Multiplexed microfluidic separations

By Dr Matt Wilkinson

- Last updated on GMT

Related tags: Gel electrophoresis

A new 'lab-on-a-chip' electrophoresis separation device allows
higher resolution separations and could enable faster diabetes
immunoassay diagnoses.

The new device, pioneered by researchers at the US National Institute of Standards and Technology (NIST), allows higher resolution separations with a smaller device footprint. The device uses a novel electrophoresis separation method where the solvent flow opposes the movement of the molecules to be separated. The nature of the opposing flow technology also removes the need for sample preparation steps. In the latest issue of Analytical Chemistry​, the researchers showed that the device could be used to effectively separate complex mixtures of fluorescence-labeled amino acids with separation times being halved by using a two-stage solvent flow gradient, as well as for separating small dye molecules, DNA and immunoassay products. The NIST researchers created the device with eight channels allowing eight simultaneous separations. The multiplexed device measures less than 1 inch square and is made from low cost polymeric materials using cheap milling techniques. The novel design means that fewer fluid ports are needed than conventional devices, further reducing the complexity of the manufacturing process. Electrophoresis is a technique for separating components of a mixture of charged molecules, such as DNA, RNA and proteins, in an electric field. The electrophoretic mobility of a molecule is directly proportional to its charge and inversely proportional to its size. Conventional and microchip moving boundary electrophoretic (MBE) separations begin with the injection of a discrete zone of analytes into a capillary or channel filled with a gel or buffer solution. The compounds 'race' down the capillary and gradually separate into different bands. Long channels are usually needed for high-resolution or high peak capacity separations. While long channels can be fitted into a small space using a serpentine pattern, with the channel snaking back and forth across a chip, each turn of the channel introduces dispersion of the analyte bands, leading to band broadening. The new technique removes the need for such long channels, and enables smaller device footprints, by using gradient elution moving boundary electrophoresis (GEMBE). The new GEMBE technique works by opposing the movement of the solution's analytes with a stream of buffering solution. At any given time, only analytes with electrophoretic mobilities greater than the counterflow enter the separation channel. The counterflow rate is then varied from high to low, with lower mobilities entering the channel at different times allowing high-resolution separations in very short channels. GEMBE allows for greater flexibility in selectivity when compared to traditional capillary zone electrophoresis (CZE) with the flow rate becoming a separation parameter. The counterflow can also remove the need for sample preparation steps as large molecules that would normally stick to the separation channels can be excluded from ever entering the channels. The researchers showed that the device could be used for insulin immunoassays, which are extremely important for studying diabetes and other metabolic diseases. Using the eight-channel device a full calibration curve for a homogenous competitive insulin immunoassay was generated in one step with less than 5 per cent relative standard deviation between the measured results and the known insulin concentration.

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