Membrane Surface-Enhanced Raman Spectroscopy for Cholesterol-Modified Lipid Systems: Effect of Gold Nanoparticle Size

Abstract

A gold nanoparticle (AuNP) has a localized surface plasmon resonance peak depending on its size, which is often utilized for surface-enhanced Raman scattering (SERS). To obtain information on the cholesterol (Chol)-incorporated lipid membranes by SERS, AuNPs (5, 100 nm) were first functionalized by 1-octanethiol and then modified by lipids (AuNP@lipid). In membrane surface-enhanced Raman spectroscopy (MSERS), both signals from 1,2-dioleoyl- sn -glycero-3-phosphocholine (DOPC) and Chol molecules were enhanced, depending on preparation conditions (size of AuNPs and lipid/AuNP ratio). The enhancement factors (EFs) were calculated to estimate the efficiency of AuNPs on Raman enhancement. The size of AuNP 100nm @lipid was 152.0 ± 12.8 nm, which showed an surface enhancement Raman spectrum with an EF 2850 value of 111 ± 9. The size of AuNP 5nm @lipid prepared with a lipid/AuNP ratio of 1.38 × 10 4 (lipid molecule/particle) was 275.3 ± 20.2 nm, which showed the highest enhancement with an EF 2850 value of 131 ± 21. On the basis of fluorescent probe analyses, the membrane fluidity and polarity of AuNP@lipid were almost similar to DOPC/Chol liposome, indicating an intact membrane of DOPC/Chol after modification with AuNPs. Finally, the membrane properties of AuNP@lipid systems were also discussed on the basis of the obtained MSERS signals.

Spectroscopy of model-membrane liposome-protein systems: complementarity of linear dichroism, circular dichroism, fluorescence and SERS

“…Small particles influenced the lipid fluidity and polarity of the membranes by weakening hydrophobic interactions between lipids' molecules. However, overall the effect was not significant and it was concluded that embedding of the particles into the lipid bilayer does not disturb the membrane properties, which is also supported by their previous observation for DOPC/CH liposomes [82].…”

“…However, the descriptor, e.g. 'gold nanoparticle' is misleading as the metallic centre invariably has another ion, such as citrate, or, any other purpose-specific functionalisation [82] on the surface of the metal core. The surface-functionalisation [83] as well as particle size [84] and shape [85] influence the membrane-particle interaction and should be considered.…”

Detection of Hypertension-Induced Changes in Erythrocytes by SERS Nanosensors

“…Increasing cholesterol leads to a decrease in membrane fluidity [ 42 , 43 ] and changes in the erythrocyte function [ 44 ]. The SERS ratio I 2872 /I 2927 was proposed as a marker of cholesterol amount by Faried et al [ 45 ]. Thus, an increase in this ratio, indicating an increase in the membrane stiffness, may be explained by an increased amount of cholesterol in the erythrocyte plasma membrane.…”

Surface enhanced Raman scattering for probing cellular biochemistry

“… 113 When the gold nanoparticles are small enough to fit the intralamellar space of liposomes, an octanethiol functionalization can direct them there, and they selectively enhance signals due to vibrations of the acyl chains. 112 Cetyltrimethylammonium bromide (CTAB), a typical surfactant used in the synthesis of gold nanorods, can be displaced from the nanostructures’ surface by lipids, and a lipid bilayer can form around such particles without the need of further functionalization. 114 SERS spectra reveal the dynamics of these membrane structures and indicate that lipid exchange occurs between the bilayer around the nanoparticles and vesicles contained in the same solution.…”