Open Access Subvention Fund Articles

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Fundamental Computer Science Conceptual Understandings for High School Students Using Original Computer Game Design
Ernst, Jeremy V.; Clark, Aaron C. (The Institute for STEM Education & Research, 2012)
Beginning in 2009, the North Carolina Virtual Public Schools worked with researchers at the William and Ida Friday Institute to produce and evaluate the use of game creation by secondary students as a form of learning content related to career awareness in Science, Technology, Engineering, and Mathematics (STEM) disciplines, with particular emphasis in computer science areas. The study required the development of different forms of multimedia, inclusive with content and activities that could be conducted over the Internet. The team worked with a game art and design graduate class to produce materials and assessment instruments to be included in the project. The multimedia-based materials were piloted and field-tested in the Career Technical Education (CTE) online curricular offering of Computer Applications I. The evaluation and assessment of this project focused on student learning gains in content specific computer science areas, and overall appreciation of the technologies and structure used during the project. Teacher and student interviews, along with teacher journals help track the progress of both the students and edited materials. Conclusions from this study include support of gaming as a pedagogical process and the need for technological literacy. From feedback, the study concluded that informational technology software is a large variable in the success of this type of instructional unit.
Water table depth, surface saturation, and drought response in bog turtle (Glyptemys muhlenbergii) wetlands
Feaga, Jeffrey B.; Haas, Carola A.; Burger, James A. (Springer, 2012)
The bog turtle (Glyptemys muhlenbergii) is known to select wetland areas that are near water with deep mud, but water table dynamics in their habitats have not been well described. We installed and monitored shallow groundwater wells to evaluate hydrology over a continuous 28-month period on six wetlands known to be frequently used by bog turtles and six similar wetlands not known to be used. Overall, water tables remained high, with mean monthly depth to the water table for all 12 wetlands varying between −1 cm and −35 cm below the soil surface.Wetlands frequently used by bog turtles had higher mean water tables and surface saturation than wetlands not known to be used, particularly during summer months. Differences in mean water table (17 cm) and saturation (25 %) were greatest during southwestern Virginia’s 2008 drought. A differential remained after the resumption of normal rainfall, demonstrating the importance of groundwater recharge to bog turtle wetlands. Relatively small differences in water table hydrology have the potential to affect bog turtle biology and wetland use because bog turtles primarily use the top 15 cm of the soil and select saturated locations even when the availability of saturated soil is limited.
Towards the development of latent heat storage electrodes for electroporation-based therapies
Arena, Christopher B.; Mahajan, Roop L.; Rylander, M. Nichole; Davalos, Rafael V. (American Institute of Physics, 2012-08-22)
Phase change materials (PCMs) capable of storing a large amount of heat upon transitioning from the solid-to-liquid state have been widely used in the electronics and construction industries for mitigating temperature development. Here, we show that they are also beneficial for reducing the peak tissue temperature during electroporation-based therapies. A numerical model is developed of irreversible electroporation (IRE) performed with hollow needle electrodes filled with a PCM. Results indicate that this electrode design can be utilized to achieve large ablation volumes while reducing the probability for thermal damage.
A Hardware-Accelerated ECDLP with High-Performance Modular Multiplication
Judge, Lyndon; Mane, Suvarna; Schaumont, Patrick R. (Hindawi, 2012-09-01)
Elliptic curve cryptography (ECC) has become a popular public key cryptography standard. The security of ECC is due to the difficulty of solving the elliptic curve discrete logarithm problem (ECDLP). In this paper, we demonstrate a successful attack on ECC over prime field using the Pollard rho algorithm implemented on a hardware-software cointegrated platform. We propose a high-performance architecture for multiplication over prime field using specialized DSP blocks in the FPGA. We characterize this architecture by exploring the design space to determine the optimal integer basis for polynomial representation and we demonstrate an efficient mapping of this design to multiple standard prime field elliptic curves. We use the resulting modular multiplier to demonstrate low-latency multiplications for curves secp112r1 and P-192. We apply our modular multiplier to implement a complete attack on secp112r1 using a Nallatech FSB-Compute platform with Virtex-5 FPGA. The measured performance of the resulting design is 114 cycles per Pollard rho step at 100 MHz, which gives 878 K iterations per second per ECC core. We extend this design to a multicore ECDLP implementation that achieves 14.05 M iterations per second with 16 parallel point addition cores.
Recombination Activating Gene-2 Regulates CpG-Mediated Interferon-α Production in Mouse Bone Marrow-Derived Plasmacytoid Dendritic Cells
Luo, Xin M.; Lei, Margarida (PLOS, 2012-10-24)
Using mice that lack recombination activating gene-2 (Rag2), we have found that bone marrow-derived plasmacytoid dendritic cells (pDCs) as main producers of interferon-α (IFNα) require Rag2 for normal development. This is a novel function for Rag2, whose classical role is to initiate B and T cell development. Here we showed that a population of common progenitor cells in the mouse bone marrow possessed the potential to become either B cells or pDCs upon appropriate stimulations, and the lack of Rag2 hindered the development of both types of progeny cells. A closer look at pDCs revealed that Rag2−/− pDCs expressed a high level of Ly6C and were defective at producing IFNα in response to CpG, a ligand for toll-like receptor 9. This phenotype was not shared by Rag1−/− pDCs. The induction of CCR7, CD40 and CD86 with CpG, however, was normal in Rag2−/− pDCs. In addition, Rag2−/− pDCs retained the function to promote antibody class switching and plasma cell formation through producing IL-6. Further analysis showed that interferon regulatory factor-8, a transcription factor important for both IFNα induction and pDC development, was dysregulated in pDCs lacking Rag2. These results indicate that the generation of interferon response in pDCs requires Rag2 and suggest the lymphoid origin of bone marrow-derived pDCs.
A strategy to study pathway cross-talks of cells under repetitive exposure to stimuli
Fu, Yan; Jiang, Xiaoshan; Zhang, Hang; Xing, Jianhua (BMC Systems Biology, 2012-12-17)
Background Cells are subject to fluctuating and multiple stimuli in their natural environment. The signaling pathways often crosstalk to each other and give rise to complex nonlinear dynamics. Specifically repetitive exposure of a cell to a same stimulus sometime leads to augmented cellular responses. Examples are amplified proinflammatory responses of innate immune cells pretreated with a sub-threshold then a high dose of endotoxin or cytokine stimulation. This phenomenon, called priming in the literature, has important pathological and clinical significances. Results In a previous study, we enumerated possible mechanisms for priming using a three-node network model. The analysis uncovered three mechanisms. Based on the results, in this work we developed a straightforward procedure to identify molecular species candidates contributing to the priming effect and the corresponding mechanisms. The procedure involves time course measurements, e.g., gene expression levels, or protein activities under low, high, and low + high dose of stimulant, then computational analysis of the dynamics patterns, and identification of functional roles in the context of the regulatory network. We applied the procedure to a set of published microarray data on Inteferon- priming of human macrophages. The analysis identified a number of network motifs possibly contributing to Interferon- priming. A further detailed mathematical model analysis further reveals how combination of different mechanisms leads to the priming effect. Conclusions One may perform systematic screening using the proposed procedure combining with high throughput measurements, at both transcriptome and proteome levels. It is applicable to various priming phenomena.
Identifying protein interaction subnetworks by a bagging Markov random field-based method
Chen, Li; Xuan, Jianhua; Riggins, Rebecca B.; Wang, Yue; Clark, Robert L. (Nucleic Acids Research, 2013)
Identification of differentially expressed subnetworks from protein-protein interaction (PPI) networks has become increasingly important to our global understanding of the molecular mechanisms that drive cancer. Several methods have been proposed for PPI subnetwork identification, but the dependency among network member genes is not explicitly considered, leaving many important hub genes largely unidentified. We present a new method, based on a bagging Markov random field (BMRF) framework, to improve subnetwork identification for mechanistic studies of breast cancer. The method follows a maximum a posteriori principle to form a novel network score that explicitly considers pairwise gene interactions in PPI networks, and it searches for subnetworks with maximal network scores. To improve their robustness across data sets, a bagging scheme based on bootstrapping samples is implemented to statistically select high confidence subnetworks. We first compared the BMRF-based method with existing methods on simulation data to demonstrate its improved performance. We then applied our method to breast cancer data to identify PPI subnetworks associated with breast cancer progression and/or tamoxifen resistance. The experimental results show that not only an improved prediction performance can be achieved by the BMRF approach when tested on independent data sets, but biologically meaningful subnetworks can also be revealed that are relevant to breast cancer and tamoxifen resistance.
Bis-(η(2)-ethyl-ene)(η(5)-inden-yl)iridium(I).
Merola, Joseph S. (2013)
The asymmetric unit of the title compound, [Ir(C9H7)(C2H4)2], consists of two independent mol-ecules. The bonding between iridium and the five-membered ring of the indenyl ligand shows the usual asymmetry associated with the typical ring slippage responsible for the enhanced activity of indenyl metal compounds when compared with the analogous cyclo-penta-dienyl metal compound. There are three short Ir-C bonds of 2.210 (3), 2.190 (4) and 2.220 (3) Å and two long Ir-C bonds to the C atoms that are part of the fused six-membered ring of 2.349 (4) and 2.366 (3) Å for one of the independent mol-ecules [2.208 (4), 2.222 (3), 2.197 (4) Å for the short distances and 2.371 (3) and 2.358 (3) Å for the long distances in the second mol-ecule]. This results in both indenyl ligands being slightly kinked, with dihedral angles of 6.8 (4)° and 6.5 (4)°.
The Influence of the Specimen Shape and Loading Conditions on the Parameter Identification of a Viscoelastic Brain Model
Untaroiu, Costin D. (Hindawi Publishing Corporation, 2013)
The mechanical properties of brain under various loadings have been reported in the literature over the past 50 years. Step-and-hold tests have often been employed to characterize viscoelastic and nonlinear behavior of brain under high-rate shear deformation; however, the identification of brain material parameters is typically performed by neglecting the initial strain ramp and/or by assuming a uniform strain distribution in the brain samples. Using finite element (FE) simulations of shear tests, this study shows that these simplifications have a significant effect on the identified material properties in the case of cylindrical human brain specimens. Material models optimized using only the stress relaxation curve under predict the shear force during the strain ramp, mainly due to lower values of their instantaneous shear moduli. Similarly, material models optimized using an analytical approach, which assumes a uniform strain distribution, under predict peak shear forces in FE simulations. Reducing the specimen height showed to improve the model prediction, but no improvements were observed for cubic samples with heights similar to cylindrical samples. Models optimized using FE simulations show the closest response to the test data, so a FE-based optimization approach is recommended in future parameter identification studies of brain.
50-kHz-rate 2D imaging of temperature and H2O concentration at the exhaust plane of a J85 engine using hyperspectral tomography
Ma, Lin; Li, Xuesong; Sanders, Scott T.; Caswell, Andrew W.; Roy, Sukesh; Plemmons, David H.; Gord, James R. (Optical Society of America, 2013-01-01)
This paper describes a novel laser diagnostic and its demonstration in a practical aero-propulsion engine (General Electric J85). The diagnostic technique, named hyperspectral tomography (HT), enables simultaneous 2-dimensional (2D) imaging of temperature and water-vapor concentration at 225 spatial grid points with a temporal response up to 50 kHz. To our knowledge, this is the first time that such sensing capabilities have been reported. This paper introduces the principles of the HT techniques, reports its operation and application in a J85 engine, and discusses its perspective for the study of high-speed reactive flows. (C) 2013 Optical Society of America
Molecular Surveillance of Viral Processes Using Silicon Nitride Membranes
Gilmore, Brian L.; Tanner, Justin R.; McKell, Allison O.; Boudreaux, Crystal E.; Dukes, Madeline J.; McDonald, Sarah M.; Kelly, Deborah F. (MDPI, 2013-03)
Here we present new applications for silicon nitride (SiN) membranes to evaluate biological processes. We determined that 50-nanometer thin films of SiN produced from silicon wafers were sufficiently durable to bind active rotavirus assemblies. A direct comparison of SiN microchips with conventional carbon support films indicated that SiN performs equivalent to the traditional substrate to prepare samples for Electron Microscopy (EM) imaging. Likewise, SiN films coated with Ni-NTA affinity layers concentrated rotavirus particles similarly to affinity-coated carbon films. However, affinity-coated SiN membranes outperformed glow-discharged conventional carbon films 5-fold as indicated by the number of viral particles quantified in EM images. In addition, we were able to recapitulate viral uncoating and transcription mechanisms directed onto the microchip surfaces. EM images of these processes revealed the production of RNA transcripts emerging from active rotavirus complexes. These results were confirmed by the functional incorporation of radiolabeled nucleotides into the nascent RNA transcripts. Collectively, we demonstrate new uses for SiN membranes to perform molecular surveillance on life processes in real-time.
Numerical and experimental validation of a three-dimensional combustion diagnostic based on tomographic chemiluminescence
Cai, Weiwei; Li, Xuesong; Li, Fei; Ma, Lin (Optical Society of America, 2013-03-25)
Three-dimensional (3D) measurements are highly desirable both for fundamental combustion research and practical monitoring and control of combustion systems. This work discusses a 3D diagnostic based on tomographic chemiluminescence (TC) to address this measurement need. The major contributions of this work are threefold. First, a hybrid algorithm is developed to solve the 3D TC problem. The algorithm was demonstrated in extensive tests, both numerical and experimental, to yield 3D reconstruction with high fidelity. Second, an experimental approach was designed to enable quantifiable metrics for examining key aspects of the 3D TC technique, including its spatial resolution and reconstruction accuracy. Third, based on the reconstruction algorithm and experimental results, we investigated the effects of the view orientations. The results suggested that for an unknown flame, it is better to use projections measured from random orientations than restricted orientations (e.g., coplanar orientations). These findings are expected to provide insights to the fundamental capabilities of the TC technique, and also to facilitate its practical application.
Non-Complexed Four Cascade Enzyme Mixture: Simple Purification and Synergetic Co-stabilization
Myung, Suwan; Zhang, Y. H. Percival (PLoS, 2013-04-09)
Cell-free biosystems comprised of synthetic enzymatic pathways would be a promising biomanufacturing platform due to several advantages, such as high product yield, fast reaction rate, easy control and access, and so on. However, it was essential to produce (purified) enzymes at low costs and stabilize them for a long time so to decrease biocatalyst costs. We studied the stability of the four recombinant enzyme mixtures, all of which originated from thermophilic microorganisms: triosephosphate isomerase (TIM) from Thermus thermophiles, fructose bisphosphate aldolase (ALD) from Thermotoga maritima, fructose bisphosphatase (FBP) from T. maritima, and phosphoglucose isomerase (PGI) from Clostridium thermocellum. It was found that TIM and ALD were very stable at evaluated temperature so that they were purified by heat precipitation followed by gradient ammonia sulfate precipitation. In contrast, PGI was not stable enough for heat treatment. In addition, the stability of a low concentration PGI was enhanced by more than 25 times in the presence of 20 mg/L bovine serum albumin or the other three enzymes. At a practical enzyme loading of 1000 U/L for each enzyme, the half-life time of free PGI was prolong to 433 h in the presence of the other three enzymes, resulting in a great increase in the total turn-over number of PGI to 6.2×109 mole of product per mole of enzyme. This study clearly suggested that the presence of other proteins had a strong synergetic effect on the stabilization of the thermolabile enzyme PGI due to in vitro macromolecular crowding effect. Also, this result could be used to explain why not all enzymes isolated from thermophilic microorganisms are stable in vitro because of a lack of the macromolecular crowding environment.
Functional Characterization of Detergent-Decellularized Equine Tendon Extracellular Matrix for Tissue Engineering Applications
Youngstrom, Daniel W.; Barrett, Jennifer G.; Jose, Rod R.; Kaplan, David L. (PLOS, 2013-05-17)
Natural extracellular matrix provides a number of distinct advantages for engineering replacement orthopedic tissue due to its intrinsic functional properties. The goal of this study was to optimize a biologically derived scaffold for tendon tissue engineering using equine flexor digitorum superficialis tendons. We investigated changes in scaffold composition and ultrastructure in response to several mechanical, detergent and enzymatic decellularization protocols using microscopic techniques and a panel of biochemical assays to evaluate total protein, collagen, glycosaminoglycan, and deoxyribonucleic acid content. Biocompatibility was also assessed with static mesenchymal stem cell (MSC) culture. Implementation of a combination of freeze/thaw cycles, incubation in 2% sodium dodecyl sulfate (SDS), trypsinization, treatment with DNase-I, and ethanol sterilization produced a non-cytotoxic biomaterial free of appreciable residual cellular debris with no significant modification of biomechanical properties. These decellularized tendon scaffolds (DTS) are suitable for complex tissue engineering applications, as they provide a clean slate for cell culture while maintaining native three-dimensional architecture.
Reclaimed water as a reservoir of antibiotic resistance genes: distribution system and irrigation implications
Fahrenfeld, Nicole; Ma, Yanjun; O'Brien, Maureen; Pruden, Amy (Frontiers, 2013-05-28)
reated wastewater is increasingly being reused to achieve sustainable water management in arid regions. The objective of this study was to quantify the distribution of antibiotic resistance genes (ARGs) in recycled water, particularly after it has passed through the distribution system, and to consider point-of-use implications for soil irrigation. Three separate reclaimed wastewater distribution systems in the western U.S. were examined. Quantitative polymerase chain reaction (qPCR) was used to quantify ARGs corresponding to resistance to sulfonamides (sul1, sul2), macrolides (ermF), tetracycline [tet(A), tet(O)], glycopeptides (vanA), and methicillin (mecA), in addition to genes present in waterborne pathogens Legionella pneumophila (Lmip), Escherichia coli (gadAB), and Pseudomonas aeruginosa (ecfx, gyrB). In a parallel lab study, the effect of irrigating an agricultural soil with secondary, chlorinated, or dechlorinated wastewater effluent was examined in batch microcosms. A broader range of ARGs were detected after the reclaimed water passed through the distribution systems, highlighting the importance of considering bacterial re-growth and the overall water quality at the point of use (POU). Screening for pathogens with qPCR indicated presence of Lmip and gadAB genes, but not ecfx or gyrB. In the lab study, chlorination was observed to reduce 16S rRNA and sul2 gene copies in the wastewater effluent, while dechlorination had no apparent effect. ARGs levels did not change with time in soil slurries incubated after a single irrigation event with any of the effluents. However, when irrigated repeatedly with secondary wastewater effluent (not chlorinated or dechlorinated), elevated levels of sul1 and sul2 were observed. This study suggests that reclaimed water may be an important reservoir of ARGs, especially at the POU, and that attention should be directed toward the fate of ARGs in irrigation water and the implications for human health.
Intra-Abdominal Fat Depots Represent Distinct Immunomodulatory Microenvironments: A Murine Model
Cohen, Courtney A.; Shea, Amanda A.; Heffron, C. Lynn; Schmelz, Eva M.; Roberts, Paul C. (PLOS, 2013-06-12)
White adipose tissue (WAT) is a multi-faceted endocrine organ involved in energy storage, metabolism, immune function and disease pathogenesis. In contrast to subcutaneous fat, visceral fat (V-WAT) has been associated with numerous diseases and metabolic disorders, indicating specific functions related to anatomical location. Although visceral depots are often used interchangeably in V-WAT-associated disease studies, there has been a recent subdivision of V-WAT into “true visceral” and non-visceral intra-abdominal compartments. These were associated with distinct physiological roles, illustrating a need for depot-specific information. Here, we use FACS analysis to comparatively characterize the leukocyte and progenitor populations in the stromal vascular fraction (SVF) of peritoneal serous fluid (PSF), parametrial (pmWAT), retroperitoneal (rpWAT), and omental (omWAT) adipose tissue from seven-month old C57BL/6 female mice. We found significant differences in SVF composition between all four microenvironments. PSF SVF was comprised almost entirely of CD45+ leukocytes (>99%), while omWAT contained less, but still almost two-fold more leukocytes than pmWAT and rpWAT (75%, 38% and 38% respectively; p<0.01). PmWAT was composed primarily of macrophages, whereas rpWAT more closely resembled omWAT, denoted by high levels of B1 B-cell and monocyte populations. Further, omWAT harbored significantly higher proportions of T-cells than the other tissues, consistent with its role as a secondary lymphoid organ. These SVF changes were also reflected in the gene expression profiles of the respective tissues. Thus, intra-abdominal fat pads represent independent immunomodulatory microenvironments and should be evaluated as distinct entities with unique contributions to physiological and pathological processes.
Pronounced hypoxia in the subventricular zone following traumatic brain injury and the neural stem/progenitor cell response
Baumann, Gisela; Travieso, Lissette; Theus, Michelle H.; Liebl, Daniel J. (Society for Experimental Biology and Medicine, 2013-07-04)
Traumatic brain injury (TBI) elicits identifiable changes within the adult subventricular zone (SVZ). Previously, we demonstrated that EphB3/ephrinB3 interaction inhibits neural stem/progenitor cell (NSPC) proliferation and downregulating this pathway following TBI plays a pivotal role in the expansion of the SVZ neurogenic compartment. It remains unclear, however, what early initiating factors may precede these changes. Using hypoxyprobe-1 (HPb) to identify regions of low oxygen tension or hypoxia (<1%), we found HPb uptake throughout the cortex (CTX), corpus callosum (CC) and SVZ within the first 24 h following controlled cortical impact (CCI) injury. At this early time point, HPb co-localized with EphB3 in the SVZ. NSPC specific markers also co-localized with HPb staining throughout the lateral wall of the ventricle. To determine the cell autonomous effects of hypoxia on EphB3/ephrinB3 signaling in NSPCs, we used an in vitro model of hypoxia to mimic 1% oxygen in the presence and absence of soluble aggregated ephrinB3 (eB3). As expected, hypoxia stimulated the uptake of 5-bromo-2'-deoxyuridine (BrdU) and reduced cell death. Coincident with these proliferative changes, both Hif1-∞ and phospho (p)-AKT were increased while EphB3 expression was decreased. Stimulation of EphB3 attenuated hypoxia-induced proliferation and prevented phosphorylation of AKT. Hif1-∞ accumulation, on the other hand, was not affected by EphB3/ephrinB3 signaling. These findings indicate that this pathway limits the NSPC response to hypoxic stimuli. These studies also suggest that early transient changes in oxygen tension following localized cortical injury may initiate a growth-promoting response in the SVZ.
Process Authentication for High System Assurance
Almohri, Hussain M.J.; Yao, Danfeng (Daphne); Kafura, Dennis G. (IEEE Computer Society, 2013-07-11)
This paper points out the need in modern operating system kernels for a process authentication mechanism, where a process of a user-level application proves its identity to the kernel. Process authentication is different from process identification. Identification is a way to describe a principal; PIDs or process names are identifiers for processes in an OS environment. However, the information such as process names or executable paths that is conventionally used by OS to identify a process is not reliable. As a result, malware may impersonate other processes, thus violating system assurance. We propose a lightweight secure application authentication framework in which user-level applications are required to present proofs at runtime to be authenticated to the kernel. To demonstrate the application of process authentication, we develop a system call monitoring framework for preventing unauthorized use or access of system resources. It verifies the identity of processes before completing the requested system calls. We implement and evaluate a prototype of our monitoring architecture in Linux. The results from our extensive performance evaluation show that our prototype incurs reasonably low overhead, indicating the feasibility of our approach for cryptographically authenticating applications and their processes in the operating system.
Type IV Pilus Proteins Form an Integrated Structure Extending from the Cytoplasm to the Outer Membrane
Li, Chengyun; Wallace, Regina A.; Black, Wesley P.; Li, Yue-zhong; Yang, Zhaomin (PLoS, 2013-07-26)
The bacterial type IV pilus (T4P) is the strongest biological motor known to date as its retraction can generate forces well over 100 pN. Myxococcus xanthus, a 𝞭-proteobacterium, provides a good model for T4P investigations because its social (S) gliding motility is powered by T4P. In this study, the interactions among M. xanthus T4P proteins were investigated using genetics and the yeast two-hybrid (Y2H) system. Our genetic analysis suggests that there is an integrated T4P structure that crosses the inner membrane (IM), periplasm and the outer membrane (OM). Moreover, this structure exists in the absence of the pilus filament. A systematic Y2H survey provided evidence for direct interactions among IM and OM proteins exposed to the periplasm. For example, the IM lipoprotein PilP interacted with its cognate OM protein PilQ. In addition, interactions among T4P proteins from the thermophile Thermus thermophilus were investigated by Y2H. The results indicated similar protein-protein interactions in the T4P system of this non-proteobacterium despite significant sequence divergence between T4P proteins in T. thermophilus and M. xanthus. The observations here support the model of an integrated T4P structure in the absence of a pilus in diverse bacterial species.
Off-chip passivated-electrode, insulator-based dielectrophoresis (O pi DEP)
Zellner, Phillip; Shake, Tyler; Sahari, Ali; Behkam, Bahareh; Agah, Masoud (Springer, 2013-08-01)
In this study, we report the first off-chip passivated-electrode, insulator-based dielectrophoresis microchip (OπDEP). This technique combines the sensitivity of electrode-based dielectrophoresis (eDEP) with the high throughput and inexpensive device characteristics of insulator-based dielectrophoresis (iDEP). The device is composed of a permanent, reusable set of electrodes and a disposable, polymer microfluidic chip with microposts embedded in the microchannel. The device operates by capacitively coupling the electric fields into the microchannel; thus, no physical connections are made between the electrodes and the microfluidic device. During operation, the polydimethylsiloxan (PDMS) microfluidic chip fits onto the electrode substrate as a disposable cartridge. OπDEP uses insulting structures within the channel as well as parallel electrodes to create DEP forces by the same working principle that iDEP devices use. The resulting devices create DEP forces which are larger by two orders of magnitude for the same applied voltage when compared to off-chip eDEP designs from literature, which rely on parallel electrodes alone to produce the DEP forces. The larger DEP forces allow the OπDEP device to operate at high flow rates exceeding 1 mL/h. In order to demonstrate this technology, Escherichia coli (E. coli), a known waterborne pathogen, was trapped from water samples. Trapping efficiencies of 100 % were obtained at flow rates as high as 400 μL/h and 60 % at flow rates as high as 1200 μL/h. Additionally, bacteria were selectively concentrated from a suspension of polystyrene beads.

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