Monitoring Electroosmotic Flow by Periodic Photobleaching of a Dilute, Neutral Fluorophore

Schrum, Kimberley F.; Lancaster, Joseph M.; Johnston, and Stephen E.; Gilman, S. Douglass

doi:10.1021/ac0005114

Cited by 92 publications

(117 citation statements)

References 36 publications

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“…The molar conductivity was measured as 7.7 × 10 −3 S m 2 mol −1 . The 10 mm buffer was seeded with 0.1 mm rhodamine B (CAS 1303-96-4, J. T. Baker, NJ, USA) which is reported to be neutral for pH values ranging from 6.0 to 10.8 (Schrum et al 2000). The ionic concentrations were low enough such that the permittivity and viscosity were the same as that of pure water (see, for example, Pottel 1973;Horvath 1985).…”

Section: Introductionmentioning

confidence: 99%

Convective and absolute electrokinetic instability with conductivity gradients

et al. 2005

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Electrokinetic flow instabilities occur under high electric fields in the presence of electrical conductivity gradients. Such instabilities are a key factor limiting the robust performance of complex electrokinetic bio-analytical systems, but can also be exploited for rapid mixing and flow control for microscale devices. This paper reports a representative flow instability phenomenon studied using a microfluidic T-junction with a cross-section of 11 µm by 155 µm. In this system, aqueous electrolytes of 10:1 conductivity ratio were electrokinetically driven into a common mixing channel by a steady electric field. Convectively unstable waves were observed with a nominal threshold field of 0.5 kV cm −1 , and upstream propagating waves were observed at 1.5 kV cm −1 . A physical model has been developed for this instability which captures the coupling between electric and flow fields. A linear stability analysis was performed on the governing equations in the thin-layer limit, and Briggs-Bers criteria were applied to select physically unstable modes and determine the nature of instability. The model predicts both qualitative trends and quantitative features that agree very well with experimental data, and shows that conductivity gradients and their associated bulk charge accumulation are crucial for such instabilities. Comparison between theory and experiments suggests the convective role of electro-osmotic flow. Scaling analysis and numerical results show that the instability is governed by two key controlling parameters: the ratio of dynamic to dissipative forces which governs the onset of instability, and the ratio of electroviscous to electro-osmotic velocities which governs the convective versus absolute nature of instability.

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Section: Introductionmentioning

confidence: 99%

Convective and absolute electrokinetic instability with conductivity gradients

et al. 2005

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“…[32][33][34][35] The most successful method that applies the traditional advanced anemometer, is micro Particle Image Velocimetry (mPIV), [36][37][38] but it is difficult to apply to commercial instruments. Photobleached Fluorescence Visualization [39][40][41] and the line writing technique [42][43][44] with photobleaching are also developed to measure the flow velocity. However, all the methods mentioned above have limited temporal resolution.…”

Section: Introductionmentioning

confidence: 99%

Laser induced fluorescence photobleaching anemometer for microfluidic devices

Wang

2005

Lab Chip

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We have developed a novel, non-intrusive fluid velocity measurement method based on photobleaching of a fluorescent dye for microfluidic devices. The residence time of the fluorescent dye in a laser beam depends on the flow velocity and approximately corresponds to the decaying time of the photobleaching of the dye in the laser beam. The residence time is inversely proportional to the flow velocity. The fluorescence intensity increases with the flow velocity due to the decrease of the residence time. A calibration curve between fluorescence intensity and known flow velocity should be obtained first. The calibration relationship is then used to calculate the flow velocity directly from the measured fluorescence intensity signal. The new method can measure the velocity very quickly and is easy to use. It is demonstrated for both pressure driven flow and electroosmotic flow.

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“…Photobleached-fluorescence imaging (where the fluorescence of a dilute and neutral fluorophore is suppressed by exposing it to visible excitation light) has also been developed for monitoring EOF [32][33][34][35], but this technique has not yet been applied to characterize surface modifications, although it offers the advantage of using a very low concentration of marker, and will work with both glass and polymer microchannels, which are transparent to visible light.…”

Section: Spatially Resolved Eof Measurementsmentioning

confidence: 99%

Surface treatment and characterization: Perspectives to electrophoresis and lab‐on‐chips

et al. 2006

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The control and modification of surface state is a major challenge in bioanalytical sciences, and in particular in electrokinetic separation methods, due to the importance of electroosmosis. This topic has gained recently a renewed interest, associated with the development of "lab-on-chips" systems that extend the range of materials in which separation channels are fabricated. The surface science community has developed through the years a large toolbox of characterization tools and surface modification protocols, which is not yet fully exploited in the bioanalytical world. In this paper, we try and present an overview of these tools, in order to stimulate new ideas for improved and more controlled surface treatment strategies for separations in capillaries and microchannels. We briefly describe some physical and chemical aspects of electroosmosis (global and spatially resolved), streaming current, and streaming potential. We also review the main strategies for surface coating, and compare the advantages of physisorption, well-organized thin self-assembled monolayers, or conversely thick polymer "brushes". Examples of existing applications to electrophoresis in microchannel are also given.

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Monitoring Electroosmotic Flow by Periodic Photobleaching of a Dilute, Neutral Fluorophore

Cited by 92 publications

References 36 publications

Convective and absolute electrokinetic instability with conductivity gradients

Convective and absolute electrokinetic instability with conductivity gradients

Laser induced fluorescence photobleaching anemometer for microfluidic devices

Surface treatment and characterization: Perspectives to electrophoresis and lab‐on‐chips

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