Direct electrochemical evidence suggests that aqueous microdroplets spontaneously produce hydrogen peroxide.
basic_science · Level V
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- Record sourced from PubMed, PMID 38466847.
- Also identified by DOI 10.1073/pnas.2321064121 and PMC identifier 10962973.
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Abstract
Recent reports have detailed the striking observation that electroactive molecules, such as hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) and radical water species (H<sub>2</sub>O<sup>.+</sup>/H<sub>2</sub>O<sup>.-</sup>), 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 (H<sub>2</sub>O<sub>2</sub>) in single aqueous microdroplets suspended in 1,2-dichloroethane. The oxidation of H<sub>2</sub>O<sub>2</sub> 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 H<sub>2</sub>O<sub>2</sub>. Further, we show that the stochastic electrochemical signal is highest at the mass transfer limitation of the H<sub>2</sub>O<sub>2</sub> couple and is dampened when the potential nears the formal potential. We validate these results by showing that the addition of a H<sub>2</sub>O<sub>2</sub> selective probe, luminol, decreases the stochastic electrochemical response at alkaline pH (11.5). Our results support the observation that H<sub>2</sub>O<sub>2</sub> is generated in water microdroplets at concentrations of ~100 s of µM.