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Selective dynamic concentration of peptides at poles of cation-selective nanoporous granules
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Image of FIG. 1.
FIG. 1.

The granule funnel: (a) vortices develop at the right of the granule; (b) saturation of the double layer saturates at the pole when counter-ions exiting the granule and field screening occurs; (c) a converging coion electromigration flux toward the positively charged pole neutralizes the concentrated protons; and (d) polar ejection and symmetric vortices on the other hemisphere (the white area in the image in Fig. 1 is due to the scattered light that reflects from a coarse surface). Reprinted with permission from Wang Biomicrofluidics , 014102 (2008). Copyright 2008 American Institute of Physics.

Image of FIG. 2.
FIG. 2.

The sequential images of the evolving solute concentration for a cation exchange granule, following an applied field 100 V/cm at an AC frequency of 0.1 Hz. By using FITC tagged angiotensin I in a buffer solution of pH 7.7. The images were taken at 0 s, 1.3 s, and 2 s. The granule image is replaced with a circle filled with brown color.

Image of FIG. 3.
FIG. 3.

The concentration factors of FITC tagged angiotensin I in various pH buffer solutions. The concentration factor increases from a moderately acidic condition (pH 6) above the pI to moderately basic condition (pH 7.7), and then decreases slightly when the pH condition becomes more alkaline (pH 8 or greater).

Image of FIG. 4.
FIG. 4.

The linear relation between the logarithmic values of the concentration factor of FITC tagged angiotensin I peptide and the absolute value of tagged peptide charge state (y = 1.074 e, R = 0.992).

Image of FIG. 5.
FIG. 5.

(a) The concentrated mixture of FITC-tagged angiotensin I and Texas red-tagged avidin at pH 8.5; (b) images of the same mixture at pH 12. The images were digitally filtered at the emission maximal wavelengths of FITC and Texas red, which were 525 nm and 615 nm and were colored in green and red, respectively. The electric field direction is shown by the black arrow above each color image. The monochrome fluorescence images, magnified from the solute trapping spot near the granule, are used to construct concentration level contour maps, shown next to the color images with a pointed arrow. The granules are shaded in white on the contour maps.

Image of FIG. 6.
FIG. 6.

The chemical structure of fluorescein isothiocyanate

Image of FIG. 7.
FIG. 7.

Dukhins vortices near the cation-exchange granules that were generated by a 70 V/cm external field were visualized using fluorescent microspheres (latex micro-particles of 2 m inner diameter (i.d.) tagged with fluorescein dyes) in buffers with differing basicity: (a) buffer pH 8 and (b) buffer pH 11. The red dashed-line circles indicate the vortex size. The larger vortex size at pH 11 became less defined.


Generic image for table
Table I.

List of the charge assignments of each amino acid unit with acidic or basic side chain groups. The carboxylic acid on the C-terminus and the conjugated FITC in the pH solutions are used to estimate the concentration factors of FITC-tagged angiotensin I.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Selective dynamic concentration of peptides at poles of cation-selective nanoporous granules