Surfactant-free Synthesis of Spiky Hollow Ag-Au Nanostars with Chemically Exposed Surfaces for Enhanced Catalysis and Single-Particle SERS.

Spiky/hollow metal nanoparticles have applications across a broad range of fields. However, the current bottom-up methods for producing spiky/hollow metal nanoparticles rely heavily on the use of strongly adsorbing surfactant molecules, which is undesirable because these passivate the product particles' surfaces. Here we report a high-yield surfactant-free synthesis of spiky hollow Au-Ag nanostars (SHAANs). Each SHAAN is composed of >50 spikes attached to a hollow ca. 150 nm diameter cubic core, which makes SHAANs highly plasmonically and catalytically active. Moreover, the surfaces of SHAANs are chemically exposed, which gives them significantly enhanced functionality compared with their surfactant-capped counterparts, as demonstrated in surface-enhanced Raman spectroscopy (SERS) and catalysis. The chemical accessibility of the pristine SHAANs also allows the use of hydroxyethyl cellulose as a weakly bound stabilizing agent. This produces colloidal SHAANs that remain stable for >1 month while retaining the functionalities of the pristine particles and allows even single-particle SERS to be realized.

Experimental and Theoretical Studies on Sustainable Synthesis of Gold Sol Displaying Dichroic Effect.

Gold nanoparticles depending on their shape and mixtures of multiple shapes can exhibit peculiar optical properties, including the dichroic effect typical of the Lycurgus cup, which has puzzled scientists for a long time. Such optical properties have been recently exploited in several fields such as paint technology, sensors, dichroic polarizers, display (LCD) devices, laser applications, solar cells and photothermal therapy among others. In this article, we have demonstrated a simple room temperature one-pot synthesis of gold sol displaying a dichroic effect using a slow reduction protocol involving only trisodium citrate as a reducing agent. We found that the dichroic gold sol can be easily formed at room temperature by reducing gold salt by trisodium citrate below a certain critical concentration. The sol displayed an orangish-brown color in scattered/reflected light and violet/blue/indigo/purple/red/pink in transmitted light, depending on the experimental conditions. With minor changes such as the introduction of a third molecule or replacing a small amount of water in the reaction mixture with ethanol, the color of the gold sol under transmitted light changed and a variety of shades of red, pink, cobalt blue, violet, magenta and purple were obtained. The main advantage of the proposed method lies in its simplicity, which involves the identification of the right ratio of the reactants, and simple mixing of reactants at room temperature with no other requirements. TEM micrographs displayed the formation of two main types of particles viz. single crystal gold nanoplates and polycrystalline faceted polyhedron nanoparticles. The mechanism of growth of the nanoplates and faceted polyhedron particles have been described by an enhanced diffusion limited aggregation numerical scheme, where it was assumed that both trisodium citrate and the gold ions in solution undergo a stochastic Brownian motion, and that the evolution of the entire system is regulated by a principle of energy minimization. The predictions of the model matched with the experiments with a good accuracy, indicating that the initial hypothesis is correct.

Plasmonic photothermal microneedle arrays and single needles for minimally-invasive deep in-skin hyperthermia.

We report, for the first time, crosslinked polymeric microneedle (MN) arrays and single needles (2 mm and 4.5 mm length) coated with gold nanorods (GnRs) to induce deep hyperthermia in a 3 mm-thickness skin model upon near infrared (NIR) laser irradiation. Using excised neonatal porcine skin as tissue model, it was seen that insertion capabilities of single prototypes were not affected by the coating, as around 80% of their length was inserted before and after coating. Insertion of MN arrays dropped from 74% to 55%, which could be attributed to a less sharp structure after the coating process. Nonetheless, GnRs-coated MN arrays achieved the highest increase in temperature in the skin model: over 15 °C after only 15 s of NIR laser irradiation (808 nm, 2 W cm-2). Surprisingly, removal of MN arrays after irradiation left no detectable polymer or plasmonic material behind, confirming the enhanced safety and minimally-invasive potential of this device for future biomedical applications of deep in skin hyperthermia.

Irreversible photo-Fenton-like triggered agglomeration of ultra-small gold nanoparticles capped with crosslinkable materials.

A photo-Fenton-like process can promote the agglomeration and LSPR red-shifting of ultra-small gold nanoparticles by triggering a crosslink-degradation pathway that involves the surface coating, Fe(iii)-citrate and hydrogen peroxide. Applications may range from controlled photo-deposition of active materials to asynchronous sensing technologies to light-focused microfabrication.

Shuttle-mediated nanoparticle transport across an in vitro brain endothelium under flow conditions.

The blood brain barrier (BBB) represents a challenge in the development of new nano-delivery systems able to reach the central nervous system (CNS). In order to test the efficacy of these nanocarriers, it is fundamental to use in vitro models that resemble the in vivo cell culture conditions. Here, we demonstrate for the first time the ability of a membranotropic peptide, namely gH625, to transport a cargo-acting as a shuttle-across the BBB layer under flow conditions that mimic the blood flow rate. To this aim, a BBB microfluidic device was designed based on a transparent polyester porous membrane sandwiched between a top and a bottom overlying channel made of poly(methyl methacrylate) (PMMA). Our data clearly indicate that this microfluidic system allows the growth of brain endothelial bEnd.3 cells and the formation of a confluent layer at 7 days of culture that hinders the passage of nanoparticles compared to porous membrane alone. The device was validated at a 5 µL/min working flow rate, where the capability of the model to remain intact after nanoparticle passage was shown. Very interestingly, the decoration with the gH625 peptide enhances the adhesion of nanoparticles to the endothelial layer and the BBB crossing in flow conditions, thus confirming the efficacy of the gH625 as a delivery platform to the brain. Biotechnol. Bioeng. 2017;114: 1087-1095. © 2016 Wiley Periodicals, Inc.

Proton transfer in oxidized adenosine self-aggregates.

The UV-vis and the IR spectra of derivativized adenosine in dichloromethane have been recorded during potentiostatic oxidation at an optically transparent thin layer electrode. Oxidized adenosine shows a broad Zundel like absorption extending from 2800 up to 3600 cm(-1), indicating that a proton transfer process is occurring. Theoretical computations predict that proton transfer is indeed favored in oxidized 1:1 self-association complexes and allow to assign all the observed transient spectroscopic signals.

Stacking interactions between adenines in oxidized oligonucleotides.

The effects of stacking interactions on the oxidation potentials of single strand oligonucleotides containing up to four consecutive adenines, alternated with thymines and cytosines in different sequences and ratios, have been determined by means of differential pulse voltammetry. Voltammetric measurements point toward the establishment in solution of structured oligonucleotide conformations, in which the nucleobases are well stacked altogether. Molecular dynamics simulations confirm that finding, indicating that single strands assume geometrical parameters characteristic of the B-DNA form. The analysis of the voltammetric signals in terms of a simple effective tight binding quantum model leads one to infer a robust set of parameters for treating hole transfer in one-electron-oxidized DNA containing adenines and thymines.