Spotlights Cite This: J. Phys. Chem. Lett. 2019, 10, 1152−1152
Spotlights: Volume 10, Issue 5
J. Phys. Chem. Lett. 2019.10:1152-1152. Downloaded from pubs.acs.org by 81.22.46.137 on 03/10/19. For personal use only.
■
■
A WATER SOLVATION SHELL CAN TRANSFORM GOLD METASTABLE NANOPARTICLES IN THE FLUXIONAL REGIME
THE DEVIL IS IN THE DETAILS: WHAT DO WE REALLY TRACK IN SINGLE-PARTICLE TRACKING EXPERIMENTS OF DIFFUSION IN BIOLOGICAL MEMBRANES? Despite its focus on the smallest of the small, nanoscience’s potential is enormous, with the possibility of breakthroughs in practically every field of scientific research. Super-resolution microscopy is emerging as the most promising imaging tool in molecular studies of life science systems, but a challenge remains: all super-resolution microscopy techniques use probes, and these probes perturb the very process being studied. The problem only gets larger as the size gets smaller; the smaller the scales one aims to study, the more serious the perturbations. This is a major threat in state-of-the-art superresolution microscopy techniques such as high-speed interferometric scattering (iSCAT) microscopy, whose spatial resolution is on the order of a few nanometers. In iSCAT, the molecule of interest (typically a lipid or a protein) is biotinylated, and this probe molecule is then linked to streptavidin protein that in turn is attached to a 5- to 50-nm gold nanoparticle (AuNP). Given that a AuNP is approximately 10 times larger than the probe molecule, it likely interferes with the system and with the process being measured. Gurtovenko et al. (10.1021/acs.jpclett.9b00065) tackle this problem in their Letter, using molecular simulations to reveal how AuNPs (as well as biotin and streptavidin) used in iSCAT microscopy experiments interfere with the motion of the probe particle. The authors focused on iSCAT applied to lateral diffusion in biomembranes because it governs a major fraction of all cellular processes. They found that nanoparticlebased labels have a significant influence on the dynamics of the labeled molecules: labeling lipids with streptavidin-functionalized AuNPs considerably slows down the lateral diffusion of the tracked lipids. Their findings also show that in the submicrosecond time domain the motion of the lipid probe is uncorrelated with the motion of the AuNP that is linked to the lipid probe in question, showing that, for even the smallest nanoparticles used, there is a microsecond limit for the temporal resolution of iSCAT.
When the now-disgraced entrepreneur Elizabeth Holmes dropped out of college to start a revolution in medical testing and treatment, she named her company Theranos, as a nod to theranostics. The term “theranostics” was coined about two decades ago to describe the combination of therapeutics and diagnostics, with testing and treatment occurring concomitantly. Although the concept remains more aspirational than practical, as Holmes was quick to discover, advances continue to be made that could eventually improve the lives and outcomes of patients undergoing treatment for innumerable conditions from infectious diseases to cancer to Alzheimer’s disease. In the context of radiotherapy and bionanotechnologies, tremendous experimental efforts have been devoted during the past decade to exploring the physical and chemical interfacial properties of functionalized gold nanoparticles. Nanohybrids based on gold have already exhibited enhanced performance with respect to theranostics: concomitant diagnosis and therapeutic treatment of specific cancer by photoexcitation and water radiolysis causing the death of cancerous cells. However, the reasons for the observed dose enhancement remain unknown, and the interfacial properties, active sites, and elementary mechanisms related to water radiolysis promoted by functionalized gold nanoparticles are poorly understood. Chan et al. (10.1021/acs.jpclett.8b03822) investigated the stability of these nanoparticles in the biological environment modeled by water monoshells in interaction with gold nanoclusters. They used an original theoretical approach based on density functional theory calculations of model clusters in the ranges of 0.9−3.4 nm (clean gold nanoparticles) and 0.9−1.8 nm (hydrated gold nanoparticles) and studied the interplay between various sizes and morphologies of gold nanoclusters and water shells. The authors present four key findings: (1) The clean gold nanoparticles present many competitive shapes in the considered range, in agreement with microscopic measurements. (2) The adsorption of water monomers is globally weak and varies significantly according to the size and the shape of the competitive gold nanoclusters. (3) The stability of water monoshells is poorly dependent on the gold nanocluster, and the enhanced stability per water molecule is explained by the formation of two hydrogen bonds between monomers in the shells. (4) Although the interaction between gold and water is globally weak, water monoshells may induce a transformation of metastable gold nanoclusters in vacuum into more stable morphologies. The results advance our understanding of the stability of the active sites in the context of radiotherapy with gold nanoparticles, which could lead to advances in the widespread use of theranostics in the field. © 2019 American Chemical Society
pubs.acs.org/JPCL
Published: March 7, 2019 1152
DOI: 10.1021/acs.jpclett.9b00565 J. Phys. Chem. Lett. 2019, 10, 1152−1152
