Abstract
Gold nanorods (AuNRs) have attracted a great deal of attention due to their potential for use in a wide range of biomedical applications. However, their production typically requires the use of the relatively toxic cationic surfactant cetyltrimethylammonium bromide (CTAB) leading to continued demand for protocols to detoxify them for in vivo applications. In this study, a robust and facile protocol for the displacement of CTAB from the surface of AuNRs using phospholipids is presented. After the displacement, CTAB is not detectable by NMR spectroscopy, surface-enhanced Raman spectroscopy, or using pH-dependent ζ-potential measurements. The phospholipid functionalized AuNRs demonstrated superior stability and biocompatibility (IC50 >200 µg mL-1 ) compared to both CTAB and polyelectrolyte functionalized AuNRs and are well tolerated in vivo. Furthermore, they have high near-infrared (NIR) absorbance and produce large amounts of heat under NIR illumination, hence such particles are well suited for plasmonic medical applications.
Highlights
The use of gold nanoparticles (AuNPs) in biomedical applications has grown to become one of the largest research areas absorbance peaks in the NIR, AuNRs have the highest absorbance cross-sections per unit mass of any AuNP, with an σabs typically an order of magnitude higher than that seen for Au nanoshells containing an equivalent mass of Au.[15]
This study focuses entirely on phospholipid exchange protocols, as oleate is too toxic to use for in vivo applications, having an intravenous median lethal dose (LD50) of 150 mg kg−1 in mammals.[45,46]
The cetyltrimethylammonium bromide (CTAB) – oleate coating was exchanged via resuspension in a DOPC – DSPE-mPEG (19:1) single unilamellar vesicles (SUVs) solution for 24 h under sonication, repeated threefold, resulting in a slight blueshift of the localized surface plasmon resonance (LSPR) to 801 nm with no indication of aggregation in spectrum
Summary
The use of gold nanoparticles (AuNPs) in biomedical applications has grown to become one of the largest research areas absorbance peaks in the NIR, AuNRs have the highest absorbance cross-sections (σabs) per unit mass of any AuNP, with an σabs typically an order of magnitude higher than that seen for Au nanoshells containing an equivalent mass of Au.[15]. This method has received some attention in the literature, remains relatively uncommon.[38,39,40,41,42,43,44] These techniques generally consist of dispersing a pellet of CTAB-functionalized AuNRs in a solution containing a large excess of the desired surfactant and providing energy to encourage exchange between the solution and the particle surface in the form of heat or sonication These techniques have been reported for several molecules including phospholipids[38,39,40,41,42] and oleate.[43,44] Phospholipids offer many benefits resulting from the highly tailorable properties of lipid membranes; including, low nonspecific binding, high biocompatibility, the easy conjugation of targeting ligands and fluorophores, and the inclusion of stericstabilizing agents such as PEG. It allows the incorporation of PEGylated lipids, for which 95 mol% DOPC with 5 mol% distearoylphosphatidylethanolamine-methoxypoly(ethylene glycol) (DSPE-mPEG) was used, to provide additional steric stabilization, which produced stable AuNRs.[50]
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