Microfluidic devices electrokinetic preconcentration techniques

Plastic microdevices for high-throughput screening with MS detection were also prepared for detection of aflatoxins and barbiturates. These devices incorporated concentration techniques interfaced with electrospray ionization MS (ESI-MS) through capillaries [2], The microfluidic device for aflatoxin detection employed an affinity dialysis technique, in which a poly (vinylidene fluoride) (PVDF) membrane was incorporated in the microchip between two channels. Small molecules were dialyzed from the aflatoxin/antibody complexes, which were then analyzed by MS. A similar device was used for concentrating barbiturate/antibody complexes using an affinity ultrafiltration technique. A barbiturate solution was mixed with antibodies and then flowed into the device, where uncomplexed barbiturates were removed by filtration. The antibody complex was then dissociated and electrokinetically mobilized for MS analysis. In each case, the affinity preconcentration improved the sensitivity by at least one to two orders of magnitude over previously reported detection limits. 

The use of recirculating flows for the preconcentration of samples in microfluidic devices is, like TGF and nanofluidic filtering (see later), a relatively new approach (early 2000s). The technique, which has been termed flow-induced electrokinetic trapping (FIET), involves the concentration and... 

Several research groups have reported ways to preconcentrate samples in Lab-on-a-Chip devices. While most on-chip preconcentration approaches evolve from conventional capillary electrophoresis and chromatographic column techniques, these preconcentration techniques play an increasingly important role in chip-based system. The basic preconcentration strategies applied on microfluidic devices can be classified into three large categories electrokinetic preconcentration, chromatographic preconcentration and membrane preconcentration. 

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