A Near-Infrared Fluorescent Nanosensor for Direct and Real-Time Measurement of Indole-3-Acetic Acid in Plants

Auxin, particularly indole-3-acetic acid (IAA), is a phytohormone critical for plant growth, development, and response to environmental stresses like shade avoidance syndrome and thermomorphogenesis. Despite its importance, there is no existing method that allows for convenient and direct detection of IAA in various plant species. Here, we introduce a near-infrared fluorescent nanosensor that directly measures IAA in planta using corona phase molecular recognition with high selectivity, specificity, and spatiotemporal resolution. The IAA sensor can be conveniently functionalized to living plants and localized in various tissues, including leaf, cotyledon, and root tip, with the capability to visualize intrinsic IAA distribution. The IAA nanosensor was further tested in Arabidopsis thaliana leaf with tunable levels of endogenous IAA, in which the sensor measured dynamic and spatiotemporal changes of IAA. We also showed that the IAA sensor can be used for qualitative and quantitative mapping of IAA induction and spatial movement in various plant species undergoing environmental or stress response, such as shade avoidance syndrome, high temperature stress, and gravitropism. This highlights the potential application of IAA sensor for monitoring plant health in agriculture.