Trapping of Proteins under Physiological Conditions in a Nanopipette

Abstract

Dielectrophoresis (DEP) uses the directed motion of particles caused by polarization effects in a nonuniform electric field, [1] and it has proved to be a powerful tool in performing sample sorting, [2][3][4][5][6] trapping, [6][7][8] and manipulation [6,[9][10][11] on micrometer-and submicrometer-sized particles to date. These experiments have been largely performed in low-conductance solutions by using metal electrodes-conditions that are nonphysiological and in which damage by electrolysis is also possible. Herein, we use a nanopipette for electrodeless dielectrophoresis and show clear evidence, by using wide-field fluorescence imaging, for the reversible trapping of Alexa-488-labeled proteins (protein G and immunoglobulin G (IgG)) and also of the fluorophore alone. Our results show a dielectrophoretic concentration enhancement for these fluorophore-labeled proteins of at least a factor of 300. This concentration enhancement was shown to take place in less than a second and to be within about a factor of two of that observed with DNA. This finding opens up new possibilities for miniaturized bioanalysis.Previous applications of DEP have focused on the separation of micrometer-and submicrometer-scale objects, such as cells, [9] viruses, [10] and colloidal particles, [12] and the manipulation and trapping of long DNA molecules. [7] More recently, DEP has been applied as a bottom-up approach to assemble functional structures by using nanosized building blocks [13][14][15][16] and submicrometer-diameter fibrils from singlewall carbon nanotubes. [17] DEP has also been utilized in separating metallic carbon nanotubes from semiconducting carbon nanotubes, [18] and evidence for the trapping of bovine serum albumin has been presented. [19] All of these studies have used metallic microelectrodes for their DEP traps. These have the advantage of flexible designs for the electrodes and a relatively low voltage being required to generate a high-field gradient on the microscale. However, there are limitations in the application of trapping by metallic DEP. Firstly, it is not compatible with biological samples, as the low-ionic-strength solutions that are used will lead to unfolding of DNA and proteins. Secondly, proteins will be easily drawn to the metal surface of the electrodes where they will become denatured. Thirdly, complex electrochemical reactions such as electrolysis may occur at the microelectrodes. These reactions not only generate gas bubbles that interfere with trapping but they may also damage the trapped molecules and degrade the electrodes. This is a particular problem at the predicted high electric fields required to trap proteins. [20] To address this problem, Chou and co-workers developed DEP traps by patterning geometrical constrictions in an insulating quartz substrate instead of the traditional metallic microelectrodes. [21] The constrictions in a microfluidic channel are used to create a high-field gradient with a local maximum; DNA was successfully trapped in this high-field region under ionic buffer c...

Self‐assembled organic nanotubes: Toward attoliter chemistry

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Dielectrophoretic monitoring of microorganisms in environmental applications

“…When working on the microscale, processing times are much shorter, only small quantities of samples and reagents are required, higher resolution and sensitivity are obtained, high level of integration, portability, and automation are achieved, and costs are lowered [4,6]. Microfluidic devices have made an impact in many fields including food and water safety [7][8][9], clinical analysis [10][11][12], medical diagnostics [12,13], DNA [14][15][16][17] and protein manipulation [15,18,19], and environmental monitoring [20][21][22][23].…”

Direct current dielectrophoretic simulation of proteins using an array of circular insulating posts

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