Low-cost hybrid copper–carbon nanotube coating with antimicrobial properties in ambient conditions

Grapes are rich in phenolic compounds with potent antioxidant properties that mitigate risks associated with cardiovascular and neurodegenerative diseases. However, postharvest storage often leads to microbial infestations, significantly deteriorating fruit quality. This study investigated the effects of two composite edible coatings i.e., Coffee Husk Pectin-Clove Oil (CHP-CO) and Freeze-Dried Coffee Husk Pectin-Clove Oil (FD-CHP-CO) on prolonging the shelf life of grapes. Coated and uncoated grapes were evaluated for their physicochemical (weight loss, colour, pH, total soluble solids and titratable acidity), bioactive compounds (total phenolics and total flavonoids), in vitro antioxidant and antimicrobial properties during 14 d of storage at ambient (RT, 25 ± 1 °C) and cold (4 ± 1 °C) storage conditions. Coated grapes maintained better quality compared to uncoated grapes, with FD-CHP-CO reducing weight loss by up to 76 % at ambient conditions (0.92 ± 0.26 % vs. 3.89 ± 1.63 % in uncoated grapes). The FD-CHP-CO coating also resulted in a significant inhibition zone increase against Staphylococcus aureus MTCC 96 from 11 to 15 mm. Additionally, the coated grapes showed higher retention of bioactive compounds, with total phenolics and total flavonoids retention of 86.9 % and 83.7 %, respectively. These results suggest that CHP-CO and FD-CHP-CO coatings effectively extend the shelf life of grapes, maintaining their quality and safety during storage, and highlight the potential of these coatings in reducing food waste and improving consumer satisfaction.Graphical

As copper and its compounds are of fundamental importance for the development of innovative materials, the synthesis of composites intended for water purification was undertaken in which submicron copper containing particles were dispersed within the matrix of a strongly basic anion exchanger, with a macroporous and gel-like structure. Due to their trimethylammonium functional groups, the host materials alone exhibited an affinity to anionic water contaminants and antimicrobial properties. The introduction of such particles as CuO, Cu2O, metallic Cu, CuO/FeO(OH), Cu4O3, Cu(OH)2, Cu4(OH)6SO4, Cu2(OH)3Cl increased these properties and demonstrated new properties. The composites were obtained unconventionally, in ambient conditions, using eco-friendly reagents. Alternative synthesis methods were compared and optimized, as a result of which a new group of hybrid ion exchangers was created (HIXs) containing 3.5–12.5 wt% of Cu. As the arrangement of the inorganic phase in the resin matrix was atypical, i.e., close to the surface of the beads, the obtained HIXs exhibited excellent kinetic properties in the process of oxidation and adsorption of As(III), as well as catalytic properties for the synthesis of triazoles via click reaction, and also antimicrobial properties in relation to Gram-positive Enterococcus faecalis and Gram-negative Pseudomonas aeruginosa and Escherichia coli, preventing biofilm formation. Using thermogravimetry, the effect of the inorganic phase on decomposition of the polymeric phase was evaluated for the first time and comprehensively, confirming the relationship and finding numerous regularities. It was also found that, depending on the oxidation state (CuO, Cu2O, Cu), copper-containing particles affected the textural properties of the polymeric phase endowing a tighter structure, limiting the porosity and reducing the affinity for water.

Biodegradable polymer electronics offer an innovative solution to the growing challenge of electronic waste, which are engineered to disintegrate after a defined functional period. Here, a new class of graft copolymer is presented, ε‐poly‐L‐lysine‐graft‐oligo(3‐hexylthiophene) (EPL‐g‐O3HTs), synthesized by covalently grafting oligo(3‐hexylthiophene) onto the biopolymer ε‐poly‐L‐lysine at three grafting densities, resulting in copolymers containing 43, 65 and 90 wt.% O3HT (EPL‐g‐O3HT‐1, EPL‐g‐O3HT‐2 and EPL‐g‐O3HT‐3, respectively). Benefiting from the “guidance” of ε‐poly‐L‐lysine on O3HT chains alignment, the graft copolymer with optimized grafting density exhibits an extended conjugation length and increased crystallite size of O3HT. Thin films of three copolymers, upon doping, demonstrate appreciable conductivity under ambient conditions. EPL‐g‐O3HT‐1 could be fully break down over 12 days by enzymatic degradation. EPL‐g‐O3HT‐1 also displays excellent broad‐spectrum antibacterial activity against Gram‐negative and Gram‐positive bacteria, attributed to its high ɛ‐poly‐L‐lysine content. It is further demonstrated the versatility of EPL‐g‐O3HTs in transient electronics for electromyography sensors for muscle signal acquisition and as the channel material in organic electrochemical transistors. Combining tunable conductivity, controlled biodegradability, and antimicrobial properties, EPL‐g‐O3HT copolymers hold significant potential for diverse transient electronic applications, including skin and implantable electronics, where degradable electronics with antimicrobial properties are highly desirable.

New bio-based packaging materials are highly interesting for replacing conventional fossil based products for a more sustainable society. Water-stable cellulose fiber foams have been produced in a simple one-batch foam-forming process with drying under ambient conditions. The cellulose fiber foams have a low density (33–66 kg/m3) and can inhibit microbial growth; two highly valuable features for insulating packaging materials, especially in combination with stability in water. Cationic chitosan and/or polyvinylamine have been added during the foam-forming process to give the foams water-stability and antimicrobial properties. The structural and mechanical properties of the cellulose fiber foams have been studied and the antimicrobial properties have been evaluated with respect to both Escherichia coli, a common model bacteria and Aspergillus brasiliensis, a sporulating mold. The cellulose foams containing chitosan had both good water-stability and good antibacterial and antifungal properties, while the foams containing PVAm did disintegrate in water and did not inhibit fungal growth when nutrients were added to the foam, showing that it is possible to produce a bio-based foam material with the desired characters. This can be an interesting low-density packaging material for protection from both mechanical and microbial damage without using any toxic compounds.

Chitosan-based film with enhanced gas permeability and antimicrobial property for fresh fruit preservation.

Cefalexin-immobilized multi-walled carbon nanotubes show strong antimicrobial and anti-adhesion properties

Despite unique and useful properties of multi-walled carbon nanotubes (MWNTs) such as high strength and a low synthesis cost, their weak antimicrobial property hampers their use as an antimicrobial material. Herein, we demonstrate that the immobilization of nisin, a natural and inexpensive antimicrobial peptide, with poly(ethylene glycol) (PEG(1000)) as a linker significantly enhanced the antimicrobial and anti-biofilm properties of MWNTs. The MWNT-nisin composite showed up to 7-fold higher antimicrobial property than pristine MWNTs against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Bacillus subtilis. Moreover, the MWNT-nisin composite had a dramatically improved capability to prevent biofilm formation both on a deposited film and in suspension. In particular, the MWNT-nisin deposit film exhibited a 100-fold higher anti-biofilm property than the MWNT deposit film. Further, it has been shown that PEG and nisin are covalently attached to MWNTs with excellent stability against leaching. We envision that our novel MWNT-nisin composite can serve as an effective and economical antimicrobial material.

TiO2 nanoparticles are highly stable, eco-friendly in nature, having low cost, act as a photo catalyst also having antimicrobial properties. Considering the effect of TiO2 nanoparticles on seeds, a study was conducted during March 2022 to June 2022 at Department of Genetics and Plant Breeding, SHUATS, Prayagraj (U.P). In this study onion seeds of variety Nasik Red N-53 were collected to investigate the effect of TiO2 nanoparticles on the seedling characters as well as on the biochemical characters under storage in ambient conditions. Onion seeds were treated with different concentration of TiO2 nanoparticles (10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130 and 140 ppm) along with control and stored in two containers; viz. tin container (C1) and aluminum foil pouch (C2). All the seedling parameters were evaluated every month during storage. The experiment was conducted in factorial CRD with 4 replications. The experimental result showed that the storage containers influenced the seedling characters of onion. Seeds stored in aluminum foil pouch (C2) exhibited highest germination per cent (52.93 %), speed of germination (3.76), root length (2.27 cm), shoot length (4.11 cm), seedling length (6.38 cm), fresh weight (0.176 gm), dry weight (0.0205 gm), seed density (1.025 gm/cm3), dehydrogenase activity (0.213 OD/g mL), catalase activity (0.0220 nmol/min/mg protein) and exhibited lowest moisture per cent (8.05 %) and lowest electrical conductivity (0.970 dS/m) as compared to tin container at the end of 3 months of storage. Seed treated with TiO2 nanoparticles @40ppm (T4) for 2 hours performed better in terms of seedling parameters; viz. germination per cent (58.5 %), speed of germination (4.20), root length (3.06 cm), shoot length (4.58 cm), seedling length (7.64 cm), fresh weight (0.222 gm), dry weight (0.0259 gm), seed density (1.056 gm/cm3), dehydrogenase activity (0.337 OD/g mL), catalase activity (0.0375 nmol/min/mg protein) and recorded lowest moisture per cent (8.04 %) and lowest electrical conductivity (0.951 dS/m) as compared to control after 3 months of storage. The study concluded that seed treated with TiO2 @40 ppm and stored in aluminum foil pouch can be used to expand the storability of onion seeds under ambient condition.

In the present study partially reduced graphene oxide‐ Silver Nanocomposite (GO−Ag NC) was chemically synthesized by using graphene oxide as a precursor and simultaneously its antimicrobial property is studied. Results indicate growth inhibition of fungi belonging to phylum Zygomycota as well as several types of microbes grown under open environment at ambient conditions in Luria Bertani Agar medium. SEM and HRTEM images represent highly exfoliated r GO layers with Silver Nanoparticles embedded on r GO flakes indicating the formation of r GO−Ag Nanocomposite. XRD and Raman spectroscopy confirmed the formation of good quality GO flakes and r GO−Ag Nanocomposite. XPS confirmed intercalation of Graphite by Oxygen containing functional groups, confirming the oxidation of Graphite and corresponding changes in functional groups introduced by the inclusion of Ag Nanoparticles. FTIR and UV‐Vis Spectroscopy confirm the formation of good quality GO, r GO, r GO−Ag Nanocomposite. The behaviour of the silver ion release from the r GO−Ag NC was studied in an acidic solution.Comparative study to see the effect of GO, r GO and Ag Nanoparticles were also carried out on microbes. SEM images of fungi shows destruction of microbial cell membrane.

Surface contamination by microbes leads to several detrimental consequences like hospital- and device-associated infections. One measure to inhibit surface contamination is to confer the surfaces with antimicrobial properties. Copper's antimicrobial properties have been known since ancient times, and the recent resurgence in exploiting copper for application as antimicrobial materials or coatings is motivated by the growing concern about antibiotic resistance and the pressure to reduce antibiotic use. Copper, unlike silver, demonstrates rapid and high microbicidal efficacy against pathogens that are in close contact under ambient indoor conditions, which enhances its range of applicability. This review highlights the mechanisms behind copper's potent antimicrobial property, the design and fabrication of different copper-based antimicrobial materials and coatings comprising metallic copper/copper alloys, copper nanoparticles or ions, and their potential for practical applications. Finally, as the antimicrobial coatings market is expected to grow, we offer our perspectives on the implications of increased copper release into the environment and the potential ecotoxicity effects and possibility of development of resistant genes in pathogens.

Aquatic environmental risk assessment of chitosan/silver, copper and carbon nanotube nanocomposites as antimicrobial agents

Microbial contamination and the need for sustainable food production are driving the shift toward biodegradable food packaging materials. There is an urgent need to develop smart food packaging materials that can prevent contamination and prolong the shelf life of meat. To achieve this, the physical-chemical characteristics of polyvinyl alcohol (PVA)-based packaging films were enhanced through incorporation of lactic acid and anthocyanins to act as a pH indicator. The mechanical, hydrophilic, barrier, and antibacterial properties of the composite films were then evaluated to test the ability of the film to act as a packaging material. In addition, the surface morphology was studied by scanning electron microscopy (SEM), the functional groups by Fourier transform infrared (FTIR) spectroscopy, optical transparency using ultraviolet-visible (UV-vis) spectrophotometer, crystallinity by powder diffraction, and their thermal properties by thermal gravimetric analysis (TGA). The films had a swelling degree (SD) of 222.60 ± 21.19%, dry content (DC) of 70.56 ± 2.54%, moisture content (MC) of 29.44 ± 2%, ALRO moisture (AM) content of 41.85 ± 5.06, and total soluble matter (TSM) of 8.05 ± 1.05%. Moreover, incorporation of lactic acid enhanced the mechanical and the thermal properties of the films but it reduced their optical transparency. The water vapor permeability (WVP) was found to be 14.32 × 10-3 g-1 s-1 Pa-1 and it inhibited the growth of Escherichia coli (EC) (10.67 ± 0.58 cm), Staphylococcus aureus (SA) (10.50 ± 0.40 cm), Pseudomonas aeruginosa (PA) (10.33 ± 0.58 cm), and Staphylococcus epidermidis (11 ± 1 cm) but not Bacillus subtilis (BS). The film's hue changed from red to green over time when used as a packaging material for meat under ambient condition indicating a deterioration in freshness. In conclusion, the developed packaging film exhibited enhanced mechanical, antimicrobial, and hydrophilic properties and it can be used to store and relay information when stored meat begins to decompose through a visible color change of the films.

This study aims to optimize the extraction conditions to obtain the highest yield, to characterize tomato peel extract (TPE) under optimized conditions, and also to determine the effect of ambient oxygen on the properties of TPE. Optimisation were performed at three temperatures (60 °C, 80 °C, 100 °C) and three periods (2, 4, 6 h) by the response surface methodology. The properties of the extract under atmospheric and oxygen-free conditions (AC, OFC) were analysed to determine whether the characteristics of both extracts changed depending on the presence of oxygen; moreover, the morphological, chemical, thermal, biochemical, and antimicrobial properties were analysed. The maximum yield was 31.3% at 100 °C/6 h. A quadratic model was used to create the best fit. Both TPE samples exhibited similar morphological structure, similar weight losses at three stages of TGA curve, similar band assignments in FTIR spectra. GC-MS analysis showed that both samples mainly consisted of cutin in abundance of 70.45% and 68.14% for AC and OFC, respectively. OFC had higher total phenolic content possibly depending on the absence of oxygen. AC and OFC extracts exhibited substantial antimicrobial activity against S. aureus, E. coli, C. albicans, and A. brasiliensis with a MIC value of 100 μg TPE/ mL.

The versatile one-pot green synthesis of a highly concentrated and stable colloidal dispersion of silver nanoparticles (Ag NPs) was carried out using the self-assembled tannic acid without using any other hazardous chemicals. Tannic acid (Plant-based polyphenol) was used as a reducing and stabilizing agent for silver nitrate in a mild alkaline condition. The synthesized Ag NPs were characterized for their concentration, capping, size distribution, and shape. The experimental results confirmed the successful synthesis of nearly spherical and highly concentrated (2281 ppm) Ag NPs, capped with poly-tannic acid (Ag NPs-PTA). The average particle size of Ag NPs-PTA was found to be 9.90 ± 1.60 nm. The colloidal dispersion of synthesized nanoparticles was observed to be stable for more than 15 months in the ambient environment (25 °C, 65% relative humidity). The synthesized AgNPs-PTA showed an effective antimicrobial activity against Staphylococcus Aureus (ZOI 3.0 mM) and Escherichia coli (ZOI 3.5 mM). Ag NPs-PTA also exhibited enhanced catalytic properties. It reduces 4-nitrophenol into 4-aminophenol in the presence of NaBH4 with a normalized rate constant (Knor = K/m) of 615.04 mL·s−1·mg−1. For comparison, bare Ag NPs show catalytic activity with a normalized rate constant of 139.78 mL·s−1·mg−1. Furthermore, AgNPs-PTA were stable for more than 15 months under ambient conditions. The ultra-high catalytic and good antimicrobial properties can be attributed to the fine size and good aqueous stability of Ag NPs-PTA. The unique core-shell structure and ease of synthesis render the synthesized nanoparticles superior to others, with potential for large-scale applications, especially in the field of catalysis and medical.

The potential of metallic copper as an intrinsically antibacterial material is gaining increasing attention in the face of growing antibiotics resistance of bacteria. However, the mechanism of the so-called "contact killing" of bacteria by copper surfaces is poorly understood and requires further investigation. In particular, the influences of bacteria-metal interaction, media composition, and copper surface chemistry on contact killing are not fully understood. In this study, copper oxide formation on copper during standard antimicrobial testing was measured in situ by spectroscopic ellipsometry. In parallel, contact killing under these conditions was assessed with bacteria in phosphate buffered saline (PBS) or Tris-Cl. For comparison, defined Cu2O and CuO layers were thermally generated and characterized by grazing incidence X-ray diffraction. The antibacterial properties of these copper oxides were tested under the conditions used above. Finally, copper ion release was recorded for both buffer systems by inductively coupled plasma atomic absorption spectroscopy, and exposed copper samples were analyzed for topographical surface alterations. It was found that there was a fairly even growth of CuO under wet plating conditions, reaching 4-10 nm in 300 min, but no measurable Cu2O was formed during this time. CuO was found to significantly inhibit contact killing, compared to pure copper. In contrast, thermally generated Cu2O was essentially as effective in contact killing as pure copper. Copper ion release from the different surfaces roughly correlated with their antibacterial efficacy and was highest for pure copper, followed by Cu2O and CuO. Tris-Cl induced a 10-50-fold faster copper ion release compared to PBS. Since the Cu2O that primarily forms on copper under ambient conditions is as active in contact killing as pure copper, antimicrobial objects will retain their antimicrobial properties even after oxide formation.