Anna Hickerson

A valveless micro impedance pump driven by electromagnetic actuation

Over the past two decades, a variety of micropumps have been explored for various applications in microfluidics such as control of pico- and nanoliter flows for drug delivery as well as chemical mixing and analysis. We present the fabrication and preliminary experimental studies of flow performance on the micro impedance pump, a previously unexplored method of pumping fluid on the microscale. The micro impedance pump was constructed of a simple thin-walled tube coupled at either end to glass capillary tubing and actuated electromagnetically. Through the cumulative effects of wave propagation and reflection originating from an excitation located asymmetrically along the length of the elastic tube, a pressure head can be established to drive flow. Flow rates were observed to be reversible and highly dependent on the profile of the excitation. Micro impedance pump flow studies were conducted in open and closed circuit flow configurations. Maximum flow rates of 16 ml min-1 have been achieved under closed loop flow conditions with an elastic tube diameter of 2 mm. Two size scales with channel diameters of 2 mm and 250 µm were also examined in open circuit flow, resulting in flow rates of 191 µl min-1 and 17 µl min-1, respectively.

On the resonance of a pliant tube as a mechanism for valveless pumping

Valveless pumping can be achieved through the periodic compression of a pliant tube asymmetrically from its interfaces to different tubing or reservoirs. A mismatch of characteristic impedance between the flow channels is necessary for creating wave reflection sites. Previous experimental studies of the behaviour of such a pump were continued in order to demonstrate the wave mechanics necessary for the build-up of pressure and net flow. Specific measurements of the transient and resonant properties were used to relate the bulk responses to the pump mechanics. Ultrasound imaging through the tube wall allowed visualization of the wall motion concurrently with pressure and flow measurements. For analysis, a one-dimensional wave model was constructed which predicted many of the characteristics exhibited by the experiments.

Simple System for Isothermal DNA Amplification Coupled to Lateral Flow Detection

Infectious disease diagnosis in point-of-care settings can be greatly improved through integrated, automated nucleic acid testing devices. We have developed an early prototype for a low-cost system which executes isothermal DNA amplification coupled to nucleic acid lateral flow (NALF) detection in a mesofluidic cartridge attached to a portable instrument. Fluid handling inside the cartridge is facilitated through one-way passive valves, flexible pouches, and electrolysis-driven pumps, which promotes a compact and inexpensive instrument design. The closed-system disposable prevents workspace amplicon contamination. The cartridge design is based on standard scalable manufacturing techniques such as injection molding. Nucleic acid amplification occurs in a two-layer pouch that enables efficient heat transfer. We have demonstrated as proof of principle the amplification and detection of Mycobacterium tuberculosis (M.tb) genomic DNA in the cartridge, using either Loop Mediated Amplification (LAMP) or the Exponential Amplification Reaction (EXPAR), both coupled to NALF detection. We envision that a refined version of this cartridge, including upstream sample preparation coupled to amplification and detection, will enable fully-automated sample-in to answer-out infectious disease diagnosis in primary care settings of low-resource countries with high disease burden.

Continuous-Flow, Rapid Lysis Devices for Biodefense Nucleic Acid Diagnostic Systems

Two mechanical lysis devices have been developed as compact, robust components to provide rapid sample preparation for nucleic acid diagnostic systems. One such component, known as the Micro Bead-Beater™ (μBB™, BBTM, Claremont BioSolutions, Upland, CA), is a compact device that is capable of ultrarapid lysis (>90% lysis in 30 s) of micro volumes (<80 μL) ofBacillus spores in a continuous-flow format or in a disposable single-tube format. The μBB is also capable of processing much larger volumes of solutions containing spores or vegetative cells using a continuous-flow mode. A second mechanical lysis device designed as a disposable component is the microfluidic bead blender, which uses a small electric motor to spin vanes within the bead-laden solution. DNA quantification results using dsDNA-binding fluorescence dyes and real-time PCR are presented, comparing the lysis of Bacillus subtilis spores using the μBB™ with other well-known lysis techniques. Nanoscale imaging results obtained using scanning electron microscopy and transmission electron microscopy on B. subtilis spores lyzed using the μBB™ are also presented

System for portable nucleic acid testing in low resource settings

Our overall goal is to enable timely diagnosis of infectious diseases through nucleic acid testing at the point-of-care and in low resource settings, via a compact system that integrates nucleic acid sample preparation, isothermal DNA amplification, and nucleic acid lateral flow (NALF) detection. We herein present an interim milestone, the design of the amplification and detection subsystem, and the characterization of thermal and fluidic control and assay execution within this system. Using an earlier prototype of the amplification and detection unit, comprised of a disposable cartridge containing flexible pouches, passive valves, and electrolysis-driven pumps, in conjunction with a small heater, we have demonstrated successful execution of an established and clinically validated isothermal loop-mediated amplification (LAMP) reaction targeting Mycobacterium tuberculosis (M.tb) DNA, coupled to NALF detection. The refined design presented herein incorporates miniaturized and integrated electrolytic pumps, novel passive valves, overall design changes to facilitate integration with an upstream sample preparation unit, and a refined instrument design that automates pumping, heating, and timing. Nucleic acid amplification occurs in a two–layer pouch that facilitates fluid handling and appropriate thermal control. The disposable cartridge is manufactured using low-cost and scalable techniques and forms a closed system to prevent workplace contamination by amplicons. In a parallel effort, we are developing a sample preparation unit based on similar design principles, which performs mechanical lysis of mycobacteria and DNA extraction from liquefied and disinfected sputum. Our next step is to combine sample preparation, amplification, and detection in a final integrated cartridge and device, to enable fully automated sample-in to answer-out diagnosis of active tuberculosis in primary care facilities of low-resource and high-burden countries.