Electrokinetic Sample Dispensing

Figure 13. Steps in the electrokinetically-controlled immunoassay. Arrows indicate flow direction. Solid arrows stand for major flows, and dashed arrows, minor flows, (a) Loading and incubation of samples. Sample solutions were dispensed from the sample weUs to the reaction region and discharged into the waste well, (b) Washing of samples. Buffer solution flushed sample solutions from the reaction region back into the sample wells, (c) Second washing of samples. Sample solutions having entered the antibody channel during the previous three steps were flushed into the waste well, (d) Loading and incubation of detection antibody, (e) Washing of detection antibody.

Fu et al. [4] presented a numerical model for electrokinetic dispensing in microfluidic chips where simple cross, double-T, and triple-T configurations were considered. In this model, the Nemst-Planck equation was employed to describe the ionic concentration instead of the Boltzmann distribution, which is a more general approach. The model was numerically solved using the finite difference method where the artificial compressibility method was employed to deal with the pressure term in the N-S equation. It is found that the applied potentials play an important role in crnitroUing the loaded and dispensed sample shape. The unique feature of this study is the concept of the multi-T injection system which can function as a simple cross, double-T, or triple-T injectimi unit. Their numerical results agreed well with their experimental results. More injection techniques were also developed by the same group later. 

Electrokinetic focusing refers to the application of electrokinetic sheath flows to confine a sample flow into a thin stream for dispensing. The most common configuration is a simple cross-linked microchannel. 

Electrokinetic focusing is one of the major techniques used in many biological and biomedical applications. As an example, on-chip electrophoresis separation utilizes electrokinetic focusing to create a very thin sample stream before dispensing a small plug for separation [1]. Electrokinetic focusing is also applied in cell cytometry and cell sorting to dispense cells one at a time before they... 

An important component of many bio- or chemical Lab-on-a-Chip devices is the microfluidic injection system, the precise control of the size and concentration of the dispensed sample in the microfluidic injection system determines the performance of these Lab-on-a-Chip devices. Two methods are commonly adopted in microfluidic injection systems electrokinetic injection and pressure injection. Pressure-driven... 

Both the theoretical studies and the experimental studies have demonstrated that the loading and dispensing of sub-nanoliter samples using a microfluidic-crossing microchannel chip can be well controlled electrokinetically. The abiUty to inject and transport large axial extent. 

The gated injector is time dependent and has an electrophoretical sample bias [9]. The performance of this valve is measured by recording temporal profiles at 1 mm downstream of the valve for injection times of 0.2, 0.4, and 0.8 s. The peak maximum does not increase at longer injection times. The peak area reproducibility is better than 0.5 % relative standard deviation for 20 injections for each injection time. As with conventional electrokinetic injection schemes, this injection is also biased by the relative electrokinetic mobility of the sample ions. This valve dispenses sample volumes that are linearly proportional to the electrophoretic mobility for which this bias is easily compensated. 

Electrokinetic dispensing is a method using electroosmotic punqting to inject a small quantity of samples, the size and concentration of which can be controlled by manipulating applied electrical potential fields, modifying channel surfaces and changing channel dimensions. A simple cross-linked microchannel is commonly employed for electrokinetic dispensing. 

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