Particle-based immobilized enzymatic reactors in microfluidic chips.

The research and applications of immobilized enzyme reactors (IMERs) have become more and more widespread due to the numerous advantages like reusability, easy handling, prolonged lifetime, easy separation from products and substrate specificity. The miniaturized form of these reactors (microchip IMERs) received outstanding attention due to their special features and advantages over the traditional, larger analytical systems. Large specific surface is essential for the efficient operation of the microreactors, thus these devices include one of the several types of porous solid supports, but in this work only the particle based microchip IMERs are reviewed. A very large variety of micro- or nanoparticles (beads) have been used in the microchip IMERs, however, incorporating these particles into microchips is still a challenge, because the common procedures used for the preparation of chromatographic columns are not well applicable at the microscopic level. Many detection systems were applied with microchip IMERs using on-chip or off-chip arrangement. The combination of microchip IMERs with mass spectrometry is particularly popular, because in these systems high-throughput analysis can be achieved by which the proteomic studies can be largely accelerated. In most chip IMER-MS systems, the chips are used for sample pretreatment including analyte (protein) digestion, preconcentration of analyte, removal of matrix materials. Additional applications of the IMERs - like the rapid protein digestion with proteolytic enzymes, the transformation of analytes to a more easily or more sensitively measurable form (detection signal amplification) and the design of microarrays/biosensors to analyze antigens based on specific interactions in immunoanalytical studies - are also reviewed.