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ABSTRACT: DNA-DNA hybridization reactions on 100 nm oligonucleotide-functionalized silica nanoparticles are found to sensitively affect the amplitude and direction of the dielectrophoretic mobility of the particles at nanomolar target ssDNA concentrations. Such sensitivity permits visual detection of the hybridization event without fluorescent labeling and confocal microscopy by imaging the cross-over frequency (cof) of the particle suspension on a quadrupole electrode array. Strong correlation with effective particle radius and zeta-potential measurements suggests that the dielectrophoretic cof offers not just sensitive signatures for successful functionalization and hybridization but also those for three distinct DNA surface conformations that appear at different surface densities of hybridized DNA. A properly normalized cof calibration chart allows simplified quantification of the target ssDNA concentrations. These results provide a simple, rapid and portable genetic detection method compatible for use outside the laboratory.
Electrophoresis 02/2009; 29(24):4808-12. · 3.30 Impact Factor
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ABSTRACT: The development of genetic detection protocols for field applications is an important aspect of modern medical diagnostic technology and environmental monitoring. In this paper, we report a rapid, portable, and inexpensive DNA hybridization technique using a bead-based microfluidic platform that functions by passing fluorescently labeled target DNA through a chamber packed with functionalized beads within a microfluidic channel. DNA hybridization is then assessed using a digital camera attached to a Clare Chemical DR-45M dark reader non-UV transilluminator that uses visible light as an excitation source and a blue and amber filter to reveal fluorescence. This microfluidic approach significantly enhances hybridization by reducing the diffusion time between target DNA and the silica surface. The use of probe-functionalized beads as solid support also enhances the sensitivity and limit of detection due to a larger surface area per unit volume. This platform could be adapted for use in medical applications and environmental monitoring, including the detection of harmful organisms in the ballast water of ships.
Biomicrofluidics 02/2009; 3(2):22407. · 3.37 Impact Factor
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ABSTRACT: We report a novel buffer electric and dielectric relaxation time tuning technique, coupled with a glutaraldehyde (Glt.) cross-linking cell fixation reaction that allows for sensitive dielectrophoretic analysis and discrimination of bovine red blood cells of different starvation age. Guided by a single-shell oblate spheroid model, a zwitterion buffer composition is selected to ensure that two measurable crossover frequencies (cof's) near 500 kHz exist for dielectrophoresis (DEP) within a small range of each other. It is shown that the low cof is sensitive to changes in the cell membrane dielectric constant, in which cross-linking by Glt. reduces the dielectric constant of the cell membrane from 10.5 to 3.8, while the high cof is sensitive to cell cytoplasm conductivity changes. We speculate that this enhanced particle polarizability that results from the cross-linking reaction is because younger (reduced starvation time) cells possess more amino groups that the reaction can release to enhance the cell interior ionic strength. Such sensitive discrimination of cells with different age (surface protein density) by DEP is not possible without the zwitterion buffer and cleavage by Glt. treatment. It is then expected that rapid identification and sorting of healthy from diseased cells can be similarly sensitized.
Electrophoresis 07/2008; 29(11):2272-9. · 3.30 Impact Factor
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ABSTRACT: We report a novel buffer electric and dielectric relaxation time tuning technique, coupled with a glutaraldehyde (Glt.) cross-linking cell fixation reaction that allows for sensitive dielectrophoretic analysis and discrimination of bovine red blood cells of different starvation age. Guided by a single-shell oblate spheroid model, a zwitterion buffer composition is selected to ensure that two measurable crossover frequencies (cof's) near 500 kHz exist for dielectrophoresis (DEP) within a small range of each other. It is shown that the low cof is sensitive to changes in the cell membrane dielectric constant, in which cross-linking by Glt. reduces the dielectric constant of the cell membrane from 10.5 to 3.8, while the high cof is sensitive to cell cytoplasm conductivity changes. We speculate that this enhanced particle polarizability that results from the cross-linking reaction is because younger (reduced starvation time) cells possess more amino groups that the reaction can release to enhance the cell interior ionic strength. Such sensitive discrimination of cells with different age (surface protein density) by DEP is not possible without the zwitterion buffer and cleavage by Glt. treatment. It is then expected that rapid identification and sorting of healthy from diseased cells can be similarly sensitized.
Electrophoresis 05/2008; 29(11):2272 - 2279. · 3.30 Impact Factor
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ABSTRACT: Deformability of erythrocyte was found to fundamentally alter the wetting dynamics of red blood cell (RBC) suspensions during their invasion into capillaries. Normal RBC suspensions failed to penetrate more than 1 cm into a glass capillary when the capillary radius was smaller than a critical value that is dependent on the erythrocyte concentration (about 50 microm for whole blood). In contrast, suspensions of rigidified RBCs, after cross-linking with different concentrations of glutaraldehyde or incubating with 100 ng/mL of an endotoxin, could penetrate any capillary larger than the erythrocyte dimension. The effect of RBC deformability on penetration was attributed to the enhanced shear-induced migration of normal deformable RBCs toward the capillary centreline, which imparted a higher average velocity to the RBCs than the average plasma velocity. As a result, the erythrocytes advanced into the capillary faster than the wetting meniscus, packing behind it to form a concentrated slug. This tightly packed slug had a high hydrodynamic resistance that could arrest the penetrating flow of concentrated suspensions into the small capillaries.
Biotechnology and Bioengineering 03/2006; 93(2):201-11. · 3.95 Impact Factor
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ABSTRACT: Hepatocytes are highly dependent upon appropriate oxygen provision for activity and viability. However, oxygen delivery to hepatocytes cultured within a hollow fiber bioreactor is believed to be problematic because of large diffusion distances, a high hepatocyte oxygen consumption rate and low aqueous media oxygen solubility. Supplementation of bioreactor media with bovine red blood cells (bRBCs) is one means of improving oxygen delivery to hepatocytes as hemoglobin contained within bRBCs binds oxygen. The impact of supplementing hepatocyte culturing media with bRBCs (approximately 5 x 10(8) bRBCs/ml) on hepatocyte activity (albumin and lactate production and glucose consumption) was studied. Decreased hepatocyte lactate production to glucose consumption ratios were found for the case when bRBCs were added to circulating culturing media, which indicated the presence of a more aerobic environment in comparison to the control (no bRBC supplementation). Additionally, albumin synthesis was found to be improved when the circulating media was supplemented with bRBCs. Our results thus support the use of bRBCs to improve oxygen delivery to hepatocytes maintained within a hollow fiber bioreactor.
Artificial Cells Blood Substitutes and Biotechnology 02/2005; 33(3):297-306. · 0.98 Impact Factor
