Microwave-assisted incorporation of silver nanoparticles in paper for point-of-use water purification

Green Synthesized Silver Nanoparticles Loaded in Polysaccharide Hydrogel Applied to Chronic Wound Healing in Mice Models

The prevalence of chronic wounds is increasing owing to the expanding population and the growing number of individuals suffering from diabetes. Such a chronic wound continues to be a significant healthcare burden for diabetic patients because it frequently carries a high chance of limb loss due to amputation and reduces survival as a result. Development of innovative wound dressing materials with the potential to stop bacterial infections and accelerate the process of tissue regeneration is needed to increase the effectiveness of diabetic wound healing. In the current study, a co-polymerization process based on a free radical reaction was used to create a hydrogel of polysaccharides blend graft acrylamide (PsB-g-Am). Starch, chitosan, and alginate make up the polysaccharides blend (PsB). The produced hydrogel's structure was characterized using FTIR spectroscopy. The antibacterial activities of silver nanoparticles synthesized through the green method using garlic bulb (Allium sativum) is reported. The silver nanoparticles' physical characteristics were examined using scanning electron microscopy, transmission electron microscopy analysis, and UV-visible spectroscopy and they were found to range in size from 50 to 100 nm. The agar well diffusion technique is used to investigate the antibacterial characteristics. Inclusion of silver nanoparticles in the hydrogels demonstrated concentration-dependent antibacterial behavior against Gram-negative Klebsiella pneumoniae and Gram-positive Staphylococcus aureus during antimicrobial testing of the hydrogels. When hydrogels were applied to diabetic mice, the system was examined for its healing abilities, and positive therapeutic results were obtained in as little as 14 days. Thus, it can be inferred that graft copolymer of chitosan-AgNPs hydrogels can promote healing in chronic wounds over time and can be utilized as an alternative to conventional therapies for chronic wounds (such as those brought on by diabetes) in mouse models.

Hierarchical Bamboo/Silver Nanoparticle Composites for Sustainable Water Purification

Water reclamation is the most effective way to continuously provide clean water to combat catastrophic global water scarcity. However, current technology for water purification is not conducive to sustainability due to the high energy consumption and negative environmental impact. Here, we introduce an innovative method by utilizing the hierarchical microstructure of bamboo for water purification. Natural bamboo was delignified followed by freeze-drying to obtain a bamboo aerogel with a porosity of 72.0%; then, the bamboo aerogel was coated with silver nanoparticles to form a hierarchical bamboo/silver nanoparticle composite. The scanning electron microscopy images and energy-dispersive X-ray spectroscopy results indicated that the silver nanoparticles were uniformly attached to the parenchyma cell surface. By physical adsorption and catalytic reduction, the bamboo/silver nanoparticle composite was able to degrade methylene blue by more than 96.7%, which is mainly attributed to the large specific surface area of the bamboo providing more space for the purification reaction. This composite can be potentially used for board applications with its high porosity, mechanical reliability, and sustainability.

Chronic wound healing by controlled release of chitosan hydrogels loaded with silver nanoparticles and calendula extract

As the skin is the main protective organ of the body, it is exposed to wounds or injuries which carry out a healing process during a period of approximately 15 days depending on the severity of the injury. In the present research, the development of chitosan-based hydrogels loaded with silver nanoparticles and calendula extract (Ch-AgNPs-Ce) was proposed. This can be used to fulfill the hemostatic, anti-infective, antibacterial, healing and anti-inflammatory functions through controlled release of the nanoparticles and calendula extract in substitution of commonly used drugs. The physical properties of the silver nanoparticles were analyzed by UV-visible spectroscopy, scanning and transmission electron microscopy, showing a size between 50 and 100 nm. The antibacterial properties were evaluated by the agar well diffusion method. Antimicrobial testing of the hydrogels showed that the inclusion of silver nanoparticles provides concentration-dependent antibacterial behavior against E. coli and S. aureus. The healing properties of the system were tested in two diabetic patients to whom said hydrogels were placed, obtaining a positive curative result after a few weeks. Therefore, it can be concluded that Ch-AgNPs-Ce hydrogels can achieve healing in chronic or exposed wounds after a period of time which can be used in alternative treatments in patients with poor healing capacity.

Well-Dispersed Silver Nanoparticles on Cellulose Filter Paper for Bacterial Removal

In this study, a polydopamine (PDA) and polyethyleneimine (PEI)-assisted approach was developed to generate well-distributed PDA/PEI/silver (PDA/PEI/Ag) nanocomplexes on the surfaces of commercial cellulose filter papers to achieve substantial bacterial reduction under gravity-driven filtration. PDA can bind to cellulose paper and act as a reducer to produce silver nanoparticles (AgNPs), while PEI can react with oxidative dopamine and act as a dispersant to avoid the aggregation of AgNPs. The successful immobilization of PDA/PEI/Ag nanocomplexes was confirmed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) were used as pathogen models to test the efficacy of the PDA/PEI/Ag nanocomplex-incorporated filter papers. The PDA/PEI/Ag nanocomplex-incorporated filter papers provided a substantial bacterial removal of up to 99% by simple gravity filtration. This work may be useful to develop a feasible industrial production process for the integration of biocidal AgNPs into cellulose filter paper and is recommended as a local-condition water-treatment technology to treat microbial-contaminated drinking water.

Lignin-mediated in-situ synthesis of CuO nanoparticles on cellulose nanofibers: A potential wound dressing material

Herein we present our research on the synthesis of CuO nanoparticles on the surface of electrospun cellulose (CE) nanofibers using alkali lignin as a reducing agent. Fascinatingly, CA nanofibers were deacetalized during alkali lignin treatment, which was verified by FTIR-ATR spectra. The morphology of the produced nanofibers was observed with SEM and TEM. The presence of CuO nanoparticles was verified by EDX, XRD, and XPS. The Cu/CE nanofibers showed low thermal stability. MVTR values of 2100-1900 g/m²/day are adequate for the transport of air and moisture from the wound surface. The Cu/CE showed faster release (80%) of copper ions to aqueous environment within 24 h and seemed to advance towards plateau for the next five days. The Cu/CE nanofibrous mats exhibited excellent antibacterial efficacy against both gram-negative Escherichia coli (E. coli) and gram-positive Staphylococcus aureus (S. aureus) bacteria. NIH3T3 fibroblast cells have excellent migrating and proliferating ability on our prepared nanofibrous mats. The presence of bound alkali lignin on the surface of nanofibers added a benefit of antioxidant activity. These findings revealed that such type of nanofibrous mats could be used as a potential wound dressing material.

Vertical flow paper-based plasmonic device for cysteine detection

Cystinuria, is an autosomal recessive genetic disorder involving increasingly high levels of poorly soluble cysteine in urine leading to formation of stones. Developing a facile, low-cost, point-of-care and selective sensor for diagnosis of cysteine is imperative. Accordingly, for the detection of cysteine, the present study demonstrates an inexpensive colorimetric, paper-based vertical flow plasmonic micro-well device with a two-minute turn-around time. The method encompasses the use of microbially-synthesized silver nanoparticles (AgNPs) that change from light brown / yellow to dark brown upon binding with Sulphur present in cysteine. This technique allows for visual detection up to 1 × 10^-5 mM cysteine and can be easily offered as a rapid diagnostic test even at setups with minimal resources.

Deactivation of E. coli in water using Fe3+-saturated montmorillonite impregnated filter paper

In areas with high exposure to pathogen contaminated water and lack the economic means for water treatment, low cost and convenient point-of-use drinking water disinfection materials/devices are essential. Using a simple craft paper making method, Fe³⁺-saturated montmorillonite impregnated filter paper was constructed to filter live Escherichia coli (E. coli)-spiked water. The Scanning Electron Microscopic images of the E. coli cells in contact with the Fe³⁺-saturated montmorillonite impregnated filter paper showed: 1) Fe³⁺-saturated montmorillonite particles were uniformly coated on the cellulose paper fiber, creating large mineral surface for cell contact; and 2) E. coli cell membrane was dehydrated and damaged, resulting cell deactivation upon contacting with the Fe³⁺-saturated montmorillonite particles impregnated in the paper. The E. coli cells passing through the Fe³⁺-saturated montmorillonite impregnated filter paper were not viable as further confirmed by the microfluidic dielectrophoresis analysis. They remained non-viable at room temperature even after 5 days, as shown by the results from both the Colony Counting test and the Colilert test. More than 99.5% deactivation efficiency was achieved when the ratio of the volume of the E. coli contaminated water to the mass of Fe³⁺-saturated montmorillonite was maintained at <1:1.5 (mL/mg). The Fe³⁺-saturated montmorillonite impregnated filter paper maintained ~74% E. coli deactivation efficiency even after the 8th consecutive use. About 0.52 mg Fe³⁺, which is bioavailable, could be leached into the water for every 2 L E coli-contaminated water that is treated with the filter paper. The treated water could therefore provide iron supplement to a person at a level within the range of the FDA recommended human daily intake of iron. The results from this study has clearly demonstrated promising potential of using the Fe³⁺-saturated montmorillonite impregnated filter paper for low cost (~$0.07/L treated water for this study) and convenient point-of-use drinking water disinfection.

Prussian blue-encapsulated Fe3O4 nanoparticles for reusable photothermal sterilization of water

Waterborne health issues continue to grow despite the large number of available solutions. Current sterilization techniques to fight with waterborne diseases struggle to meet the demands on cost, efficiency and reach. Effective alternatives are pressingly required. Here we introduce Prussian blue coated ferroferric oxide (Fe₃O₄@PB) composites for water sterilization. The composites exhibit superior photothermal inactivation of bacteria under solar-light irradiation, with nearly complete inactivation of bacterial cells in only 15 min. Even for the mixed bacteria in authentic water matrices, the composites show excellent bacterial inactivation performance. Moreover, the highly magnetized iron core of the Fe₃O₄@PB enables magnetic separation and recycling. Multiple cycle runs reveal that Fe₃O₄@PB composites have exceptional stability and reusability. This work demonstrates a scalable, low-cost, high-efficiency and reusable sterilization method to improve water quality and safety.

Killing Two Birds with One Stone: Coating Ag NPs Embedded Filter Paper with Chitosan for Better and Durable Point-of-Use Water Disinfection

In this study, porous chitosan (CS) coated Ag NPs embedded filter paper (CAEFP) was fabricated for point-of-use water disinfection application. Thanks for the presence of CS coating, the tensile strength of the CAEFP in wet condition was found to be 1.8 MPa, 700% increase compared with where there was no CS coating, making it much more durable. In addition, the coating with CS could greatly boost the Ag NPs loading without worrying about the excessive release of Ag into the treated water, thereby significantly improving the bactericidal efficiency but still be safe to drink in terms of Ag release. Furthermore, by controlling the amount of CS used, the flow rate and bactericidal efficiency of the CAEFP could be manipulated (customized). When the CS content increased from 0.5 to 2.0 wt %, the flow rate of CAEFP would drop from 9.3 to 0.53 L/min/m², and the bactericidal efficiency against Escherichia coli and Bacillus subtilis could improve from 4 and 3.6 to 4.9 and 4.8 log reduction, respectively. At optimum condition, the total Ag in treated water by CAEFP was below 45 μg/L, only 1/10 of that from Ag NPs loaded filter paper without CS coating, half of the WHO drinking water requirement (<100 μg/L). Natural surface water samples were used for the demonstration of the bactericidal performance of the CAEFP. Both the total bacterial and E. coli counts met the WHO standard.

Bio-fabrication of silver nanoparticles by Pseudomonas aeruginosa: optimisation and antibacterial activity against selected waterborne human pathogens

Multiple drug resistance and treatment of contaminated water has become a serious issue in past years. Silver nanoparticles (AgNPs), being bactericidal, non-toxic, cheap and environment friendly behaviour, have drawn attention to overcome these problems. This study has been designed to synthesise AgNPs from Pseudomonas aeruginosa. AgNPs formation was confirmed by colour change and UV-vis spectroscopy. Furthermore, Fourier transform infrared spectroscopy peaks demonstrated the presence of capped proteins as reducing and stabilising agent. Transmission electron microscopy micrograph revealed spherical shape AgNPs with the size ranging between 10 and 20 nm. Antibacterial activity of AgNPs was evaluated against the most prevalent waterborne pathogens enterohaemorrhagic Escherichia coli and Salmonellae typhimurium. Moreover, the antibacterial activity of AgNPs was tested for the treatment of contaminated water which showed attenuation in bacterial load within 8 h as demonstrated by growth kinetics data. Furthermore, AgNPs did not exhibit haemolytic effects on human red blood cells (RBCs) even at 100 mg L-1 concentration of AgNPs. The results herein suggest that AgNPs synthesised by P. aeruginosa under optimised conditions exhibit microbicidal property against waterborne pathogens and having no toxic effect on human RBCs. These AgNPs could be employed for treatment of contaminated water after process optimisation.

In Situ Preparation of Silver Nanoparticles in Paper by Reduction with Alkaline Glucose Solutions

Percolation of contaminated water through paper sheets containing silver nanoparticles is a promising way to provide emergency drinking water. The silver nanoparticles are deposited by the in situ reduction of silver nitrate on the cellulose fibers of an absorbent blotting paper sheet. Sodium borohydride has been used as the reductant but is toxic and expensive. Glucose is a benign alternative but is much less reactive. In this note, we demonstrate an improved way to produce silver nanoparticles in paper sheets by adding sodium hydroxide to the glucose reductant. The silver content of the sheets, measured by diffuse reflectance spectroscopy, was around 2-3 mg of silver per gram of dry paper. This was sufficient to reduce the concentration of a model Escherichia coli suspension after percolation through the sheet.

A New Method for the Deposition of Metallic Silver on Porous Ceramic Water Filters

A new method of silver application to a porous ceramic water filter used for point-of-use water treatment is developed. We evaluated filter performance for filters manufactured by the conventional method of painting an aqueous suspension of silver nanoparticles onto the filter and filters manufactured with a new method that applies silver nitrate to the clay-water-sawdust mixture prior to pressing and firing the filter. Filters were evaluated using miscible displacement flow-through experiments with pulse and continuous-feed injections of E. coli. Flow characteristics were quantified by tracer experiments using [3H]H2O. Experiments using pulse injections of E. coli showed similar performance in breakthrough curves between the two application methods. Long-term challenge tests performed with a continuous feed of E. coli and growth medium resulted in similar log removal rates, but the removal rate by nanosilver filters decreased over time. Silver nitrate filters provided consistent removal with lower silver levels in the effluent and effective bacterial disinfection. Results from continued use with synthetic groundwater over 4 weeks, with a pulse injection of E. coli at 2 and 4 weeks, support similar conclusions—nanosilver filters perform better initially, but after 4 weeks of use, nanosilver filters suffer larger decreases in performance. Results show that including silver nitrate in the mixing step may effectively reduce costs, improve silver retention in the filter, increase effective lifespan, and maintain effective pathogen removal while also eliminating the risk of exposure to inhalation of silver nanoparticles by workers in developing-world filter production facilities.

Power and Time Dependent Microwave Assisted Fabrication of Silver Nanoparticles Decorated Cotton (SNDC) Fibers for Bacterial Decontamination

Plasmonic nanoparticles (NPs) such as silver and gold have fascinating optical properties due to their enhanced optical sensitivity at a wavelength corresponding to their surface plasmon resonance (SPR) absorption. Present work deals with the fabrication of silver nanoparticles decorated cotton (SNDC) fibers as a cheap and efficient point of contact disinfectant. SNDC fibers were fabricated by a simple microwave assisted route. The microwave power and irradiation time were controlled to optimize size and density of silver nanoparticles (SNPs) on textile fibers. As prepared cotton fabric was characterized for ATR-FTIR, UV-VIS diffuse reflectance, SEM and TEM investigations. Size of SNPs as well as total density of silver atoms on fabric gets increased with the increase of microwave power from 100 W to 600 W. The antibacterial efficacy of SNPs extracted from SNDC fibers was found to be more effective against Gram-negative bacteria than Gram-positive bacteria with MIC 38.5 ± 0.93 μg/mL against Salmonella typhimurium MTCC-98 and 125 ± 2.12 μg/mL against Staphylococcus aureus MTCC-737, a linear correlation coefficient with R² ranging from ∼0.928–0.935 was also observed. About >50% death cells were observed through Propidium Iodide (PI) internalization after treatment of SNPs extracted from SNDC fibers with concentration 31.25 μg/mL. Generation of ROS and free radical has also been observed which leads to cell death. Excellent Escherichia coli deactivation efficacy suggested that SNDC fibers could be used as potentially safe disinfectants for cleaning of medical equipment, hand, wound, water and preservation of food and beverages.

Cellulose as a Scaffold for Self-Assembly: From Basic Research to Real Applications

Cellulose has received a tremendous amount of attention both in academia and industry owing to its unique structural features, impressive physical-chemical properties, and wide applications. This natural polymer is originally used for packaging, paper, lightweight composites, and so forth and is now being developed for various new areas, such as antibacterial treatment, catalysis, water purification and separation, and biological and environmental analysis. In the current article, we summarize the recent developments in the self-assembly of cellulose with various species including metal ions and metal and metal oxide nanoparticles. Then we highlight several key application areas of cellulose-based composites by reviewing the recent representative literature in each area. A significant part of this review demonstrates some exciting innovations for a wide range of practical applications of cellulose-based composites. Some challenges are also discussed with a view toward future developments.

Inactivation of bacteria from contaminated streams in Limpopo, South Africa by silver- or copper-nanoparticle paper filters

There is an urgent need for inexpensive point-of-use methods to purify drinking water in developing countries to reduce the incidence of illnesses caused by waterborne pathogens. Previously, our work showed the deactivation of laboratory-cultured bacteria by percolation through a thick paper sheet containing either silver (Ag) or copper (Cu) nanoparticles (NP). In this study, these paper filters containing AgNPs or CuNPs have been tested with water sourced from contaminated streams in Limpopo, South Africa. Following the percolation of the contaminated stream water through the metal nanoparticle (MNP) papers, the water quality of the filtered effluent was evaluated with respect to the colony counts of total coliform and E. coli bacteria, turbidity, and either silver or copper ions. Influent total coliform bacteria concentrations from the stream water in Limpopo ranged from 250 CFU/100 mL to 1,750,000 CFU/100 mL. With the less contaminated stream water (250 - 15,000 CFU/100 mL), both AgNP and CuNP papers showed complete inactivation of the coliform bacteria. With the surface water with higher coliform bacteria levels (500,000 - 1,000,000 CFU/100 mL), both the AgNP and CuNP papers showed similar results with a slightly higher bacteria reduction of log10 5.1 for the AgNP papers than the log10 4.8 reduction for the CuNP papers. E. coli results followed similar trends. For most water purification experiments, the metal release from the sheets was minimal, with values under 0.1 ppm for Ag and 1.0 ppm for Cu (the current US EPA and WHO drinking water limits for Ag and Cu, respectively). These results show good potential for the use of paper embedded with silver and/or copper nanoparticles as effective point-of-use water purifiers.

Incorporation of copper nanoparticles into paper for point-of-use water purification

As a cost-effective alternative to silver nanoparticles, we have investigated the use of copper nanoparticles in paper filters for point-of-use water purification. This work reports an environmentally benign method for the direct in situ preparation of copper nanoparticles (CuNPs) in paper by reducing sorbed copper ions with ascorbic acid. Copper nanoparticles were quickly formed in less than 10 min and were well distributed on the paper fiber surfaces. Paper sheets were characterized by x-ray diffraction, scanning electron microscopy, energy dispersive x-ray spectroscopy, and atomic absorption spectroscopy. Antibacterial activity of the CuNP sheets was assessed for by passing Escherichia coli bacteria suspensions through the papers. The effluent was analyzed for viable bacteria and copper release. The CuNP papers with higher copper content showed a high bacteria reduction of log 8.8 for E. coli. The paper sheets containing copper nanoparticles were effective in inactivating the test bacteria as they passed through the paper. The copper levels released in the effluent water were below the recommended limit for copper in drinking water (1 ppm).