SERS imaging for label-free detection of the phospholipids distribution in hybrid lipid membrane

Abstract

A label-free and low-cost mapping method based on SERS imaging was reported for illustrating the distribution of phospholipids with similar structures in binary lipid membranes on Ag nanoparticles (Ag NPs) films. The Ag NPs films exhibited strong SERS activity and good reproducibility which were investigated with p-aminothiophenol (p-ATP) as probe molecules. Atomic force microscope (AFM) measurement proved that compact lipid membranes formed on the Ag NPs films. Basing on the Ag NPs films, the SERS spectra of phospholipids in the mixed lipid membranes were achieved and the inherent vibration of 1,2-dimyristoyl-sn-lycero-3-phosphoglycerol, sodium salt (DMPG), 1482 cm−1, was used to distinguish between DMPG and dimyristoylphosphatidylcholine (DMPC). The proportions of phospholipids in the mixed lipid membranes were represented by the intensity ratio of peaks at 1482 cm−1 and 1650 cm−1 (R 1482/1650) simultaneously: increasing R 1482/1650 indicated higher proportion of DMPG and lower proportion of DMPC. SERS imaging of the lipid membranes was constructed as a combination of spacial information and the semiquantitative detection of phospholipids according to R 1482/1650, which showed that the charged phospholipids, DMPG, aggregated in the hybrid lipid membranes. The presented mapping strategy based on SERS imaging carried out on Ag NPs films supplied a facile, label-free and inexpensive way for potential applications in the research on the structure of the lipid membrane, such as lipid domains and rafts.