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1. Laser-induced fluorescence detector with a fiber-coupled micro GRIN lens for capillary electrophoresis

   https://doi.org/10.1364/AO.391661  

   Dada, Oluwatosin_O (May 2020, Applied Optics)

   Capillary electrophoresis coupled with sheath-flow laser-induced fluorescence (LIF) detection has been shown to offer outstanding sensitivity for chemical and biochemical analysis. However, a major drawback remains with the complexity of the optical configuration traditionally employed. Here we present a simplified confocal optics based on fiber optics and micro gradient-index (GRIN) lenses for modular optical design in capillary electrophoresis with laser-induced fluorescence. We demonstrate the use of the optical system with a sheath-flow cuvette as the laser-induced fluorescence detector for capillary electrophoresis. The system’s performance was established with concentration detection limits of $8\pm <\#comment/>2\mathrm{p}\mathrm{M}$and mass detection limits of 57 zeptomole for a standard sodium fluorescein sample. 

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2. Assessment of the Nonlinear Electrophoretic Migration of Nanoparticles and Bacteriophages

   https://doi.org/10.3390/MI15030369  

   Lomeli-Martin, Adrian; Azad, Zakia; Thomas, Julie A; Lapizco-Encinas, Blanca H (March 2024, Micromachines)

   Bacteriophage therapy presents a promising avenue for combating antibiotic-resistant bacterial infections. Yet, challenges exist, particularly, the lack of a straightforward purification pipeline suitable for widespread application to many phage types, as some phages are known to undergo significant titer loss when purified via current techniques. Electrokinetic methods offer a potential solution to this hurdle, with nonlinear electrophoresis emerging as a particularly appealing approach due to its ability to discern both the size and shape of the target phage particles. Presented herein is the electrokinetic characterization of the mobility of nonlinear electrophoresis for two phages (SPN3US and ϕKZ) and three types of polystyrene nanoparticles. The latter served as controls and were selected based on their sizes and surface charge magnitude. Particle tracking velocimetry experiments were conducted to characterize the mobility of all five particles included in this study. The results indicated that the selected nanoparticles effectively replicate the migration behavior of the two phages under electric fields. Further, it was found that there is a significant difference in the nonlinear electrophoretic response of phages and that of host cells, as first characterized in a previous report, illustrating that electrokinetic-based separations are feasible. The findings from this work are the first characterization of the behavior of phages under nonlinear electrophoresis effects and illustrate the potential for the development of electrokinetic-based phage purification techniques that could aid the advancement of bacteriophage therapy. 

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3. Measuring the electrophoretic mobility and size of single particles using microfluidic transverse AC electrophoresis (TrACE)

   https://doi.org/10.1039/D3LC00413A  

   Choi, M. Hannah; Hong, Liu; Chamorro, Leonardo P.; Edwards, Boyd; Timperman, Aaron T. (November 2023, Lab on a Chip)

   Wheeler, Aaron (Ed.)

   The ability to measure the charge and size of single particles is essential to understanding particle adhesion and interaction with their environment. Characterizing the physical properties of biological particles, like cells, can be a powerful tool in studying the association between the changes in physical properties and disease development. Currently, measuring charge via the electrophoretic mobility (μep) of individual particles remains challenging, and there is only one prior report of simultaneously measuring μep and size. We introduce microfluidic transverse AC electrophoresis (TrACE), a novel technique that combines particle tracking velocimetry (PTV) and AC electrophoresis. In TrACE, electric waves with 0.75 to 1.5 V amplitude are applied transversely to the bulk flow and cause the particles to oscillate. PTV records the particles' oscillating trajectories as pressure drives bulk flow through the microchannel. A simple quasi-equilibrium model agrees well with experimental measurements of frequency, amplitude, and phase, indicating that particle motion is largely described by DC electrophoresis. The measured μep of polystyrene particles (0.53, 0.84, 1, and 2 μm diameter) are consistent with ELS measurements, and precision is enhanced by averaging ∼100 measurements per particle. Particle size is simultaneously measured from Brownian motion quantified from the trajectory for particles <2 μm or image analysis for particles ≥2 μm. Lastly, the ability to analyze intact mammalian cells is demonstrated with B cells. TrACE systems are expected to be highly suitable as fieldable tools to measure the μep and size of a broad range of individual particles. 

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4. Nonlinear Electrokinetic Methods of Particles and Cells

   https://doi.org/10.1146/annurev-anchem-061622-040810  

   Lapizco-Encinas, Blanca H (July 2024, Annual Review of Analytical Chemistry)

   Nonlinear electrokinetic phenomena offer label-free, portable, and robust approaches for particle and cell assessment, including selective enrichment, separation, sorting, and characterization. The field of electrokinetics has evolved substantially since the first separation reports by Arne Tiselius in the 1930s. The last century witnessed major advances in the understanding of the weak-field theory, which supported developments in the use of linear electrophoresis and its adoption as a routine analytical technique. More recently, an improved understanding of the strong-field theory enabled the development of nonlinear electrokinetic techniques such as electrorotation, dielectrophoresis, and nonlinear electrophoresis. This review discusses the operating principles and recent applications of these three nonlinear electrokinetic phenomena for the analysis and manipulation of particles and cells and provides an overview of some of the latest developments in the field of nonlinear electrokinetics. 

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5. Analysis of drug interactions with serum proteins and related binding agents by affinity capillary electrophoresis: A review

   https://doi.org/10.1002/elps.202200191  

   Sharmeen, Sadia; Kyei, Isaac; Hatch, Arden; Hage, David_S (November 2022, ELECTROPHORESIS)

   Abstract Biomolecules such as serum proteins can interact with drugs in the body and influence their pharmaceutical effects. Specific and precise methods that analyze these interactions are critical for drug development or monitoring and for diagnostic purposes. Affinity capillary electrophoresis (ACE) is one technique that can be used to examine the binding between drugs and serum proteins, or other agents found in serum or blood. This article will review the basic principles of ACE, along with related affinity‐based capillary electrophoresis (CE) methods, and examine recent developments that have occurred in this field as related to the characterization of drug–protein interactions. An overview will be given of the various formats that can be used in ACE and CE for such work, including the relative advantages or weaknesses of each approach. Various applications of ACE and affinity‐based CE methods for the analysis of drug interactions with serum proteins and other binding agents will also be presented. Applications of ACE and related techniques that will be discussed include drug interaction studies with serum agents, chiral drug separations employing serum proteins, and the use of CE in hybrid methods to characterize drug binding with serum proteins. 

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