Three-dimensional periodic structures of gold nanoclusters in the interstices of sub-100 nm polymer particles toward surface-enhanced Raman scattering

Regularly ordered polymer nanoparticle (PNP) assemblies incorporating gold nanoparticle (Au NP) clusters into the PNP interstices were fabricated by a simultaneous deposition of PNPs and Au NPs on a glass substrate. Monodisperse PNPs with an average size of 66 nm were employed as a template in the co-assembly to create the sub-100 nm periodic Au nanostructures on the substrate. First, mono-layering of PNP array with incorporation of 14 nm Au NPs was performed by a drop-casting to examine the number ratio of Au NPs to PNPs for multi-layering. Absorption spectra of the mono-layered co-assemblies of PNPs and Au NPs were employed to characterize the clustered state of Au NPs in the interstices of mono-layered PNPs. The number ratio suitable for homogeneous incorporation of Au NPs clustered in the interstice was found to be ranged from 6 to 8 in the characterization. Then, multi-layered co-assemblies of PNPs and clustered Au NPs were fabricated by a vertical deposition method with the Au NP number ratio of 8 to PNPs. Lifting rate of the substrate on which the PNPs were deposited was varied in the vertical deposition method to tune the film thickness of NP co-assembly. A decrease in the lifting rate to 1 μm/s could thicken the film to 0.71 μm corresponding to 13 layers of PNPs, resulting in the fabrication of periodic structures of Au NP clusters with a high packing density. Signal-to-noise ratio in the Raman measurement using p-mercaptobenzoic acid as a target molecule was successfully enhanced by multi-layering of the co-assembly, indicating that Au NP clusters were homogeneously incorporated into the interstices of PNPs in the co-assemblies.     

Immersed-boundary/soft-sphere method for particle–particle-fluid interaction in a viscous flow: An OpenFOAM solver

We developed a stable OpenFOAM solver for Immersed Boundary Method based on direct forcing and regularized delta function. The soft-sphere model and a lubrication model were implemented to consider particle–particle collision in a viscous flow. We proposed a fluid–structure interaction (FSI) coupling method to accurately calculate the fluid forcing term and particle velocity. Our solver was validated for fixed and moving bodies, including rotation. The accuracy of various FSI schemes was evaluated in predicting the solid and fluid flow behavior in a viscous flow. It was demonstrated that neglecting or simplifying the fluid momentum change affects the accuracy of the solid velocity and fluid flow dynamic; for higher solid-to-fluid density ratios, a larger deviation was predicted. Furthermore, the FSI schemes highly influenced the behavior of the formed vortices.The solver was validated to predict the effective restitution coefficient of particles in a viscous flow as a function of the Stokes number. We also thoroughly analyzed the dynamic flow behavior of colliding particles through the pressure and velocity field and fluid force. This analysis helped us accurately determine the rebound velocity of particles in case of high Stokes numbers when the effect of viscous force is significant.     

Drug self-assembly: A phenomenon at the nanometer scale with major impact in the structure–biological properties relationship and the treatment of disease

Under water-rich conditions, small amphiphilic and hydrophobic drug molecules self-assemble into supramolecular nanostructures. Thus, substantial modifications in their interaction with cellular structures and the ability to reach intracellular targets could happen. Additionally, drug aggregates could be more toxic than the non-aggregated counterparts, or vice versa. Moreover, since self-aggregation reduces the number of effective “monomeric” molecules that interact with the target, the drug potency could be underestimated. In other cases, the activity could be ascribed to the non-aggregated molecule while it stems from its aggregates. Thus, drug self-assembly could mislead from drug throughput screening assays to advanced preclinical and clinical trials. Finally, aggregates could serve as crystallization nuclei. The impact that this phenomenon has on the biological performance of active compounds, the inconsistent and often controversial nature of the published data and the need for recommendations/guidelines as preamble of more harmonized research protocols to characterize drug self-aggregation were main motivations for this review. First, the key molecular and environmental parameters governing drug self-aggregation, the main drug families for which this phenomenon and the methods used for its characterization are described. Then, promising nanotechnology platforms investigated to prevent/control it towards a more efficient drug development process are briefly discussed.     

Influence of the solvent evaporation rate on the β-Phase content of electrosprayed PVDF particles and films studied by a fast Multi-Overtone QCM

A combination of an electrospray setup and a quartz crystal microbalance with dissipation monitoring (QCM-D) was employed to study the drying of droplets of poly(vinylidene fluoride) (PVDF) dissolved in dimethylformamide (DMF). A novel variant of the QCM was used, which interrogates the resonance frequency and the resonance bandwidth on four overtones at the same time, achieving a time resolution of 2 ms. This instrument allowed to elucidate the mechanism of β-phase formation in electrospray deposition of PVDF. When the distance between the nozzle and the substrate was small, the droplets landed in a partially wet state, as evidenced from an increase in the resonance bandwidth. No such increase in bandwidth was observed when the distance was large. From the flight time (milliseconds) and the drying time on the substrate (seconds), one concludes that drying in the plume is faster than drying on the substrate. IR spectra show that the β–phase content is close to 100 % for particles, which dried in the plume. It is less than 50 % for particles having dried on the substrate. Fast drying promotes the formation of the β-phase. Follow-up experiments with thicker films on steel substrates also show increased β-phase content for larger distances.     

Virus meet metal-organic frameworks: A nanoporous solution to a world-sized problem?

Laboratory diagnosis of pathologies caused by virus plays a critical role in outbreak response efforts and establishing safe and expeditious testing strategies. Detection of pathogenic virus using commercial solutions require specific tools and laborious laboratory procedures. This makes the day-to-day on time detection of virus infections the limiting step in any outbreak. The need for new diagnostic tools easily available to poor and rural underdeveloped areas where health infrastructure and trained personnel are scarce is highly desirable. The widely known intrinsic properties of Metal-Organic Frameworks (MOFs) embody them with the potential to overcome some of the challenges inherent to virus detection. MOFs are already components of functional devices capable of perform an uninterrupted detection of molecular targets in real time. In this review, we summarise the few studies concerning the reported MOFs used as sensors for pathogenic virus. We emphasise the structural and physical properties of these materials which can open the possibility for their use in this type of sensors and conclude on how the field can progress to envisage the usage of MOFs by the pharmaceutical industry to develop new sensors for these sub-microscopic infectious agents.