Aliquoting structure for centrifugal microfluidics based on a new pneumatic valve

We present a new microvalve that can be monolithically integrated in centrifugally driven lab-on-a-chip systems. In contrast to existing operation principles that use hydrophobic patches, geometrically defined capillary stops or siphons, here we present a pneumatic principle. It needs neither additional local coatings nor expensive micro sized geometries. The valve is controlled by the spinning frequency and can be switched to be open when the centrifugal pressure overcomes the pneumatic pressure inside an unvented reaction cavity. We designed and characterized valves ranging in centrifugal burst pressure from 6700 Pa to 2100 Pa. Based on this valving principle we present a new structure for aliquoting of liquids. We experimentally demonstrated this by splitting 105 muL volumes into 16 aliquots with a volume CV of 3 %

Physics and Applications of a PDMS Based Centrifugal Microfluidic System

The objective of this research work is to develop a centrifugal microfluidic system for general purposes based on microfabrication technologies including SU-8 photolithography, polydimethylsiloxane (PDMS) casting. The main contribution of this research is to integrate a flyball governor system into the polymer based centrifugal microfluidic platform. A series of function units are developed based on this unique mechanism. In the first part, three pinch valve systems were designed and tested. The first one is based on the magnetic force and the second one is on the basis of spring force and the last one is a membrane valve. All valving system demonstrate good control of the fluid movement. The latter two valves are capable of sequential control. It proves that the flyball governor system is very compatible with centrifugal fluidic technologies. The major advantage of this new actuation technology is that its burst frequency can be conveniently manipulated by adjusting the parameters of the mechanical system without changes in the fluidic pattern. Next, two types of inward pumping systems were designed and tested. The result shows that both the inward pumps were capable of the pumping over a radial distance of 21mm in a short time. It thus improves the usage of space on the disc and paves the way to interconnect several functional units. Then as a proof of concept, a sequential valving system capable of metering and centrifugal sediment was developed for plasma extraction from whole blood. The resulting residual cell concentration was less than 0.5%. In the last part, a micromixer was developed based on the similar principle. The results show that the flyball governor system can effectively agitate the chaotic mixing of the sample liquids by periodically deflecting the PDMS membrane of the mixing chamber. The mixing effect can thus be enhanced

Reciprocating, buoyancy-driven radial pumping on centrifugal microfluidic platforms

Centrifugal microfluidic systems bear great potential for applications where ruggedness, portability, ease-of-use, and cost efficiency are critical. However, due to the unidirectional nature of the centrifugal pumping force, the number of sequential process steps which can be integrated on these “Lab-on-a-Disc” (LoaD) devices is limited by their finite radial extension. To significantly widen this bottleneck and thus expand the scope of applications that can be ported on these LoaD platforms, various groups have developed a range of centripetal pumping mechanisms. Here, we present two advancements over our previous efforts in this area by combining buoyancy-based pumping with dissolvable film (DF) valves. First, we present a buoyancy-driven, reciprocating flow of a dense liquid initially located an upper reservoir and a sample in a peripheral reservoir. Secondly, we combine buoyancy-driven centripetal pumping with sample discretization and metering to fully integrate and automate a liquid handling protocol towards implementing a multi-parameter bioassay on a disc

A centrifugal microfluidic platform for capturing, assaying and manipulation of beads and biological cells

Microfluidics is deemed a field with great opportunities, especially for applications in medical diagnostics. The vision is to miniaturize processes typically performed in a central clinical lab into small, simple to use devices - so called lab-on-a-chip (LOC) systems. A wide variety of concepts for liquid actuation have been developed, including pressure driven flow, electro-osmotic actuation or capillary driven methods. This work is based on the centrifugal platform (lab-on-a-disc). Fluid actuation is performed by the forces induced due to the rotation of the disc, thus eliminating the need for external pumps since only a spindle motor is necessary to rotate the disc and propel the liquids inside of the micro structures. Lab-on-a-disc systems are especially promising for point-of-care applications involving particles or cells due to the centrifugal force present in a rotating system. Capturing, assaying and identification of biological cells and microparticles are important operations for lab-on-a-disc platforms, and the focus of this work is to provide novel building blocks towards an integrated system for cell and particle based assays. As a main outcome of my work, a novel particle capturing and manipulation scheme on a centrifugal microfluidic platform has been developed. To capture particles (biological cells or micro-beads) I designed an array of V-shaped micro cups and characterized it. Particles sediment under stagnant flow conditions into the array where they are then mechanically trapped in spatially well-defined locations. Due to the absence of flow during the capturing process, i.e. particle sedimentation is driven by the artificial gravity field on the centrifugal platform, the capture efficiency of this approach is close to 100% which is notably higher than values reported for typical pressure driven systems. After capturing the particles, the surrounding medium can easily be exchanged to expose them to various conditions such as staining solutions or washing buffers, and thus perform assays on the captured particles. By scale matching the size of the capturing elements to the size of the particles, sharply peaked single occupancy can be achieved. Since all particles are arrayed in the same focal plane in spatially well defined locations, operations such as counting or fluorescent detection can be performed easily. The application of this platform to perform multiplexed bead-based immunoassays as well as the discrimination of various cell types based on intra cellular and membrane based markers using fluorescently tagged antibodies is demonstrated. Additionally, methods to manipulate captured particles either in batch mode or on an individual particle level have been developed and characterized. Batch release of captured particles is performed by a novel magnetic actuator which is solely controlled by the rotation frequency of the disc. Furthermore, the application of this actuator to rapidly mix liquids is shown. Manipulation of individual particles is performed using an optical tweezers setup which has been developed as part of this work. Additionally, this optical module also provides fluorescence detection capabilities. This is the first time that optical tweezers have been combined with a centrifugal microfluidic system. This work presents the core technology for an integrated centrifugal platform to perform cell and particle based assays for fundamental research as well as for point-of- care applications. The key outputs of my specific work are: 1. Design, fabrication and characterization of a novel particle capturing scheme on a centrifugal microfluidic platform (V-cups) with very high capture efficiency (close to 100%) and sharply peaked single occupancy (up to 99.7% single occupancy). 2. A novel rotation frequency controlled magnetic actuator for releasing captured particles as well as for rapidly mixing liquids has been developed, manufactured and characterized. 3. The V-cup platform has successfully been employed to capture cells and perform multi-step antibody staining assays for cell discrimination. 4. An optical tweezers setup has been built and integrated into a centrifugal teststand, and successful manipulation of individual particles trapped in the V-cup array is demonstrated

Development of a centrifugal microfluidic device for separation and sorting in biological fluids

A wide interest in employing micron-scale, integrated biochemical analysis systems for economical and rapid diagnosis has been the principal motivation behind this project. Low operating costs, portability and fast diagnosis times make centrifugal microfluidic devices an attractive option in patient-side diagnostics. Some essential tasks to be performed in microfluidic devices are sample-reagent transport, mixing, separation and detection. All these tasks require precise control of the RPM and spinning time. Centrifugal micro-fluidic platforms have been successfully implemented for detection of hepatitis A, tetanus, as well as for measurement of haemoglobin and hematocrit, for DNA analysis, and for assessment of cardiac disease etc. by assaying biological fluids like blood, saliva, and urine. This thesis presents the construction, including the micro-machining and testing of a multi-channel centrifugal microfluidic device for point-of-care (POC) diagnostics. A low cost device capable of delivering controlled revolutions per minute was made by modifying a CD-ROM drive and a polymer disk was used to handle the fluids. A network of microfluidic channels and reservoirs was fabricated on the CD by using a rapid prototyping method. The reservoirs hold the biofluid sample, meter the volume of fluid accurately and also serve as a component of capillary burst valves to gate the flow of fluid. Micromachining techniques like photolithography, wet-etching have been discussed for mass production of the prototype used for this research. Theoretical analysis of the burst frequency for passive capillary valves is reported and compared with practical results. The goal of this thesis was to develop a low cost device and demonstrate its use in the separation, and metering of plasma from blood using centrifugal microfluidics. One challenge when using blood for diagnosis is to separate the blood plasma from the rest of the blood cells. Concepts of blood centrifugation and particle displacement on a spinning disk have been employed to calculate the required RPM. Experiments were carried out on various geometries in order to achieve the maximum level of separation. The results of these experiments have been reported. It has been established that centrifugal microfluidics can be used to accurately control the flow of fluids in microchannels and this can be used for reliable low cost point-of-care diagnostics

Study on Microchannel Design and Burst Frequency Detection for Centrifugal Microfluidic System

A centrifugal microfluidic system has been developed in this study, enabling the control and measurement of the burst frequency in order to manipulate the liquid. The radial microfluid chips with different microchannel dimensions were designed for simulation analyses and experimental verifications. The microfluidic flow in the microchannel was analyzed using software CFDRC, providing an accurate result compared with that from experiment. The results show that the design of the overflow microchannel can correctly keep the liquid volume with error as low as 5%. For mercurochrome, the burst frequency has an inverse proportion to the channel width, and the simulation results agree with the experimental results. For oil, however, the experimental and simulation results indicate that the relationship between the burst frequency and channel width is not obvious due to oil properties. Since the simulation approach can provide an accurate prediction of flow behavior in the microchannel, the design of radial microfluid chip and the control of burst frequency can be achieved effectively. A practical application to design the centrifugal microfluidic disc for blood typing test was also carried out in this study. The centrifugal microfluidic system can successfully control the spinning speed to achieve the result of adding reagents in a specific sequence

Parametric analysis of a novel semi-circular microfluidic CD-ELISA valve

CD-ELISA uses the microfluidic ranking method and centrifugal force to control the testing solution as it flows into the reaction region. The most challenging part of CD-ELISA is controlling the flow process for different biological testing solutions, i.e. the controlling sequence for the microfluidic channel valves. The microfluidic channel valve is therefore the most important fluid channel structure for CD-ELISA. In this study, we propose a valve design suitable for a wide range rotational speeds which can be applied for mass production (molding). Together with supporting experiments, simulation based on two-phase flow theory is used in this study, and the feasibility of this novel valve design is confirmed. Influencing design factors for the microfluidic channel valves in CD-ELISA are investigated, including various shapes of the arc, distance d, radius r, the location of the center of the circle, and the contact angle. From both the experimental results and the simulated results, it is evident that the narrowest channel width and the contact angle are the primary factors influencing valve burst frequency. These can be used as the main controlling factors during the design

Auto-actuated sequential relelase valves for lab-on-a-disc systems

In microfluidic biomedical systems valving is often of critical importance for process control. In centrifugal microfluidics valves are typically actuated through changing the centrifugal force seen by the working liquid. Here we present for the first time a new valving structure (based on dissolvable films) where the entry of liquid into a chamber on the disc can trigger the release of liquid from a chamber located elsewhere on the disc. These valves can be configured such that multiple valves can be released in a sequential manner independent of external inputs

Microfluidic Technology and Application in Urinal Analysis

Microfluidic technology offers numerous advantages in minimizing and integrating the traditional assays. However, the lack of efficient control components of the microfluidic systems has been hindering the widely commercialization of the technology. The research work in this dissertation focused on the development of effective control components for microfluidic applications. A linear peristaltic pump was firstly designed, fabricated, and tested for conventional microfluidics by synchronously compressing the microfluidic channel with a miniature cam-follower system in Chapter 2. The miniature cam-follower system and microfluidic chip was prototyped using three-dimensional (3D) printing technology and soft lithography technology. Results from experimental test showed that the pump is self-priming and tolerant of bubbles. The pumping flowrate and back pressure could be controlled by changing the driving speed of the motor. Then a novel pinch-type valving system that can be used to realize both normally closed and normally open valves for centrifugal microfluidics was demonstrated in Chapter 3. A sliding wedge was actuated by centrifugal force to drive the valves. Experimental test and theoretical predication showed that the burst frequency of the valves could be tuned by changing the physical parameters of the valving system. In Chapter 4, the pinch type valving system was then further improved for better integration of multiple valves in limited space to realize sequential control of microfluidics. A valve chip with grooves on the surface was used to drive multiple valves. A flow switch which is capable of working at low rotation frequency and constant rotation direction is realized. Finally, the microfluidic platform was utilized for automatic urinalysis for the application at point of care (POC) to eliminate the difficulties in control of sample distribution and read-out time in manually conducted colorimetric urinalysis. 3D printed prototype of the microfluidic chip was used to test the proposed system. Commercial urinalysis strips was integrated with the microfluidic system for detecting glucose, specific gravity, PH, and protein from simulated urine sample. The color change of the pads was recorded using smartphone camera and analyzed to quantify the interested parameters

High-Efficiency Small Sample Microparticle Fractionation on a Femtosecond Laser-Machined Microfluidic Disc

The fabrication and testing of microfluidic spinning compact discs with embedded trapezoidal microchambers for the purpose of inertial microparticle focusing is reported in this article. Microparticle focusing channels require small features that cannot be easily fabricated in acrylic sheets and are complicated to realize in glass by traditional lithography techniques; therefore, the fabrication of microfluidic discs with femtosecond laser ablation is reported for the first time in this paper. It could be demonstrated that high-efficiency inertial focusing of 5 and 10 µm particles is achieved in a channel with trapezoidal microchambers regardless of the direction of disc rotation, which correlates to the dominance of inertial forces over Coriolis forces. To achieve the highest throughput possible, the suspension concentration was increased from 0.001% (w/v) to 0.005% (w/v). The focusing efficiency was 98.7% for the 10 µm particles and 93.75% for the 5 µm particles