Direct Investigation of Intracellular Presence of Gold Nanoparticles via Photothermal Heterodyne Imaging

Abstract

Nanotechnology as well as advanced microscopy can play a fundamental role in understanding biological mechanisms. Here we present a study that combines a new type of nanomaterial with a new type of microscopy and highlights the potential for gathering novel information about cell membrane penetration and cytosol local viscosity. On the material side, we used gold nanoparticles that have an ordered stripe-like arrangement of domains. These "striped" nanoparticles are able to penetrate cell membranes directly without porating them. On the microscopy side, we used photothermal heterodyne imaging which allows detection of individual nanometer-sized gold particles in complex media. We showed that we can probe cytosolic presence as well as dynamics of these nanoparticles even at very low concentrations. We used the fluctuations of the photothermal signal from particles diffusing in the detection volume to estimate local cytosol viscosity which is about 20 times larger than that of water. This work opens new perspectives for mapping local diffusion properties of nano-objects inside living cells.

Dynamic Cellular Uptake of Mixed-Monolayer Protected Nanoparticles

“…After particle decomposition (see Supplementary Information), we calculate that less than 10% of the total ligands presented on the NP surface are place-exchanged by dye molecules, and therefore assume that their presence does not significantly affect the surface structure. We have also previously shown that the presence of the fluorophore does not affect the penetration properties of our NPs, by comparing penetration results with and without fluorophores determined via TEM [20] or photothermal heterodyne imaging [26], techniques that do not necessitate the use of fluorophores for quantification.…”

“…We concluded that the structural organization of the ligand shell regulated cell-membrane penetration, and that active endocytotic or pinocytotic pathways were not required for the NPs to reach the cytosol of the cells [20]. These results were confirmed by intracellular photothermal heterodyne imaging of the same type of NPs [26]. Additionally recently we have shown that cell membrane penetrating particles can be used to cargo genetic materials in B16-F0 melanoma cells [27].…”

“…Also only limited time points were studied, and the core of the experiments was based on either 4 h [27], 3 h [20], or 1 h [20,26] incubation times. To better establish the time evolution of NP uptake and to quantitatively compare between particle compositions and cell type, we have conducted here a set of systematic NP internalization experiments.…”

Photothermal Microscopy for High Sensitivity and High Resolution Absorption Contrast Imaging of Biological Tissues

“…It has been applied to visualize the distribution of endogenous chromoproteins in biological specimens such as cytochromes in mitochondria [1][2][3][4], hemoglobin in red blood cells in blood vessels [5,6], and melanin pigments in skin cancer [7]. Furthermore, gold nanoparticles have been used to identify biomolecules in antibody labelling techniques applied in cellular imaging [8][9][10][11][12]. As gold nanoparticles are physiologically inert and do not suffer from photobleaching, they are highly useful in live cell imaging.…”

Direct visualization of carbon nanotube degradation in primary cells by photothermal imaging

“…These include gold nanoparticles, even within a cell matrix and for membrane receptor dynamics studies in live cells, 18,19 molecules, quantum dots or single walled carbon nanotubes. [19][20][21][22][23][24][25] Interestingly, PhI signal intensities can be correlated to the dimension 26 and concentration 27 of the nanoparticles under investigation, while quantitative optical imaging of individual nanotubes down to ~10 nm in length was possible. 28 In addition, PhI is totally unaffected by non-absorbing scatterers, even when large objects with strong refractive index contrast are present within the surroundings of the imaged nanoparticles, as it is often the case in biological samples.…”