to an electric field, overcoming a former lack, have already been made available to the users. Other features, namely the different kinds of low energy deuteron interactions as well as the synchrotron radiation emission in the course of charged particle transport in vacuum regions subject to magnetic fields, are currently undergoing systematic testing and benchmarking prior to release. FLUKA is widely used to evaluate radiobiological effects, with the powerful support of the Flair graphical interface, whose new generation (Available at http://flair.cem) offers now additional capabilities, e.g., advanced 3D visualization with photorealistic rendering and support for industry-standard volume visualization of medical phantoms. FLUKA has also been playing an extensive role in the characterization of radiation environments in which electronics operate. In parallel, it has been used to evaluate the response of electronics to a variety of conditions not included in radiation testing guidelines and standards for space and accelerators, and not accessible through conventional ground level testing. Instructive results have been obtained from Single Event Effects (SEE) simulations and benchmarks, when possible, for various radiation types and energies. The code has reached a high level of maturity, from which the FLUKA.CERN Collaboration is planning a substantial evolution of its present architecture. Moving towards a modern programming language allows to overcome fundamental constraints that limited development options. Our long term goal, in addition to improving and extending its physics performances with even more rigorous scientific oversight, is to modernize its structure to integrate independent contributions more easily and to formalize quality assurance through state-of-the-art software deployment techniques. This includes a continuous integration pipeline to automatically validate the codebase as well as automatic processing and analysis of a tailored physics-case test suite. With regard to the aforementioned objectives, several paths are currently envisaged, like finding synergies with Geant4, both at the core structure and interface level, this way offering the user the possibility to run with the same input different Monte Carlo codes and crosscheck the results.