OPTIMAL CONTROL OF OBJECTS ON THE MICRO- AND NANO-SCALE BY ELECTROKINETIC AND ELECTROMAGNETIC MANIPULATION: FOR BIO-SAMPLE PREPARATION, QUANTUM INFORMATION DEVICES AND MAGNETIC DRUG DELIVERY

In this thesis I show achievements for precision feedback control of objects inside micro-fluidic systems and for magnetically guided ferrofluids. Essentially, this is about doing flow control, but flow control on the microscale, and further even to nanoscale accuracy, to precisely and robustly manipulate micro and nano-objects (i.e. cells and quantum dots). Target applications include methods to miniaturize the operations of a biological laboratory (lab-on-a-chip), i.e. presenting pathogens to on-chip sensing cells or extracting cells from messy bio-samples such as saliva, urine, or blood; as well as non-biological applications such as deterministically placing quantum dots on photonic crystals to make multi-dot quantum information systems. The particles are steered by creating an electrokinetic fluid flow that carries all the particles from where they are to where they should be at each time step. The control loop comprises sensing, computation, and actuation to steer particles along trajectories. Particle locations are identified in real-time by an optical system and transferred to a control algorithm that then determines the electrode voltages necessary to create a flow field to carry all the particles to their next desired locations. The process repeats at the next time instant. I address following aspects of this technology. First I explain control and vision algorithms for steering single and multiple particles, and show extensions of these algorithms for steering in three dimensional (3D) spaces. Then I show algorithms for calculating power minimum paths for steering multiple particles in actuation constrained environments. With this microfluidic system I steer biological cells and nano particles (quantum dots) to nano meter precision. In the last part of the thesis I develop and experimentally demonstrate two dimensional (2D) manipulation of a single droplet of ferrofluid by feedback control of 4 external electromagnets, with a view towards enabling feedback control of magnetic drug delivery to reach deeper tumors in the long term. To this end, I developed and experimentally demonstrated an optimal control algorithm to effectively manipulate a single ferrofluid droplet by magnetic feedback control. This algorithm was explicitly designed to address the nonlinear and cross-coupled nature of dynamic magnetic actuation and to best exploit available electromagnetic forces for the applications of magnetic drug delivery

Development of an Integrated Chip for Automatic Tracking and Positioning Manipulation for Single Cell Lysis

This study adopted a microelectromechanical fabrication process to design a chip integrated with electroosmotic flow and dielectrophoresis force for single cell lysis. Human histiocytic lymphoma U937 cells were driven rapidly by electroosmotic flow and precisely moved to a specific area for cell lysis. By varying the frequency of AC power, 15 V AC at 1 MHz of frequency configuration achieved 100% cell lysing at the specific area. The integrated chip could successfully manipulate single cells to a specific position and lysis. The overall successful rate of cell tracking, positioning, and cell lysis is 80%. The average speed of cell driving was 17.74 μm/s. This technique will be developed for DNA extraction in biomolecular detection. It can simplify pre-treatment procedures for biotechnological analysis of samples

Precise steering of particles in electroosmotically actuated microfluidic devices

In this thesis, we show how to combine microfluidics and feedback control to independently steer multiple particles with micrometer accuracy in two dimensions. The particles are steered by creating a fluid flow that carries all the particles from where they are to where they should be at each time step. Our control loop comprises sensing, computation, and actuation to steer particles along user-input trajectories. Particle positions are identified in real-time by an optical system and transferred to a control algorithm that then determines the electrode voltages necessary to create a flow field to carry all the particles to their next desired locations. The process repeats at the next time instant. Our method achieves inexpensive steering of particles by using conventional electroosmotic actuation in microfluidic channels. This type of particle steering has significant advantages over other particle steering methods, such as laser tweezers. (Laser tweezers cannot steer reflective particles, or particles where the index of refraction is lower than (or for more sophisticated optical vortex holographic tweezers does not differ substantially from) that of the surrounding medium.). In this thesis, we address three specific aspects of this technology. First, we develop the control algorithms for steering multiple particles independently and validate our control techniques using simulations with realistic sources of initial position errors and system uncertainties. Second, we develop optimal path planning methods to efficiently steer particles between given initial and final positions. Third, we design high performance microfluidic devices that are capable of simultaneously steering five particles in experiment

Cell Sorting in Pillar Arrays based on Electrokinetics and Morphology

Deterministic Lateral Displacement (DLD) is a method capable of sorting cells based on size where mechanicalinteractions between a sufficiently large particle and obstacles in a microfludic pillar array force the particle tofollow a different trajectory than their smaller counterparts, resulting in continuous lateral separation. To extendthe capability of DLD, electrical interaction between particles and pillars can be employed to complement themechanical interaction, making electrical/dielectric properties additional parameters for sorting. Another idea isto exploit the morphologies of cells and as a concequence, their dynamical properties, to sort them in DLD. Thedevelopment of DLD cell sorting methods based on those two ideas has brought forth five papers appended to thisthesis: paper I, III, and V (combination of electrokinetics and DLD), and paper II and IV (exploiting morphologyin sorting by DLD).In the first topic, differences in electric properties or dielectric properties of particles and cells are employed toextend the capability of DLD. In Paper I, an AC electric field was applied across DLD devices having insulatingpillars to sort similar-sized polystyrene particles having different surface charge, viable from non-viable yeast cells,and viable from non-viable E. coli bacteria. In Paper III, the same method was utilised on open channel DLDdevices, showing unaltered effectiveness but offering the ability to flexibly change the distance between the electrodes.Also in the topic of combining electrokinetics and DLD, Paper V introduced a new type of DLD devicewhere the electrodes were defined locally on every pillar, making it easier to generate a high electric field strength.Besides electrical properties, morphology is another useful accompaniment to DLD. In Paper II, pathogenicStreptococcus pneumoniae bacteria were fractionated in DLD devices according to the difference in their morphology,viz. their chain length. It was also demonstrated, in paper IV, that an AC field can be used to rotatenon-spherical red blood cells and in turn, change their trajectory in a DLD device. This implies an opportunity tosort red blood cells from cells having different morphology, either spherical cells or parasites like trypanosomes

Graphical User Interface for Automated Biological Cell Manipulation Tasks

This report is the final project of a student in ISR's 2008 Research Experiences for Undergraduates program.Precise manipulation of particles at a microscopic level can be accomplished by a number of means with varying degrees of success and benefits. Many biological and pharmaceutical laboratories employ optical tweezers that use dielectrophoresis to trap and move particles [1]. Optical tweezers can manipulate hundreds of particles at a time in three dimensional space to within nanometers of each intended position. The advantages of such optical trapping systems can not be understated, but come at a price. Optical tweezers require lasers and delicate optics that require significant power and space relative to less accurate and extensive alternatives. Alternative particle trapping systems have been created as alternatives to optical tweezers utilizing: electric fields, taking advantage of particles with dielectric properties; magnetic fields, which manipulate particles with magnets attached to them; and arrays of microelectromechanical air nozzles that can steer particles along a control surface. These solutions can be executed more cheaply, and built on a small scale, but lack significant steering capabilities. The control system described in this section aims to reach some middle ground between the steering capabilities of optical tweezers and the attractive size and scale of the alternatives.The National Science Foundation sponsors the Research Experiences for Undergraduates program

Using Feedback Control of Microflows to Independently Steer Multiple Particles

In this paper, we show how to combine microfluidics and feedback control to independently steer multiple particles with micrometer accuracy in two spatial dimensions. The particles are steered by creating a fluid flow that carries all the particles from where they are to where they should be at each time step. Our control loop comprises sensing, computation, and actuation to steer particles along user-input trajectories. Particle locations are identified in real-time by an optical system and transferred to a control algorithm that then determines the electrode voltages necessary to create a flow field to carry all the particles to their next desired locations. The process repeats at the next time instant. Our method achieves inexpensive steering of particles by using conventional electroosmotic actuation in microfluidic channels. This type of particle steering does not require optical traps and can noninvasively steer neutral or charged particles and objects that cannot be captured by laser tweezers. (Laser tweezers cannot steer reflective particles, or particles where the index of refraction is lower than (or for more sophisticated optical vortex holographic tweezers does not differ substantially from) that of the surrounding medium.)We show proof-of-concept PDMS devices, having four and eightelectrodes, with control algorithms that can steer one and three particles, respectively. In particular, we demonstrate experimentally that it is possible to use electroosmotic flow to accurately steer and trap multiple particles at once

Fabrication and characterization of a mcro/nanofluidic platform for electroporation.

For traditional electroporation devices, there are a number of problems associated with these devices such as insufficient understanding of its theoretical mechanism, low cell viability, inadequate electroporation efficiency, excess voltage applied to generate required electric field due to the large size of these devices and sample contamination. Although newly developed microfluidic electroporation devices have solved most of the above existing problems in traditional bulk electroporation devices, they appear to lack the ability to control the precise dose of biomolecules or genes transfecting into cells and, from a manufacturing perspective, the fabrication methods do not enable repeatable production of such devices on the large scale. Here, we introduce a new, repeatable method for fabricating 3-D Micro/Nanofluidic electroporation platforms and characterize these platforms to demonstrate their ability to electroporate live cells. Some of the new methods developed in this work include a direct-write fiber technique via three-axis robotic dispensing system, dry film resist photolithography, film-to-film bonding and replica molding to create the desired electroporation platform. A robotic dispensing system was utilized to control the fiber diameter, which was determined vii by the: 1) prescribed dispense time; 2) pressure of the dispensing system valve; 3) rate at which the stage traversed; 4) diameter of the dispensing tip; 5) polymer solution viscosity and surface tension; and, 6) programmed drawing length. Thin dry film photoresist was utilized to replace liquid photoresist in order to achieve high-quality film-to-film bonding after drawing nanofibers onto one substrate containing the thin-film structure. Polydimethylsiloxane (PDMS) was employed as the bulk material to fabricate the target micro/nano electroporation substrate using replica molding and micro/nanofibers etching. Characterization of the direct-write fiber technique via robotic dispensing system to acquire suspended and complex fibers of the required dimension repeatedly under prescribed conditions were completed. Combining this fiber direct-write method and traditional clean room techniques, a total of 18 micro- to nano-scale electroporation devices (6 for each group of 1 ìm, 500 nm, and 300 nm diameter) were successfully developed and mass produced in two weeks with relatively high repeatability (within 20% of the design). Finally, metrology and characterization studies were performed on the electroporation platforms to validate the micro/nanochannel’s existence and its connectivity to two micro-chambers. Furthermore, biomolecules and other fluorescent particles were successfully transported through the micro/nanochannel and transferred (via electroporation) into the cells. Preliminary results of electroporation experiment performed on this micro/nano-electroporation platform illustrated that the duration of the entire electroporation process was significantly shorter than times reported previously by other investigator’s nano-electroporation platforms

The Design and Evaluation of a Microfluidic Cell Sorting Chip

Many applications for the analysis and processing of biological materials require the enrichment of cell subpopulations. Conventional cell sorting systems are large and expensive with complex equipment that necessitates specialized personnel for operation. Employing microfluidics technology for lab-on-a-chip adaptation of these devices provides several benefits: improved transport control, reduced sample volumes, simplicity of operation, portability, greater accessibility, and reduced cost. The designs of microfluidic cell sorting chips vary widely in literature; evaluation and optimization efforts are rarely reported. This study intends to investigate the primary components of the design to understand the effect of various parameters and to improve the performance of the microfluidic chip. Optimized individual elements are incorporated into a proposed cell sorter chip with the ability to dynamically sort target cells from a non-homogeneous solution using electrical driving forces. Numerical and experimental results are used to evaluate the sample focusing element for controlled cell dispensing, the sorting configuration for target cell collection, and the flow elements for reduced pressure effects and prevention of flow blockages. Compact models are adapted to solve the potential field and flow field in the chip and to predict the focused sample stream width. A commercial CFD package is used to perform 2-D simulations of the potential, velocity, and concentration fields. A fluorescence microscopy visualization system is implemented to conduct experiments on several generations of chip designs. The data from sample focusing experiments, performed with fluorescent dye samples, is analyzed using a Gaussian distribution model proposed in this work. A technique for real-time monitoring of fluorescent microspheres in the microfluidic chip enables the use of dynamic cell sorting to emulate fully autonomous operation. The performance values obtained from these experiments are used to characterize the various design configurations. Sample focusing is shown to depend largely on the relative size of the sheath fluid channel and the sample channel, but is virtually independent of the junction shape. Savings in the applied potential can be achieved by utilizing the size dependency. The focusing performance also provides information for optimizing the widths of the channels relative to the cell size. Successful sorting of desired cells is demonstrated for several designs. Key parameters that affect the sorting performance are discussed; a design employing the use of supplemental fluid streams to direct the particle during collection is chosen due to a high sorting evaluation and a low sensitivity to flow anomalies. The necessary reduction of pressure influences to achieve reliable flow conditions is accomplished by introducing channel constrictions to increase the hydrodynamic resistance. Also, prolonged operation is realized by including particle filters in the proposed design to prevent blockages caused by the accumulation of larger particles. A greater understanding of the behaviour of various components is demonstrated and a design is presented that incorporates the elements with the best performance. The capability of the microfluidic chip is summarized based on experimental results of the tested designs and theoretical cell sorting relationships. Adaptation of this chip to a stand-alone, autonomous device can be accomplished by integrating an optical detection system and further miniaturization of the critical components

Optical and magnetic tweezers for applications in single-molecule biophysics and nanotechnology

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de la Materia Condensada. Fecha de lectura: 22-01-201