467 research outputs found

    Rapid rotation of micron and submicron dielectric particles measured using optical tweezers

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    We demonstrate the use of a laser trap (‘optical tweezers’) and back-focal-plane position detector to measure rapid rotation in aqueous solution of single particles with sizes in the vicinity of 1 μm. Two types of rotation were measured: electrorotation of polystyrene microspheres and rotation of the flagellar motor of the bacterium Vibrio alginolyticus. In both cases, speeds in excess of 1000 Hz (rev s−1) were measured. Polystyrene beads of diameter about 1 μm labelled with smaller beads were held at the centre of a microelectrode array by the optical tweezers. Electrorotation of the labelled beads was induced by applying a rotating electric field to the solution using microelectrodes. Electrorotation spectra were obtained by varying the frequency of the applied field and analysed to obtain the surface conductance of the beads. Single cells of V. alginolyticus were trapped and rotation of the polar sodium-driven flagellar motor was measured. Cells rotated more rapidly in media containing higher concentrations of Na+, and photodamage caused by the trap was considerably less when the suspending medium did not contain oxygen. The technique allows single-speed measurements to be made in less than a second and separate particles can be measured at a rate of several per minute

    EXPLORING THE ROLE AND IMPACT OF MICROSCALE PHENOMENA ON ELECTRODE, MICRODEVICE, AND CELLULAR FUNCTION

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    Microfluidic technologies enable the development of portable devices to perform multiple high-resolution unit operations with small sample and reagent volumes, low fabrication cost, facile operation, and quick response times. Microfluidic platforms are expected to effectively interpret both wanted and unwanted phenomena; however, a comprehensive evaluation of the unwanted phenomena has not been appropriately investigated in the literature. This work explored an attenuative evaluation of unwanted phenomena, also called here as secondary phenomena, in a unique approach. Upon electric field utilization within microfluidic devices, electrode miniaturization improves device sensitivity. However, electrodes in contact with medium solution can yield byproducts that can change medium properties such as pH as well as bulk ion concentration and eventually target cell viability. While electrode byproducts are sometimes beneficial; but, this is not always the case. Two strategies were employed to protect cells from the electrode byproducts: (i) coating the electrodes with hafnium oxide (HfO2), and (ii) stabilization of the cell membrane using a low concentration of Triton X-100 surfactant. Our results showed that both strategies are a plausible way to selectively isolate cell and reduce the risk of contamination from electrode byproducts. The design of a medium solution is also critical to minimize unwanted cell-medium interaction. Surfactants are frequently added to cell-medium solutions to improve sensitivity and reproducibility without disrupting protein composition of cell membranes or cell viability. In non-electrokinetic systems, surfactants have been shown to reduce interfacial tensions and prevent analyte sticking. However, the impacts of surfactant interactions with cell membranes have not previously been explored in electrokinetic systems. This work indicated the dynamic surfactant interactions with cell membranes which altered the cell membrane integrity. It is important that the effects of the chemical interactions between cells to be fully explored and to be separately attributed to reported cellular responses to accurate catalog properties and engineer reliable microfluidic electrokinetic devices. Finally, a comprehensive level of understanding led us to utilize dielectrophoresis in its full capacity as a tool to monitor the state and progression of virus infection as well as anti-viral activities of regenerative compound. Glycine was utilized as potential antiviral compounds to reduce porcine parvovirus (PPV) infection in porcine kidney (PK-13) cells. Our results demonstrate that the glycine altered the virus-host interactions during virus assembly. Thus, elucidating the mechanisms of these novel antiviral compounds is crucial to their development as potential therapeutic drugs

    Microdevices and Microsystems for Cell Manipulation

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    Microfabricated devices and systems capable of micromanipulation are well-suited for the manipulation of cells. These technologies are capable of a variety of functions, including cell trapping, cell sorting, cell culturing, and cell surgery, often at single-cell or sub-cellular resolution. These functionalities are achieved through a variety of mechanisms, including mechanical, electrical, magnetic, optical, and thermal forces. The operations that these microdevices and microsystems enable are relevant to many areas of biomedical research, including tissue engineering, cellular therapeutics, drug discovery, and diagnostics. This Special Issue will highlight recent advances in the field of cellular manipulation. Technologies capable of parallel single-cell manipulation are of special interest

    REVERSE INSULATOR DIELECTROPHORESIS: UTILIZING DROPLET MICROENVIRONMENTS FOR DISCERNING MOLECULAR EXPRESSIONS ON CELL SURFACES

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    Lab-on-a-chip (LOC) technologies enable the development of portable analysis devices that use small sample and reagent volumes, allow for multiple unit operations, and couple with detectors to achieve high resolution and sensitivity, while having small footprints, low cost, short analysis times, and portability. Droplet microfluidics is a subset of LOCs with the unique benefit of enabling parallel analysis since each droplet can be utilized as an isolated microenvironment. This work explored adaptation of droplet microfluidics into a unique, previously unexplored application where the water/oil interface was harnessed to bend electric field lines within individual droplets for insulator dielectrophoretic (iDEP) characterizations. iDEP polarizes particles/cells within non-uniform electric fields shaped by insulating geometries. We termed this unique combination of droplet microfluidics and iDEP reverse insulator dielectrophoresis (riDEP). This riDEP approach has the potential to protect cell samples from unwanted sample-electrode interactions and decrease the number of required experiments for dielectrophoretic characterization by ~80% by harnessing the parallelization power of droplet microfluidics. Future research opportunities are discussed that could improve this reduction further to 93%. A microfluidic device was designed where aqueous-in-oil droplets were generated in a microchannel T-junction and packed into a microchamber. Reproducible droplets were achieved at the T-junction and were stable over long time periods in the microchamber using Krytox FSH 157 surfactant in the continuous oil FC-40 phase and isotonic salts and dextrose solutions as the dispersed aqueous phase. Surfactant, salts, and dextrose interact at the droplet interface influencing interfacial tension and droplet stability. Results provide foundational knowledge for engineering stable bio- and electro-compatible droplet microfluidic platforms. Electrodes were added to the microdevice to apply an electric field across the droplet packed chamber and explore riDEP responses. Operating windows for droplet stability were shown to depend on surfactant concentration in the oil phase and aqueous phase conductivity, where different voltage/frequency combinations resulted in either stable droplets or electrocoalescence. Experimental results provided a stability map for strategical applied electric field selection to avoid adverse droplet morphological changes while inducing riDEP. Within the microdevice, both polystyrene beads and red blood cells demonstrated weak dielectrophoretic responses, as evidenced by pearl-chain formation, confirming the preliminary feasibility of riDEP as a potential characterization technique. Two additional side projects included an alternative approach to isolate electrode surface reactions from the cell suspension via a hafnium oxide film over the electrodes. In addition, a commercially prevalent water-based polymer emulsion was found to adequately duplicate microchannel and microchamber features such that it could be used for microdevice replication

    A Multifunctional Tool for the Electrokinetic Manipulation and Characterization of Cells

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    In a field dominated by risk assessment, diagnostics could greatly benefit from the use of electric characterization tools. Electric field based diagnostic tools are low risk to the patient, offer high throughputs, and are versatile in the diseases they can diagnose. Even if electrical characterization tools, aren’t yet equal in the diagnostic confidence level produced compared to more established FDA approved techniques like the agar plate, when a patients symptoms indicate the necessity for time efficient treatment, electrical characterization could provide a rapid, safe alternative diagnostic tool to be used in tandem with other existing techniques. The work presented in this dissertation will focus on gaining understanding for a single electrokinetic domain; Dielectrophoresis (DEP). DEP is a proven and reliable technique for the manipulation, separation, and enrichment of many microorganisms including but certainly not limited to bacteria, DNA and bloodborne pathogens [1–8]. DEP is a noncontact, non invasive technique that would pose low patient risk with regards to diagnosis. The versatility in the variety of microorganisms that exhibit a DEP response and its proven ability to separate cells are a promising characteristics that can be exploited for the development of a novel diagnostic tool

    In Situ Preconcentration by AC Electrokinetics for Rapid and Sensitive Nanoparticle Detection

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    Reducing cost and time is a major concern in clinical diagnostics. Current molecular diagnostics are multi-step processes that usually take at least several hours or even days to complete multiple reagents delivery, incubations and several washing processes. This highly labor-intensive work and lack of automation could result in reduced reliability and low efficiency. The Laboratory-on-a-chip (LOC), taking advantage of the merger and development of microfluidics and biosensor technology, has shown promise towards a solution for performing analytical tests in a self-contained and compact unit, enabling earlier and decentralized testing. However, challenges are to integrate the fluid regulatory elements on a single platform and to detect target analytes with high sensitivity and selectivity. The goal of this research work is to develop an AC electrokinetic (ACEK) flow through concentrator for in-situ concentration of biomolecules and develop a comprehensive understanding of effects of ACEK flow on the biomolecule transport (in-situ concentration) and their impact on electronic biosensing mechanism and performance, achieving automation and miniaturization. ACEK is a new and promising technique to manipulate micro/bio-fluids and particles. It has many advantages over other techniques for its low applied voltage, portability and compatibility for integration into lab-on-a-chip devices. Numerical study on preconcentration system design in this work has provided an optimization rule for various biosensor designs using ACEK technique. And the microfluidic immunoassay lab-chip designed based on ACET effect has showed promising prospect for accelerated diagnostics. With optimized design of channel geometry, electrode patterns, and properly selected operation condition (ac frequency and voltage), the preconcentration system greatly reduced the reaction time to several minutes instead of several hours, and improved sensitivity of the assay. With the design of immunoassay lab-chip, one can quantitatively study the effect of ACET micropumping and mixing on molecular level binding. Improved sensors with single-chip form factor as a general platform could have a significant impact on a wide-range of biochemical detection and disease diagnostics including pathogen/virus detection, whole blood analysis, immune-screening, gene expression, as well as home land security
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