Increased stability of mercapto alkane functionalized Au nanoparticles towards DNA sensing

A universal polymer shell-isolated nanoparticle (SHIN) design for single particle spectro-electrochemical SERS sensing using different core shapes

Shell-isolated nanoparticles (SHINs) have attracted increasing interest for non-interfering plasmonic enhanced sensing in fields such as materials science, biosensing, and in various electrochemical systems. The metallic core of these nanoparticles is isolated from the surrounding environment preventing direct contact or chemical interaction with the metal surface, while still being close enough to enable localized surface plasmon enhancement of the Raman scattering signal from the analyte. This concept forms the basis of the shell isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) technique. To date, the vast majority of SHIN designs have focused on SiO₂ shells around spherical nanoparticle cores and there has been very limited published research considering alternatives. In this article, we introduce a new polymer-based approach which provides excellent control over the layer thickness and can be applied to plasmonic metal nanoparticles of various shapes and sizes without compromising the overall nanoparticle morphology. The SHIN layers are shown to exhibit excellent passivation properties and robustness in the case of gold nanosphere (AuNP) and anisotropic gold nanostar (AuNS) core shapes. In addition, in situ SHINERS spectro-electrochemistry measurements performed on both SHIN and bare Au nanoparticles demonstrate the utility of the SHIN coatings. Correlated confocal Raman and SEM mapping was achieved to clearly establish single nanoparticle SERS sensitivity. Finally, confocal in situ SERS mapping enabled visualisation of the redox related molecular structure changes occurring on an electrode surface in the vicinity of individual SHIN-coated nanoparticles.

Gold Nanoparticle Size and Shape Effects on Cellular Uptake and Intracellular Distribution of siRNA Nanoconstructs

Gold nanoparticles (AuNPs) show potential for transfecting target cells with small interfering RNA (siRNA), but the influence of key design parameters such as the size and shape of the particle core is incomplete. This paper describes a side-by-side comparison of the in vitro response of U87 glioblastoma cells to different formulations of siRNA-conjugated gold nanoconstructs targeting the expression of isocitrate dehydrogenase 1 (IDH1) based on 13 nm spheres, 50 nm spheres, and 40 nm stars. 50 nm spheres and 40 nm stars showed much higher uptake efficiency compared to 13 nm spheres. Confocal fluorescence microscopy showed that all three formulations were localized in the endosomes at early incubation times (2 h), but after 24 h, 50 nm spheres and 40 nm stars were neither in endosomes nor in lysosomes while 13 nm spheres remained in endosomes. Transmission electron microscopy images revealed that the 13 nm spheres were enclosed and dispersed within endocytic vesicles while 50 nm spheres and 40 nm stars were aggregated, and some of these NPs were outside of endocytic vesicles. In our comparison of nanoconstructs with different sizes and shapes, while holding siRNA surface density and nanoparticle concentration constant, we found that larger particles (50 nm spheres and 40 nm stars) showed higher potential as carriers for the delivery of siRNA.

Limiting the protein corona: A successful strategy for in vivo active targeting of anti-HER2 nanobody-functionalized nanostars

Gold nanoparticles hold great promise as anti-cancer theranostic agents against cancer by actively targeting the tumor cells. As this potential has been supported numerously during in vitro experiments, the effective application is hampered by our limited understanding and control of the interactions within complex in vivo biological systems. When these nanoparticles are exposed to a biological environment, their surfaces become covered with proteins and biomolecules, referred to as the protein corona, reducing the active targeting capabilities. We demonstrate a chemical strategy to overcome this issue by reducing the protein corona's thickness by blocking the active groups of the self-assembled monolayer on gold nanostars. An optimal blocking agent, 2-mercapto ethanol, has been selected based on charge and length of the carbon chain. By using a nanobody as a biological ligand of the human epidermal growth factor 2 receptor (HER2), the active targeting is demonstrated in vitro and in vivo in an experimental tumor model by using darkfield microscopy and photoacoustic imaging. In this study, we have established gold nanostars as a conceivable theranostic agent with a specificity for HER2-positive tumors.

Development of nanostars as a biocompatible tumor contrast agent: toward in vivo SERS imaging

The need for sensitive imaging techniques to detect tumor cells is an important issue in cancer diagnosis and therapy. Surface-enhanced Raman scattering (SERS), realized by chemisorption of compounds suitable for Raman spectroscopy onto gold nanoparticles, is a new method for detecting a tumor. As a proof of concept, we studied the use of biocompatible gold nanostars as sensitive SERS contrast agents targeting an ovarian cancer cell line (SKOV3). Due to a high intracellular uptake of gold nanostars after 6 hours of exposure, they could be detected and located with SERS. Using these nanostars for passive targeting after systemic injection in a xenograft mouse model, a detectable signal was measured in the tumor and liver in vivo. These signals were confirmed by ex vivo SERS measurements and darkfield microscopy. In this study, we established SERS nanostars as a highly sensitive contrast agent for tumor detection, which opens the potential for their use as a theranostic agent against cancer.

Role of gold nanoparticles capping density on stability and surface reactivity to design drug delivery platforms

Five-nanometer sized gold nanoparticles (Au NPs) stabilized with citrate ions have been reacted with various amounts of dihydrolipoic acid (DHLA) (×28, ×56, ×140, ×222, relative to Au NPs). Ligand exchange between citrate and the dithiol resulted in DHLA-capped Au NPs, whose degree of inertia was found to be related to the density of capping. The results revealed the importance of DHLA coating density to enhance the colloidal stability and modulate the reactivity toward free radicals and proteins of biological relevance. Thus, Au NPs capped with the highest amount of DHLA were found to be the ones that were, first, the most resistant to environmental changes, then characterized by the lowest residual catalytic reactivity of their metallic core, and finally the lowest interacting with proteins through nonspecific adsorption. The physicochemical properties conferred to Au NPs prepared with the ×222 excess should be valuable for further pharmaceutical development of nanoparticle platforms.

Shape-controlled synthesis of NIR absorbing branched gold nanoparticles and morphology stabilization with alkanethiols

Gold nanoparticles are ideal candidates for clinical applications if their plasmon absorption band is situated in the near infrared region (NIR) of the electromagnetic spectrum. Various parameters, including the nanoparticle shape, strongly influence the position of this absorption band. The aim of this study is to produce stabilized NIR absorbing branched gold nanoparticles with potential for biomedical applications. Hereto, the synthesis procedure for branched gold nanoparticles is optimized varying the different synthesis parameters. By subsequent electroless gold plating the plasmon absorption band is shifted to 747.2 nm. The intrinsic unstable nature of the nanoparticles' morphology can be clearly observed by a spectral shift and limits their use in real applications. However, in this article we show how the stabilization of the branched structure can be successfully achieved by exchanging the initial capping agent for different alkanethiols and disulfides. Furthermore, when using alkanethiols/disulfides with poly(ethylene oxide) units incorporated, an increased stability of the gold nanoparticles is achieved in high salt concentrations up to 1 M and in a cell culture medium. These achievements open a plethora of opportunities for these stabilized branched gold nanoparticles in nanomedicine.