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1. Insulator Based Dielectrophoresis: Micro, Nano, and Molecular Scale Biological Applications

   https://doi.org/10.3390/s20185095  

   Benhal, Prateek; Quashie, David; Kim, Yoontae; Ali, Jamel (September 2020, Sensors)

   null (Ed.)

   Insulator based dielectrophoresis (iDEP) is becoming increasingly important in emerging biomolecular applications, including particle purification, fractionation, and separation. Compared to conventional electrode-based dielectrophoresis (eDEP) techniques, iDEP has been demonstrated to have a higher degree of selectivity of biological samples while also being less biologically intrusive. Over the past two decades, substantial technological advances have been made, enabling iDEP to be applied from micro, to nano and molecular scales. Soft particles, including cell organelles, viruses, proteins, and nucleic acids, have been manipulated using iDEP, enabling the exploration of subnanometer biological interactions. Recent investigations using this technique have demonstrated a wide range of applications, including biomarker screening, protein folding analysis, and molecular sensing. Here, we review current state-of-art research on iDEP systems and highlight potential future work. 

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2. Joule heating effects in optimized insulator‐based dielectrophoretic devices: An interplay between post geometry and temperature rise

   https://doi.org/10.1002/elps.201800490  

   Gallo‐Villanueva, Roberto_C; Perez‐Gonzalez, Victor_H; Cardenas‐Benitez, Braulio; Jind, Binny; Martinez‐Chapa, Sergio_O; Lapizco‐Encinas, Blanca_H (March 2019, ELECTROPHORESIS)

   Abstract Insulator‐based dielectrophoresis (iDEP) is the electrokinetic migration of polarized particles when subjected to a non‐uniform electric field generated by the inclusion of insulating structures between two remote electrodes. Electrode spacing is considerable in iDEP systems when compared to electrode‐based DEP systems, therefore, iDEP systems require high voltages to achieve efficient particle manipulation. A consequence of this is the temperature increase within the channel due to Joule heating effects, which, in some cases, can be detrimental when manipulating biological samples. This work presents an experimental and modeling study on the increase in temperature inside iDEP devices. For this, we studied seven distinct channel designs that mainly differ from each other in their post array characteristics: post shape, post size and spacing between posts. Experimental results obtained using a custom‐built copper Resistance Temperature Detector, based on resistance changes, show that the influence of the insulators produces a difference in temperature rise of approximately 4°C between the designs studied. Furthermore, a 3D COMSOL model is also introduced to evaluate heat generation and dissipation, which is in good agreement with the experiments. The model allowed relating the difference in average temperature for the geometries under study to the electric resistance posed by the post array in each design. 

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3. Expanding Opportunities for Systems Thinking, Conceptual Learning, and Participation through Embodied and Computational Modeling

   https://doi.org/10.3390/systems8040048  

   Pierson, Ashlyn E.; Brady, Corey E. (December 2020, Systems)

   Previous research has established that embodied modeling (role-playing agents in a system) can support learning about complexity. Separately, research has demonstrated that increasing the multimodal resources available to students can support sensemaking, particularly for students classified as English Learners. This study bridges these two bodies of research to consider how embodied models can strengthen an interconnected system of multimodal models created by a classroom. We explore how iteratively refining embodied modeling activities strengthened connections to other models, real-world phenomena, and multimodal representations. Through design-based research in a sixth grade classroom studying ecosystems, we refined embodied modeling activities initially conceived as supports for computational thinking and modeling. Across three iterative cycles, we illustrate how the conceptual and epistemic relationship between the computational and embodied model shifted, and we analyze how these shifts shaped opportunities for learning and participation by: (1) recognizing each student’s perspectives as critical for making sense of the model, (2) encouraging students to question and modify the “code” for the model, and (3) leveraging multimodal resources, including graphs, gestures, and student-generated language, for meaning-making. Through these shifts, the embodied model became a full-fledged component of the classroom’s model system and created more equitable opportunities for learning and participation. 

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4. Fine-Tuning Electrokinetic Injections Considering Nonlinear Electrokinetic Effects in Insulator-Based Devices

   https://doi.org/10.3390/mi12060628  

   Miller, Abbi; Hill, Nicole; Hakim, Kel; Lapizco-Encinas, Blanca H. (June 2021, Micromachines)

   null (Ed.)

   The manner of sample injection is critical in microscale electrokinetic (EK) separations, as the resolution of a separation greatly depends on sample quality and how the sample is introduced into the system. There is a significant wealth of knowledge on the development of EK injection methodologies that range from simple and straightforward approaches to sophisticated schemes. The present study focused on the development of optimized EK sample injection schemes for direct current insulator-based EK (DC-iEK) systems. These are microchannels that contain arrays of insulating structures; the presence of these structures creates a nonuniform electric field distribution when a potential is applied, resulting in enhanced nonlinear EK effects. Recently, it was reported that the nonlinear EK effect of electrophoresis of the second kind plays a major role in particle migration in DC-iEK systems. This study presents a methodology for designing EK sample injection schemes that consider the nonlinear EK effects exerted on the particles being injected. Mathematical modeling with COMSOL Multiphysics was employed to identify proper voltages to be used during the EK injection process. Then, a T-microchannel with insulating posts was employed to experimentally perform EK injection and separate a sample containing two types of similar polystyrene particles. The quality of the EK injections was assessed by comparing the resolution (Rs) and number of plates (N) of the experimental particle separations. The findings of this study establish the importance of considering nonlinear EK effects when planning for successful EK injection schemes. 

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5. Determination of the Empirical Electrokinetic Equilibrium Condition of Microorganisms in Microfluidic Devices

   https://doi.org/10.3390/bios10100148  

   Coll De Peña, Adriana; Hill, Nicole; Lapizco-Encinas, Blanca H. (October 2020, Biosensors)

   null (Ed.)

   The increased concern regarding emerging pathogens and antibiotic resistance has drawn interest in the development of rapid and robust microfluidic techniques to analyze microorganisms. The novel parameter known as the electrokinetic equilibrium condition (EEEC) was presented in recent studies, providing an approach to analyze microparticles in microchannels employing unique electrokinetic (EK) signatures. While the EEEC shows great promise, current estimation approaches can be time-consuming or heavily user-dependent for accurate values. The present contribution aims to analyze existing approaches for estimating this parameter and modify the process into an accurate yet simple technique for estimating the EK behavior of microorganisms in insulator-based microfluidic devices. The technique presented here yields the parameter called the empirical electrokinetic equilibrium condition (eEEEC) which works well as a value for initial approximations of trapping conditions in insulator-based EK (iEK) microfluidic systems. A total of six types of microorganisms were analyzed in this study (three bacteria and three bacteriophages). The proposed approach estimated eEEEC values employing images of trapped microorganisms, yielding high reproducibility (SD 5.0–8.8%). Furthermore, stable trapping voltages (sTVs) were estimated from eEEEC values for distinct channel designs to test that this parameter is system-independent and good agreement was obtained when comparing estimated sTVs vs. experimental values (SD 0.3–19.6%). The encouraging results from this work were used to generate an EK library of data, available on our laboratory website. The data in this library can be used to design tailored iEK microfluidic devices for the analysis of microorganisms. 

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