Effect of DNA length on dielectrophoretic characteristics of DNA-labeled microbeads

Polymerase chain reaction (PCR) is a powerful tool for diagnostic procedures in bacterial and viral infections. We have developed a new electrical technique for rapid detection of DNA amplified by PCR using dielectrophoresis (DEP) of microbeads that are chemically labeled with the amplicons. The DNA immobilization on the microbeads alters their DEP behavior in such a way that they are trapped on a microelectrode under the action of positive DEP, whereas pristine microbeads are not. Combining the dramatic alteration in DEP characteristics with impedance measurement leads to rapid and quantitative detection of amplicons. The method is based on the surface conductivity dependence of microbeads DEP characteristics. It was expected that the surface conductivity would depend on the length of DNA fragments immobilized on a microbeads. In this study, it was found that the crossover frequency was dependent on the length of DNA.