Green synthesis of silver nanoparticles and investigation of their colorimetric sensing and cytotoxicity effects

Mechanistic investigation of formation of highly-dispersed silver nanoparticles using sea buckthorn extract

Nowadays, the greener pathways for the synthesis of nanostructures are being explored. The extracts of different parts of plantsvizleaves, stems, and roots have been investigated. However, these extracts have been prepared by simply boiling or microwaving, or sonicating the parts of plants with water. Therefore, to have deeper insight and to investigate the full potential of plant extracts, serial extraction of leaves of sea buckthorn (Hippophae rhamnoides L.) which is a medicinally important plant was attempted using the soxhlet apparatus. The as-obtained polyphenolic-rich extract was employed for the preparation of silver nanoparticles (Ag-NPs). Under optimized reaction conditionsviz60 °C temperature and 500μl of extract solution (5 mg ml^-1) highly disperse spherical nanoparticles of the average size of 15.8 ± 4.8 nm were obtained. Further, the optical band gap of Ag-NPs prepared using optimized reaction conditions was found to be 2.6 eV using the Tauc equation. Additionally, to understand the reduction by the extract, kinetic studies were also carried out which suggest the predominant occurrence of pseudo-first-order reaction. Furthermore, the mechanism of formation of Ag-NPs using major components of extractvizgallic acid and catechin which were identified by HPLC were also investigated using DFT. The mechanistic investigation was performed for both the keto-enol and radical-mediated preparation of Ag-NPs. Such theoretical investigations will help in the efficient designing of greener and novel routes for the synthesis of Ag-NPs. Additionally, the prepared silver was also employed for the colorimetric detection of H₂O₂.

OXA-CuS@UiO-66-NH2 as a drug delivery system for Oxaliplatin to colorectal cancer cells

In this work, UiO-66-NH2 was used to prepare a new delivery system by incorporating copper sulfide (CuS) into the pores. The CuS nanoparticles (NPs) were prepared to enhance the anticancer effects of Oxaliplatin (OXA) against colorectal cancer. The oxaliplatin was loaded into CuS@UiO-66-NH2. To characterize and investigate their cytotoxicity effects, powder X-ray diffraction (PXRD), Fourier transformation infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) analysis, UV-Visible analysis, inductively coupled plasma mass spectrometry (ICP-MS), and MTT assay were considered to be performed. According to the observations, the cytotoxicity of OXA-CuS@UiO-66-NH2 was greater than that of the OXA alone.

Surface plasmon resonance allied applications of silver nanoflowers synthesized from Breynia vitis-idaea leaf extract

An environmentally friendly, green synthesis process has been adopted to synthesize silver nanoparticles (AgNPs) in an aqueous solution from a new remedial plant. Breynia vitis-idaea leaves act like natural capping and reducing agents. The resulting AgNPs were characterized and analyzed using different characterization techniques, such as UV-Vis spectroscopy, X-ray diffraction, zeta potential, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The UV-Vis absorption spectrum showed high stability and a surface plasmon resonance (SPR) peak around 430 nm. The effects of several processing variables, such as reaction time, temperature, concentration and pH, were analyzed. High temperature and alkaline pH intensify the ability to form flower-shaped AgNPs with enhanced properties. AgNPs were investigated for antibacterial activity against Gram-negative E. coli bacterial strains with a 10 mm zone of inhibition. These AgNPs showed dye degradation up to 88% when an aqueous crystal violet dye solution was mixed with AgNPs as the catalyst. Further, AgNPs alone were effectively used in the detection of hydrogen peroxide (H2O2) in an aqueous medium with a LOD (limit of detection) of 21 μM, limit of quantification (LOQ) of 64 μM and a decrease in absorption intensity up to 89%. Based on these results, these AgNPs were effectively used in numerous fields, such as biomedical, water purification, antibacterial and sensing of H2O2.

Sustainable and green trends in using plant extracts for the synthesis of biogenic metal nanoparticles toward environmental and pharmaceutical advances: A review

Conventionally utilized physical and chemical routes for constructing nanoparticles are not eco-friendly. They are associated with many shortcomings like the requirement of specially designed equipment, templates, extremely high temperature, and pressure. Biosynthesis seems to be drawn unequivocal attention owing to its upsurge of applications in different fields like; energy, nutrition, pharmaceutical, and medicinal sciences. To harness the biological sources, the present review describes an environment-friendly route to generate biogenic nanoparticles from the natural plant extracts and the followed mechanisms for their synthesis, growth, and stabilization. The present review summarizes the recent trends involved in the photosynthesis of metallic nanoparticles and their effective use in controlling malaria, hepatitis, cancer, like various endemic diseases. Also, various characterization approaches, such as UV-visible spectrophotometry, Fourier transform infrared spectroscopy, powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy, are discussed here examine the properties of as-fabricated nanoparticles. Various plant parts like leaves, stems, barks, fruit, and flowers are rich in flavonoids, phenols, steroids, terpenoids, enzymes, and alkaloids, thereby playing an essential role in reducing metal ions that generate metallic nanoparticles. Herein, the uniqueness of phytofabricated nanoparticles along with their distinctive antibacterial, antioxidant, cytotoxic, and drug delivery properties are featured. Lastly, this work highlights the various challenges and future perspectives to further synthesize biogenic metal nanoparticles toward environmental and pharmaceutical advances in the coming years.

Development of a surface-modified paper-based colorimetric sensor using synthesized Ag NPs-alginate composite

There has been an increase in the discovery and usage of sensors for the detection of chemical compounds in the field of analytical chemistry since the last several years. This has led to progressive research in nanotechnology for developing efficient nanomaterials for bio-chemical sensing applications. Thereby, a deft synthesis of silver nanoparticles (Ag NPs) under microwave irradiation was achieved using sodium alginate as a reducing and capping agent in a fast and cost-effective approach. As per the X-ray diffraction analysis, the average particle size of Ag NPs was found to be 10 nm. X-ray photoelectron spectroscpopy analysis showed characteristic peaks at binding energies of 368.10 and 374.11 eV indicating the formation of Ag NPs. The synthesized Ag NPs-alginate composite was further used to develop a paper-based sensor for the detection of H₂O₂. Detection of H₂O₂ is based on the discolouration of the Ag NPs-alginate composite modified paper sensor as a function of H₂O₂ concentration. The analysis of the decoloured paper strips was done by a smartphone camera and an RGB Colour Reader application (app) to measure colour intensity. The sensing characteristics were found in the range of 0.1-10 mM. The colour analysis revealed piecewise linear relationship of intensity of RGB to H₂O₂ concentration in the range of 0.1-1.5 and 2-10 mM with R² values of 0.97 and 0.9778, respectively. Owing to the high sensitivity, selectivity, and cost-effectiveness, the developed paper sensor can be a potential tool for real-time analysis of H₂O₂.

Biosynthesis of silver nanospheres, kinetic profiling and their application in the optical sensing of mercury and chlorite ions in aqueous solutions

Pollution of water linked to microbial decontamination and extensive use of sodium chlorite (NaClO₂) as a disinfectant, especially in the face of the current COVID-19 situation, is a serious water pollution issue that needs to be addressed. In this context, an environmentally friendly and cost-effective method has been developed for the biomimetic synthesis of Ag nanospheres (Ag NSs) using aqueous extract of Piper nigrum for the detection of chlorite (ClO₂^-) and mercury (Hg²⁺) ions. The strong antioxidant properties of the biomolecules present in the Piper nigrum extract reduce silver ions (Ag⁺) to Ag⁰. After optimization of the formulation parameters, it was observed that 1 mL of piper nigrum extract was sufficient to reduce and stabilize 100 mL of 1.5 mM of Ag⁺ in 2.5 h at 30 °C. X-ray diffraction (XRD) pattern of Ag NSs revealed their crystalline nature and the characteristic Bragg's diffraction peaks confirmed their face cubic crystal (FCC) lattice. The characteristic reddish-brown color and absorption surface plasmon resonance (SPR) band at 435 nm confirmed the successful fabrication of Ag NSs. Kinetic analysis revealed a three-phase growth pattern involving nucleation, growth and stabilization. Transmission electron microscopy (TEM) and High-resolution transmission electron microscopy (HRTEM) micrograms, showed spherical NSs with narrow polydispersity with particle size ranging from 10 to 30 nm. The synthesized NSs were exposed to various metal ions and anions. The absorption intensity of Ag NSs quenched in the presence of mercury ions (Hg²⁺) among the cations and Chlorite ions (ClO₂^-) among the anions. The limit of detection (LOD) of 7.47 μM and 1.11 μM was evaluated from the calibration curve for Hg²⁺ and ClO₂^-, respectively. Based on these promising results, it is suggested that the method reported is a low-cost and one step biogenic protocol for the synthesis of Ag NSs and their employment for the detection of Hg²⁺ and ClO₂^-ions.

Antimicrobial activity of silver nanoparticles synthesised by using microbial biosurfactant produced by a newly isolated Bacillus vallismortis MDU6 strain

Microbial biosurfactants has evolved as green molecules and their chemical diversity has gained momentum in recent time not only in the field of environmental and industrial sectors but also in the pharmaceutical sector. In this study, an effort was made for the biosynthesis of silver nanoparticle (AgNPs) having antimicrobial and non-cytotoxic activities with the help of microbial biosurfactant extracted from a novel Bacillus vallismortis strain MDU6 (Genbank accession no. MH382951) from petroleum oil logged soil sample in Dibrugarh, Assam. The isolate shows excellent potential for the production of biosurfactant by reducing the surface tension of diesel supplemented medium up to 56.57% only within 5 days. FTIR spectra of the crude biosurfactant show the presence of ʋ_CH2 (asymmetric stretching), ʋ_CH2 (symmetric stretching), ʋ_C=C (stretch), ʋ_C-C (stretch), ʋ_C-H (bending), ʋ_C-O (stretch) and ʋ_C-H (bending) functional groups and LC-MS/MS analysis confirms it as a cyclic lipopeptide which is a mixture of surfactin and iturin. The synthesized AgNPs showed excellent antimicrobial activities against Escherichia coli (ATCC no. 25922), Listeria monocytogenes (ATCC No. BAA-751), Staphylococcus aureus (ATCC No. 9542) and Bacillus subtilis (ATCC no. 6051) and showed no cytotoxicity against primary mouse liver cell lines.

Green Synthesis of Ag-MnO2 Nanoparticles using Chelidonium majus and Vinca minor Extracts and Their In Vitro Cytotoxicity

Medicinal plants are often used as reducing agents to prepare metal nanoparticles through green-synthesis due to natural compounds and their potential as chemotherapeutic drugs. Thus, three types of eco-friendly Ag-MnO₂ nanoparticles (Ag-MnO₂NPs) were synthesized using C. majus (CmNPs), V. minor (VmNPs), and a 1:1 mixture of the two extracts (MNPs). These NPs were characterized using S/TEM, EDX, XRD, and FTIR methods, and their biological activity was assessed in vitro on normal keratinocytes (HaCaT) and skin melanoma cells (A375). All synthesized NPs had manganese oxide in the middle, and silver oxide and plant extract on the exterior. The NPs had different forms (polygonal, oval, and spherical), uniformly distributed, with crystalline structures and different sizes (9.3 nm for MNPs; 10 nm for VmNPs, and 32.4 nm for CmNPs). The best results were obtained with VmNPs, which reduced the viability of A375 cells up 38.8% and had a moderate cytotoxic effect on HaCaT (46.4%) at concentrations above 500 µg/mL. At the same concentrations, CmNPs had a rather proliferative effect, whereas MNPs negatively affected both cell lines. For the first time, this paper proved the synergistic action of the combined C. majus and V. minor extracts to form small and uniformly distributed Ag-MnO₂NPs with high potential for selective treatments.

Role of Ribes khorassanicum in the biosynthesis of AgNPs and their antibacterial properties

Silver nanoparticles (AgNPs) have been biosynthesised through the extracts of Ribes khorassanicum fruits, which served as the reducing agents and capping agents. Biosynthesised AgNPs have been found to be ultraviolet-visible (UV-vis) absorption spectra since they have displayed one surface plasmon resonance peak at 438 nm, attesting the formation of spherical NPs. These particles have been characterised by UV-vis, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electron microscopy analysis. The formation of AgNPs at 1.0 mM concentration of AgNO3 has resulted in NPs that contained mean diameters in a range of 20-40 nm. The green-synthesised AgNPs have demonstrated high antibacterial effect against pathogenic bacteria (i.e. Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa). Biosynthesising metal NPs through plant extracts can serve as the facile and eco-friendly alternative for chemical and/or physical methods that are utilised for large-scale nanometal fabrication in various medical and industrial applications.