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Abstract：
Our previous study showed that nanobubbles (NBs) encapsulating CO2 gas have bactericidal activity due to reactive oxygen species (ROS) (Yamaguchi et al., 2020). Here, we report that bulk NBs encapsulating CO2 can be efficiently generated by ultrasonically irradiating carbonated water using a piezoelectric transducer with a frequency of 1.7 MHz. The generated NBs were less than 100 nm in size and had a lifetime of 500 h. Furthermore, generation of ROS in the NB suspension was investigated using electron spin resonance spectroscopy and fluorescence spectrometry. The main ROS was found to be the hydroxyl radical, which is consistent with our previous observations. The bactericidal activity lasted for at least one week. Furthermore, a mist generated by atomizing the NB suspension with ultrasonic waves was confirmed to have the same bactericidal activity as the suspension itself. We believe that the strong, persistent bactericidal activity and radical generation phenomenon are unique to NBs produced by ultrasonic irradiation of carbonated water. We propose that entrapped CO2 molecules strongly interact with water at the NB interface to weaken the interface, and high-pressure CO2 gas erupts from this weakened interface to generate ROS with bactericidal activity.
摘要：
我们先前的研究表明，由于活性氧（ROS），封装CO2气体的纳米气泡（NBs）具有杀菌活性（Yamaguchi等人。,2020）。这里,我们报告说，通过使用频率为1.7MHz的压电换能器超声辐照碳酸水，可以有效地产生包裹CO2的大量NB。产生的NB的大小小于100纳米，寿命为500小时。用电子自旋共振光谱和荧光光谱法研究了NB悬浮液中ROS的产生。发现主要的ROS是羟基自由基，这与我们之前的观察是一致的。杀菌活性持续至少一周。此外，通过用超声波雾化NB悬浮液产生的雾被证实具有与悬浮液本身相同的杀菌活性。我们相信强者,持续的杀菌活性和自由基产生现象是超声波辐照碳酸水产生的NBs所特有的。我们认为，截留的CO2分子在NB界面与水强烈相互作用，削弱界面，高压CO2气体从这个弱化的界面喷出，产生具有杀菌活性的ROS。
