On Electronic and Charge Interference in Second Harmonic Generation Responses from Gold Metal Nanoparticles at Supported Lipid Bilayers

Abstract

Second harmonic generation (SHG) is useful for studying the properties of interfaces, including the surfaces of nanoparticles and the interaction of nanoparticles with biologically relevant surfaces. Gold nanoparticles at the biological membrane represent a particularly interesting system to be probed by SHG spectroscopy given the rich electronic structure of gold nanoparticles and the charged nature of the nano-bio interface. Here we describe the interplay between the resonant and nonresonant components of the second harmonic response as 4 and 14 nm spherical gold nanoparticles (AuNPs) wrapped in the cationic polyelectrolyte poly­(allylamine hydrochloride) (PAH) adsorb to negatively charged supported lipid bilayers. In contrast to the SHG response of 4 nm PAH-AuNPs, that we have shown previously to be dominated by resonance enhancement, the SHG response from the adsorption of the 14 nm PAH-AuNPs, with similar hydrodynamic diameters, to a 9:1 DOPC:DOTAP bilayer is dominated by the nonresonant, interfacial, potential-dependent component of the signal. We hypothesize that the difference in the SHG response is attributable to the differences in the number of PAH molecules associated with the particles and, therefore, differences in the number of positively charged ammonium groups associated with the 4 vs the 14 nm particles. For 14 nm PAH-AuNPs with larger hydrodynamic diameters, we determined two regimes in the adsorption behavior, one where the resonance enhancement from the gold core of the nanoparticle dominates the signal and a second where the nonresonant, interfacial, potential-dependent term dominates the signal. The results presented in this study provide insight into the interplay between resonant and nonresonant components of the second harmonic signal from the adsorption of charged AuNPs and are valuable for future studies with other functionalized particles and lipid systems by SHG.

Lipid Corona Formation from Nanoparticle Interactions with Bilayers

“…This outcome is consistent with result reported for supported lipid bilayers formed from pure 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) 33 as well as pure 1-palmitoyl-2-oleoylsn-glycero-3-phosphocholine (POPC) 34 exposed to MPA-functionalized AuNPs. Yet the SHG measurements provided evidence for the presence of some particles, 39 albeit presumably at much smaller surface coverage than what is observed for the cationic particles. We conclude that the 4-nm-sized anionic particles interact weakly, if at all, with the bilayers studied under these experimental conditions.…”

Lipid Corona Formation from Nanoparticle Interactions with Bilayers and Membrane-Specific Biological Outcomes

“…The propensity of biological species to form coronas around nanoparticles [1][2][3][4] has been used for preparing engineered nanomaterials that can be distributed in biological systems with some control [5][6][7][8][9][10] . While protein coronas in particular have been studied extensively [1][2][3]5,6 , our understanding of lipid coronas is now just beginning to emerge 11,12 , especially of those formed upon unintended nanoparticle contacts with living cells. The protein and lipid corona formation mechanisms appear to differ substantially, as "hard" and "soft" coronas 13 , typical for the former, have not been described for the latter 3 .…”

“…Microsecond-long simulations show significant bilayer bending upon nanoparticle attachment (see Supplementary Note V and Supplementary Fig. [10][11][12][13]. Given that potential of mean force calculations show lipid extraction by PAH models to be associated with a significant free energy penalty (see Supplementary Fig.…”

Polylysine as a functional biopolymer to couple gold nanorods to tumor-tropic cells

“…Here, we address the modification of gold nanorods for their efficient and harmless coupling to tumor-tropic cells, which should retain their tumor-homing and pro-inflammatory profiles, in order to serve as a biological taxi. A robust strategy to promote the cellular uptake of these particles combines their termination with biopolymers that provide for steric stabilization, such as polyethylene glycol (PEG) [ 44 , 45 ], and cationic moieties [ 29 , 34 , 35 , 46 ] that are prone to interact with the anionic phospholipids on plasmatic membranes [ 47 – 49 ] and/or to induce receptor-mediated endocytic and phagocytic pathways [ 50 , 51 ]. In our recent work, we have disclosed a modification of gold nanorods with PEG and mercaptoundecyl trimethyl ammonium bromide (MUTAB) that provides high efficiency and reproducibility of phagocytosis from tumor-tropic macrophages [ 28 , 29 ].…”