Near-Infrared Fluorescent Probe for High-Fidelity and On-Site Quantitative Detection of Lipid Droplets in Food Crops

Lipid droplets (LDs) play pivotal roles in crop physiology, stress adaptation, and product quality by serving as dynamic reservoirs of energy and essential nutrients. However, the lack of rapid and accurate methods for on-site quantitative detection of LDs has hindered their comprehensive analysis in agricultural systems. Herein, we report the rational design and synthesis of three near-infrared (NIR) fluorescent probes, YD-1, YD-2, and YD-3, for the sensitive and specific detection of LDs in crops. These probes feature a hydrophobic donor–π–acceptor (D-π-A) framework comprising a 7-diethylaminoquinoline electron donor and distinct electron-accepting groups, including (5,5-dimethylcyclohex-2-en-1-ylidene)malononitrile (DCM), 4-fluorophenyl, and phenyl moieties. Among them, YD-1 exhibited the most pronounced fluorescence response to LDs, displaying intense NIR emission within LDs and remarkable quenching in non-LD regions, enabling high-fidelity LD imaging. TD-DFT calculations revealed that the superior sensitivity of YD-1 originates from its efficient intramolecular charge transfer (ICT) process, which is highly responsive to the polarity differences between LDs and their surroundings. YD-1 was successfully applied to monitor LDs dynamics in living cells, zebrafish under a high-fat diet, and soybeans at different growth stages. Furthermore, a custom-built mobile fluorescence analysis device was developed and coupled to probe YD-1 to achieve rapid, on-site quantitative detection of LDs in crop samples. This work provides a powerful analytical platform for on-site monitoring of LDs dynamics, offering insights into crop lipid metabolism and quality control.