Water-Dispersible Activatable Nanoprobe for Detecting Cadmium-Ion-Induced Oxidative Stress in Edible Crops via Near-Infrared Second-Window Fluorescence Imaging

Edible crops are important in terms of food security and sustainable agriculture. Heavy-metal-ion contamination of water/soil has deleterious impacts on the growth of edible crops. Among the heavy metals, cadmium (Cd) is toxic to plants, people, and animals, as it is widely used in industry; it has become the most important metal ion in the soil/water pollution. Once the toxic Cd ion enters edible crops via the water/soil in which the crops grow, it will induce oxidative stress (overproduction of reactive oxygen species with H₂O₂ being the most abundant) in the crops, and strong oxidative stress leads to the crops' growth depression or inhibition. Hence, it is of great significance to accurately monitor the oxidative stress induced by Cd ions in edible crops, as the monitoring results could be employed for the early warning of Cd-ion pollution in water/soil. Herein, we design an activatable nanoprobe that can detect Cd-ion-induced oxidative stress in edible crops via near-infrared second-window (NIR-II) fluorescence imaging. The molecular probe IXD-B contains the diphenylamine-modified xanthene group acting as the electron-donating unit, bis(methylenemalononitrile)indan as the electron-accepting unit, and the methenephenylboronic acid group as the recognition moiety for H₂O₂ and the fluorescence quencher. The probe molecules being encapsulated by the amphiphilic DSPE-PEG2000 render the water-dispersible nanoprobe (IXD-B@DSPE-PEG2000). When the nanoprobe enters the edible crops, it can be activated by the overexpressed H₂O₂ therein and consequently emit strong NIR-II fluorescence signals for visualizing and tracking the oxidative stress in edible crops induced by Cd ions.