Frequency-dependent conductance change of dielectrophoretic-trapped DNA-labeled microbeads and its application in DNA size determinations

DNA amplification is essential in several types of molecular biology approaches. A more rapid and easy analysis of amplicons is still required although many analysis methods have been developed. We have recently devised a new DNA detection method, where DNA amplicons are attached to dielectric microbead surfaces, so that their dielectrophoresis (DEP) force on the microbead reverses polarity, from negative to positive. The DNA-labeled microbeads are trapped on a microelectrode by positive DEP, enabling their rapid detection via DEP impedance measurement. In this paper, we report frequency-dependent conductance of DNA-labeled microbeads. To measure the impedance, sweep-frequency voltage was superimposed on fixed-frequency voltage, with the aim of inducing frequency-dependent conformational change of microbead-attached DNA, ultimately resulting in a change in the conductance of DNA-labeled microbeads. Microbeads labeled with DNA of various sizes (142-, 204-, 391-, and 796-bp) were examined. The normalized conductance sharply decreased at a specific frequency; the frequency was higher with larger DNA size, suggesting a potential application of this method in distinguishing DNA targets according to their size. By combining this method with previously devised DNA detection techniques, both the size and amount of target DNA can be determined within 20 min. This approach is easier and more rapid than conventional methods, such as a gel electrophoresis.