Capillary electrophoresis-based immunoassay and aptamer assay: A reviewOver the last two decades, the group of techniques called affinity probe CE has been widely used for the detection and the determination of several types of biomolecules with high sensitivity. These techniques combine the low sample consumption and high separation power of CE with the selectivity of the probe to the target molecule. The assays can be defined according to the type of probe used: CE immunoassays, with an antibody as the probe, or aptamer-based CE, with an aptamer as the probe. Immunoassays are generally divided into homogeneous and heterogeneous groups, and homogeneous variant can be further performed in competitive or noncompetitive formats. Interacting partners are free in solution at homogeneous assay, as opposed to heterogeneous analyses, where one of them is immobilized onto a solid support. Highly sensitive fluorescence, chemiluminescence or electrochemical detections were typically used in this type of study. The use of the aptamers as probes has several advantages over antibodies such as shorter generation time, higher thermal stability, lower price, and lower variability. The aptamer-based CE technique was in practice utilized for the determination of proteins in biological fluids and environmentally or clinically important small molecules. Both techniques were also transferred to microchip. This review is focused on theoretical principles of these techniques and a summary of their applications in research.Abbreviations: Ag, antigen; CEIA, CE immunoassay; MCE, microchip CE; SELEX, systematic evolution of ligands by exponential enrichment and they are produced by the immune system of living organisms. Ag that start the immunological response are also called immunogens. These Ab-Ag complexes are stabilized by dipole-dipole, van der Waals or hydrophobic interactions and hydrogen bonds [5,6].The most often used immunoassays are ELISA with Ab or Ag immobilized onto solid support (plates, glass fibers, or plastic tubes), immunofluorescence assay, fluorescence polarization immunoassay, luminescence immunoassay, microparticle enzyme immunoassay, and biosensors. The major disadvantages of immunoassays are the tedious process, time-consuming reactions, and problems with reproducibility and nonspecific interactions [6].CE is a powerful analytical method for the separation of a wide range of molecules. The coupling of CE and immunoassay in the new CE immunoassay (CEIA) technique provided both separation power and specificity of interactions. Other advantages are the possibility of multianalyte analyses, automation, low sample consumption, high speed, flexibility, a lower amount of false-positive results, and also the possibility of connection with highly sensitive detectors [5].In CEIA, the Fab fragments of Ab containing Ag-specific regions are more often used than the whole monoclonal and Color online: See article online to view Figs. 4 and 7 in color.