Microwave-irradiated green synthesis of gold nanoparticles for catalytic and anti-bacterial activity

A comprehensive review of cancer therapies mediated by conjugated gold nanoparticles with nucleic acid

Nucleic acids provide a promising therapeutic platform by targeting various cell signaling pathways involved in cancer and genetic disorders. However, maintaining optimal stability during delivery limits their utility. Nucleic acid delivery vehicles are generally categorized into biological and synthetic carriers. Regardless of the efficiency of biological vectors, such as viral vectors, issues related to their immunogenicity and carcinogenesis are very important and vital for clinical applications. On the other hand, synthetic vectors such as lipids or polymers, have been widely used for nucleic acid delivery. Despite their transfection efficiency, low storage stability, targeting inefficiency, and tracking limitations are among the limitations of the clinical application of these vectors. In the past decades, gold nanoparticles with unique properties have been shown to be highly efficient mineral vectors for overcoming these obstacles. In this review, we focus on gold nanoparticle-nucleic acid combinations and highlight their use in the treatment of various types of cancers. Furthermore, by stating the biological applications of these structures, we will discuss their clinical applications.

A Critical Review of the Antimicrobial and Antibiofilm Activities of Green-Synthesized Plant-Based Metallic Nanoparticles

Metallic nanoparticles (MNPs) produced by green synthesis using plant extracts have attracted huge interest in the scientific community due to their excellent antibacterial, antifungal and antibiofilm activities. To evaluate these pharmacological properties, several methods or protocols have been successfully developed and implemented. Although these protocols were mostly inspired by the guidelines from national and international regulatory bodies, they suffer from a glaring absence of standardization of the experimental conditions. This situation leads to a lack of reproducibility and comparability of data from different study settings. To minimize these problems, guidelines for the antimicrobial and antibiofilm evaluation of MNPs should be developed by specialists in the field. Being aware of the immensity of the workload and the efforts required to achieve this, we set out to undertake a meticulous literature review of different experimental protocols and laboratory conditions used for the antimicrobial and antibiofilm evaluation of MNPs that could be used as a basis for future guidelines. This review also brings together all the discrepancies resulting from the different experimental designs and emphasizes their impact on the biological activities as well as their interpretation. Finally, the paper proposes a general overview that requires extensive experimental investigations to set the stage for the future development of effective antimicrobial MNPs using green synthesis.

Polyquaternium enhances the colloidal stability of chitosan-capped platinum nanoparticles and their antibacterial activity

Here, for the first time, we have developed a novel green synthesis method where chitosan acts as a reducing agent and as a colloidal stabilizer, together with polyquaternium for the synthesis of platinum nanoparticles (PtNPs). It was observed that only chitosan-stabilized PtNPs (Ch@PtNPs) were stable up to pH 5, with a diameter of around 89 nm. The diameter of the Ch@PtNPs increased with the increase in pH, indicating the instability of Ch@PtNPs at neutral and alkaline mediums. However, when polyquaternium (PQ) (a cationic polymer) was added as a stabilizer along with chitosan, the diameter of chitosan/polyquaternium stabilized PtNPs (Ch/PQ@PtNPs), i.e. 87 nm, remained almost constant up to pH 9. Similarly, the pH-dependent decrease in the surface charge of Ch@PtNPs was also attenuated with the addition of polyquaternium. This indicates high colloidal stability of Ch/PQ@PtNPs in acidic, neutral, as well as alkaline mediums. It was observed that Ch/PQ@PtNPs exhibited high antibacterial activity againstStaphylococcus aureus, as compared to uncapped PtNPs and Ch@PtNPs. Thus, the addition of PQ increases the antibacterial properties of Ch/PQ@PtNPs againstStaphylococcus aureusby enhancing the stability of PtNPs at neutral pH.

Recent progress in plant-gold nanoparticles fabrication methods and bio-applications

The preparation of gold nanoparticles via green routes applying plant extracts as the reducing agents and stabilizers has received broad interest in the last decades. Plant-gold nanoparticles have been well-developed and applied in biochemical and medical research, but there are still challenges that must be overcome. The main challenges include the construction of chemically-robust plant-gold nanoparticles, the precise design of biomimetic surfaces to fabricate nanozymes with high catalytic activities, and the development of approaches to construct biosensors with high selectivities and sensitivities. The cores and surfaces of plant-gold nanoparticles must be considered, as well as their catalytic activities and biosensing mechanisms. This review highlights the latest achievements in plant-gold nanoparticle preparation, heterogeneous nucleation, and surface functionalization, while also focusing on their optical properties and various biological and catalytic activities. Moreover, their antioxidant and cell apoptosis mechanisms, and biological activities are described. Plant-gold nanoparticles have shown great potential in high-performance analytical assays, high-activity catalysts, effective intracellular imaging, and clinical treatment.

Rapid synchronous synthesis of Ag nanoparticles and Ag nanoparticles/holocellulose nanofibrils: Hg(II) detection and dye discoloration

A novel microwave-assisted green method that synchronously synthesizes silver nanoparticles (AgNPs) and AgNPs decorated holocellulose nanofibrils (AgNPs/HCNF) within a minute and without using a reducing agent is reported. As obtained nanomaterials were well characterized using various analytical techniques. AgNPs applied as a colorimetric probe for the selective recognition of Hg(II) (linear range 10-200 μg L^-1, detection limit 1.16 μg L^-1). The probe was able to quantify Hg(II) in spiked tap, bore, and lake water samples and paper strips were developed to facilitate the onsite detection. Furthermore, freeze-drying of the AgNPs/HCNF nanocomposite produced aerogel that served as an excellent catalyst for the reduction of Congo red and methylene blue. The aerogel was easily recovered and reused without a decrease in activity or deterioration of its structure for five cycles. These results indicate the great potential of the AgNPs/HCNF aerogel for waste water treatment and catalytic applications.

Metallic Nanoparticles Obtained via “Green” Synthesis as a Platform for Biosensor Construction

Novel nanomaterials, including metallic nanoparticles obtained via green synthesis (gNPs), have a great potential for application in biotechnology, industry and medicine. The special role of gNPs is related to antibacterial agents, fluorescent markers and carriers for drug delivery. However, application of gNPs for construction of amperometric biosensors (ABSs) is not well documented. The aim of the current research was to study potential advantages of using gNPs in biosensorics. The extracellular metabolites of the yeast Ogataea polymorpha were used as reducing agents for obtaining gNPs from the corresponding inorganic ions. Several gNPs were synthesized, characterized and tested as enzyme carriers on the surface of graphite electrodes (GEs). The most effective were Pd-based gNPs (gPdNPs), and these were studied further and applied for construction of laccase- and alcohol oxidase (AO)-based ABSs. AO/GE, AO-gPdNPs/GE, laccase/GE and laccase-gPdNPs/GE were obtained, and their analytical characteristics were studied. Both gPdNPs-modified ABSs were found to have broader linear ranges and higher storage stabilities than control electrodes, although they are less sensitive toward corresponding substrates. We thus conclude that gPdNPs may be promising for construction of ABSs for enzymes with very high affinities to their substrates.

Eco-friendly synthesis of silver and gold nanoparticles with enhanced antimicrobial, antioxidant, and catalytic activities

The present work is emphasised on the bio-fabrication of silver and gold nanoparticles in a single step by a microwave-assisted method using the leaf extract of Synedrella nodiflora as both reducing and stabilising agent. The synthesised nanoparticles are highly stable and show surface plasmon resonance peak at 413 and 535 nm, respectively, for silver and gold nanoparticles in UV-Vis spectrum. The functional group responsible for the reduction of metal ions were obtained from Fourier transform infrared spectroscopy. The crystalline nature of nanoparticles with face-centred cubic geometry was confirmed by the X-ray diffraction and selected area electron diffraction patterns. The morphology and sizes of the silver and gold nanoparticles were obtained from transmission electron microscopy images. The nanoparticles exhibit effective antimicrobial activities against various pathogenic strains. These antimicrobial properties were analysed by employing agar well diffusion method. The nanoparticles show significant antioxidant properties, and it was determined using 2, 2-diphenyl-1-picrylhydrazyl assay. The nanoparticles also show potent catalytic activity in the degradation of anthropogenic pollutant dyes Congo red and eosin Y by excess NaBH4. Thus, the current study demonstrates the potential use of S. nodiflora as a reducing and stabilising agent for the synthesis of silver and gold nanoparticles and their relevance in the field of biomedicine and catalysis.

One-pot synthesis of layered double hydroxide hollow nanospheres with ultrafast removal efficiency for heavy metal ions and organic contaminants

Herein, Mg/Fe layered double hydroxide (MF-LDH) hollow nanospheres were successfully prepared by a one-step thermal method. After the thermal treatment of MF-LDH nanospheres at 400 °C, the MF-LDH was converted into the corresponding oxide, Mg/Fe layered double oxide (MF-LDO), which maintained the hollow nanosphere structure. The MF-LDO hollow nanospheres exhibited excellent adsorption efficiency for both As(V) and Cr(VI), showing 99% removal within 5 min and providing maximum removal capacities of 178.6 mg g^-1 [As(VI)] and 148.7 mg g^-1 [Cr(VI)]. Moreover, it met the maximum contaminant level requirements recommended by World Health Organization (WHO); 10 ppm for As(V) and 50 ppm for Cr(VI) in 10 and 20 min, respectively. Furthermore, Au nanoparticles were successfully introduced in the MF-LDO hollow nanospheres, and the products showed a conversion rate of 100% for the reduction of 4-nitrophenol into 4-aminophenol within 5 min. It is believed that these excellent and versatile abilities integrated with a facile synthetic strategy will facilitate the practical application of this material in cost-effective wastewater purification.

Detection of Intracellular Gold Nanoparticles: An Overview

Photothermal therapy (PTT) takes advantage of unique properties of gold nanoparticles (AuNPs) (nanospheres, nanoshells (AuNSs), nanorods (AuNRs)) to destroy cancer cells or tumor tissues. This is made possible thanks principally to both to the so-called near-infrared biological transparency window, characterized by wavelengths falling in the range 700–1100 nm, where light has its maximum depth of penetration in tissue, and to the efficiency of cellular uptake mechanisms of AuNPs. Consequently, the possible identification of intracellular AuNPs plays a key role for estimating the effectiveness of PTT treatments. Here, we review the recognized detection techniques of such intracellular probes with a special emphasis to the exploitation of near-infrared biological transparency window.