No abstract

In this study, we report on the formation of gold nanosheets with different morphologies using a naturally occurring amino acid, viz, tryptophan, as a reducing and capping agent at ambient conditions. The importance of in situ-oxidized tryptophan for promoting anisotropic growth of gold (Au) nuclei to form two-dimensional gold nanosheets is demonstrated. Furthermore, we investigated the effect of high frequency ultrasound (490 kHz) and tryptophan to fabricate ultrathin gold nanosheets with controlled morphologies (triangular and polygonal shapes), without using any other reagents/stabilizers. The size of gold sheets (200 nm to micrometer range) can be controlled by tuning the experimental conditions. A possible mechanism for the formation of well-defined gold nanostructures with different morphologies is provided. High frequency sonication leads to the simultaneous dimerization of tryptophan and Au reduction, and we show that the interaction of tryptophan dimers with Au nuclei plays an important role in the formation of gold sheets. The sonochemically synthesized AuNSs displayed superior catalytic activity in the reduction of 4-nitrophenol to 4-aminophenol with a specific rate constant of 1.96 × 103 s–1 per unit gram of active catalyst and with excellent recyclability.

High-frequency ultrasound treatment is found to be a one-pot green technique to produce peptide-based nanostructures by ultrasound assisted self-assembly of oligopeptides. [Arg-Phe]4 octapeptides, consisting of alternating arginine (Arg/R) and phenylalanine (Phe/F) sequences, were subjected to 430 kHz ultrasound in aqueous solution in the absence of any external agents, to form [RF]4 nanoparticles ([RF]4-NPs), ~220 nm in diameter. A comprehensive analysis of the obtained nanoparticles demonstrated that the aromatic moieties of the oligopeptides can undergo oxidative coupling to form multiple oligomeric species, which then self-assemble into well-defined fluorescent nanoparticles. [RF]4-NPs were functionalized with polyethylene glycol (PEGylated) to improve their colloidal stability. Unlike the parent peptide, the PEGylated [RF]4-NPs showed limited cytotoxicity towards MDA-MB-231 cells. Furthermore, the intracellular trafficking of PEGylated [RF]4-NPs was investigated after incubation with MDA-MB-231 cells to demonstrate their efficient endo-lysosomal escape. This work highlights that the combined use of ultrasonic technologies and peptides enables easy fabrication of nanoparticles, with potential application in drug delivery.

Ultrasonically synthesized core-shell microcapsules can be made of synthetic polymers or natural biopolymers, such as proteins and polysaccharides, and have found applications in food, drug delivery and cosmetics. This study reports on the ultrasonic synthesis of microcapsules using unmodified (natural) and biodegradable glycogen nanoparticles derived from various sources, such as rabbit and bovine liver, oyster and sweet corn, for the encapsulation of soybean oil and vitamin D. Depending on their source, glycogen nanoparticles exhibited differences in size and ‘bound’ proteins. We optimized various synthetic parameters, such as ultrasonic power, time and concentration of glycogens and the oil phase to obtain stable core-shell microcapsules. Particularly, under ultrasound-induced emulsification conditions (sonication time 45 s and sonication power 160 W), native glycogens formed microcapsules with diameter between 0.3 μm and 8 μm. It was found that the size of glycogen as well as the protein component play an important role in stabilizing the Pickering emulsion and the microcapsules shell. This study highlights that native glycogen nanoparticles without any further tedious chemical modification steps can be successfully used for the encapsulation of nutrients.

The development of simple, green, reproducible, and scalable approaches for synthesizing nanoparticles from biomolecules is important to advance nanomaterials towards therapeutic applications. Microreactors generated by high frequency ultrasound provide a...