Difference by Frequencies on Cell Killing Effect by Superposing Low Frequency on High-Frequency Bipolar Burst Pulse

An ultrashort pulse high electric field provides new biological applications, such as sterilization of a packaged food. In this study, we investigate the effect on yeast cells by a high-frequency and high-intensity burst pulse for the purpose of killing cells in packaged food. Previously, we showed that applying a burst pulse to cells was more effective in causing cell death than repeatedly supplying a single pulse. However, in case of a unipolar burst pulse, a low-frequency component caused by a burst pulsewidth was included in addition to the high-frequency component to be investigated. Therefore, it was not clear which frequency was effective in killing cells. Here, we investigate how the low-frequency component superposed on the high-frequency burst pulse affects cell death by comparing the unipolar burst pulse having the-low frequency component, the bipolar burst pulse not having the low-frequency component, and a single pulse that was the low-frequency component of the unipolar burst pulse. As a result, the cell death ratio was higher by applying 150-MHz band unipolar burst pulses including 150-MHz band as a high-frequency component and 15-MHz band as a low-frequency component to the cells than by applying bipolar burst pulses with only frequency component of 150-MHz band to the cells. Also, the cell death ratio was higher by applying the 150-MHz band unipolar burst pulses to the cells than by applying the 15-MHz band single pulse that was the low-frequency component of the 150-MHz band unipolar burst pulse to the cells. These results show that the burst pulse is possible in causing cell death more effectively by superposing low frequency on high frequency.