Tunable growth of gold nanostructures at a PDMS surface to obtain plasmon rulers with enhanced optical features

Efficient coupling of plasmonic nanomaterials to optically transparent polymers still is a challenge in order to obtain affordable, versatile, and sensitive surface plasmonic devices. The in-situ fabrication of gold and silver nanoparticles on PDMS has been reported, but the resulting bulk sensitivities (of up to 70 nm RIU^?1) may still be improved. The authors report that few simple modifications to the general preparation of these composites (AuNPs@PDMS) can result in substantial improvements of the optical features. A two-steps growth of AuNPs@PDMS is found to be particularly effective. It includes chemical treatment of the PDMS surface before the formation of well-exposed and densely-packed 3D conglomerates of gold spheroids with enhanced bulk sensitivity. Differently from available approaches, the structures obtained by this method display sensitivity to refractive index change of about 250 nm per RIU. This is 3.5 times higher than spherical nanoparticles prepared by similar protocols and is near the optical performance of anisotropic NPs. Due to the strong 3D character of the structures, excellent plasmon coupling is realized on PDMS surface. The authors also show that these nanocomposite substrates can be subjected to external stimuli and then exhibit red shifts or blue shifts typical of induced plasmon coupling and uncoupling. Hence, the method represents a major step forward in terms of high-performance composite plasmonic nanomaterials for use in biosensing.

Open image in new window

Graphical abstract The growth of gold nanoparticles on polydimethylsiloxane can be tuned toward the formation of plasmonically coupled nanostructures acting as plasmon rulers. Biological stimuli elicit red or blue shifts due to induced plasmon coupling and uncoupling. Refractive index sensitivity reach 250 nm RIU^?1.

     

Near-infrared spectroscopy investigation of the water confined in tricalcium silicate pastes

Near-infrared (NIR) spectroscopy has been employed to investigate the evolution of the vibrational spectrum of water entrapped in a tricalcium silicate paste. The overall free water, which decreases as a function of time due to the formation of the hydrated phases (portlandite, Ca(OH)(2), and hydrated calcium silicate, C-S-H) during the hydration reaction, is quantified by the decrease in the area of the NIR band at about 5000 cm(-1). The coexistence of two types of water in the hydrated phases (a "surface-interacting water" (type I) and a "bulklike water" (type II)) during the hydration is obtained by the analysis of the band at about 7000 cm(-1). The deconvolution of this band allows the quantification of the two water types. As the reaction advances, part of the "bulklike water" is converted to "surface-interacting water" in direct agreement with the C-S-H surface development. Finally, the Ca(OH)(2) formation can be concurrently monitored by NIR through the increase of a very sharp peak at 7083 cm(-1). Near-infrared spectroscopy allows determination in a very simple way of the most important features of the tricalcium silicate setting process.     

Random effects clustering in multilevel modeling: choosing a proper partition

A novel criterion for estimating a latent partition of the observed groups based on the output of a hierarchical model is presented. It is based on a loss function combining the Gini income inequality ratio and the predictability index of Goodman and Kruskal in order to achieve maximum heterogeneity of random effects across groups and maximum homogeneity of predicted probabilities inside estimated clusters. The index is compared with alternative approaches in a simulation study and applied in a case study concerning the role of hospital level variables in deciding for a cesarean section.

     

Dynamic behavior of gear pumps: effect of variations in operational and design parameters

This work presents a wide number of results about the influence that variations in terms of operational and design parameters play on the dynamic behavior of external gear pumps. These results are obtained by using a non-linear lumped-parameter kineto-elastodynamic model developed and experimentally assessed with the aim of including all the important dynamic effects. On the one hand, the effects of variations in the operational parameters—namely output pressure, rotational speed and oil viscosity—are analysed; on the other hand, the effects of modifications of some design parameters are shown: clearances and relief groove dimension. The results in terms of gear eccentricity, pressure evolution, pressure forces, gear accelerations and variable forces exciting the pump casing enlighten the dynamic behavior of gear pumps and give useful indications for design improvements and vibration and noise reduction. As regards specifically gear accelerations as well as forces exciting the casing, they strongly increase with both output pressure and rotational speed, but variations in rotational speed in the operational range give lower effects. Conversely, the modifications of the clearances give negligible effects, while the relief groove dimension is very important: the larger the relief grooves are, the higher the gear accelerations and forces exciting the casing become.     

Aplysiopsenes: an additional example of marine polyketides with a mixed acetate/propionate pathway

First chemical study of the Hermaeidae sacoglossan Aplysiopsis formosa from Azores led to aplysiopsenes, α-pyrone polyketides with a mixed acetate/propionate structural pathway.