Analysis of Nanostar Reshaping Kinetics for Optimal Substrate Fabrication

Gold nanostars (NS) are emerging as a versatile tool in surface-enhanced Raman scattering (SERS) applications because of their wide localized surface plasmon resonance (LSPR) tunability, simple synthesis procedure, and high SERS enhancement. These particles are commonly used in solutions with a stabilizing coating shell (e.g., thiolated molecules or silver shell). However, coatings cannot be used for the fabrication of SERS substrates as the NS have to interact with the substrate planar surface. Without coating, NS have been observed to change over time, leading to a hypochromic shift of the LSPR. To understand this shift, we synthesized surfactant-free gold NS with different spike morphologies and investigated their reshaping morphology and kinetics. Using TEM, the NS sharp spike features were observed to reshape over time. The kinetics of this process were analyzed and determined by monitoring the LSPR, which was observed to follow an exponential decay over time. We used an empirical fit for the LSPR-shift data as a function of time, which permits to predict the LSPR at a specific time based only on the initial LSPR (independently of the initial spike morphology). We show the effect of the LSPR on the SERS signal for the NS and how the SERS signal correlated to our prediction. Finally, we evaluated our approach by fabricating SERS substrates with immobilized NS and collecting the reflectance spectra. We were able to predict the substrate LSPR and aim for an optimal LSPR with an average 3% deviation. These new insights on NS reshaping can permit the fabrication of NS-based substrates with desirable optical/plasmonic properties.

Protein corona modulates interaction of spiky nanoparticles with lipid bilayers

The impact of protein corona on the interactions of nanoparticles (NPs) with cells remains an open question. This question is particularly relevant to NPs which sizes, ranging from tens to hundreds nanometers, are comparable to the sizes of most abundant proteins in plasma. Protein sizes match with typical thickness of various coatings and ligands layers, usually present at the surfaces of larger NPs. Such size match may affect the properties and the designed function of NPs. We offer a direct demonstration of how protein corona can dramatically change the interaction mode between NPs and lipid bilayers. To this end, we choose the most extreme case of NP surface modification: nanostructures in the form of rigid spikes of 10-20 nm length at the surface of gold nanoparticles. In the absence of proteins we observe the formation of reversible pores when spiky NPs adsorb on lipid bilayers. In contrast, the presence of bovine serum albumin (BSA) proteins adsorbed at the surface of spiked NPs, effectively reduces the length of spikes exposed to the interaction with lipid bilayers. Thus, protein corona changes qualitatively the dynamics of pore formation, which is completely suppressed at high protein concentrations. These results suggest that protein corona can not only be critical for interaction of NPs with membranes, it may change their mode of interaction, thus offsetting the role of surface chemistry and ligands.

Shape-dependent cytotoxicity and cellular uptake of gold nanoparticles synthesized using green tea extract

In the present report, three different shapes of chitosan-capped gold nanoparticles (nanospheres, nanostars, and nanorods) were synthesized to investigate the effects of shape on cytotoxicity and cellular uptake in cancer cells. Green tea extract was utilized as a reducing agent to reduce gold salts to gold nanospheres. Gold nanostars were prepared using an as-prepared nanosphere solution as a seed solution. Gold nanorods were synthesized using a conventional method. All three types of gold nanoparticles showed their characteristic surface plasmon resonance bands upon UV-visible spectrophotometry. In high-resolution transmission electron microscopy images, lattice structures were clearly observed in all three shapes, confirming the crystalline nature of the nanoparticles. All three colloidal solutions of gold nanoparticles retained colloidal stability in various solutions. To assess cytotoxicity, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was performed on four cancer cell lines. The cytotoxicity was the highest in nanorods, followed by nanostars and finally nanospheres. The cellular uptake of gold nanoparticles in human hepatocyte carcinoma cells (HepG2) was measured, and the results followed the order nanospheres > nanorods > nanostars. The outcomes of the current study may assist in the shape design of gold nanoparticles for therapeutic applications as drug delivery vehicles in the field of nanomedicine.

TMV Particles: The Journey From Fundamental Studies to Bionanotechnology Applications

Ever since its initial characterization in the 19th century, tobacco mosaic virus (TMV) has played a prominent role in the development of modern virology and molecular biology. In particular, research on the three-dimensional structure of the virus particles and the mechanism by which these assemble from their constituent protein and RNA components has made TMV a paradigm for our current view of the morphogenesis of self-assembling structures, including viral particles. More recently, this knowledge has been applied to the development of novel reagents and structures for applications in biomedicine and bionanotechnology. In this article, we review how fundamental science has led to TMV being at the vanguard of these new technologies.

Synthesis of reduced-size gold nanostars and internalization in SH-SY5Y cells

The synthesis of large pentatwinned five-branched gold nanostars (GNS) has been modified so to obtain overall dimensions shrunk to 60% and a lower branches aspect ratio, leading to a dramatic blue shift of their two near-infrared (NIR) localized surface plasmon resonances (LSPR) absorptions but still maintaining one LSPR in the biotransparent NIR range. The interactions of polyethylene glycol (PEG) coated large and shrunk GNS with SH-SY5Y cells revealed that the large ones (DCI - diameter of the circumference in which GNS can be inscribed=76nm) are internalized more efficiently than the shrunk ones (DCI=46nm), correlating with a decreased cells surviving fraction.

Gold Nanostars For Surface-Enhanced Raman Scattering: Synthesis, Characterization and Optimization

The controlled synthesis of high-yield gold nanostars of varying sizes, their characterization and use in surface-enhanced Raman scattering (SERS) measurements are reported for the first time. Gold nanostars ranging from 45 to 116-nm in size were synthesized in high-yield, physically modeled and optically characterized using transmission and scanning electron microscopy and UV-Visible absorption spectroscopy. The nanostar characterization involved both studying morphology evolution over time and size as a function of nucleation. The nanostars properties as substrates for SERS were investigated and compared with respect to size. As the overall star size increases, so does the core size, the number of branches and branch aspect ratio; the number of branch tips per star surface area decreases with increasing size. The stars become more inhomogeneous in shape, although their yield is high and overall size remains homogeneous. Variations in star size are also accompanied by shifts of the long plasmon band in the NIR region, which hints towards tuning capabilities that may be exploited in specific SERS applications. The measured SERS enhancement factors suggest an interesting correlation between nanostar size and SERS efficiencies, and were relatively consistent across different star samples, with the enhancement factor estimated as 5×103 averaged over the 52-nm nanostars for 633-nm excitation.