Citrate-coated, size-tunable octahedral platinum nanocrystals: a novel route for advanced electrocatalysts

The development of green and scalable syntheses for the preparation of size- and shape-controlled metal nanocrystals is of high interest in many areas, including catalysis, electrocatalysis, nanomedicine, and electronics. In this work, a new synthetic approach based on the synergistic action of physical parameters and reagents produces size-tunable octahedral Pt nanocrystals, without the use of catalyst-poisoning reagents and/or difficult-to-remove coatings. The synthesis requires only sodium citrate, ascorbic acid, and fine control of the reduction rate in aqueous environment. Pt octahedral nanocrystals with particle size as low as 7 nm and highly developed {111} facets have been achieved, as demonstrated by Transmission Electron Microscopy, X-ray Diffraction, and electrochemical methods. The absence of sticky molecules together with the high quality of the surface renders these nanocrystals ideal candidates in electrocatalysis. Notably, 7 nm bismuth-decorated octahedral nanocrystals exhibit superior performance for the electro-oxidation of formic acid in terms of both specific and mass activities.JMF and VM acknowledge financial support from MINECO (projects CTQ2016-76221-P and CTQ2016-76231-C2-2-R (AEI/FEDER, UE)). JSG acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante (UATALENTO16-02)

Facile formation of highly mobile supported lipid bilayers on surface-quaternized pH-responsive polymer brushes

Poly(2-dimethylamino)ethyl methacrylate) (PDMA) brushes are grown from planar substrates via surface atom transfer radical polymerization (ATRP). Quaternization of these brushes is conducted using 1-iodooctadecane in n-hexane, which is a non-solvent for PDMA. Ellipsometry, AFM, and water contact angle measurements show that surface-confined quaternization occurs under these conditions, producing pH-responsive brushes that have a hydrophobic upper surface. Systematic variation of the 1-iodooctadecane concentration and reaction time enables the mean degree of surface quaternization to be optimized. Relatively low degrees of surface quaternization (ca. 10 mol % as judged by XPS) produce brushes that enable the formation of supported lipid bilayers, with the hydrophobic pendent octadecyl groups promoting in situ rupture of lipid vesicles. Control experiments confirm that quaternized PDMA brushes prepared in a good brush solvent (THF) produce non-pH-responsive brushes, presumably because the pendent octadecyl groups form micelle-like physical cross-links throughout the brush layer. Supported lipid bilayers (SLBs) can also be formed on the non-quaternized PDMA precursor brushes, but such structures proved to be unstable to small changes in pH. Thus, surface quaternization of PDMA brushes using 1-iodooctadecane in n-hexane provides the best protocol for the formation of robust SLBs. Fluorescence recovery after photobleaching (FRAP) studies of such SLBs indicate diffusion coefficients (2.8 ± 0.3 μm s–1) and mobile fractions (98 ± 2%) that are comparable to the literature data reported for SLBs prepared directly on planar glass substrates

Scanning tunneling microscopy and small angle neutron scattering study of mixed monolayer protected gold nanoparticles in organic solvents

When a binary mixture of ligand molecules is used to coat gold nanoparticles, stripe-like domains can occur. These nanodomains confer nanoparticles unique structure-dependent properties. The domain structure has been characterized primarily using scanning tunneling microscopy (STM) in air and in vacuum. Here we show the first STM images of striped nanoparticles in a solvent, 1-phenyloctane. We achieve stable imaging conditions on dodecanethiol hexanethiol (C12 : C6) 2 : 1 protected gold nanoparticles. These features are persistent across many images and retain their direction and overall morphology when recorded at different scan angles. We also perform small angle neutron scattering (SANS) on two hybrid C6 : C12 nanoparticle samples dissolved in chloroform. The hybrid nanoparticles have the same composition and size distribution as samples imaged with STM, but one of the two ligands (either C6 or C12) is deuterated. Low resolution models reconstructed ab initio by simultaneous fitting of the SANS data reveal striped patterns of C6 and C12 on the gold surface. We use image analysis to quantitatively compare STM and SANS data, achieving remarkable agreement. This is the first paper to compare evidence of the existence of stripe-like domains for particles in solution using two independent techniques, and we believe that a combination of STM and SANS could become a major approach to characterize mixed ligand nanomaterials in solution

Particle size affects the cytosolic delivery of membranotropic peptide-functionalized platinum nanozymes

Delivery of therapeutic agents inside the cytosol, avoiding the confinement in endo-lysosomal compartments and their degradative environment, is one of the key targets of nanomedicine to gain the maximum remedial effects. Current approaches based on cell penetrating peptides (CPPs), despite improving the cellular uptake efficiency of nanocarriers, have shown controversial results in terms of intracellular localization. To elucidate the delivery potential of CPPs, in this work we analyzed the role of the particle size in influencing the ability of a membranotropic peptide, namely gH625, to escape the endo-lysosomal pathway and deliver the particles in the cytosol. To this aim, we carried out a systematic assessment of the cellular uptake and distribution of monodisperse platinum nanoparticles (PtNPs), having different diameters (2.5, 5 and 20 nm) and citrate capping or gH625 peptide functionalization. The presence of gH625 significantly increased the amount of internalized NPs in human cervix epithelioid carcinoma cells, as a function of particle size. However, scanning transmission electron microscopy (STEM) and electron tomography (ET) revealed a prevalent confinement of PtNPs within vesicular structures, regardless of the particle size and surface functionalization. Only in the case of the smallest 2.5 nm particles, the membranotropic peptide was able to partly maintain its functionality, enabling cytosolic delivery of a small fraction of internalized PtNPs, though particle agglomeration in culture medium limited single-particle transport across the cell membrane. Interestingly, membrane crossing by 2.5 nm functionalized-PtNPs seemed to occur by diffusion through the lipid bilayer, with no apparent membrane damage. For larger particle sizes (>= 5 nm), their hindrance likely blocked the membranotropic mechanism. Combining the enhanced uptake and partial cytosolic delivery promoted by gH625, we were able to achieve a strong improvement of the antioxidant nanozyme function of 2.5 nm PtNPs, decreasing both the endogenous ROS level and its overproduction following an external oxidative insult

PMA-Induced THP-1 Macrophage Differentiation is Not Impaired by Citrate-Coated Platinum Nanoparticles

The innate immune system consists of several complex cellular and molecular mechanisms. During inflammatory responses, blood-circulating monocytes are driven to the sites of inflammation, where they differentiate into tissue macrophages. The research of novel nanomaterials applied to biomedical sciences is often limited by their toxicity or dangerous interactions with the immune cell functions. Platinum nanoparticles (PtNPs) have shown efficient antioxidant properties within several cells, but information on their potential harmful role in the monocyte-to-macrophage differentiation process is still unknown. Here, we studied the morphology and the release of cytokines in PMA-differentiated THP-1 pre-treated with 5 nm PtNPs. Although NP endocytosis was evident, we did not find differences in the cellular structure or in the release of inflammatory cytokines and chemokines compared to cells differentiated in PtNP-free medium. However, the administration of PtNPs to previously differentiated THP-1 induced massive phagocytosis of the PtNPs and a slight metabolism decrease at higher doses. Further investigation using undifferentiated and differentiated neutrophil-like HL60 confirmed the harmlessness of PtNPs with non-adherent innate immune cells. Our results demonstrate that citrate-coated PtNPs are not toxic with these immune cell lines, and do not affect the PMA-stimulated THP-1 macrophage differentiation process in vitro

Nanocatalyst-Enabled Physically Unclonable Functions as Smart Anticounterfeiting Tags with AI-Aided Smartphone Authentication

Counterfeiting is a worldwide issue affecting many industrial sectors, ranging from specialized technologies to retail market, such as fashion brands, pharmaceutical products, and consumer electronics. Counterfeiting is not only a huge economic burden (>$ 1 trillion losses/year), but it also represents a serious risk to human health, for example, due to the exponential increase of fake drugs and food products invading the market. Considering such a global problem, numerous anticounterfeit technologies have been recently proposed, mostly based on tags. The most advanced category, based on encryption and cryptography, is represented by physically unclonable functions (PUFs). A PUF tag is based on a unique physical object generated through chemical methods with virtually endless possible combinations, providing remarkable encoding capability. However, most methods adopted nowadays are based on expensive and complex technologies, relying on instrumental readouts, which make them not effective in real-world applications. To achieve a simple yet cryptography-based anticounterfeit method, herein we exploit a combination of nanotechnology, chemistry, and artificial intelligence (AI). Notably, we developed platinum nanocatalyst-enabled visual tags, exhibiting the properties of PUFs (encoding capability >10300) along with fast (1 min) ON/OFF readout and full reversibility, enabling multiple onsite authentication cycles. The development of an accurate AI-aided algorithm powers the system, allowing for smartphone-based PUF authentications

Interaction of sodium dodecyl sulfate and high charge density comb polymers at the silica/water interface

The structures of interfacial layers formed from mixtures of comb polymers, comprising a high charge density cationic backbone and poly(ethylene oxide) (PEO) side-chains, with the anionic surfactant sodium dodecyl sulfate (SDS) at the silica/water interface, have been determined using neutron reflectivity measurements. The use of mixtures in which only the isotopic composition of the surfactant is changed has made it possible to determine the interfacial volume fraction profiles for both the polymer and the surfactant. For the polymer with 90% of the segments charged and 10% of the segments carrying PEO side-chains, there are four regimes of interfacial behavior with increasing surfactant composition of the bulk solution. First there is adsorption of surfactant to the polymer-covered surface, then, slightly above polymer charge stoichiometry, there is adsorption of near-neutral polymer/surfactant complexes followed by the adsorption of polymer/surfactant aggregates, with a well-defined internal structure. If the concentration of SDS is increased directly from below polymer charge stoichiometry to above the cmc, micelles or polymer/micelle complexes interact with the pre-existing polymer layer. Increasing the fraction of segments carrying PEO side-chains to 25% suppresses the formation of charge-neutral polymer/surfactant complexes at the interface. There is an increase in the adsorption of surfactant, which interacts with the pre-existing layer of polymers. This results in the surface aggregation of SDS and a swelling of the PEO side-chains from a mushroom to a brush-like configuration