Cristina Lucena-Serrano

The periostracum is the outermost shell layer and the first produced during shell formation in molluscs. This organic layer isolates the extrapallial space from the external environment and provides a scaffold for subsequent calcification. In cephalopods with an internal shell, some organic shell structures are putatively homologous to the periostracum of other molluscan groups. However, neither their detailed structure nor their mode of formation has been described, leaving the extent of this homology unresolved. To address this issue, we investigated the morphology and formation of the organic layer of the dorsal shield and the gladius in embryos of the cuttlefish Sepia officinalis Linnaeus, 1758, and the squid Loligo vulgaris Lamarck, 1798, respectively, using light microscopy and transmission electron microscopy. In both species, the periostracum forms within a periostracal groove located along the lateral and anterior margins of the shell sac. As in other molluscs, secretions from columnar cells at the bottom of the groove produce a dense layer, while a translucent layer is subsequently added beneath it through secretions from cuboidal cells. The main difference is the absence of both a pellicle and of the specialized glandular cells that typically secrete it at the bottom of the periostracal groove.

Background: In this review, we summarized the relevance of anisotropic morphologies in the synthesis and applications of metal nanoparticles, including Janus nanoparticles. In recent years, the control over the shape of metal particles has successfully achieved. Non-spherical gold nanoparticles such as rods, wires, cubes, triangular prisms, decahedra, or octahedra exhibit unique properties that differ from those of symmetric, spherical gold nanoparticles. Objective: This article provides a general view of current research in the field of anisotropic metal nanoparticles. We begin by explaining the relevance of anisotropic metal nanoparticles in the field of nanotechnology. Then, we distinguish between physical and chemical method frequently performed for the preparation of metallic nanoparticles. In this review we only focus in chemical methods, and the following sections divide the most recently published procedures in two different methods for chemical synthesis: seed-mediated growth and seedless procedures. For each of these routes, we present the fabrication of metal particles in aqueous or organic media. Conclusion: In this review, we also describe numerous procedures for the functionalization of several anisotropic morphologies with silica, poly(N-isopropylacrylamide) (pNIPAM), as well as the fabrication of bimetallic core shell structures. We hope that this review will help the scientists to carry out several general routes for the synthesis of non-spherical particles to exploit their efficacy for wide applications.

Here we describe the first seedless synthesis of vinyl-terminated Au nanotriangular prisms (AuNTPs) and nanooctahedra (AuNOC) in aqueous media. This synthesis is performed by chemical reduction of chloroauric acid (HAuCl₄) with 3-butenoic acid (3BA) in the presence of benzyldimethylammonium chloride (BDAC). The principal novelties of the presented method are the use of a mixture of 3BA and BDAC, the synthesis of gold prisms and octahedra with controllable size, and the presence of terminal double bonds on the metal surface. Initially this method produces a mixture of triangular gold nanoprisms and octahedra; however, both morphologies are successfully separated by surfactant micelle induced depletion interaction, reaching percentages up to ∼90%. Moreover, the alkene moieties present on the gold surface are exploited for the fabrication of hybrid core@shell particles. Gold octahedra and triangular prisms are easily encapsulated by free radical polymerization of N-isopropylacrylamide (NIPAM). Finally, in order to obtain a gold core with the most number of tips, AuNTP@pNIPAM microgels were subjected to gold core overgrowth, thus resulting in star-shaped nanoparticles (AuSTs@pNIPAM). We use 4-amino-benzenethiol as the model analyte for SERS investigations. As expected, gold cores with tips and high curvature sites produced the highest plasmonic responses.