Dielectrophoretic detection of molecular bindings

The specificity of molecular binding between the "target" and the "probe" m olecule, for example, between antigen and antibody or between two complemen tary deoxyribonucleic acid (DNA) sequences, is the principle of affinity as says. In the assay, the target is mixed with the fluorescence-labeled probe , so that the probe binds to the target to form a target-probe complex. The n, the bound complex is separated from the free (unbound) probe somehow (bo und/free (BF) separation), and the fluorescence emission from the separated complex is measured to obtain the target concentration in the original sam ple. In this paper, we propose and experimentally demonstrate the use of di electrophoresis (DEP) for such B/F separations. Using DEP chromatography, D EP characteristics of various biomolecules are measured, and: 1) separation of lambda -DNA (48.5 kbp) and oligonucleotide (22base) and 2) quantitative detection of antigen-antibody bindings, are demonstrated. Using the triple complex formation to facilitate DEP separation, a method is developed to d etect B/F binding by a direct observation of the separation pattern on the microelectrode system. It is applied for: 1) quantitative detection of alph a-fetoprotein, the diagnostic marker of liver cancer, through antigen-antib ody reaction and 2) the detection of DNA sequence through hybridization. Th e methods developed here are compatible with micro fabrication, and suitabl e for affinity assays in micro-total analysis systems.