Microchip-based electrophoresis electrophoretic separations

One of the earliest efforts of qualitative measurement of a protein (human serum albumin) in a microchip-based device was based on bead agglutination in a microchamber (approximately lOjaL). Subsequently, several quantitative immunoassays have been performed using microchip electrophoretic systems that permit separation and quantitation of free- and bound-labeled antigens in competitive assays (see Chapter 5). Most are carried out in channels micro-machined into fused silica substrates. Early work on quantitative assays achieved measurement of cortisol in serum.The assay used cortisol labeled with fluorescein and an argon laser detector at 488 nm and required only 80 pL of a 40x dilution of serum as the sample. Other capillary electrophoresis-based assays for a variety of antibodies have also been developed that include immunoglobulins (IgG, IgA, and IgM), antibovine serum albumin, and antiestradiol. ... 

An assay for uric acid in urine employing a PDMS and/or glass microchip for capillary electrophoresis has also been developed. This device can achieve separation and quantitation of uric acid in less than 30 seconds and a linear response over a range of 0 to lOOpM/L. To facilitate this measurement, dilutions of urine of the order of fiftyfold to seventy-fivefold were required. Other similar devices for the renal markers creatine, creatinine, p-aminohippuric acid, and uric acid in urine,and a microchip-based method for zone electrophoretic analysis of oxalate m urine have been reported. 

Petersen NJ, Nikolajsen RPH, Mogensen KB et al (2004) Effect of Joule heating on efficiency and performance for microchip-based and capillary-based electrophoretic separation systems a closer look. Electrophoresis 2 253-269... 

Capillary zone electrophoresis (CZE) is the most commonly used separation mode in CE microchip due to its versatility, ease of operation, and separation power. This electrophoretic mode is based on the theory and mechanism of action directly transferred from the conventional CE. In CZE the channel contains only a buffered medium and the electrophoretic mobilities of the analytes depend on their charge/mass ratio, acting as separation mechanism. These different velocities make possible to separate cations and anions if the EOF is strong, in order to lead anionic substances to the detector located usually at the cathode. It has the limitation of being useful only for separation of charged species. 

Fig. 4 A novel flowthrough sampling design for continuous sampling on an electrophoresis-based microchip, in which electrical voltages are applied to the electrophoretic channels to control sample loading for separation and detection as well as to inhibit sample leakage (Reproduced with permission from [5])...

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