Facile design and nanostructural evaluation of silver-modified titania used as disinfectant

Development of Nano-Antifungal Therapy for Systemic and Endemic Mycoses

Fungal mycoses have become an important health and environmental concern due to the numerous deleterious side effects on the well-being of plants and humans. Antifungal therapy is limited, expensive, and unspecific (causes toxic effects), thus, more efficient alternatives need to be developed. In this work, Copper (I) Iodide (CuI) nanomaterials (NMs) were synthesized and fully characterized, aiming to develop efficient antifungal agents. The bioactivity of CuI NMs was evaluated using Sporothrix schenckii and Candida albicans as model organisms. CuI NMs were prepared as powders and as colloidal suspensions by a two-step reaction: first, the CuI2 controlled precipitation, followed by hydrazine reduction. Biopolymers (Arabic gum and chitosan) were used as surfactants to control the size of the CuI materials and to enhance its antifungal activity. The materials (powders and colloids) were characterized by SEM-EDX and AFM. The materials exhibit a hierarchical 3D shell morphology composed of ordered nanostructures. Excellent antifungal activity is shown by the NMs against pathogenic fungal strains, due to the simultaneous and multiple mechanisms of the composites to combat fungi. The minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of CuI-AG and CuI-Chitosan are below 50 μg/mL (with 5 h of exposition). Optical and Atomic Force Microscopy (AFM) analyses demonstrate the capability of the materials to disrupt biofilm formation. AFM also demonstrates the ability of the materials to adhere and penetrate fungal cells, followed by their lysis and death. Following the concept of safe by design, the biocompatibility of the materials was tested. The hemolytic activity of the materials was evaluated using red blood cells. Our results indicate that the materials show an excellent antifungal activity at lower doses of hemolytic disruption.

Biogenic Fabrication, Characterization and Drug Loaded Antimicrobial Assay of Silver Nanoparticles Using Centratherum anthalminticum (L.) Kuntze

Bionanotechnology is considered a safe and ecofriendly route for the biosynthesis of metal nanoparticles from plant extracts, microorganisms, and biomaterials. The present study was focused on the fabrication of silver nanoparticles (<50 nm) biogenically from the novel Centratherum anthelmminticum's aqueous seed extract. The obtained nanoproduct was evaluated by X-ray diffraction analysis (XRD), Scanning electron microscopy (SEM), UV-Visible spectroscopy, FTIR and Raman spectroscopy. The particle size and surface charge were estimated by Dynamic light scattering (DLS) and Zeta potential measurements. The nanoparticles showed cubic close packed (ccp) morphology with miller indices (111), (200), (220), (311) and (222). The λ_max for synthesized silver nanoparticles was measured in the range of 436 nm, 464 nm and 467 nm for 1 mM, 5 mM and 10 mM samples, respectively. The bioreduction of silver ions exhibited a gradual color change which confirms the formation of silver nanoparticles under UV-visible spectrum. Ag-O and Ag-N stretching vibrations corresponding to the bond formation between silver and oxygen of the carboxylate group and nitrogen of amine was corroborated by the presence of a sharp peak in Raman spectra at 245 cm^-1. Antimicrobial activity was assessed against eight bacterial and three fungal strains. The silver nanoparticles fabricated from 10 mM AgNO₃ solution showed significant results against all Gram-negative bacteria, with the further restriction in growth of C. albicans and A. niger. From in-vitro antimicrobial assay, it was observed that drug-loaded silver nanoparticles (Ciprofloxacin +10 mM) displayed a stronger potential than the synthesized silver nanoparticles and ciprofloxacin alone to restrain the development of E. coli, and E. aerogenes.

Antimicrobial Metal Nanomaterials: From Passive to Stimuli-Activated Applications

The development of antimicrobial drug resistance among pathogenic bacteria and fungi is one of the most significant health issues of the 21st century. Recently, advances in nanotechnology have led to the development of nanomaterials, particularly metals that exhibit antimicrobial properties. These metal nanomaterials have emerged as promising alternatives to traditional antimicrobial therapies. In this review, a broad overview of metal nanomaterials, their synthesis, properties, and interactions with pathogenic micro-organisms is first provided. Secondly, the range of nanomaterials that demonstrate passive antimicrobial properties are outlined and in-depth analysis and comparison of stimuli-responsive antimicrobial nanomaterials are provided, which represent the next generation of microbiocidal nanomaterials. The stimulus applied to activate such nanomaterials includes light (including photocatalytic and photothermal) and magnetic fields, which can induce magnetic hyperthermia and kinetically driven magnetic activation. Broadly, this review aims to summarize the currently available research and provide future scope for the development of metal nanomaterial-based antimicrobial technologies, particularly those that can be activated through externally applied stimuli.

Use of natural products as green reducing agents to fabricate highly effective nanodisinfectants

Disinfection of water using nanoparticles (NPs) can be achieved through selection of either metals (M) or transition metal oxides (TMO). In this research, 64 formulations of silver-titania nanocomposites (Ag/TiO2) were prepared via a feasible wet-chemistry technique using different natural products as reducing agents. Four selected products successfully reduced Ag(+) ions to Ag, allowing Ag/TiO2 composite to efficiently inactivate microbes found in the activated sludge. The degree of antibacterial activity was measured using zone of inhibition, which indicated all formulations inactivated the bacteria with high potency (0.01 I/6 h). The results from this study and comparison of literature values collectively suggest that light roasted coffee acted as one of the best natural reducing agents due to its low antioxidant index (LAI). Our selection framework also suggested any M/TMO with an oxygen reduction potentials (ORP) range of -0.41 to +1.23 V and any natural product with a LAI (<0.5) would be suitable as a reducing agent. Collectively, the high ORP and low AI provide effective disinfection of water-borne microbes.

Highly potent bactericidal activity of porous metal-organic frameworks

Recent outbreaks of bacterial infection leading to human fatalities have been a motivational force for us to develop antibacterial agents with high potency and long-term stability. A novel cobalt (Co) based metal-organic framework (MOF) was tested and shown to be highly effective at inactivating model microorganisms. Gram-negative bacteria, Escherichia coli (strains DH5alpha and XL1-Blue) were selected to determine the antibacterial activities of the Co MOF. In this MOF, the Co serves as a central element and an octa-topic carboxylate ligand, tetrakis [(3,5-dicarboxyphenyl)-oxamethyl] methane (TDM(8-) ) serves as a bridging linker. X-ray crystallographic studies indicate that Co-TDM crystallizes in tetragonal space group P$\overline 4$2(1) m with a porous 3D framework. The potency of the Co-TDM disinfectant was evaluated using a minimal bactericidal concentration (MBC) benchmark and was determined to be 10-15 ppm within a short incubation time period (<60 min). Compared with previous work using silver nanoparticles and silver-modified TiO(2) nano- composites over the same time period, the MBC and effectiveness of Co-TDM are superior. Electron microscopy images indicate that the Co-TDM displayed distinctive grain boundaries and well-developed reticulates. The Co active sites rapidly catalyzed the lipid peroxidation, causing rupture of the bacterial membrane followed by inactivation, with 100% recycling and high persistence (>4 weeks). This MOF-based approach may lead to a new paradigm for MOF applications in diverse biological fields due to their inherent porous structure, tunable surface functional groups, and adjustable metal coordination environments.

Green synthesis and antibacterial effect of silver nanoparticles using Vitex negundo L

Different biological methods are gaining recognition for the production of silver nanoparticles (Ag-NPs) due to their multiple applications. One of the most important applications of Ag-NPs is their use as an anti-bacterial agent. The use of plants in the synthesis of nanoparticles emerges as a cost effective and eco-friendly approach. In this study the biosynthesis of silver nanoparticles using Vitex negundo L. extract and its antimicrobial properties has been reported. The resulting silver particles are characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV-Visible (UV-Vis) spectroscopic techniques. The TEM study showed the formation of silver nanoparticles in the 10-30 nm range and average 18.2 nm in size. The XRD study showed that the particles are crystalline in nature, with a face centered cubic (fcc) structure. The silver nanoparticles showed the antimicrobial activity against Gram positive and Gram negative bacteria. Vitex negundo L. was found to display strong potential for the synthesis of silver nanoparticles as antimicrobial agents by rapid reduction of silver ions (Ag+ to Ag0).