Role of Common Cell Culture Media Supplements on Citrate-Stabilized Gold Nanoparticle Protein Corona Formation, Aggregation State, and the Consequent Impact on Cellular Uptake.

Sodium citrate-stabilized gold nanoparticles (AuNPs) are destabilized when dispersed in cell culture media (CCMs). This may promote their aggregation and subsequent sedimentation, or under the proper conditions, their interaction with dispersed proteins can lead to the formation of a NP-stabilizing protein corona. CCMs are ionic solutions that contain growth substances which are typically supplemented, in addition to serum, with different substances such as dyes, antioxidants, and antibiotics. In this study, the impact of phenol red, penicillin-streptomycin, l-glutamine, and ß-mercaptoethanol on the formation of the NP-protein corona in CCMs was investigated. Similar protein coronas were obtained except in the presence of antibiotics. Under these conditions, the protein corona took more time to be formed, and its density and composition were altered, as indicated by UV-vis spectroscopy, Z potential, dynamic light scattering, and liquid chromatography-mass spectrometry analyses. As a consequence of these modifications, a significantly different AuNP cellular uptake was measured, showing that NP uptake increased as did the NP aggregate formation. AuNP uptake studies performed in the presence of clathrin- and caveolin-mediated endocytosis inhibitors showed that neither clathrin receptors nor lipid rafts were significantly involved in the internalization mechanism. These results suggest that in these conditions, NP aggregation is the main mechanism responsible for their cellular uptake.

Sculpting Windows onto AuAg Hollow Cubic Nanocrystals.

Using surfactants in the galvanic replacement reaction (GRR) offers a versatile approach to modulating hollow metal nanocrystal (NC) morphology and composition. Among the various surfactants available, quaternary ammonium cationic surfactants are commonly utilised. However, understanding how they precisely influence morphological features, such as the size and void distribution, is still limited. In this study, we aim to uncover how adding different surfactants-CTAB, CTAC, CTApTS, and PVP-can fine-tune the morphological characteristics of AuAg hollow NCs synthesised via GRR at room temperature. Our findings reveal that the halide counterion in the surfactant significantly controls void formation within the hollow structure. When halogenated surfactants, such as CTAB or CTAC, are employed, multichambered opened nanoboxes are formed. In contrast, with non-halogenated CTApTS, single-walled closed nanoboxes with irregularly thick walls form. Furthermore, when PVP, a polymer surfactant, is utilised, changes in concentration lead to the production of well-defined single-walled closed nanoboxes. These observations highlight the role of surfactants in tailoring the morphology of hollow NCs synthesised through GRR.

Asymmetrical Plasmon Distribution in Hybrid AuAg Hollow/Solid Coded Nanotubes.

Morphological control at the nanoscale paves the way to fabricate nanostructures with desired plasmonic properties. In this study, we discuss the nanoengineering of plasmon resonances in 1D hollow nanostructures of two different AuAg nanotubes, including completely hollow nanotubes and hybrid nanotubes with solid Ag and hollow AuAg segments. Spatially resolved plasmon mapping by electron energy loss spectroscopy (EELS) revealed the presence of high order resonator-like modes and localized surface plasmon resonance (LSPR) modes in both nanotubes. The experimental findings accurately correlated with the boundary element method (BEM) simulations. Both experiments and simulations revealed that the plasmon resonances are intensely present inside the nanotubes due to plasmon hybridization. Based on the experimental and simulated results, we show that the novel hybrid AuAg nanotubes possess two significant coexisting features: (i) LSPRs are distinctively generated from the hollow and solid parts of the hybrid AuAg nanotube, which creates a way to control a broad range of plasmon resonances with one single nanostructure, and (ii) the periodicity of the high-order modes are disrupted due to the plasmon hybridization by the interaction of solid and hollow parts, resulting in an asymmetrical plasmon distribution in 1D nanostructures. The asymmetry could be modulated/engineered to control the coded plasmonic nanotubes.

Tailoring of the photocatalytic activity of CeO2 nanoparticles by the presence of plasmonic Ag nanoparticles.

The present study investigates basic features of a photoelectrochemical system based on CeO2 nanoparticles fixed on gold electrodes. Since photocurrent generation is limited to the absorption range of the CeO2 in the UV range, the combination with metal nanoparticles has been studied. It can be shown that the combination of silver nanoparticles with the CeO2 can shift the excitation range into the visible light wavelength range. Here a close contact between both components has been found to be essential and thus, hybrid CeO2@Ag nanoparticles have been prepared and analyzed. We have collected arguments that electron transfer occurs between both compositional elements of the hybrid nanoparticles.The photocurrent generation can be rationalized on the basis of an energy diagram underlying the necessity of surface plasmon excitation in the metal nanoparticles, which is also supported by wavelength-dependent photocurrent measurements. However, electrochemical reactions seem to occur at the CeO2 surface and consequently, the catalytic properties of this material can be exploited as exemplified with the photoelectrochemical reduction of hydrogen peroxide. It can be further demonstrated that the layer-by layer technique can be exploited to create a multilayer system on top of a gold electrode which allows the adjustment of the sensitivity of the photoelectrochemical system. Thus, with a 5-layer electrode with hybrid CeO2@Ag nanoparticles submicromolar hydrogen peroxide concentrations can be detected.

Introducing visible-light sensitivity into photocatalytic CeO2 nanoparticles by hybrid particle preparation exploiting plasmonic properties of gold: enhanced photoelectrocatalysis exemplified for hydrogen peroxide sensing.

In this report we combine the catalytic properties of CeO2 nanoparticles with their transduction ability for photoelectrochemical sensing. This study highlights the usage of CeO2 providing catalytic activity towards H2O2, but only with a limited excitation range in the UV for the construction of a sensing system. In order to improve the photoelectrocatalysis of CeO2 nanoparticles by extending their excitation to visible light, Au/CeO2 core/shell hybrid nanoparticles have been synthesized. The hybrid nanoparticles are fixed on electrodes, allowing for the generation of photocurrents, the direction of which can be controlled by the electrode potential (without bias). The application of the hybrid nanoparticles results in an enhanced photocurrent amplitude under white light illumination as compared to the pure CeO2 nanoparticles. Wavelength-dependent measurements confirm the participation of the Au core in the signal transduction. This can be explained by improved charge carrier generation within the hybrid particles. Thus, by using a plasmonic element the photoelectochemical response of a catalytic nanoparticle (i.e. CeO2) has been spectrally extended. The effect can be exploited for sensorial hydrogen peroxide detection. Here higher photocatalytic current responses have been found for the hybrid particles fixed to gold electrodes although the catalytic reduction has been comparable for both types of nanoparticles. Thus, it can be demonstrated that Au/CeO2 core-shell nanoparticles allow the utilization of visible light for photoelectrochemical hydrogen peroxide (H2O2) detection with improved sensitivity under white light illumination or application of such particles with only visible light excitation, which is not possible for pure CeO2. With help of the layer-by-layer (LbL) technique for nanoparticle immobilization, the electrode response can be adjusted and with a 5 layers electrode a low detection limit of about 3 µM H2O2 with a linear detection range up to 2000 µM is obtained.

Writing chemical patterns using electrospun fibers as nanoscale inkpots for directed assembly of colloidal nanocrystals.

Applications that range from electronics to biotechnology will greatly benefit from low-cost, scalable and multiplex fabrication of spatially defined arrays of colloidal inorganic nanocrystals. In this work, we present a novel additive patterning approach based on the use of electrospun nanofibers (NFs) as inkpots for end-functional polymers. The localized grafting of end-functional polymers from spatially defined nanofibers results in covalently bound chemical patterns. The main factors that determine the width of the nanopatterns are the diameter of the NF and the extent of spreading during the thermal annealing process. Lowering the surface energy of the substrates via silanization and a proper choice of the grafting conditions enable the fabrication of nanoscale patterns over centimeter length scales. The fabricated patterns of end-grafted polymers serve as the templates for spatially defined assembly of colloidal metal and metal oxide nanocrystals of varying sizes (15 to 100 nm), shapes (spherical, cube, rod), and compositions (Au, Ag, Pt, TiO2), as well as semiconductor quantum dots, including the assembly of semiconductor nanoplatelets.

Hollow PdAg-CeO2 heterodimer nanocrystals as highly structured heterogeneous catalysts.

In the present work, hollow PdAg-CeO2 heterodimer nanocrystals (NCs) were prepared and tested as catalysts for the selective hydrogenation of alkynes. These nanostructures combine for the first time the beneficial effect of alloying Pd with Ag in a single NC hollow domain with the formation of active sites at the interface with the CeO2 counterpart in an additive manner. The PdAg-CeO2 NCs display excellent alkene selectivity for aliphatic alkynes. For the specific case of hydrogenation of internal alkynes such as 4-octyne, very low over-hydrogenation and isomerization products were observed over a full conversion regime, even after prolonged reaction times. These catalytic properties were remarkably superior in comparison to standard catalysts. The promotion of Ag on the moderation of the reactivity of the Pd phase, in combination with the creation of interfacial sites with the CeO2 moiety in the same nanostructure, is pointed as the responsible of such a remarkable catalytic performance.

Plasmonic assemblies of gold nanorods on nanoscale patterns of poly(ethylene glycol): Application in surface-enhanced Raman spectroscopy.

Approaches are needed for the tailored assembly of plasmonic building blocks on the surface of substrates to synergistically enhance their properties. Here we demonstrate selective immobilization and assembly of gold nanorods (NRs) on substrates modified and patterned with end-grafted poly(ethylene glycol) (PEG) layers. The ligand exchange from the initial cetyltrimethylammonium bromide to sodium citrate was necessary for the immobilization of gold NRs onto PEG grafted substrates. Linear nanopatterns of PEG were fabricated using electrospun nanofibers as masks in oxygen plasma etching. The selective immobilization of citrate-stabilized gold NRs with a length of ∼50 nm and a width of 20 nm on the nanopatterned PEG layers led to linear and registered arrays of rods. The number of gold NRs per line depended on the width of the patterns and approached 1 when the width of the patterns was comparable to the length of the rods. The confinement of the binding regions led to a ∼3 fold increase in the number of gold NRs immobilized per unit area. The selective and dense immobilization of gold NRs on the nanoscale patterns of PEG resulted in spatially defined and strong surface-enhanced Raman scattering activity enabling detection of molecules at concentrations as low as 1 nM.

Assembly of Plasmonic Nanoparticles on Nanopatterns of Polymer Brushes Fabricated by Electrospin Nanolithography.

This paper presents electrospin nanolithography (ESPNL) for versatile and low-cost fabrication of nanoscale patterns of polymer brushes to serve as templates for assembly of metallic nanoparticles. Here electrospun nanofibers placed on top of a substrate grafted with polymer brushes serve as masks. The oxygen plasma etching of the substrate followed by removal of the fibers leads to linear patterns of polymer brushes. The line-widths as small as ∼50 nm can be achieved by precise tuning of the diameter of fibers, etching condition, and fiber-substrate interaction. Highly aligned and spatially defined patterns can be fabricated by operating in the near-field electrospinning regime. Patterns of polymer brushes with two different chemistries effectively directed the assembly of gold nanoparticles and silver nanocubes. Nanopatterned brushes imparted strong confinement effects on the assembly of plasmonic nanoparticles and resulted in strong localization of electromagnetic fields leading to intense signals in surface-enhanced Raman spectroscopy. The scalability and simplicity of ESPNL hold great promise in patterning of a broad range of polymer thin films for different applications.

One-pot polyol synthesis of highly monodisperse short green silver nanorods.

Green silver nanorods (Ag NRs) of a low aspect ratio (2.8) have been produced in high yields via an optimized, simple, and robust one-pot polyol method in the presence of tannic acid, which favors the nucleation of decahedral seeds needed for the production of monodisperse Ag NRs. These Ag NRs were further used as sacrificial templates to produce Au hollow nanostructures via galvanic replacement reaction with HAuCl4 at room temperature.