Prevention of the Aggregation of Nanoparticles during the Synthesis of Nanogold-Containing Silica Aerogels

Au-CeO2 composite aerogels with tunable Au nanoparticle sizes as plasmonic photocatalysts for CO2 reduction

Tuning the size of Au nanoparticles is always an interesting task when constructing Au/semiconductor heterojunctions for surface plasmon resonance-enhanced photocatalysis. In particular, the size of Au nanoparticles in the newly emerging "plasmonic aerogel" photocatalyst concept could approach the size of the semiconductor phase. This work provides an alternative route to realize the size tuning of Au nanoparticles in Au-CeO2 composite aerogels to some extent, within the framework of the well-established epoxide addition sol-gel method. The size tuning is achieved by exploiting the multi-functionalities of a mixed organic acid additive containing a thiol group in the gelation step. The obtained aerogel photocatalysts are composed of a porous backbone of interconnected CeO2 nanoparticles and Au nanoparticles, and the size of Au nanoparticles ranges from ∼30 nm to sub-10 nm, while the size of CeO2 remains at ∼15-10 nm. The surface plasmon resonance peak position and intensity contributed by the Au nanoparticles then vary accordingly. Photocatalytic CO2 reduction at the gas-solid interface is chosen as a model reaction to study the effect of Au nanoparticle size on the photocatalytic activity of composite aerogel photocatalysts. The addition of Au nanoparticles undoubtedly enhances the overall activity of the CeO2 aerogel photocatalyst, while the degree of enhancement (in terms of total charge consumption) and product selectivity (CH4 or CO) are different and correlated with the size of the Au nanoparticles. The best performance can be achieved in a composite in which the Au sizes are the smallest.

Ceftazidime-Decorated Gold Nanoparticles: a Promising Strategy against Clinical Ceftazidime-Avibactam-Resistant Enterobacteriaceae with Different Resistance Mechanisms

Nanoparticle-based antibiotic delivery systems are essential in combating antibiotic-resistant bacterial infections arising from acquired resistance and/or biofilm formation. Here, we report that the ceftazidime-decorated gold nanoparticles (CAZ_Au NPs) can effectively kill clinical ceftazidime-avibactam-resistant Enterobacteriaceae with various resistance mechanisms. Further study of underlying antibacterial mechanisms suggests that CAZ_Au NPs can damage the bacterial cell membrane and increase the level of intracellular reactive oxygen species. Moreover, CAZ_Au NPs show great potential in inhibiting biofilm formation and eradicating mature biofilms via crystal violet and scanning electron microscope assays. In addition, CAZ_Au NPs demonstrate excellent performance in improving the survival rate in the mouse model of abdominal infection. In addition, CAZ_Au NPs show no significant toxicity at bactericidal concentrations in the cell viability assay. Thus, this strategy provides a simple way to drastically improve the potency of ceftazidime as an antibiotic and its use in further biomedical applications.

Photothermal effects of gold nanorods in aqueous solution and gel media: Influence of particle size and excitation wavelength

Gold nanorods (GNRs) have emerged as the most efficient photothermal agent in cancer therapy and photocatalysis. Understanding the influence of the surrounding medium, particle size, and excitation wavelength is critical to optimising the photothermal conversion rate. Here, three pairs of large and small gold nanorods of different aspect ratios and their heat generation under laser radiation at on and off surface plasmon resonance wavelengths in aqueous solution and gel-like media are investigated. In the aqueous solution, the temperature rise of the large gold nanorods is more than with small gold nanorods at resonance excitation. In contrast to the large gold nanorods (LGNRs), the small gold nanorods (SGNRs) were less sensitive to excitation wavelength. At off-resonance excitation, the temperature rise of the SGNRs is larger than that of the LGNRs. In the agarose gel, the photothermal effect of the SGNRs is greater than LGNRs excited at the wavelength near their solution phase longitudinal surface plasmon resonance wavelength. The temperature increase of LGNRs in gel is significantly less than in aqueous solution. These findings suggest that SGNRs could be more beneficial than the LGNRs for photothermal applications in biological systems and provides further insight when selecting GNRs.

Intra-Organ Delivery of Nanotherapeutics for Organ Transplantation

Targeted delivery of therapeutics through the use of nanoparticles (NPs) has emerged as a promising method that increases their efficacy and reduces their side effects. NPs can be tailored to localize to selective tissues through conjugation to ligands that bind cell-specific receptors. Although the vast majority of nanodelivery platforms have focused on cancer therapy, efforts have begun to introduce nanotherapeutics to the fields of immunology as well as transplantation. In this review, we provide an overview from a clinician's perspective of current nanotherapeutic strategies to treat solid organ transplants with NPs during the time interval between organ harvest from the donor and placement into the recipient, an innovative technology that can provide major benefits to transplant patients. The use of ex vivo normothermic machine perfusion (NMP), which is associated with preserving the function of the organ following transplantation, also provides an ideal opportunity for a localized, sustained, and controlled delivery of nanotherapeutics to the organ during this critical time period. Here, we summarize previous endeavors to improve transplantation outcomes by treating the organ with NPs prior to placement in the recipient. Investigations in this burgeoning field of research are promising, but more extensive studies are needed to overcome the physiological challenges to achieving effective nanotherapeutic delivery to transplanted organs discussed in this review.

Synthesis of Polyaniline Coated Magnesium and Cobalt Oxide Nanoparticles through Eco-Friendly Approach and Their Application as Antifungal Agents

Plant-mediated synthesis of nanoparticles exhibits great potential to minimize the generation of chemical waste through the utilization of non-toxic precursors. In this research work, we report the synthesis of magnesium oxide (MgO) and cobalt oxide (Co₃O₄) nanoparticles through a green approach using Manilkara zapota leaves extract, their surface modification by polyaniline (PANI), and antifungal properties against Aspergillus niger. Textural and structural characterization of modified and unmodified metal oxide nanoparticles were evaluated using FT-IR, SEM, and XRD. The optimal conditions for inhibition of Aspergillus niger were achieved by varying nanoparticles’ concentration and time exposure. Results demonstrate that PANI/MgO nanoparticles were superior in function relative to PANI/Co₃O₄ nanoparticles to control the growth rate of Aspergillus niger at optimal conditions (time exposure of 72 h and nanoparticles concentration of 24 mM). A percentage decrease of 73.2% and 65.1% in fungal growth was observed using PANI/MgO and PANI/Co₃O₄ nanoparticles, respectively, which was higher than the unmodified metal oxide nanoparticles (67.5% and 63.2%).

Resveratrol isomeric switching during bioreduction of gold nanoparticles: a gateway for cis-resveratrolArchita

Resveratrol, a polyphenolic and biocompatible molecule, exhibits significant pharmacological effects but has poor bioavailability and metabolic stability. It appears in two isomeric forms trans-(E)-resveratrol (tRes) and cis-(Z)-resveratrol (cRes). Many pharmacological activities studied so far are of tRes and is the most stable, predominant, and natural form. cRes is not commercially available due to difficulty in its purification and hence not explored much for its biological activities. Therefore, our study focuses on investigating the stability and therapeutic potential of cRes through its bio-conjugation to nanomaterial. In this study, tRes reduces gold ions to gold nanoparticles (GNPs) and itself gets oxidized to its isomeric form cRes. The isomeric switching was evidenced through cRes characteristic spectral differences and chromatographic elution pattern. The monodispersed GNPs of 25.6 ± 0.4 nm size was formed having zeta potential of -19 ± 3.82 mV confirming it to be a stable formulation. The stability studies were further extended to be tested under different physiological fluids. The cRes loaded GNPs (cRGNPs) reflecting the biological activity of cRes presented equivalent antioxidant property to that of tRes even at low concentrations. Also, cRGNPs showed the hemocompatibility by presenting no hemotoxicity and simultaneous in vitro anti-hemolytic activity. Therefore, the stability provided to cRes upon conjugating to GNPs can further be exploited to study the biological activities of cRes through its nano-conjugated delivery.

Editorial on Special Issues "Aerogels" and "Aerogels 2018"

Aerogels can be defined as ultralight materials with a 3D porous structure, similar to their parent wet gels, where the solvent has been replaced by a gas without a collapse of the gel structure, thanks to the drying process used (supercritical CO₂ drying, freeze drying, etc.). (...).

Nanoparticle processing: Understanding and controlling aggregation

Nanoparticles (NPs) are commonly defined as particles with size <100 nm and are currently of considerable technological and academic interest, since they are often the starting materials for nanotechnology. Novel properties develop as a bulk material is reduced to nanodimensions and is reflected in new chemistry, physics and biology. With reduction in size, a greater function of the atoms is at the surface, and promote different interaction with its environment, as compared to the bulk material. In addition, the reduction in size alters the electronic structure of the material, resulting in novel quantum effects. Size also influences mobility, primarily controlled by Brownian motion for NPs, and relevant in biological and environmental processes. However, the small size also leads to high surface energy, and NPs tend to aggregate, thereby lowering the surface energy. In all applications, the uncontrolled aggregation of NPs can have negative effects and needs to be avoided. There are however examples of controlled aggregation of NPs which give rise to novel effects. This review article is focused on the NP features that influences aggregation. Common strategies for synthesis of NPs from the gas and liquid phases are discussed with emphasis on aggregation during and after synthesis. The theory involving Van der Waals attractive force and electrical repulsive force as the controlling features of the stability of NPs is discussed, followed by examples of how repulsive and attractive forces can be manipulated experimentally to control NP aggregation. In some applications, NPs prepared by liquid methods need to be isolated for further applications. The process of solvent removal introduces new forces such as capillary forces that promote aggregation, in many cases, irreversibly. Strategies for controlling aggregation upon drying are discussed. There are also many methods for redispersing aggregated NPs, which involve mechanical forces, as well as manipulating capillary forces and surface characteristics. We conclude this review with a discussion of aggregation relevant real-world applications of NPs. This review should be relevant for scientists and technologists interested in NPs, since emphasis has been on the practical aspects of NP-based technology, and especially, strategies relevant to controlling NP aggregation.

Green Nanotechnology-based Gold Nanomaterials for Hepatic Cancer Therapeutics: A Systematic Review

The objective of the current study was to systematically review the in-vitro anticancer activity of green synthesized gold nanoparticles (AuNPs) against hepatic cancer cells. The articles were identified through electronic databases, including PubMed, Scopus, Embase, Web of Science, Science Direct, ProQuest, and Cochrane. In total, 20 articles were found eligible to enter into our systematic review. Our findings showed that 65% of the articles used herbal extracts for the synthesis of AuNPs. Significantly, almost all of the articles stated the biofabrication of AuNPs below 100 nm in diameter. Impressively, most of the studies showed significant anticancer activity against HepG2 cells. Molecular studies stated the induction of apoptosis through the AuNPs-treated cells. We provided valuable information about the molecular mechanisms of AuNPs-induced cytotoxicity against HepG2 cells as well as their biocompatibility. The studies represented that AuNPs can be effective as anticancer drug nanocarrier for drug delivery systems. In addition, AuNP surface functionalization provides an opportunity to design multifunctional nanoparticles by conjugating them to diagnostic and/or therapeutic agents for theranostic purposes. Overall, our findings depicted considerable biogenic AuNPs-induced cytotoxicity, however, future studies should assess the anticancer activity of biogenic AuNPs through in-vivo studies, which was missing from such studies.