Iranian professor's research featured on American Chemical Society journal cover
Tehran - BORNA - The study, titled "Single-Rain Droplet Amperometry Reveals Spontaneous and Regulated H2O2 Formation on Leaf Surfaces," was co-authored by Amir Hatamie, faculty member at IASBS, Shohreh Madani, and Richard N. Zare.
Published on May 6, 2026, in Volume 42, Issue 21 of Langmuir (pages 15023–15034), the research investigates a microscopic chemical process wherein tiny raindrops spontaneously generate hydrogen peroxide (H2O2) upon contact with leaf surfaces.
Spontaneous chemical reaction on leaf interfaces
Hydrogen peroxide is a reactive oxygen species and oxidizing compound. Previous studies demonstrated that water microdroplets—including sprays and condensate—can generate hydroxyl radicals via interfacial reactions and contact electrification, facilitating H2O2 formation. However, the occurrence of this process under natural environmental conditions within micro-raindrops remained largely unexamined.
In this study, researchers analyzed single raindrops with volumes of approximately 5 microliters to observe in-situ H2O2 generation on natural leaf surfaces. Results revealed that hydrogen peroxide forms spontaneously within these microdroplets without the presence of catalysts.
To detect the compound, researchers employed electrochemical methods using a combined microelectrode approximately 1.2 mm in diameter to measure H2O2 directly within individual droplets. The detection limit of this method was recorded at 0.27 ppm (approximately 8 uM), with colorimetric assays conducted in parallel to validate the electrochemical findings.
Impact of leaf morphology and environmental factors
The study demonstrated that physical leaf characteristics significantly influence the rate of hydrogen peroxide generation. Utilizing rose (Rosa) and boxwood (Buxus) leaves as model systems, researchers observed that surface structure, micro-topography, and hydrophobicity impact H2O2 yields in droplets.
Furthermore, H2O2 production rates differed between raindrops exposed to sunlight and those in shade—a variance attributed primarily to temperature fluctuations rather than direct ultraviolet (UV) radiation. Droplet pH was also identified as a key factor influencing synthesis rates.
Control experiments confirmed that UV radiation and plant photosynthetic processes were not the primary drivers of H2O2 production in these tests. Replicated experiments on synthetic plastic surfaces and behind UV-blocking glass confirmed that formation relies directly on interfacial phenomena between the droplet surface and its surrounding environment.
Conversely, when larger water volumes (approximately 0.5 mL) or macro-droplets were tested, no detectable oxidizing agents were observed, underscoring the critical role of droplet scale and surface-to-volume ratio in driving the reaction.
Potential ecological and biological implications
The findings suggest that micro-raindrops serve not only to wash plant surfaces but also act as reaction sites for generating oxidizing compounds upon contact.
Researchers hypothesize that this natural process may create an inhospitable environment for certain microbial pathogens or participate in localized surface oxidation. The authors noted, however, that further field studies under natural conditions are required to fully assess the biological role of this phenomenon in plant defense.
Additionally, the authors noted that similar interfacial chemical processes likely extend beyond raindrops to other natural phenomena, including dew, fog, and atmospheric aerosols, highlighting the broader necessity of studying spontaneous reactive oxygen species formation at water-air interfaces.
End Article