Determination of the size, concentration, and refractive index of silica nanoparticles from turbidity spectra

Green synthesis of sacrificial UV-sensitive core and biobased shell for obtaining optically hollow nanoparticles

Hollow nanoparticles have been extensively studied in recent years. Obtaining such structures with biobased materials, following greener synthetic routes, is still challenging, especially if accurate particle dimensions are required. This work reports the use of an innovative hybrid silica core (Si@azo) containing UV-sensitive molecule, wrapped in biobased multilayer shell composed of polysaccharides. It is a promising strategy for obtaining optically hollow nanoparticles. Indeed, Si@azo cores have the ability to be partially degraded when irradiated with UV light. Combined with a well-controlled and monodisperse diameter, they provide a good basis for layer-by-layer assembly, leading to a multilayer shell with controlled composition and thickness. Finally, UV irradiation of such a core-shell structure is harmless to the polysaccharide shell, but does impact the hybrid silica core, as revealed by turbidity measurements, among other. Each step, i.e. core synthesis, shell addition, and core-shell irradiation, has been carefully characterized at the macro (Fourier-transform infrared spectroscopy - FTIR, Dynamic Light Scattering - DLS, Zeta-potential measurement, Surface Plasmon Resonance - SPR, turbidity) and microscale (Transmission and Scanning Electron Microscopies). Emphasis is put on how turbidity measurements can be related to the core refractive index (ncore), giving information on the state of core degradation and whether the core-shell particle is optically hollow.

Ti-containing NPs in raw water and their removal with conventional treatments in four water treatment plants in Taiwan

The ingestion of Ti-containing nanoparticles from drinking water has emerged as a concern in recent years. This study therefore aimed to characterize Ti-containing nanoparticles in water samples collected from four water treatment plants in Taiwan and to explore the challenges associated with measuring them at low levels using single particle-inductively coupled plasma mass spectrometry. Additionally, the study sought to identify the most effective processes for the removal of Ti-containing nanoparticles. For each water treatment plant, two water samples were collected from raw water, sedimentation effluent, filtration effluent, and finished water, respectively. Results revealed that Ti-containing nanoparticles in raw water, with levels at 8.69 μg/L and 296.8 × 103 particles/L, were removed by approximately 35% and 98%, respectively, in terms of mass concentration and particle number concentration, primarily through flocculation and sedimentation processes. The largest most frequent nanoparticle size in raw water (112.0 ± 2.8 nm) was effectively reduced to 62.0 ± 0.7 nm in finished water, while nanoparticles in the size range of 50-70 nm showed limited changes. Anthracite was identified as a necessary component in the filter beds to further improve removal efficiency at the filtration unit. Moreover, the most frequent sizes of Ti-containing nanoparticles were found to be influenced by salinity. Insights into the challenges associated with measuring low-level Ti-containing nanoparticles in aqueous samples provide valuable information for future research and management of water treatment processes, thereby safeguarding human health.

Real-Time Multiscale Imaging of Heterogeneous Multistage Reactions: Insights into Nanoscale TiO2 Synthesis

Hydrothermal methods are widely used to synthesize functional inorganic materials. The interplay between the reactive species, solution chemistry, and the nanoscale product makes it challenging to control the reaction pathway to achieve a uniform product. Here, we resolve the heterogeneity that arises during hydrothermal synthesis across different length scales. We combine spatially resolved in situ X-ray pair distribution function (PDF) and small-angle X-ray scattering analysis, which are sensitive to structure on the atomic and nanoscale, with a novel time-lapse optical imaging strategy that reveals heterogeneity and phase separations across the entire reaction. For TiO2 synthesis via hydrothermal hydrolysis of TiCl4, we identify multiple cycles of TiO2 formation and separation that contribute to nonuniformity in the polymorphic product. The PDF data show that the characteristics of TiO2 formed during each formation-separation cycle differ, contributing to the ongoing challenge of precisely identifying reaction controls. The imaging strategy pioneered here provides an efficient in situ means to systematically compare how the reaction evolves under different chemical conditions, thereby advancing our understanding of functional inorganic material synthesis.

Influence of Phthalein dyes on structural, optical, and sensing properties of zinc oxide supported Silica-titania nanocomposite

Owed to rapid responsive pH sensing attributes, the zinc-supported Silica-titania (Z/ST) nanocomposite is synthesized by the sol-gel method. Three distinct pH dyes such as phenolphthalein, creosol red, and phenol red are immobilized in Z/ST to examine their influence on the structural and optical properties of Z/ST nanocomposite. Microscopic analyses possessed that Z/ST and dyes immobilized Z/ST have crack-free porous morphology. The phenol red immobilized Z/ST (P-Z/ST) has a low surface roughness ∼0.5 nm, ultra-thin coating ∼2.1 nm, and more hydrophilic features than C-Z/ST (creosol red immobilized Z/ST), and HPh-Z/ST (phenolphthalein immobilized Z/ST). The P-Z/ST possessed 0.3 s against pH 12 and pka 10, C-Z/ST shows a time response 0.5 s and pka (negative log of the acid dissociation constant) value around 8, while Hph-Z/ST revealed a time response 0.68 s and high pka around 11. All three nanocomposites attributed stable and fast responses in basic media.

Construction Strategy for Flexible and Breathable SiO2/Al/NFs/PET Composite Fabrics with Dual Shielding against Microwave and Infrared-Thermal Radiations for Wearable Protective Clothing

Microwave and infrared-thermal radiation-compatible shielding fabrics represent an important direction in the development of wearable protective fabrics. Nevertheless, effectively and conveniently integrating compatible shielding functions into fabrics while maintaining breathability and moisture permeability remains a significant challenge. Here, we take hydrophilic PVA-co-PE nanofibrous film-coated PET fabric (NFs/PET) as a flexible substrate and deposit a dielectric/conductive (SiO2/Al) bilayer film via magnetron sputtering. This strategy endows the fabric surface with high electrical conductivity, nanoscale roughness comparable to visible and infrared waves, and a dielectric-metal contact interface possessing localized plasmon resonance and Mie scattering effects. The results demonstrate that the optimized SiO2/Al/NFs/PET composite conductive fabric (referred to as S4-1) possesses favorable X-band electromagnetic interference (EMI) shielding effectiveness (50 dB) as well as excellent long-wave infrared (LWIR) shielding or IR stealth performance (IR emissivity of 0.60). Notably, the S4-1 fabric has a cooling effect of about 12.4 °C for a heat source (80 °C) and an insulating effect of about 17.2 °C for a cold source (-20 °C), showing excellent shielding capability for heat conduction and heat radiations. Moreover, the moisture permeability of the S4-1 fabric is about 300 g/(m2·h), which is better than the requirement concerning moisture permeability for wearable fabrics (≥2500-5000 g/(m2·24 h)), indicating excellent heat and moisture comfort. In short, our fabrics have lightweight, thin, moisture-permeable and excellent shielding performance, which provides novel ideas for the development of wearable multi-band shielding fabrics applied to complex electromagnetic environments.

Wavelength exponent based calibration for turbidity spectroscopy: Monitoring the particle size during emulsion polymerization reactions

Particle size and particle size distribution (PSD) are important properties of polymer latexes because they strongly affect the film formation and the rheological properties of the latexes. Thus, monitoring the particle size is of paramount importance during the production of waterborne polymeric dispersions, for which online/inline measurements of the particle size are required. Herein, turbidity spectroscopy (TUS) is used to measure the particle size of nanoparticles in dispersed media. Calibration curves based on a modified wavelength exponent method are introduced and assessed to monitor the evolution of a broad range of particle sizes in seeded semibatch emulsion polymerizations of methyl methacrylate, butyl acrylate, methacrylic acid (MMA/BA/MAA 51/47/2) terpolymers. It is shown that the wavelength exponent based calibration curves can be successfully used to retrieve the particle size during the polymerization process.

Multiscale stress deconcentration amplifies fatigue resistance of rubber

Rubbers reinforced with rigid particles are used in high-volume applications, including tyres, dampers, belts and hoses1. Many applications require high modulus to resist excessive deformation and high fatigue threshold to resist crack growth under cyclic load. The particles are known to greatly increase modulus but not fatigue threshold. For example, adding carbon particles to natural rubber increases its modulus by one to two orders of magnitude1-3, but its fatigue threshold, reinforced or not, has remained approximately 100 J m-2 for decades4-7. Here we amplify the fatigue threshold of particle-reinforced rubbers by multiscale stress deconcentration. We synthesize a rubber in which highly entangled long polymers strongly adhere with rigid particles. At a crack tip, stress deconcentrates across two length scales: first through polymers and then through particles. This rubber achieves a fatigue threshold of approximately 1,000 J m-2. Mounts and grippers made of this rubber bear high loads and resist crack growth over repeated operation. Multiscale stress deconcentration expands the space of materials properties, opening doors to curtailing polymer pollution and building high-performance soft machines.

Enhanced Photoacoustic Response by Synergistic Ag-Melanin Interplay at the Core of Ternary Biocompatible Hybrid Silica-Based Nanoparticles

Photoacoustics (PA) is gaining increasing credit among biomolecular imaging methodologies by virtue of its poor invasiveness, deep penetration, high spatial resolution, and excellent endogenous contrast, without the use of any ionizing radiation. Recently, we disclosed the excellent PA response of a self-structured biocompatible nanoprobe, consisting of ternary hybrid nanoparticles with a silver core and a melanin component embedded into a silica matrix. Although preliminary evidence suggested a crucial role of the Ag sonophore and the melanin-containing nanoenvironment, whether and in what manner the PA response is controlled and affected by the self-structured hybrid nanosystems remained unclear. Because of their potential as multifunctional platforms for biomedical applications, a detailed investigation of the metal-polymer-matrix interplay underlying the PA response was undertaken to understand the physical and chemical factors determining the enhanced response and to optimize the architecture, composition, and performance of the nanoparticles for efficient imaging applications. Herein, we provide the evidence for a strong synergistic interaction between eumelanin and Ag which suggests an important role in the in situ-generated metal-organic interface. In particular, we show that a strict ratio between melanin and silver precursors and an accurate choice of metal nanoparticle dimension and the kind of metal are essential for achieving strong enhancements of the PA response. Systematic variation of the metal/melanin component is thus shown to offer the means of tuning the stability and intensity of the photoacoustic response for various biomedical and theranostic applications.

A magnetic assembly approach to chiral superstructures

Colloidal assembly into chiral superstructures is usually accomplished with templating or lithographic patterning methods that are only applicable to materials with specific compositions and morphologies over narrow size ranges. Here, chiral superstructures can be rapidly formed by magnetically assembling materials of any chemical compositions at all scales, from molecules to nano- and microstructures. We show that a quadrupole field chirality is generated by permanent magnets caused by consistent field rotation in space. Applying the chiral field to magnetic nanoparticles produces long-range chiral superstructures controlled by field strength at the samples and orientation of the magnets. Transferring the chirality to any achiral molecules is enabled by incorporating guest molecules such as metals, polymers, oxides, semiconductors, dyes, and fluorophores into the magnetic nanostructures.

The Employment of the Surface Plasmon Resonance (SPR) Microscopy Sensor for the Detection of Individual Extracellular Vesicles and Non-Biological Nanoparticles

A wide-field surface plasmon resonance (SPR) microscopy sensor employs the surface plasmon resonance phenomenon to detect individual biological and non-biological nanoparticles. This sensor enables the detection, sizing, and quantification of biological nanoparticles (bioNPs), such as extracellular vesicles (EVs), viruses, and virus-like particles. The selectivity of bioNP detection does not require biological particle labeling, and it is achieved via the functionalization of the gold sensor surface by target-bioNP-specific antibodies. In the current work, we demonstrate the ability of SPR microscopy sensors to detect, simultaneously, silica NPs that differ by four times in size. Employed silica particles are close in their refractive index to bioNPs. The literature reports the ability of SPR microscopy sensors to detect the binding of lymphocytes (around 10 μm objects) to the sensor surface. Taken together, our findings and the results reported in the literature indicate the power of SPR microscopy sensors to detect bioNPs that differ by at least two orders in size. Modifications of the optical sensor scheme, such as mounting a concave lens, help to achieve homogeneous illumination of a gold sensor chip surface. In the current work, we also characterize the improved magnification factor of the modified SPR instrument. We evaluate the effectiveness of the modified and the primary version of the SPR microscopy sensors in detecting EVs isolated via different approaches. In addition, we demonstrate the possibility of employing translation and rotation stepper motors for precise adjustments of the positions of sensor optical elements-prism and objective-in the primary version of the SPR microscopy sensor instrument, and we present an algorithm to establish effective sensor-actuator coupling.

Color Transferability from Solution to Solid Using Silica Coated Silver Nanoparticles

The interpretation of color change in sensors and tests can be linked to incorrect conclusions if the intrinsic color changes are not accounted for. In this work, we study the intrinsic color change associated with the process of embedding nanoparticles in a polymer to create nanocomposite films. We present a safer, faster method to coat silver nanoparticles with silica and employ a seven-factor Plackett-Burman design to identify critical factors in the synthesis. Silver nanodisks with increasing thicknesses of the silica shell showed a decreasing sensitivity of their localized surface plasmon resonance (LSPR) toward changes in the refractive index surrounding the nanoparticle. A color shift of up to 72 nm was observed when bare nanoparticles were embedded in poly(vinyl alcohol), but no color change was perceived when nanoparticles were coated with a 25-nm-thick silica shell. Understanding the origin of color changes intrinsic to the preparation of polymeric nanocomposites aids in the design and correct use of plasmonic sensors.

Effect of scatterer interactions on photon transport in diffusing wave spectroscopy

We calculate the effect of particle size, concentration, and interactions on the photon transport mean-free path l^{*} that characterizes the multiple light scattering in diffusing wave spectroscopy (DWS). For scatterers of sufficient size, such that the first peak of the suspension structure factor S(q_{max}) remains in the range of accessible scattering vectors, neither repulsive nor attractive interactions between scatterers contribute strongly to l^{*}; its values are bounded by those for hard spheres and scatterers without interactions. However, for scatterers smaller than the wavelength of light, crowding induced by attraction or repulsion can lead to nonmonotonic behavior in l^{*} with increasing scatterer concentration. The effect is strongest for repulsive particles.

The stiffness-dependent tumor cell internalization of liquid metal nanoparticles

The properties of nanoparticle (NP) carriers, such as size, shape and surface state, have been proven to dramatically affect their uptake by tumor cells, thereby influencing and determining the effect of nanomedicine on tumor theranostics. However, the effect of the stiffness of NPs on their cellular internalization remains unclear, especially for circumstances involving active or passive NP targeting. In this work, we constructed eutectic gallium indium liquid metal NPs with the same particle size, shape and surface charge properties but distinct stiffness via tailoring the surface oxidation and silica coating. It has been found that the softer NPs would be endocytosed much slower than their stiffer counterparts in the presence of specific ligand-receptor interaction. Interestingly, once the interaction is eliminated, softer NPs are internalized faster than the stiffer ones. Based on experimental observations and theoretical verification, we demonstrate that this phenomenon is mainly caused by varying degrees of deformation of soft NPs induced by ligand-receptor interactions. Such a finding of the stiffness effect of NPs implies great potential for fundamental biomedical applications, such as the rational design of nanomedicines.

Nanoparticle-Protein Interaction: Demystifying the Correlation between Protein Corona and Aggregation Phenomena

Protein corona formation and nanoparticles' aggregation have been heavily discussed over the past years since the lack of fine-mapping of these two combined effects has hindered the targeted delivery evolution and the personalized nanomedicine development. We present a multitechnique approach that combines dynamic light and small-angle X-ray scattering techniques with cryotransmission electron microscopy in a given fashion that efficiently distinguishes protein corona from aggregates formation. This methodology was tested using ∼25 nm model silica nanoparticles incubated with either model proteins or biologically relevant proteomes (such as fetal bovine serum and human plasma) in low and high ionic strength buffers to precisely tune particle-to-protein interactions. In this work, we were able to differentiate protein corona, small aggregates formation, and massive aggregation, as well as obtain fractal information on the aggregates reliably and straightforwardly. The strategy presented here can be expanded to other particle-to-protein mixtures and might be employed as a quality control platform for samples that undergo biological tests.

Photoactive Red Fluorescent SiO2 Nanoparticles Based on Controlled Methylene Blue Aggregation in Reverse Microemulsions

We present a reverse microemulsion synthesis procedure for incorporating methylene blue (MB), a known FDA-approved type-II red-absorbing photosensitizer and ¹O₂ generator, into the matrix of hydrophobic-core/hydrophilic-shell SiO₂ nanoparticles. Different synthesis conditions were explored with the aim of controlling the entrapped-dye aggregation at high dye loadings in the hydrophobic protective core; minimizing dye aggregation ensured highly efficient photoactive nanoentities for ¹O₂ production. Monitoring the synthesis in real time using UV-vis absorption allowed tracking of the dye aggregation process. In particular, silica nanoparticles (MB@SiO₂ NPs) of ∼50 nm diameter size with a high local entrapped-MB concentration (∼10^-2 M, 1000 MB molecules per NP) and a moderate proportion of dye aggregation were obtained. The as-prepared MB@SiO₂ NPs showed a high singlet oxygen photogeneration efficiency (Φ_Δ = 0.30 ± 0.05), and they can be also considered as red fluorescent probes (Φ_F ∼ 0.02, λ_max ∼ 650 nm). The distinctive photophysical and photochemical characteristics of the synthesized NPs reveal that the reverse microemulsion synthesis procedure offers an interesting strategy for the development of complex theranostic nano-objects for photodynamic therapy.

Precision size and refractive index analysis of weakly scattering nanoparticles in polydispersions

Characterization of the size and material properties of particles in liquid suspensions is in very high demand, for example, in the analysis of colloidal samples or of bodily fluids such as urine or blood plasma. However, existing methods are limited in their ability to decipher the constituents of realistic samples. Here we introduce iNTA as a new method that combines interferometric detection of scattering with nanoparticle tracking analysis to reach unprecedented sensitivity and precision in determining the size and refractive index distributions of nanoparticles in suspensions. After benchmarking iNTA with samples of colloidal gold, we present its remarkable ability to resolve the constituents of various multicomponent and polydisperse samples of known origin. Furthermore, we showcase the method by elucidating the refractive index and size distributions of extracellular vesicles from Leishmania parasites and human urine. The current performance of iNTA already enables advances in several important applications, but we also discuss possible improvements.

Importance of the Structural and Physicochemical Properties of Silica Nanoshells in the Photothermal Effect of Silica-Coated Au Nanoparticles Suspensions

In this work, monodisperse silica-coated gold nanoparticles (NPs) were synthesized and used for obtaining aqueous colloidal dispersions with an optimum relationship between colloidal stability and photothermal activity. The idea behind this design was to produce systems with the advantages of the presence of a silica shell (biocompatibility, potential for surface modification, and protecting effect) with a minimal loss of optical and thermal properties. With this aim, the photothermal properties of NPs with silica shells of different thicknesses were analyzed under conditions of high radiation extinction. By using amorphous, gel-like silica coatings, thicknesses higher than 40 nm could be obtained without an important loss of the light absorption capacity of the colloids and with a significant photothermal response even at low NP concentrations. The effects produced by changes in the solvent and in the NP concentration were also analyzed. The results show that the characteristics of the shell control both, the photothermal effect and the optical properties of the colloidal dispersions. As the presence of a silica shell strongly enhances the possibilities of adding cargo molecules or probes, these colloids can be considered of high interest for biomedical therapies, sensing applications, remote actuation, and other technological applications.

Kinetic Processes in Enzymatic Nanoreactors for In Vivo Detoxification

Enzymatic nanoreactors are enzyme-encapsulated nanobodies that are capable of performing biosynthetic or catabolic reactions. For this paper, we focused on therapeutic enzyme nanoreactors for the neutralization of toxicants, paying special attention to the inactivation of organophosphorus compounds (OP). Therapeutic enzymes that are capable of detoxifying OPs are known as bioscavengers. The encapsulation of injectable bioscavengers by nanoparticles was first used to prevent fast clearance and the immune response to heterologous enzymes. The aim of enzyme nanoreactors is also to provide a high concentration of the reactive enzyme in stable nanocontainers. Under these conditions, the detoxification reaction takes place inside the compartment, where the enzyme concentration is much higher than in the toxicant diffusing across the nanoreactor membrane. Thus, the determination of the concentration of the encapsulated enzyme is an important issue in nanoreactor biotechnology. The implications of second-order reaction conditions, the nanoreactor’s permeability in terms of substrates, and the reaction products and their possible osmotic, viscosity, and crowding effects are also examined.

Control of the Nanoparticles Content in Cosmetic Medicines

The safety of nanoparticles used in medical cosmetology and dermatology raises significant concerns. One of the tasks of analyzing the concentration of nanoparticles that must be solved for the practical analysis of the quality of products with nanoparticles is the quantitative analysis of the content of nanoparticles. The previously developed acousto-magnetic method (AMM) for determining the concentration of APIs as magnetic nanoparticles can be used to determine the nanoparticles' concentration when samples are prepared as a colloidal solution. It is shown that the described method not only can be applied for quality control in cosmetology and dermatology but also can be simplified by using a less sensitive magnetometer, which makes this direct method more available in the entire range of values ​​of the concentration of magnetic nanoparticles used in medical cosmetology and dermatology.

Sub-Kelvin Feedback Cooling and Heating Dynamics of an Optically Levitated Librator

Rotational optomechanics strives to gain quantum control over mechanical rotors by harnessing the interaction of light and matter. We optically trap a dielectric nanodumbbell in a linearly polarized laser field, where the dumbbell represents a nanomechanical librator. Using measurement-based parametric feedback control in high vacuum, we cool this librator from room temperature to 240 mK and investigate its heating dynamics when released from feedback. We exclude collisions with residual gas molecules as well as classical laser noise as sources of heating. Our findings indicate that we observe the torque fluctuations arising from the zero-point fluctuations of the electromagnetic field.

Effects of the Method of Preparation and Dispersion Media on the Optical Properties and Particle Sizes of Aqueous Dispersions of a Double-Chain Cationic Surfactant

As inferred from visual observations and turbidity measurements, the average radius of the unilamellar vesicles formed in water from the cationic double-chain surfactant didodecyldimethylammonium bromide (DDAB) varies with the method of preparation, being ∼24 nm after sonication (SS method) and ∼74 nm after extrusion/ultrafiltration (SE method). The radii were larger when the vesicles were produced in 10 mM NaBr, ∼65 nm for the SS method and ∼280 nm for the SE method. The specific turbidity, or turbidity per unit path length divided by the surfactant weight fraction, w, of these vesicular dispersions increased with decreasing w until a constant value was reached at w*, which depends on the preparation method and the dispersion medium. The constant specific turbidities are indicative of single and independent scattering and were used to estimate vesicle radii by solving the specific turbidity equations derived for the Rayleigh-Debye-Gans (RDG) regime. Two turbidity equations were used, one accounting for absorbance errors due to some scattered light reaching the detector and another with no correction. Estimates of the average distances between the vesicles and their corresponding Debye lengths were obtained for evaluating the importance of intervesicle electrostatic interactions, which could lead to dependent scattering at higher weight fractions.

Nanoparticle Determination in Water by LED-Excited Surface Plasmon Resonance Imaging

The increasing popularity of nanoparticles in many applications has led to the fact that these persistent materials pollute our environment and threaten our health. An online sensor system for monitoring the presence of nanoparticles in fresh water would be highly desired. We propose a label-free sensor based on SPR imaging. The sensitivity was enhanced by a factor of about 100 by improving the detector by using a high-resolution camera. This revealed that the light source also needed to be improved by using LED excitation instead of a laser light source. As a receptor, different self-assembled monolayers have been screened. It can be seen that the nanoparticle receptor interaction is of a complex nature. The best system when taking sensitivity as well as reversibility into account is given by a dodecanethiol monolayer on the gold sensor surface. Lanthanide-doped nanoparticles, 29 nm in diameter and with a similar refractive index to the most common silica nanoparticles were detected in water down to 1.5 µg mL−1. The sensor can be fully regenerated within one hour without the need for any washing buffer. This sensing concept is expected to be easily adapted for the detection of nanoparticles of different size, shape, and composition, and upon miniaturization, suitable for long-term applications to monitor the quality of water.

Multi-level characteristics of TiOx transparent non-volatile resistive switching device by embedding SiO2 nanoparticles

TiOx-based resistive switching devices have recently attracted attention as a promising candidate for next-generation non-volatile memory devices. A number of studies have attempted to increase the structural density of resistive switching devices. The fabrication of a multi-level switching device is a feasible method for increasing the density of the memory cell. Herein, we attempt to obtain a non-volatile multi-level switching memory device that is highly transparent by embedding SiO2 nanoparticles (NPs) into the TiOx matrix (TiOx@SiO2 NPs). The fully transparent resistive switching device is fabricated with an ITO/TiOx@SiO2 NPs/ITO structure on glass substrate, and it shows transmittance over 95% in the visible range. The TiOx@SiO2 NPs device shows outstanding switching characteristics, such as a high on/off ratio, long retention time, good endurance, and distinguishable multi-level switching. To understand multi-level switching characteristics by adjusting the set voltages, we analyze the switching mechanism in each resistive state. This method represents a promising approach for high-performance non-volatile multi-level memory applications.

Translucency of nanoparticle-reinforced PMMA denture base material: An in-vitro comparative study

The aim of this study was to assess the translucency of denture base acrylic resin reinforced with zirconium dioxide (ZrO₂NPs), silicon dioxide (SiO₂NPs), and diamond (DNPs) nanoparticles. A total of 130 heat-polymerized acrylic discs (15×2.5 mm) were fabricated conventionally and divided into control and experimental groups according to nanoparticle type and concentration (0.5, 1, 1.5, and 2.5 wt%). Unmodified acrylic resin specimens served as control. All specimens were thermocycled (5,000 cycles). Translucency was measured using a spectrophotometer. ANOVA and post-hoc Turkeys' test were used for data analysis at α=0.05. The translucency of modified PMMA was significantly lower than control (p<0.05) except 0.5% ZrO₂NPs and SiO₂NPs (p>0.05) which exhibited the highest translucency values among modified groups. As the NPs concentration increased, the translucency decreased and the lowest value was seen with 2.5% DNPs (1.18±0.10). The addition of ZrO₂NPs, SiO₂NPs, and DNPs into denture base resin decreased the translucency.

Rapid Determination of Emulsion Stability Using Turbidity Measurement Incorporating Artificial Neural Network (ANN): Experimental Validation Using Video/Optical Microscopy and Kinetic Modeling

Determination of emulsion stability has important applications in crude oil production, separation, and transportation. The turbidimetry method offers advantage of rapid determination of stability at a relatively low cost with good accuracy. In this study, the stability of an oil-in-water (O/W) emulsion prepared by dispersing heavy oil particles in the aqueous solution containing poly(vinyl alcohol) (PVA) has been determined using turbidity measurements. The turbidimetry theory of emulsion stability has been validated using experimental data of turbidity at different wavelengths (350-800 nm) and storage times (0-300 min). The artificial neural network (ANN) has been found to give good predictive performance of the turbidity data. The characteristic change in turbidity has been supported using particle size and distribution analyses performed using optical/video microscopy. The results obtained from the turbidimetry correlation show that the emulsion destabilization rate constant (κ', min^-1) is in the range of 0.01-0.04 min^-1 (at wavelengths between 350 and 800 nm, respectively). The rate constant remains unchanged (κ' = 0.02 min^-1) between the wavelength of 375 and 650 nm. In addition, the demulsification rate constant (κ' = 0.015 min^-1) obtained from kinetic modeling using the bottle test is in close agreement with this value. The overall findings ultimately revealed that the turbidimetry method could be used to determine stability of typical O/W emulsions with an acceptable level of accuracy.

Label-free optical antibody testing kit based on a self-assembled whispering-gallery-mode microsphere

The appearance of antibodies in blood is a critical signal to suggest the infection. A rapid and accurate detection method for the antibody is significant to the disease diagnosis, especially for the epidemic. To this end, a highly sensitive whispering-gallery-mode (WGM) optical testing kit is designed and fabricated for detecting the specific immunoglobulin antibodies. The key component of the kit is a silica self-assembled microsphere decorated with the nucleocapsid proteins (N-proteins) of the SARS-CoV-2 virus. After the N-protein antibody immunoglobulin G (N-IgG) and immunoglobulin M (N-IgM) solutions being injected into the kit, the WGM red-shifts due to the antigen-antibody reaction. The wavelength displacement rates are proportional to the concentrations of these two antibodies from 1 to 100 μg/mL. A good specificity of the kit is demonstrated by the nonspecific human immunoglobulin G (H-IgG) and immunoglobulin M (H-IgM).

Insight into the effect of oxidation degree of graphene oxides on their removal from wastewater via froth flotation

The effect of oxidation degree of graphene oxides (GO) on their removal from wastewater via froth flotation was studied in this work. Four types of GO samples with different oxidation degrees were synthesized and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), atomic force spectroscopy (AFM) et al. The effects of cetyl trimethyl ammonium bromide (CTAB) concentration, pH, stirring time on the removal of GO by froth flotation had been discussed. It was found that the addition of CTAB could improve surface hydrophobicity of GO, endowing GO to be easily separated by froth flotation. The removal was dependent on CTAB dosage, pH and stirring time. Moreover, the removal first increased and then decreased with the increasing oxidation degree of GO, and less kinetic energy input was needed to overcome the energy barrier between GO flocs with the increase of oxidation degree. The removal mechanism was proven to be electrostatic attraction, and the different contents of oxgenous-containing functional groups in GOs with various oxidation degrees played a vital role in their removal via froth flotation.

Merging Mie solutions and the radiative transport equation to measure optical properties of scattering particles in optical phantoms

We present a new method to calculate the complex refractive index of spherical scatterers in a novel optical phantom developed by using homemade monodisperse silica nanospheres embedded into a polyester resin matrix and an ethanol-water mixture for applications in diffuse imaging. The spherical geometry of these nanoparticles makes them suitable for direct comparison between the values of the absorption and reduced scattering coefficients (μ_a and μs', respectively) obtained by the diffusion approximation solution to the transport equation from scattering measurements and those obtained by the Mie solution to Maxwell's equations. The values of the optical properties can be obtained by measuring, using an ultrafast detector, the time-resolved intensity distribution profiles of diffuse light transmitted through a thick slab of the silica nanosphere phantom, and by fitting them to the time-dependent diffusion approximation solution to the transport equation. These values can also be obtained by Mie solutions for spherical particles when their physical properties and size are known. By using scanning electron microscopy, we measured the size of these nanospheres, and the numerical results of μ_a and μs' can then be inferred by calculating the absorption and scattering efficiencies. Then we propose a numerical interval for the imaginary part of the complex refractive index of SiO₂ nanospheres, n_s, which is estimated by fixing the fitted values of μ_a and μs', using the known value of the real part of n_s, and finding the corresponding value of Im(n_s) that matches the optical parameters obtained by both methods finding values close to those reported for silica glass. This opens the possibility of producing optical phantoms with scattering and absorption properties that can be predicted and designed from precise knowledge of the physical characteristics of their constituents from a microscopic point of view.

Features of Sizing and Enumeration of Silica and Polystyrene Nanoparticles by Nanoparticle Tracking Analysis (NTA)

Nanoparticle Tracking Analysis (NTA) allows for the simultaneous determination of both size and concentration of nanoparticles in a sample. This study investigates the accuracy of particle size and concentration measurements performed on an LM10 device. For experiments, standard nanoparticles of different sizes composed of two materials with different refractive indices were used. Particle size measurements were found to have a decent degree of accuracy. This fact was verified by the manufacturer-reported particle size—determined by transmission electron microscopy (TEM)—as well as by performed scanning electron microscopy (SEM) measurements. On the other hand, concentration measurements resulted in overestimation of the particle concentration in majority of cases. Thus, our findings confirmed the accuracy of nanoparticle sizing performed by the LM10 instrument and highlighted the overestimation of particle concentration made by this device. In addition, an approach of swift correction of the results of concentration measurements received for samples is suggested in the presented study.

Antifungal Efficacy and Physical Properties of Poly(methylmethacrylate) Denture Base Material Reinforced with SiO2 Nanoparticles

PURPOSE

To evaluate the effect of the addition of low concentration of silicon-dioxide nanoparticles (nano-SiO₂ ) to poly(methylmethacrylate) (PMMA) denture base material on Candida albicans adhesion, surface roughness, contact angle, hardness, and translucency.

MATERIALS AND METHODS

A total of 150 acrylic disks were fabricated from heat-polymerized acrylic resin and specimens were divided into 3 groups of 50 per test. They were further subdivided into 5 subgroups (n = 10) according to the concentration of nano-SiO₂ : control (no addition) and four tested groups modified with 0.05, 0.25, 0.5, and 1.0 wt% nano-SiO₂ of acrylic powder. Slide count and direct culture methods were used to measure C. albicans count (CFU/mL). The surface roughness values (R_a ; μm) were determined using a profilometer. The contact angle (^o ) measurement was performed by a goniometer using the sessile drop method. Vickers hardness was used to analyze surface hardness. Translucency was measured using a spectrophotometer. Data analysis was conducted through analysis of variance and Tukey's post hoc tests (α = 0.05).

RESULTS

Compared to the control group, direct culture and slide count methods illustrated a significant decrease in C. albicans count (p ˂ 0.001) with the addition of nano-SiO₂ , and this decrease was correlated with the concentration of nano-SiO₂ . The addition of nano-SiO₂ significantly decreased the contact angle (p ˂ 0.001), whereas hardness and surface roughness significantly increased (p ˂ 0.001). The addition of nano-SiO₂ significantly decreased translucency (p ˂ 0.001), and this decrease was concentration dependent.

CONCLUSION

Addition of low concentration of nano-SiO₂ decreased C. albicans adhesion to PMMA denture base resin. Also, low additions of nano-SiO₂ have positive effects on contact angle and hardness, whereas surface roughness and translucency were adversely affected at high concentrations.

Development of Novel High-Resolution Size-Guided Turbidimetry-Enabled Particle Purification Liquid Chromatography (PPLC): Extracellular Vesicles and Membraneless Condensates in Focus

Acellular particles (extracellular vesicles and membraneless condensates) have important research, drug discovery, and therapeutic implications. However, their isolation and retrieval have faced enormous challenges, impeding their use. Here, a novel size-guided particle purification liquid chromatography (PPLC) is integrated into a turbidimetry-enabled system for dye-free isolation, online characterization, and retrieval of intact acellular particles from biofluids. The chromatographic separation of particles from different biofluids-semen, blood, urine, milk, and cell culture supernatants-is achieved using a first-in-class gradient size exclusion column (gSEC). Purified particles are collected using a fraction collector. Online UV-Vis monitoring reveals biofluid-dependent particle spectral differences, with semen being the most complex. Turbidimetry provides the accurate physical characterization of seminal particle (Sp) lipid contents, sizes, and concentrations, validated by a nanoparticle tracking analysis, transmission electron microscopy, and naphthopyrene assay. Furthermore, different fractions of purified Sps contain distinct DNA, RNA species, and protein compositions. The integration of Sp physical and compositional properties identifies two archetypal membrane-encased seminal extracellular vesicles (SEV)-notably SEV large (SEVL), SEV small (SEVS), and a novel nonarchetypalμμembraneless Sps, herein named membraneless condensates (MCs). This study demonstrates a comprehensive yet affordable platform for isolating, collecting, and analyzing acellular particles to facilitate extracellular particle research and applications in drug delivery and therapeutics. Ongoing efforts focus on increased resolution by tailoring bead/column chemistry for each biofluid type.

"DIY" Silica Nanoparticles: Exploring the Scope of a Simplified Synthetic Procedure and Absorbance-Based Diameter Measurements

In this study, the classical Stöber silica synthesis protocol was used to test the limits of simplification in the preparation and size determination of nanoparticles. The scope of three-ingredient, one-pot synthesis was established in conditions of regular 96% and 99.8% ethanol as solvent, with aqueous ammonia as the only source of base and water. Particles with diameters in the 15-400 nm range can be reliably obtained with this straightforward approach, and the direct relationship between the size and the product of concentrations of water and ammonia is evidenced. Furthermore, the idea of a linear approximation for Mie scattering in particular conditions is discussed, using experimental data and theoretical calculations. A simple, fast method for particle size determination utilizing a UV-Vis spectrophotometer-an easily accessible instrument-is explained, and shows a level of error (<0.5 SD) that can be acceptable for less rigorous laboratory use of nanoparticles or serve as a quick means for testing the influence of minor alterations to known synthetic protocols. This work aims to show that nanoparticle synthesis can (and should) become a regular occurrence, even in non-specialized labs, facilitating research into their new applications and inspiring outside-the-box solutions, while discussing the drawbacks of a more relaxed synthetic regimen.

Multimodal and Covert-Overt Convertible Structural Coloration Transformed by Mechanical Stress

Most materials and devices with structurally switchable color features responsive to external stimuli can actively and flexibly display various colors. However, realizing covert-overt transformation behavior, especially switching between transparent and colored states, is more challenging. A composite laminate of soft poly(dimethylsiloxane) (PDMS) with a rigid SiO₂ -nanoparticle (NP) structure pattern is developed as a multidimensional structural color platform. Owing to the similarity in the optical properties of PDMS and SiO₂ NPs, this device is fully transparent in the normal state. However, as their mechanical strengths differ considerably, upon compressive loading, a buckling-type instability arises on the surface of the laminate, leading to the generation of 1D or 2D wrinkled patterns in the form of gratings. Finally, an application of the device in which quick response codes are displayed or hidden as covert-overt convertible colored patterns for optical encryption/decryption, showing their remarkable potential for anticounterfeiting applications, is demonstrated.

Determination of refractive index, size, and solid content of monodisperse polystyrene microsphere suspensions for the characterization of optical phantoms

Monodisperse polystyrene microspheres are often utilized in optical phantoms since optical properties such as the scattering coefficient and the scattering phase function can be calculated using the Mie theory. However, the calculated values depend on the inherent physical parameters of the microspheres which include the size, refractive index, and solid content. These parameters are often provided only approximately or can be affected by long shelf times. We propose a simple method to obtain the values of these parameters by measuring the collimated transmission of polystyrene microsphere suspensions from which the wavelength-dependent scattering coefficient can be calculated using the Beer-Lambert law. Since a wavelength-dependent scattering coefficient of a single suspension is insufficient to uniquely derive the size, refractive index and solid content by the Mie theory, the crucial and novel step involves suspending the polystyrene microspheres in aqueous sucrose solutions with different sucrose concentrations that modulates the refractive index of the medium and yields several wavelength-dependent scattering coefficients. With the proposed method, we are able to obtain the refractive index within 0.2% in the wavelength range from 500 to 800 nm, the microsphere size to approximately 15 nm and solid content within 2% of their respective reference values.

CXCL5 Modified Nanoparticle Surface Improves CXCR2+ Cell Selective Internalization

Driving nanomaterials to specific cell populations is still a major challenge for different biomedical applications. Several strategies to improve cell binding and uptake have been tried thus far by intrinsic material modifications or decoration with active molecules onto their surface. In the present work, we covalently bound the chemokine CXCL5 on fluorescently labeled amino-functionalized SiO₂ nanoparticles to precisely targeting CXCR2⁺ immune cells. We synthesized and precisely characterized the physicochemical features of the modified particles. The presence of CXCL5 on the surface was detected by z-potential variation and CXCL5-specific electron microscopy immunogold labeling. CXCL5-amino SiO₂ nanoparticle cell binding and internalization performances were analyzed in CXCR2⁺ THP-1 cells by flow cytometry and confocal microscopy. We showed improved internalization of the chemokine modified particles in the absence or the presence of serum. This internalization was reduced by cell pre-treatment with free CXCL5. Furthermore, we demonstrated CXCR2⁺ cell preferential targeting by comparing particle uptake in THP-1 vs. low-CXCR2 expressing HeLa cells. Our results provide the proof of principle that chemokine decorated nanomaterials enhance uptake and allow precise cell subset localization. The possibility to aim at selective chemokine receptor-expressing cells can be beneficial for the diverse pathological conditions involving immune reactions.

A combination therapy of nanoethosomal piroxicam formulation along with iontophoresis as an anti-inflammatory transdermal delivery system for wound healing

Inflammation accounts as one of the major phases in wound healing, while prolonged and chronic inflammation may lead to adverse pathological conditions. Therefore, transdermal delivery of nonsteroidal anti-inflammatory (NSAIDs) such as encapsulated piroxicam into a nanocarrier seems to be promising. For the first time, a nanoethosomal piroxicam of <200 nm was prepared and combined with iontophoresis. Results showed that there was a critical point at the concentration of 5 mg lecithin with the smallest particle size. Besides, lecithin concentration had direct and inverse linear relationships with turbidity and pH of nanocarriers, respectively. Moreover, as there was no linear relationship between the lecithin concentration and particle size, the effect of lecithin concentration was dominant on turbidity compared with particle size. It seems that a pH higher than 5.5 disturbed the linear relationship of pH and entrapment efficacy percentage (EE%) while at the pH range of 4 to 5.5, the relationship was linear and EE% gradually decreased with increasing pH. These data showed that an optimised nanocarrier with special physicochemical properties is dominant to the just particle size. Besides, ex vivo permeation studies in rat skin showed that there was no significant difference between the permeation of free drug and ethosomal ones. However, iontophoresis significantly enhanced ethosomal piroxicam permeation compared with the free drug. Overall, these data emphasise the superiority of iontophoresis for the transdermal delivery of nanoethosomal medications while nanoethosomal delivery without iontophoresis did not show significant transdermal potential. To sum up, transdermal nanoethosomal piroxicam along with iontophoresis seems to be promising in wound healing.

Characterization of Nanoparticles: Advances

Over the past two decades, the unique properties of engineered nanoparticles (NPs) have placed them at the centre of revolutionary advancements in many sectors of science, technology and commerce. Multi-technique and multi-disciplinary analytical approaches are required to identify, quantify, and characterize the chemical composition, size and size distribution, surface properties and the number and concentration of NPs. In this chapter, an overview of the recent advances in the characterization of NPs will be presented.

Self-assembly three-dimensional optical devices: from microsphere to microlens array

We report rapid formation of three-dimensional micro optical devices by silica nanoparticle self-assembly in a face-centered cubic (fcc) structure. By controlling the hydrophobic interactions, the self-assembled products are fabricated into different morphologies, which include microsphere and hemisphere. These structures have specific applications in microsphere resonant cavities and microlens arrays. The whispering gallery mode of the formed microsphere is excited by the tapered fiber to demonstrate the optical characters of the microsphere. Moreover, the properties of the fabricated microlens and microlens array are tested through insertion in an imaging system. Ultimately, the optical devices with advanced functions are demonstrated by the secondary phase infiltrating into the interstitial space of silica nanoparticles. This report will open a new direction in manufacturing multifunctional and miniature optical devices by an ultrasimple self-assembly approach.

Macroscopic Aerogels with Retained Nanoscopic Plasmonic Properties

Aerogels can bridge the nanoscopic to the macroscopic world. One physical phenomenon typically limited to the nanoscopic world is the occurrence of localized surface plasmon resonances (LSPRs), which are observed in conductive nanoparticles. Once brought into close contact, assemblies or superstructures of these nanoparticles often lose their plasmonic properties in the transition stage towards the bulk material. Therefore, LSPRs are typically not observed in macroscopic objects. The present work aims at voluminous nanoparticle-based aerogels with optical properties close to that of the initial colloidal solution and the possibility to manipulate the final plasmonic properties by bringing the particles into defined distances. In detail, Ag nanocrystals with silica shells ranging from 0 to 12 nm are employed as building blocks, which are assembled from their solution into macroscopic three-dimensional superstructures by freezing and subsequent lyophilization. These cryogelated aerogels are synthesized as monoliths and thin films in which the Ag nanocrystals are arranged in defined distances according to their silica shell. The resulting aerogels exhibit plasmonic properties ranging from a behavior similar to that of the building blocks for the thickest shell to a heavily distorted behavior for bare Ag nanocrystals.

Extinction spectra of suspensions of microspheres: determination of the spectral refractive index and particle size distribution with nanometer accuracy

A method is presented to infer simultaneously the wavelength-dependent real refractive index (RI) of the material of microspheres and their size distribution from extinction measurements of particle suspensions. To derive the averaged spectral optical extinction cross section of the microspheres from such ensemble measurements, we determined the particle concentration by flow cytometry to an accuracy of typically 2% and adjusted the particle concentration to ensure that perturbations due to multiple scattering are negligible. For analysis of the extinction spectra, we employ Mie theory, a series-expansion representation of the refractive index and nonlinear numerical optimization. In contrast to other approaches, our method offers the advantage to simultaneously determine size, size distribution, and spectral refractive index of ensembles of microparticles including uncertainty estimation.

Quantification of nanoparticle concentration in colloidal suspensions by a non-destructive optical method

The estimation of nanoparticle number concentration in colloidal suspensions is a prerequisite in many procedures, and in particular in multi-stage, low-yield reactions. Here, we describe a rapid, non-destructive method based on optical extinction and dynamic light scattering (DLS), which combines measurements using common bench-top instrumentation with a numerical algorithm to calculate the particle size distribution (PSD) and concentration. These quantities were derived from Mie theory applied to measurements of the optical extinction spectrum of homogeneous, non-absorbing nanoparticles, and the relative PSD of a colloidal suspension. The work presents an approach to account for PSDs achieved by DLS which, due to the underlying model, may not be representative of the true sample PSD. The presented approach estimates the absolute particle number concentration of samples with mono-, bi-modal and broad size distributions with <50% precision. This provides a convenient and practical solution for number concentration estimation required during many applications of colloidal nanomaterials.

Determination of the Exact Particle Radius Distribution for Silica Nanoparticles via Capillary Electrophoresis and Modeling the Electrophoretic Mobility with a Modified Analytic Approximation

In this study, we use aqueous dispersions of amorphous silica nanoparticles of various sizes to investigate whether electropherograms recorded from capillary electrophoresis experiments can be converted directly into exact number-based particle radius distributions, provided that there is a relaxation effect-based size selectivity of the electrophoretic mobility and provided that the electrokinetic potential ζ of the particles can be regarded to be homogeneous over the surface of the particles, independent of the particle size. The results of this conversion procedure are compared with number-based particle radius distributions obtained from a large set of transmission electron microscopy (TEM) data. For this specific example, it is shown that the modified analytic approximation developed by Ohshima adequately describes the mobility-dependent relaxation effect and the electrophoretic mobility of the particle as a function of the reduced hydrodynamic radius and electrokinetic potential, which is a prerequisite for the presented procedure. Simultaneously, we confirmed that for the given Debye length/particle diameter ratio the electrokinetic surface charge density can be regarded to be size-invariant (including spherical geometry and planar limiting case). It is shown that the accuracy of the results of the developed method is comparable to that gained by a large set of TEM data, which is important when a precise description of the particle size distribution is needed to deduce conclusions regarding the underlying mechanism(s) of particle growth. The values obtained for the dispersion (width) of the distribution show only a small negative deviation, when compared with the TEM data (4-16%).

Determining Number Concentrations and Diameters of Polystyrene Particles by Measuring the Effective Refractive Index of Colloids Using Surface Plasmon Resonance

The capabilities of surface plasmon resonance (SPR) for characterization of colloidal particles were evaluated for 100, 300, and 460 nm nominal diameter polystyrene (PS) latexes. First the accuracy of measuring the effective refractive index (n_eff) of turbid colloids using SPR was quantified. It was concluded that for submicrometer sized PS particles the accuracy is limited by the reproducibility between replicate injections of samples. An SPR method was developed for obtaining the particle mean diameter (d_part) and the particle number concentration (c_p) by fitting the measured n_eff of polystyrene (PS) colloids diluted in series with theoretical values calculated using the coherent scattering theory (CST). The d_part and c_p determined using SPR agreed with reference values obtained from size distributions measured by scanning electron microscopy (SEM), and the mass concentrations stated by the manufacturer. The 100 nm particles adsorbed on the sensing surface, which hampered the analysis. Once the adsorption problem has been overcome, the developed SPR method has potential to become a versatile tool for characterization of colloidal particles. In particular, SPR could form the basis of rapid and accurate methods for measuring the c_p of submicrometer particles in dispersion.