Characterization Of Colloids Research Articles

Responses of the human gut microbiota to physiologically digested insect powders or isolated chitin thereof

As part of the quest for sustainable food choices, edible insects draw increasing attention. Nevertheless, not enough is known regarding their digestive fate and specifically little is known on the colonic fermentability of edible insects or chitin, which is found in many insects or crustaceans. This study interrogated the properties and fermentability of powders from crickets (Acheta domestica), silkworm pupae (Bombyx mori) or isolated chitin. This was done following their in vitro oral, gastric and intestinal digestion and subsequent fermentation in anaerobic bioreactors inoculated with human feces from 10 healthy volunteers. Specifically, each fecal sample was split into 5-parallel anerobic reactors fed with insect samples and fructooligosaccharides or negative control. These were sampled after 0, 5, 10 and 24 h and subjected to 16S rRNA gene sequencing and GC–MS determination of short-chain fatty acids. First, we show colloidal characteristics delineate the static in vitro digestibility of samples and the properties of effluents reaching the colon. Colonic fermentations reveal chitin significantly (p<0.05) supported an increase in biodiversity measures (e.g., alpha diversity using the Shannon index) more than whole insect powders but without any pronounced fluctuations in the production of short-chain fatty acids. Specific analyses further highlight that chitin may be partially responsible for this observation and that its isolated form may induce the growth of symbionts like members of the Ruminococcaceae and Lachnospiraceae families and the genera Faecalibacterium and Roseburia. Overall, this study suggests that chitin from insects may be a potential novel prebiotic, however further research is needed to ascertain this notion.

Dynamics of a colloidal particle coupled to a Gaussian field: from a confinement-dependent to a non-linear memory

The effective dynamics of a colloidal particle immersed in a complex medium is often described in terms of an overdamped linear Langevin equation for its velocity with a memory kernel which determines the effective (time-dependent) friction and the correlations of fluctuations. Recently, it has been shown in experiments and numerical simulations that this memory may depend on the possible optical confinement the particle is subject to, suggesting that this description does not capture faithfully the actual dynamics of the colloid, even at equilibrium. Here, we propose a different approach in which we model the medium as a Gaussian field linearly coupled to the colloid. The resulting effective evolution equation of the colloidal particle features a non-linear memory term which extends previous models and which explains qualitatively the experimental and numerical evidence in the presence of confinement. This non-linear term is related to the correlations of the effective noise via a novel fluctuation-dissipation relation which we derive.

Neuroprotective Effect of Artichoke-Based Nanoformulation in Sporadic Alzheimer's Disease Mouse Model: Focus on Antioxidant, Anti-Inflammatory, and Amyloidogenic Pathways.

The vast socio-economic impact of Alzheimer’s disease (AD) has prompted the search for new neuroprotective agents with good tolerability and safety profile. With its outstanding role as antioxidant and anti-inflammatory, alongside its anti-acetylcholinesterase activity, the artichoke can be implemented in a multi-targeted approach in AD therapy. Moreover, artichoke agricultural wastes can represent according to the current United Nations Sustainable Development goals an opportunity to produce medicinally valuable phenolic-rich extracts. In this context, the UPLC-ESI-MS/MS phytochemical characterization of artichoke bracts extract revealed the presence of mono- and di-caffeoylquinic acids and apigenin, luteolin, and kaempferol O-glycosides with remarkable total phenolics and flavonoids contents. A broad antioxidant spectrum was established in vitro. Artichoke-loaded, chitosan-coated, solid lipid nanoparticles (SLNs) were prepared and characterized for their size, zeta potential, morphology, entrapment efficiency, release, and ex vivo permeation and showed suitable colloidal characteristics, a controlled release profile, and promising ex vivo permeation, indicating possibly better physicochemical and biopharmaceutical parameters than free artichoke extract. The anti-Alzheimer potential of the extract and prepared SLNs was assessed in vivo in streptozotocin-induced sporadic Alzheimer mice. A great improvement in cognitive functions and spatial memory recovery, in addition to a marked reduction of the inflammatory biomarker TNF-α, β-amyloid, and tau protein levels, were observed. Significant neuroprotective efficacy in dentate Gyrus sub-regions was achieved in mice treated with free artichoke extract and to a significantly higher extent with artichoke-loaded SLNs. The results clarify the strong potential of artichoke bracts extract as a botanical anti-AD drug and will contribute to altering the future medicinal outlook of artichoke bracts previously regarded as agro-industrial waste.

Optical Absorption in N-Dimensional Colloidal Quantum Dot Arrays: Influence of Stoichiometry and Applications in Intermediate Band Solar Cells.

We present a theoretical atomistic study of the optical properties of non-toxic InX (X = P, As, Sb) colloidal quantum dot arrays for application in photovoltaics. We focus on the electronic structure and optical absorption and on their dependence on array dimensionality and surface stoichiometry motivated by the rapid development of experimental techniques to achieve high periodicity and colloidal quantum dot characteristics. The homogeneous response of colloidal quantum dot arrays to different light polarizations is also investigated. Our results shed light on the optical behaviour of these novel multi-dimensional nanomaterials and identify some of them as ideal building blocks for intermediate band solar cells.

Development and Evaluation of Novel Leflunomide SPION Bioemulsomes for the Intra-Articular Treatment of Arthritis.

Systemic treatments for rheumatoid arthritis are associated with many side effects. This study aimed to minimize the side effects associated with the systemic administration of leflunomide (LEF) by formulating LEF-loaded emulsomes (EMLs) for intra-articular administration. Additionally, EMLs were loaded with supramagnetic nanoparticles (SPIONs) to enhance joint localization, where a magnet was placed on the joint area after intra-articular administration. Full in vitro characterization, including colloidal characteristics, entrapment efficiency, and in vitro release were conducted besides the in vivo evaluation in rats with adjuvant-induced arthritis. In vivo study included joint diameter measurement, X-ray radiographic analysis, RT-PCR analysis, Western blotting, ELISA for inflammatory markers, and histopathological examination of dissected joints. The particle size and entrapment efficiency of the selected LEF SPION EMLs were 198.2 nm and 83.7%, respectively. The EMLs exhibited sustained release for 24 h. Moreover, in vivo evaluation revealed LEF SPION EMLs to be superior to the LEF suspension, likely due to the increase in LEF solubility by nanoencapsulation that improved the pharmacological effects and the use of SPION that ensured the localization of EMLs in the intra-articular cavity upon administration.

Aggregation Kinetics and Mechanism of Humic Acid Reaction with Cs+ and Co2+ Metal Ions Using Batch Techniques

Humic substances have a potential role in the fate and transport of toxic metal ions in the environment due to their colloidal characteristics and abundant surface functional groups. Batch techniques (DLS, EPM, FT-IR and fluorescence EEM) were developed to assess the aggregation mechanisms of humic acid (HA) reacting with Cs+ or Co2+ electrolyte ions in this work. The kinetic experimental results indicated that a much lower Co2+ ion concentration (0.03–1.50 mmol/L) induced rapid aggregation of HA compared to that of Cs+ (3.0–15 mmol/L), and the divalent Co2+ ion was far more effective in enhancing HA aggregation than monovalent Cs+. The aggregation kinetics of HA were also found to be pH-dependent, and a much lower pH condition (pH 5.0) caused more rapid aggregation (the largest hydrodynamic diameter of ~3000 nm) compared to those at pH 7.0 (the largest hydrodynamic diameter of ~2000 nm). Positively charged metal ions in the solution can lower the electrostatic repulsive force between HA molecules through charge neutralization, thus leading to the rapid aggregation of HA aggregates. Furthermore, the carboxylic and phenolic groups on the HA surface were also involved in the aggregation reaction to form inner complexes and accelerate the aggregation process.

Chiral Liquid Crystalline Properties of Cellulose Nanocrystals: Fundamentals and Applications.

By using an independent self-assembly process that is occasionally controlled by evaporation, cellulose nanocrystals (CNCs) may create films (pure or in conjunction with other materials) that have iridescent structural colors. The self-forming chiral nematic structures and environmental safety of a new class of photonic liquid crystals (LCs), referred to as CNCs and CNC-embedded materials, make them simple to make and treat. The structure of the matrix interacts with light to give structural coloring, as opposed to other dye pigments, which interact with light by adsorption and reflection. Understanding how CNC self-assembly constructs structures is vital in several fields, including physics, science, and engineering. To constructure this review, the colloidal characteristics of CNC particles and their behavior during the formation of liquid crystals and gelling were studied. Then, some of the recognized applications for these naturally occurring nanoparticles were summarized. Different factors were considered, including the CNC aspect ratio, surface chemistry, concentration, the amount of time needed to produce an anisotropic phase, and the addition of additional substances to the suspension medium. The effects of alignment and the drying process conditions on structural changes are also covered. The focus of this study however is on the optical properties of the films as well as the impact of the aforementioned factors on the final transparency, iridescent colors, and versus the overall response of these bioinspired photonic materials. Control of the examined factors was found to be necessary to produce reliable materials for optoelectronics, intelligent inks and papers, transparent flexible support for electronics, and decorative coatings and films.

Terahertz transmission characteristics of xanthan gum colloids in a microfluidic chip

Terahertz time-domain spectroscopy (THz-TDS) technology has great application prospects for the detection of biological macromolecules, whereas microfluidic technology uses micro-channel networks to manipulate liquids, which can reduce the influence of hydrogen bonds in liquids on THz waves. The combination of these two technologies makes the detection of THz waves in aqueous solutions of biomolecules more accurate and efficient. In this study, microfluidic technology and THz-TDS technology were applied to study the THz transmission characteristics of xanthan gum, providing three feasible methods for the detection of xanthan gum colloids.

Emulsifier-free (meth)acrylic colloids stabilized by cationic monomer containing two charged moieties

Emulsifier-free cationic polymer colloids produced by emulsion polymerization have gained important relevance for diverse applications. However, the control of colloidal characteristics is still challenging due to the cationic monomers structure, in which the charge is placed between two hydrophobic moieties making them less efficient in providing colloidal stabilization. This challenge was confronted by employing a minor quantity of cationic monomer containing two charges, styrenic 1,4-diazabicyclo[2.2.2]octane, to provide colloidal stability to waterborne (meth)acrylic dispersions. For first time, high throughput production of cationic dispersions with controlled colloidal and film properties is achieved. High solids content stable dispersions comprising monodispersed particles with 170 nm average diameter and high charge density ranging 24–180 μC·cm−2 are produced, giving rise to films with tunable mechanical and water resistance. This work offers a novel concept for colloidal stabilization of polymer colloids and can be extended towards stabilization of challenging colloidal dispersions or design of novel surfactants.

Pulsatile Controlled Release and Stability Evaluation of Polymeric Particles Containing Piper nigrum Essential Oil and Preservatives

Considerable efforts have been spent on environmentally friendly particles for the encapsulation of essential oils. Polymeric particles were developed to encapsulate the essential oil from Piper nigrum based on gelatin and poly–ε–caprolactone (PCL) carriers. Gas Chromatography ((Flame Ionization Detection (GC/FID) and Mass Spectrometry (GC/MS)), Atomic Force Microscopy (AFM), Nanoparticle Tracking Analysis (NTA), Confocal Laser Scanning Microscopy (CLSM), Attenuated Total Reflectance–Fourier-transform Infrared Spectroscopy (ATR–FTIR), and Ultraviolet–Visible (UV–VIS) spectroscopy were used for the full colloidal system characterization. The essential oil was mainly composed of β-caryophyllene (~35%). The stability of the encapsulated systems was evaluated by Encapsulation Efficiency (EE%), electrical conductivity, turbidity, pH, and organoleptic properties (color and odor) after adding different preservatives. The mixture of phenoxyethanol/isotialzoni-3-one (PNE system) resulted in enhanced stability of approximately 120 and 210 days under constant handling and shelf-life tests, respectively. The developed polymeric system presented a similar controlled release in acidic, neutral, or basic pH, and the release curves suggested a pulsatile release mechanism due to a complexation of essential oil in the PCL matrix. Our results showed that the developed system has potential as an alternative stable product and as a controlling agent, due to the pronounced bioactivity of the encapsulated essential oil.

Prediction of colloid sticking efficiency at pore-scale and macroscale using a pore network model

The sticking efficiency (α) is a vital parameter to predict the transport and deposition of colloids in porous media. The value of α depends on various factors such as the interaction energy between colloids and the solid-water interface (SWI), kinetic energy fluctuations of diffusing colloids, and the hydrodynamics of the flow field in the pore structure. However, α is usually assumed to be spatially constant and fitted from experimental data. In this study, a theoretical method is proposed to predict the distribution of the sticking efficiency at pore scale (αt) using a pore network model (PNM) and the macroscale sticking efficiency of the whole porous media (αM) by means of upscaling. A PNM is established to simulate the pore structure of porous media and to obtain the flow field, and energy and torque balances are calculated throughout the spatial pore structure to determine the distribution of αt under different physiochemical conditions. The value of αM is determined through breakthrough curves provided by the PNM under favorable and unfavorable conditions. Results show the distribution of αt is sensitive to various factors including colloid characteristics, pore surface features, geochemical environment and hydrodynamic conditions. Colloid characteristics like colloid surface zeta potential, geochemical environment such as solution ionic strength, and pore surface characteristics including nanoscale roughness and especially charge heterogeneity have a controlling influence on αt for nanoparticles (<100 nm) due to their impact on interaction energies. Hydrodynamic conditions played an increasingly important and eventually dominant role in determining αt for larger colloids by changing the sticking of weakly associated colloids (e.g., at secondary minima). When hydrodynamic torques are weak, the influence of colloid size on αt can be non-monotonic due to the combined influence of interaction energy and hydrodynamic torques. As a result, higher values of αM occurred for smaller colloid sizes, lower flow velocities, larger pore sizes, and in the presence of microscopic roughness. The method proposed by this study can be used to predict the sticking efficiency under different solution and solid phase chemistries, nanoscale heterogeneities, microscopic roughness, flow velocities, and pore structure conditions.

Regioselective Seeded Polymerization in Block Copolymer Nanoparticles: Post‐Assembly Control of Colloidal Features

AbstractPost‐assembly modifications are efficient tools to adjust colloidal features of block copolymer (BCP) particles. However, existing methods often address particle shape, morphology, and chemical functionality individually. For simultaneous control, we transferred the concept of seeded polymerization to phase separated BCP particles. Key to our approach is the regioselective polymerization of (functional) monomers inside specific BCP domains. This was demonstrated in striped PS‐b‐P2VP ellipsoids. Here, polymerization of styrene preferably occurs in PS domains and increases PS lamellar thickness up to 5‐fold. The resulting asymmetric lamellar morphology also changes the particle shape, i.e., increases the aspect ratio. Using 4‐vinylbenzyl azide as co‐monomer, azides as chemical functionalities can be added selectively to the PS domains. Overall, our simple and versatile method gives access to various multifunctional BCP colloids from a single batch of pre‐formed particles.

Regioselective Seeded Polymerization in Block Copolymer Nanoparticles: Post-Assembly Control of Colloidal Features.

Post‐assembly modifications are efficient tools to adjust colloidal features of block copolymer (BCP) particles. However, existing methods often address particle shape, morphology, and chemical functionality individually. For simultaneous control, we transferred the concept of seeded polymerization to phase separated BCP particles. Key to our approach is the regioselective polymerization of (functional) monomers inside specific BCP domains. This was demonstrated in striped PS‐b‐P2VP ellipsoids. Here, polymerization of styrene preferably occurs in PS domains and increases PS lamellar thickness up to 5‐fold. The resulting asymmetric lamellar morphology also changes the particle shape, i.e., increases the aspect ratio. Using 4‐vinylbenzyl azide as co‐monomer, azides as chemical functionalities can be added selectively to the PS domains. Overall, our simple and versatile method gives access to various multifunctional BCP colloids from a single batch of pre‐formed particles.

A Deep Learning Framework Discovers Compositional Order and Self-Assembly Pathways in Binary Colloidal Mixtures.

Binary colloidal superlattices (BSLs) have demonstrated enormous potential for the design of advanced multifunctional materials that can be synthesized via colloidal self-assembly. However, mechanistic understanding of the three-dimensional self-assembly of BSLs is largely limited due to a lack of tractable strategies for characterizing the many two-component structures that can appear during the self-assembly process. To address this gap, we present a framework for colloidal crystal structure characterization that uses branched graphlet decomposition with deep learning to systematically and quantitatively describe the self-assembly of BSLs at the single-particle level. Branched graphlet decomposition is used to evaluate local structure via high-dimensional neighborhood graphs that quantify both structural order (e.g., body-centered-cubic vs face-centered-cubic) and compositional order (e.g., substitutional defects) of each individual particle. Deep autoencoders are then used to efficiently translate these neighborhood graphs into low-dimensional manifolds from which relationships among neighborhood graphs can be more easily inferred. We demonstrate the framework on in silico systems of DNA-functionalized particles, in which two well-recognized design parameters, particle size ratio and interparticle potential well depth can be adjusted independently. The framework reveals that binary colloidal mixtures with small interparticle size disparities (i.e., A- and B-type particle radius ratios of rA/rB = 0.8 to rA/rB = 0.95) can promote the self-assembly of defect-free BSLs much more effectively than systems of identically sized particles, as nearly defect-free BCC-CsCl, FCC-CuAu, and IrV crystals are observed in the former case. The framework additionally reveals that size-disparate colloidal mixtures can undergo nonclassical nucleation pathways where BSLs evolve from dense amorphous precursors, instead of directly nucleating from dilute solution. These findings illustrate that the presented characterization framework can assist in enhancing mechanistic understanding of the self-assembly of binary colloidal mixtures, which in turn can pave the way for engineering the growth of defect-free BSLs.

Synthesis and Comparative Studies of Glucose Oxidase Immobilized on Fe3O4 Magnetic Nanoparticles Using Different Coupling Agents.

Squaric acid (SA) is a compound with potential to crosslink biomacromolecules. Although SA has become over the last years a well-known crosslinking agent as a result of its good biocompatibility, glutaraldehyde (GA), a compound with proven cytotoxicity is still one of the most used crosslinkers to develop nanomaterials. In this regard, the novelty of the present study consists in determining whether it may be possible to substitute GA with a new bifunctional and biocompatible compound, such as SA, in the process of enzyme immobilization on the surface of magnetic nanoparticles (MNPs). Thus, a direct comparison between SA- and GA-functionalized magnetic nanoparticles was realized in terms of physico-chemical properties and ability to immobilize catalytic enzymes. The optimal conditions of the synthesis of the two types of GOx-immobilized MNPs were described, thus emphasizing the difference between the two reagents. Scanning Electron Microscopy and Dynamic Light Scattering were used for size, shape and colloidal stability characterization of the pristine MNPs and of those coupled with GOx. Binding of GOx to MNPs by using GA or SA was confirmed by FT-IR spectroscopy. The stability of the immobilized and free enzyme was investigated by measuring the enzymatic activity. The study confirmed that the resulting activity of the immobilized enzyme and the optimization of enzyme immobilization depended on the type of reagent used and duration of the process. The catalytic performance of immobilized enzyme was tested, revealing that the long-term colloidal stability of SA-functionalized MNPs was superior to those prepared with GA. In conclusion, the SA-functionalized bioconjugates have a better potential as compared to the GA-modified nanosystems to be regarded as catalytic nanodevices for biomedical purposes such as biosensors.

Hyaluronic acid coated teriflunomide (A771726) loaded lipid carriers for the oral management of rheumatoid arthritis

Systemic rheumatoid arthritis treatment has been associated with numerous side effects. We attempted to formulate hyaluronic acid (HA)-coated teriflunomide (TER)-loaded nanostructured lipid carriers (NLCs) that can target inflamed rheumatic joints following oral administration. In vitro evaluation including colloidal characteristics, drug release and stability studies were conducted. Also, cytotoxicity studies on THP1 and peripheral blood mononuclear cells besides testing the binding of HA coated TER-NLCs to CD44 receptors were carried out. Furthermore, pharmacokinetics following oral administration, anti-arthritic effects, hepato and nephrotoxicity of NLCs were assessed.Selected NLCs formulation was approximately 284.9 ± 3.8 nm in size with 96.89 ± 0.45% entrapment efficiency and provided a sustained release for 30 days. NLCs showed good stability that was confirmed by TEM examination. Cell culture studies revealed that HA-coated TER- NLCs showed superior cytotoxicity and binding affinity to CD44 receptors compared with TER suspension. In vivo studies demonstrated the superiority of NLCs in increasing TER bioavailability, reducing TNF-α serum levels and improving joint healing that was evidenced in both histopathological and X-ray radiographic examination. This may be attributed to the ability of HA-coated TER-NLCs to target rheumatic joints passively and actively by targeting CD44 receptors that are overexpressed in rheumatic joints.

Relationship between Some Colloidal Properties of Non-Ionic-Anionic Surfactant Mixtures

Non-ionic surfactants are compatible with different types of materials, therefore they can be applied in various packages. Fatty-acid derivates as non-ionic surfactants and their mixtures were investigated to study their colloidal behavior. The HLB value, the particle size, the emulsification capacity and the interfacial tension of various commercial, non-ionic surfactants, and their mixtures with sodium lauryl-ether-sulfate (SLES), were determined. The surfactant mixtures were prepared in different non-ionic: anionic surfactant ratios to examine their effect on several surfactant characteristics. The interfacial tension between the oil phase and aqueous phase was measured using the spinning drop method and the average hydrodynamic diameter of surfactants in the aqueous solution was determined using the dynamic light scattering method. The relationship between various colloidal properties of surfactants was investigated. It was found that there is a significant relationship between the colloidal characteristics and the structure of surfactants that can contribute to their efficient selection method.

Nanochitin: Chemistry, Structure, Assembly, and Applications.

Chitin, a fascinating biopolymer found in living organisms, fulfills current demands of availability, sustainability, biocompatibility, biodegradability, functionality, and renewability. A feature of chitin is its ability to structure into hierarchical assemblies, spanning the nano- and macroscales, imparting toughness and resistance (chemical, biological, among others) to multicomponent materials as well as adding adaptability, tunability, and versatility. Retaining the inherent structural characteristics of chitin and its colloidal features in dispersed media has been central to its use, considering it as a building block for the construction of emerging materials. Top-down chitin designs have been reported and differentiate from the traditional molecular-level, bottom-up synthesis and assembly for material development. Such topics are the focus of this Review, which also covers the origins and biological characteristics of chitin and their influence on the morphological and physical-chemical properties. We discuss recent achievements in the isolation, deconstruction, and fractionation of chitin nanostructures of varying axial aspects (nanofibrils and nanorods) along with methods for their modification and assembly into functional materials. We highlight the role of nanochitin in its native architecture and as a component of materials subjected to multiscale interactions, leading to highly dynamic and functional structures. We introduce the most recent advances in the applications of nanochitin-derived materials and industrialization efforts, following green manufacturing principles. Finally, we offer a critical perspective about the adoption of nanochitin in the context of advanced, sustainable materials.

Lipidic cubic-phase leflunomide nanoparticles (cubosomes) as a potential tool for breast cancer management

Despite the fact of availability of several treatments for breast cancer, most of them fail to attain the desired therapeutic response due to their poor bioavailability, high doses, non-selectivity and as a result systemic toxicity. Here in an attempt made to study the transdermal effect of leflunomide (LEF) against breast cancer. In order to improve the poor physicochemical properties of LEF, it was loaded into cubosomes. Cubosomes were prepared by the emulsification method. Colloidal characteristics of cubosomes including particle size, ζ-potential, entrapment efficiency, in-vitro release profile and ex-vivo permeation were studied. In addition, morphology, stability, cytotoxicity and cell uptake in MDA-MB-231 cell line were carried out for the selected cubosomal formulation. The selected LEF loaded cubosomal formulation showed a small particle size (168 ± 1.08) with narrow size distribution (PI 0.186 ± 0.125) and negative ζ potential (–25.5 ± 0.98). Its Entrapment efficiency (EE%) was 93.2% and showed sustained release profile that extended for 24 h. The selected formulation showed stability when stored at 25 °C for three months in terms of size and EE%. TEM images illustrated the cubic structure of the cubosome. Cell culture results revealed the superiority of LEF cubosomes compared to LEF suspension in their cytotoxic effects with an IC50 close to that of doxorubicin. Furthermore, LEF cell uptake was significantly higher for LEF cubosomes. This may be attributed to the effect of nano-encapsulation on enhancing drug pharmacological effects and uptake indicating the potential usefulness of LEF cubosomes for breast cancer management.

The comparison of colloidal, optical, and solar collection characteristics between Fe2O3 and Fe3O4 nanofluids operated in an evacuated tubular volumetric absorption solar collector

BackgroundThe iron oxide nanoparticles as low-cost, eco-friendly, and efficient nanomaterials exhibit interesting optical properties which make them valuable for nanofluids-based volumetric absorption solar collectors. MethodsThe first aim of this study is to experimentally compare the colloidal stability and optical properties of Fe2O3 and Fe3O4 nanofluids in three volume fractions of 0.005, 0.01, and 0.02%. To the following, it is intended to examine the energy conversion efficiency of these nanofluids in an evacuated tubular volumetric absorption solar collector according to the ASHREA standard. Significant findingsBased on the results, the size and morphology of the iron oxide nanoparticles were nearly similar together, but when dispersed in water they exhibited different colloidal and optical properties. For example, the Fe2O3 nanofluids showed considerable spectral extinction coefficients in the visible range, while the Fe3O4 nanofluids presented limited extinction coefficients in the ultraviolet region with the lower values. At penetration depth of 4 cm, the 0.02%-Fe2O3 nanofluid resulted in a 100% solar weighted absorption fraction in comparison to 83.2% of the Fe3O4 nanofluid with the same volume fraction. According to the collector results, the Fe2O3 nanofluids displayed greater enhancement in the solar to thermal energy conversion than the Fe3O4 nanofluids. The maximum efficiency was 73% at 0.02%-Fe2O3 nanofluid and 51% at 0.02%-Fe3O4 nanofluid.