Gold/phospholipid nanoconstructs as label-free optical probes for evaluating phospholipase A2 activity

A facile, monophasic strategy, involving a cooperative solvent, dimethylformamide (DMF), to synthesize core/shell architectured gold-phospholipid hybrid nanoconstructs (PLGNPs) was presented herein. We employed the as-synthesized PLGNPs as enzymatic substrates and detecting probes, leading to the development of a novel, lag time-free quantitative assay to evaluate the activity of Ca(2+)-dependent phospholipase A2 (PLA2), an inflammatory protein that (i) plays a role in the pathogenesis of many inflammatory diseases, (ii) is a mediator in atherosclerosis and ischemic damage to cardiomyocytes, and (iii) has been implicated in the cause of neurodegenerative diseases. Our new bioassay exhibited high specificity, improved speed (assay time:≤ 20 min), acceptable sensitivity, and a limit of detection (1.82 nM, equivalent to 0.04 unit/mL and 260 ng/dL) below the cut-off value of circulating PLA2 (2.07 nM, equivalent to 290 ng/dL) present in serum samples collected from healthy testers. We characterized the as-obtained PLGNPs using UV-vis spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering (DLS). These PLGNPs were considerably robust and biocompatible-displaying extraordinary stability against salt-induced aggregation, oxidant etching, and repetitive freeze/thaw treatment-because of the presence of their modifying interfacial thiol (1-dodecanethiol) and phospholipid [1,2-dihexadecanoyl-sn-glycero-3-phosphocholine, 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol)] units.