Finite Element Simulation of Microfluidic Biochip for High Throughput Hydrodynamic Single Cell Trapping

In this paper, a microfluidic device capable of trapping a single cell in a high throughput manner and at high trapping efficiency is designed simply through a concept of hydrodynamic manipulation. The microfluidic device is designed with a series of trap and bypass microchannel structures for trapping individual cells without the need for microwell, robotic equipment, external electric force or surface modification. In order to investigate the single cell trapping efficiency, a finite element model of the proposed design has been developed using ABAQUS-FEA software. Based on the simulation, the geometrical parameters and fluid velocity which affect the single cell trapping are extensively optimized. After optimization of the trap and bypass microchannel structures via simulations, a single cell can be trapped at a desired location efficiently

Micromanipulation in microfluidics using optoelectronic and acoustic tweezing

The thesis introduces a concept for a unified platform that enables the use of acoustic and electric fields for particle manipulations in microfluidic environments. In particular, optoelectronic tweezing (OET), also known as light induced dielectrophoresis is fused with acoustic tweezing, also known as acoustophoresis, on a versatile system. The system can be divided into two individual physical units. The first one represents the OET unit which integrates light induced electric fields into a robust microfluidic chip. The OET chip not only operates as a device for electric field generation but also as a transverse resonator to confine acoustic fields. These fields are the result of travelling surface acoustic waves excited by a piezoelectric transducer which defines the second unit. The developed platform is applied to a range of applications such as particle trapping, transporting, focussing, sorting as well particle alterations in form of cell lysis and microbubble insonation

Beyond solid-state lighting: Miniaturization, hybrid integration, and applications og GaN nano- and micro-LEDs

Gallium Nitride (GaN) light-emitting-diode (LED) technology has been the revolution in modern lighting. In the last decade, a huge global market of efficient, long-lasting and ubiquitous white light sources has developed around the inception of the Nobel-price-winning blue GaN LEDs. Today GaN optoelectronics is developing beyond lighting, leading to new and innovative devices, e.g. for micro-displays, being the core technology for future augmented reality and visualization, as well as point light sources for optical excitation in communications, imaging, and sensing. This explosion of applications is driven by two main directions: the ability to produce very small GaN LEDs (microLEDs and nanoLEDs) with high efficiency and across large areas, in combination with the possibility to merge optoelectronic-grade GaN microLEDs with silicon microelectronics in a fully hybrid approach. GaN LED technology today is even spreading into the realm of display technology, which has been occupied by organic LED (OLED) and liquid crystal display (LCD) for decades. In this review, the technological transition towards GaN micro- and nanodevices beyond lighting is discussed including an up-to-date overview on the state of the art

Dielectrophoresis for capillary flow microfluidic optoelectronics

The development of a novel photonic integrated platform with three dimensional (3D) capillary flow and dielectrophoresis elements for chip based flow cytometers is discussed. Size-independent single stream particle focusing is the key for the efficient operation of a flow cytometer and many efforts have been made to reproduce it properly on a microchip scale. In this work, capillary and negative Dielectrophoresis (n-DEP) components were integrated onto a single chip of III-V semiconductor material for conducting scattering measurements of microparticles. The integration of all components on a single chip is intended to result in low cost, portable and disposable microfluidic devices for point-of-care diagnostics. The design, fabrication and investigation of a system combining n-DEP with the capillary driven flow to align and reposition microparticles with fluid flow in a single stream around the centreline of the microchannel is considered. This is followed by testing the potential of n-DEP for efficient on-chip light scatter measurements. Planar microelectrodes face-to-face below and above the surface of the 3D microchannel are employed to create a localized non-uniform electric field to focus polystyrene microparticles in flowing fluid via n-DEP. The functionality of the device is assessed by detecting and counting 6 - 15 µm polystyrene microparticles (suspended in Deionised (DI) water) as an example to assess how similarly sized biological cells, such as blood cells, would flow within the fabricated 3D microchannel. The results show that the polystyrene microparticles are focused successfully in a single stream around the centreline of the 3D microchannel when operating the microelectrodes with an AC potential of 10 MHz and no more than 30 V peak-to-peak. The n-DEP focused microparticles show narrower velocity distribution, compared to randomly flowing particles, as well as exhibiting higher speeds (at the centre of the channel). The latter result suggests that a capillary-like speed profile is only present at the fluid front, and that the fluid flow becomes faster at the centre, behind the advancing meniscus, due to the greater friction at the microchannel’s side walls. Consistent pulse shapes and peaks are observed in the laser data from the similarly sized polystyrene microparticles using a fully-integrated platform with lasers and photo-detectors. This suggests that the n-DEP focusing microelectrodes can significantly improve the operation efficiency of the device by regulating the flow of microparticles and passing them through a consistent scanning zone albeit with an increase in the precision of the fabrication required

A concise review of microfluidic particle manipulation methods

Particle manipulation is often required in many applications such as bioanalysis, disease diagnostics, drug delivery and self-cleaning surfaces. The fast progress in micro- and nano-engineering has contributed to the rapid development of a variety of technologies to manipulate particles including more established methods based on microfluidics, as well as recently proposed innovative methods that still are in the initial phases of development, based on self-driven microbots and artificial cilia. Here, we review these techniques with respect to their operation principles and main applications. We summarize the shortcomings and give perspectives on the future development of particle manipulation techniques. Rather than offering an in-depth, detailed, and complete account of all the methods, this review aims to provide a broad but concise overview that helps to understand the overall progress and current status of the diverse particle manipulation methods. The two novel developments, self-driven microbots and artificial cilia-based manipulation, are highlighted in more detail

An Integrative Approach to Elucidating the Governing Mechanisms of Particles Movement under Dielectrophoretic and Other Electrokinetic Phenomena

Dielectrophoresis (DEP) has been a subject of active research in the past decades and has shown promising applications in Lab-on-Chip devices. Currently researchers use the point dipole method to predict the movement of particles under DEP and guide their experimental designs. For studying the interaction between particles, the Maxwell Stress Tensor (MST) method has been widely used and treated as providing the most robust and accurate solution. By examining the derivation processes, it became clear that both methods have inherent limitations and will yield incorrect results in certain occasions. To overcome these limitations and advance the theory of DEP, a new numerical approach based on volumetric-integration has been established. The new method has been proved to be valid in quantifying the DEP forces with both homogeneous and non-homogeneous particles as well as particle-particle interaction through comparison with the other two methods. Based on the new method, a new model characterizing the structure of electric double layer (EDL) was developed to explain the crossover behavior of nanoparticles in medium. For bioengineering applications, this new method has been further expanded to construct a complete cell model. The cell model not only captures the common crossover behavior exhibited by cells, it also explains why cells would initiate self-rotation under DEP, a phenomenon we first observed in our experiments. To take a step further, the new method has also been applied to investigate the interaction between multiple particles. In particular, this new method has been proved to be powerful in elucidating the underlying mechanism of the tumbling motion of pearl chains in a flow condition as we observed in our experiments. Moreover, it also helps shed some new insight into the formation of different alignments and configurations of ellipsoidal particles. Finally, with the consideration of the Faradic current from water electrolysis and effect of pH, a new model has been developed to explain the causes for the intriguing flow reversal phenomenon commonly observed (but not at all understood) in AC-electroosmosis (ACEO) with reasonable outcomes