Dynamic Imaging of Carbon Monoxide in Cotton Roots under Insecticide Stress Using a Quinoline-Malononitrile Derivative Probe

Abstract Carbon monoxide (CO) is a gaseous signaling molecule involved in plant stress responses, yet its dynamics under pesticide exposure remains poorly understood. Here, we report QM-CO, a quinoline-malononitrile-based, intramolecular charge-transfer-regulated turn-on fluorescent probe for imaging CO-associated changes in zebrafish and cotton roots. QM-CO exhibited high sensitivity and selectivity toward CO, with fluorescence reaching a plateau within 10 min, while the activated fluorophore displayed an aggregation-induced emission enhancement. Hemin stimulation increased fluorescence, whereas pharmacological inhibition of heme oxygenase-1 attenuated the response, providing bidirectional evidence for HO-1-related CO production. QM-CO further revealed concentration- and time-dependent fluorescence increases in cotton roots exposed to thiamethoxam and imidacloprid, accompanied by pesticide-induced growth inhibition and visible phenotypic alterations, thereby linking molecular fluorescence changes to observable plant-level stress phenotypes. These findings establish QM-CO as a rapid and practical imaging platform for monitoring CO-associated responses and investigating insecticide-induced stress processes in agriculturally relevant plant tissues.