Sustainable Utilization of Food Biowaste (Papaya Peel) Extract for Gold Nanoparticle Biosynthesis and Investigation of Its Multi-Functional Potentials

Papaya contains high amounts of vitamins A, C, riboflavin, thiamine, niacin, ascorbic acid, potassium, and carotenoids. It is confirmed by several studies that all food waste parts such as the fruit peels, seeds, and leaves of papaya are potential sources of phenolic compounds, particularly in the peel. Considering the presence of numerous bioactive compounds in papaya fruit peels, the current study reports a rapid, cheap, and environmentally friendly method for the production of gold nanoparticles (AuNPs) employing food biowaste (vegetable papaya peel extract (VPPE)) and investigated its antioxidant, antidiabetic, tyrosinase inhibition, anti-inflammatory, antibacterial, and photocatalytic degradation potentials. The phytochemical analysis gave positive results for tannins, saponins, steroids, cardiac steroidal glycoside, protein, and carbohydrates. The manufactured VPPE-AuNPs were studied by UV-Vis scan (with surface plasmon resonance of 552 nm), X-ray diffraction analysis (XRD) (with average crystallite size of 44.41 nm as per the Scherrer equation), scanning electron microscopy-energy-dispersive X-ray (SEM-EDS), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), particle size, zeta potential, etc. The mean dimension of the manufactured VPPE-AuNPs is 112.2 d.nm (PDI-0.149) with a -26.1 mV zeta potential. The VPPE-AuNPs displayed a significant antioxidant effect (93.24% DPPH scavenging and 74.23% SOD inhibition at 100 µg/mL); moderate tyrosinase effect (with 30.76%); and substantial α-glucosidase (95.63%) and α-amylase effect (50.66%) at 100 µg/mL. Additionally, it was found to be very proficient in the removal of harmful methyl orange and methylene blue dyes with degradation of 34.70% at 3 h and 24.39% at 5 h, respectively. Taken altogether, the VPPE-AuNPs have been proven to possess multiple biopotential activities, which can be explored by the food, cosmetics, and biomedical industries.

In Situ Biosynthesis of Reduced Alpha Hematite (α-Fe2O3) Nanoparticles by Stevia Rebaudiana L. Leaf Extract: Insights into Antioxidant, Antimicrobial, and Anticancer Properties

In the present study, we utilized Stevia rebaudiana L. (SRLe) extract to in situ biosynthesize nanoscale alpha hematite (α-Fe₂O₃) nanoparticles (NPs) with potent antioxidant, antimicrobial, and anticancer properties. SRLe-α-Fe₂O₃ was characterized using physiochemical analyses, including UV/Vis, FTIR, XRD, DLS, EDX, SEM, and TEM studies. Among tested solvents, CHCl₃/MeOH (2:1 v/v) SRL extract (least polar solvent) contained the highest EY, TPC, and antioxidant capacity of ~3.5%, ~75 mg GAE/g extract, and IC₅₀ = 9.87 ± 0.7 mg/mL, respectively. FTIR confirmed the engagement of coating operation to the colloidal α-Fe₂O₃ NPs. TEM, SEM, and DLS revealed that SRLe-α-Fe₂O₃ has a spherical shape, uniform size distribution with aggregation for an average size of ~18.34 nm, and ζ = −19.4 mV, forming a repulsive barrier that helped to improve stability. The synthesized nanoparticles displayed considerable antibacterial activity against E. coli and S. aureus bacterial growth, and exhibited superior activity against the A549 lung cancer cell lines. These findings indicate that the increased availability of bioactive substances with antioxidant properties of SRLe makes it a potentially interesting material for the preparation of biologically active compounds and green synthesis of nanoparticles.

Microenvironmental Behaviour of Nanotheranostic Systems for Controlled Oxidative Stress and Cancer Treatment

The development of smart, efficient and multifunctional material systems for diseases treatment are imperative to meet current and future health challenges. Nanomaterials with theranostic properties have offered a cost effective and efficient solution for disease treatment, particularly, metal/oxide based nanotheranostic systems already offering therapeutic and imaging capabilities for cancer treatment. Nanoparticles can selectively generate/scavenge ROS through intrinsic or external stimuli to augment/diminish oxidative stress. An efficient treatment requires higher oxidative stress/toxicity in malignant disease, with a minimal level in surrounding normal cells. The size, shape and surface properties of nanoparticles are critical parameters for achieving a theranostic function in the microenvironment. In the last decade, different strategies for the synthesis of biocompatible theranostic nanostructures have been introduced. The exhibition of therapeutics properties such as selective reactive oxygen species (ROS) scavenging, hyperthermia, antibacterial, antiviral, and imaging capabilities such as MRI, CT and fluorescence activity have been reported in a variety of developed nanosystems to combat cancer, neurodegenerative and emerging infectious diseases. In this review article, theranostic in vitro behaviour in relation to the size, shape and synthesis methods of widely researched and developed nanosystems (Au, Ag, MnO_x, iron oxide, maghemite quantum flakes, La₂O_3−x, TaO_x, cerium nanodots, ITO, MgO_1−x) are presented. In particular, ROS-based properties of the nanostructures in the microenvironment for cancer therapy are discussed. The provided overview of the biological behaviour of reported metal-based nanostructures will help to conceptualise novel designs and synthesis strategies for the development of advanced nanotheranostic systems.

Green synthesis of iron oxide nanoparticle using Carica papaya leaf extract: application for photocatalytic degradation of remazol yellow RR dye and antibacterial activity

Synthesis of iron oxide nanoparticles by the recently developed green approach is extremely promising because of its non-toxicity and environmentally friendly behavior. In this study, nano scaled iron oxide particles (α-Fe₂O₃) were synthesized from hexahydrate ferric chloride (FeCl₃.6H₂O) with the addition of papaya (Carica papaya) leaf extract under atmospheric conditions. The synthesis of iron oxide nanoparticles was confirmed by systematic characterization using FTIR, XRD, FESEM, EDX and TGA studies. The removal efficiency of remazol yellow RR dye with the synthesized iron oxide nanoparticles as a photocatalyst was determined along with emphasizing on the parameters of catalyst dosage, initial dye concentration and pH. Increasing the dose of iron oxide nanoparticles enhanced the decolorization of the dyes and a maximum 76.6% dye degradation was occurred at pH 2 after 6 h at a catalyst dose of 0.8 g/L. Unit removal capacity of the photocatalyst was found to be 340 mg/g at dye concentration of 70 ppm and at a catalyst dose of 0.4 g/L. The synthesized nanoparticles showed moderate antibacterial activity against Klebsiella spp., E.Coli, Pseudomonas spp., S.aureus bacterial strains. Although the cytotoxic effect of nanoparticles against Hela, BHK-21 and Vero cell line was found to be toxic at maximum doses but it can be considered for tumor cell damage because it showed excellent activity against the Hela and BHK-21 cell lines.

Development of CeO2 nanodot encrusted TiO2 nanoparticles with reduced photocatalytic activity and increased biocompatibility towards a human keratinocyte cell line

The cytotoxic and genotoxic effects of titanium dioxide (TiO2) nanoparticles when exposed to ultraviolet (UV) radiation, particularly wavelengths between 320-400 nm, has raised concern over their safe use in health and cosmetic related products such as sunscreens. Cerium dioxide (CeO2) nanoparticles have been demonstrated to display biocompatible properties and antioxidant activity due to redox cycling of the Ce3+/Ce4+ oxidation states. In this work, CeO2/TiO2 nanocomposites were prepared through a standard precipitation method at atomic concentrations (at%) of Ce relative to Ti of 2.5, 5 and 10 at%, with the aim of reducing the photocatalytic activity of the core TiO2 nanoparticles and improve biocompatibility. The UV absorptive properties of the nanocomposite samples revealed excellent absorbance across the UV region as compared to pristine TiO2 and CeO2. Furthermore, a drastic reduction in the photocatalysed decomposition of crystal violet, when in the presence of the nanocomposite samples, under both UV and solar simulated light was observed compared to the highly photoactive pristine TiO2. An optimal CeO2 nanodot loading, displaying both high UV attenuation and low photocatalytic performance was determined at 5 at% and further in vitro biological testing revealed minimal impact on the cell viability of the human keratinocyte cell line (HaCaT) over a 24 h period with and without prior exposure to UV irradiation. In contrast, pristine TiO2 nanoparticles induced toxicity to HaCaT cells with prior UV exposure before incubation, particularly at a dosage of 100 mg L-1. Our findings demonstrate the effectiveness of CeO2 nanodots in improving biocompatibility and its potential as a coating material for active inorganic UV filters.

Y2O3 decorated TiO2 nanoparticles: Enhanced UV attenuation and suppressed photocatalytic activity with promise for cosmetic and sunscreen applications

Nanoparticulate titanium dioxide (TiO₂) is widely used in cosmetic products and sunscreens. However, primarily due to their photocatalytic activity, some TiO₂ products have been shown to be cytotoxic. Thus, the aim of this study was to reduce the photoactivity and consequent cytotoxicity of TiO₂nanoparticles. As such, in this work, yttrium oxide (Y₂O₃) was deposited onto TiO₂, at 5% and 10% Y/Ti weight ratio, via a hydrothermal method. The nanocomposites produced, TiO₂@Y₂O₃ 5 and 10 wt%, were characterised to assess their physical, photochemical and toxicological properties. These materials exhibit a uniform yttria coating, enhanced UV attenuation in the 280-350 nm range and significantly reduced photoactivity compared with a pristine commercial TiO₂ sample (Degussa Aeroxide® P25). Furthermore, the comparative cytotoxicity and photo-cytotoxicity of these materials to a human keratinocyte cell line (HaCaT), was assessed using a colorimetric tetrazolium salt (MTS) assay. Following 24-hour incubation with cells, both Y₂O₃ loadings exhibited improved biocompatibility with HaCaT cells, compared to the pristine TiO₂ sample, under all subsequent test conditions. In conclusion, the results highlight the potential of these materials for use in products, applied topically, with sun protection in mind.

Mechanistic insights into the acetate-accelerated synthesis of crystalline ceria nanoparticles

Lithium acetate was reported to accelerate the growth of crystalline ceria nanoparticles in ozone-mediated synthesis through promoting alcohol-like condensation reactions.

Redox Trimetallic Nanozyme with Neutral Environment Preference for Brain Injury

Metal nanozyme has attracted wide interest for biomedicine, and a highly catalytic material in the physiological environment is highly desired. However, catalytic selectivity of nanozyme is still highly challenging, limiting its wide application. Here, we show a trimetallic (triM) nanozyme with highly catalytic activity and environmental selectivity. Enzyme-mimicked investigations find that the triM system possesses multi-enzyme-mimetic activity for removing reactive oxygen species (ROS) and reactive nitrogen species (RNS), such as ¹O₂, H₂O₂, ^•OH, and ^•NO. Importantly, triM nanozyme exhibits the significant neutral environment preference for removing the ^•OH, ¹O₂, and ^•NO free radical, indicating its highly catalytic selectivity. The density functional theory (DFT) calculations reveal that triM nanozyme can capture electrons very easily and provides more attraction to reactive oxygen and nitrogen species (RONS) radicals in the neutral environment. In vitro experiments show that triM nanozyme can improve the viability of injured neural cell. In the LPS-induced brain injury model, the superoxide dismutase (SOD) activity and lipid peroxidation can be greatly recovered after triM nanozyme treatment. Moreover, the triM nanozyme treatment can significantly improve the survival rate, neuroinflammation, and reference memory of injured mice. Present work provides a feasible route for improving selectivity of nanozyme in the physiological environment as well as exploring potential applications in brain science.