Quantum dot cluster (QDC)-loaded phospholipid micelles as a FRET probe for phospholipase A₂ detection

A simple assay for phospholipase A₂ (PLA₂) enzyme was developed based on a fluorescence resonance energy transfer (FRET) probe using the quantum dot cluster (QDC)-loaded phospholipid micelles. The probe was prepared by encapsulating many small hydrophobic quantum dots (QDs) within the hydrophobic core of micelles that were formed from the coassembly of hydrogenated soy phosphatidylcholine phospholipids (HSPC) and fluorescent lipids (NBD-PC). QDCs formed within the micelle core served as the substrate for NBD fluorescence quenching through FRET. The QDC-loaded micelles showed very low background fluorescence. As the PLA₂ enzyme selectively digested lipids, the NBD fluorescence was recovered from its quenched state, leading to the sensitive detection of PLA₂. This assay provided a limit of detection (at a signal-to-noise ratio of 3) of 3 U/L for PLA₂. In the presence of a PLA₂ inhibitor, the fluorescent response of the sensor for PLA₂ decreased, indicating that the assay could also be used for screening the PLA₂ inhibitors.