Krushinski Lynn E, Dick Jeffrey E
Department of Chemistry, Purdue University, West Lafayette, IN 47907.
Elmore Family School of Electrical and Computer Engineering, Purdue University, West Lafayette, IN 47907.
Proc Natl Acad Sci U S A. 2024 Mar 19;121(12):e2321064121. doi: 10.1073/pnas.2321064121. Epub 2024 Mar 11.
Recent reports have detailed the striking observation that electroactive molecules, such as hydrogen peroxide (HO) and radical water species (HO/HO), are spontaneously produced in aqueous microdroplets. Stochastic electrochemistry allows one to study reactions in real-time occurring inside subfemtoliter droplets, one droplet at a time, when a microdroplet irreversibly adsorbs to an ultramicroelectrode surface (radius ~ 5 µm). Here, we use stochastic electrochemistry to probe the formation of hydrogen peroxide (HO) in single aqueous microdroplets suspended in 1,2-dichloroethane. The oxidation of HO at alkaline pH (11.5) differs from near-neutral conditions (6.4), allowing us to create a digital, turn-off sensing modality for the presence of HO. Further, we show that the stochastic electrochemical signal is highest at the mass transfer limitation of the HO couple and is dampened when the potential nears the formal potential. We validate these results by showing that the addition of a HO selective probe, luminol, decreases the stochastic electrochemical response at alkaline pH (11.5). Our results support the observation that HO is generated in water microdroplets at concentrations of ~100 s of µM.
电活性分子，如过氧化氢（HO）和自由基水物种（HO/HO），会在水性微滴中自发产生。当一个微滴不可逆地吸附到超微电极表面（半径约5微米）时，随机电化学使人们能够实时研究亚飞升液滴内部一次一个液滴发生的反应。在这里，我们使用随机电化学来探测悬浮在1,2 - 二氯乙烷中的单个水性微滴中过氧化氢（HO）的形成。HO在碱性pH值（11.5）下的氧化与近中性条件（6.4）不同，这使我们能够创建一种用于检测HO存在的数字式关闭传感模式。此外，我们表明随机电化学信号在HO电对的传质限制时最高，而当电位接近形式电位时会减弱。我们通过表明添加HO选择性探针鲁米诺会降低碱性pH值（11.5）下的随机电化学响应来验证这些结果。我们的结果支持了在水微滴中以约100 s的微摩尔浓度生成HO的观察结果。
