Colloidal Suspensions Of Nanoparticles Research Articles

Experimental study and modeling of the energy density and time-dependent rheological behavior of carbon nanotube nanofluids with sonication

Nanofluids are colloidal suspensions of nanoparticles in liquids. Nanoparticles have superior properties, which means that they can improve the performance characteristics of nanofluids. To press their advantages, the characteristics of nanofluids should be investigated to understand their underlying mechanisms. In this sense, fluidity is an important concept for examining the colloidal structure and interactions among nanoparticles based on their morphologies and intrinsic properties. Viscosity determines the fluidity of nanofluids, thereby indicating their degree of resistance to deformation and molecular dynamicity. Herein, we experimentally studied the rheological behavior of sonicated nanofluids with multi-walled carbon nanotubes (MWCNTs), which had long, tube-like, and flexible structures. The change in viscosity at an increasing energy density (Eρ) due to sonication at the specific total energy (ET) indicates that the nanotubes experienced a size phase change from “debundling” to “nano-cutting”. These phases agree well with the results of the hydrodynamic radii from dynamic light scattering (DLS) measurements. In the debundling phase, the unordered colloidal structure due to randomized entanglement increased the resistance to shear flow, thereby leading to a higher viscosity. With higher Eρ, the nanotubes broke owing to nano-cutting. In this phase, the short and exfoliated nanotubes functioned as rigid rods in the nanofluids and tended to align easily under shear flow. Finally, we discovered a well-fitted correlation between the viscosity of the nanofluids and sonication conditions (i.e., Eρ and ET). We found that the characteristic change in the colloidal structure of the MWCNT nanofluids was reflected in their rheological behavior during their preparation via sonication. Furthermore, the relationship between sonication conditions and viscosity helped us to predict the colloidal structure of the MWCNT nanofluids in the early stages of preparation. We expect that this work will contribute to promote the availability of MWCNTs in various application fields in terms of rheology and intermolecular structure.

Dry Powder Formulation of Simvastatin Nanoparticles for Potential Application in Pulmonary Arterial Hypertension.

It has been hypothesized that simvastatin could be used to treat pulmonary arterial hypertension (PAH). This study is intended to formulate a simvastatin nanoparticle dry powder inhalation (DPI) formulation. Simvastatin nanoparticles were prepared via an emulsification and homogenization-extrusion method, followed by spray drying of the colloidal suspension of simvastatin nanoparticles containing mannitol to get it into a respirable size. Particle size distribution, morphology, and crystallinity of the fabricated nanoparticles of the obtained microparticles for DPI formulation were assessed by dynamic light scattering (DLS), scanning electron microscopy (SEM), and X-ray diffraction pattern (XRPD), respectively. Aerosolization performance of the DPI formulation was assessed by the Next Generation Impactor (NGI) equipped with an Aerolizer®. Simvastatin nanoparticles were around 100 nm with a very narrow size distribution (PDI = 0.105). The X-ray diffraction pattern revealed that the crystallinity of simvastatin was decreased by the spray drying procedure. Microscopic images displayed that gathered nanoparticles were in the suitable inhalable range and had the appropriate shape and surface properties for pulmonary delivery. Aerosolization assessment by the NGI indicated a suitable inhalation performance (fine particle fraction of 20%). In conclusion, the results confirmed that the spray drying technique for simvastatin can be optimized to obtain simvastatin aggregated nanoparticles without any coarse carrier to be used in DPI formulation for better deposition of the drug in the lungs for local treatment of PAH.

Controlling the volume fraction of glass-forming colloidal suspensions using thermosensitive host "mesogels".

The key parameter controlling the glass transition of colloidal suspensions is φ, the fraction of the sample volume occupied by the particles. Unfortunately, changing φ by varying an external parameter, e.g., temperature T as in molecular glass formers, is not possible, unless one uses thermosensitive colloidal particles, such as the popular poly(N-isopropylacrylamide) (PNiPAM) microgels. These, however, have several drawbacks, including high deformability, osmotic deswelling, and interpenetration, which complicate their use as a model system to study the colloidal glass transition. Here, we propose a new system consisting of a colloidal suspension of non-deformable spherical silica nanoparticles, in which PNiPAM hydrogel spheres of ∼100-200μm size are suspended. These non-colloidal "mesogels" allow for controlling the sample volume effectively available to the silica nanoparticles and hence their φ, thanks to the T-induced change in mesogels' volume. Using optical microscopy, we first show that the mesogels retain their ability to change size with T when suspended in Ludox suspensions, similarly as in water. We then show that their size is independent of the sample thermal history such that a well-defined, reversible relationship between T and φ may be established. Finally, we use space-resolved dynamic light scattering to demonstrate that, upon varying T, our system exhibits a broad range of dynamical behaviors across the glass transition and beyond, comparable with those exhibited by a series of distinct silica nanoparticle suspensions of various φ.

Approaches on Ferrofluid Synthesis and Applications: Current Status and Future Perspectives.

Ferrofluids are colloidal suspensions of iron oxide nanoparticles (IONPs) within aqueous or nonaqueous liquids that exhibit strong magnetic properties. These magnetic properties allow ferrofluids to be manipulated and controlled when exposed to magnetic fields. This review aims to provide the current scope and research opportunities regarding the methods of synthesis of nanoparticles, surfactants, and carrier liquids for ferrofluid production, along with the rheology and applications of ferrofluids within the fields of medicine, water treatment, and mechanical engineering. A ferrofluid is composed of IONPs, a surfactant that coats the magnetic IONPs to prevent agglomeration, and a carrier liquid that suspends the IONPs. Coprecipitation and thermal decomposition are the main methods used for the synthesis of IONPs. Despite the fact that thermal decomposition provides precise control on the nanoparticle size, coprecipitation is the most used method, even when the oxidation of iron can occur. This oxidation alters the ratio of maghemite/magnetite, influencing the magnetic properties of ferrofluids. Strategies to overcome iron oxidation have been proposed, such as the use of an inert atmosphere, adjusting the Fe(II) and Fe(III) ratio to 1:2, and the exploration of other metals with the oxidation state +2. Surfactants and carrier liquids are chosen according to the ferrofluid application to ensure stability. Hence, a compatible carrier liquid (polar or nonpolar) is selected, and then, a surfactant, mainly a polymer, is embedded in the IONPs, providing a steric barrier. Due to the variety of surfactants and carrier liquids, the rheological properties of ferrofluids are an important response variable evaluated when synthesizing ferrofluids. There are many reported applications of ferrofluids, including biosensing, medical imaging, medicinal therapy, magnetic nanoemulsions, and magnetic impedance. Other applications include water treatment, energy harvesting and transfer, and vibration control. To progress from synthesis to applications, research is still ongoing to ensure control of the ferrofluids’ properties.

Gas–Liquid Slug Flow Studies in Microreactors: Effect of Nanoparticle Addition on Flow Pattern and Pressure Drop

Colloidal suspensions of nanoparticles (e.g., metals and oxides) have been considered as a promising working fluid in microreactors for achieving significant process intensification. Existing examples include their uses in microflow as catalysts for enhancing the reaction efficiency, or as additives to mix with the base fluid (i.e., to form the so-called nanofluids) for heat/mass transfer intensification. Thus, hydrodynamic characterization of such suspension flow in microreactors is of high importance for a rational design and operation of the system. In this work, experiments have been conducted to investigate the flow pattern and pressure drop characteristics under slug flow between N2 gas and colloidal suspensions in the presence of TiO2 or Al2O3 nanoparticles through polytetrafluoroethylene (PTFE) capillary microreactors. The base fluid consisted of water or its mixture with ethylene glycol. The slug flow pattern with nanoparticle addition was characterized by the presence of a lubricating liquid film around N2 bubbles, in contrast to the absence of liquid film in the case of N2-water slug flow. This shows that the addition of nanoparticles has changed the wall wetting property to be more hydrophilic. Furthermore, the measured pressure drop under N2-nanoparticle suspension slug flow is well described by the model of Kreutzer et al. (AIChE J 51(9):2428–2440, 2005) at the mixture Reynolds numbers ca. above 100 and is better predicted by the model of Warnier et al. (Microfluidics and Nanofluidics 8(1):33–45, 2010) at lower Reynolds numbers given a better consideration of the effect of film thickness and bubble velocity under such conditions in the latter model. Therefore, the employed nanoparticle suspension can be considered as a stable and pseudo single phase with proper fluid properties (e.g., viscosity and density) when it comes to the pressure drop estimation.

Impact of Smoluchowski Temperature and Maxwell Velocity Slip Conditions on Axisymmetric Rotated Flow of Hybrid Nanofluid past a Porous Moving Rotating Disk.

Colloidal suspensions of regular fluids and nanoparticles are known as nanofluids. They have a variety of applications in the medical field, including cell separation, drug targeting, destruction of tumor tissue, and so on. On the other hand, the dispersion of multiple nanoparticles into a regular fluid is referred to as a hybrid nanofluid. It has a variety of innovative applications such as microfluidics, heat dissipation, dynamic sealing, damping, and so on. Because of these numerous applications of nanofluids in minds, therefore, the objective of the current exploration divulged the axisymmetric radiative flow and heat transfer induced by hybrid nanofluid impinging on a porous stretchable/shrinkable rotating disc. In addition, the impact of Smoluchowski temperature and Maxwell velocity slip boundary conditions are also invoked. The hybrid nanofluid was formed by mixing the copper (Cu) and alumina (Al2O3) nanoparticles scattered in the regular (viscous) base fluid (H2O). Similarity variables are used to procure the similarity equations, and the numerical outcomes are achieved using bvp4c in MATLAB software. According to the findings, double solutions are feasible for stretching and shrinking cases . The heat transfer rate is accelerated as the hybrid nanoparticles increases. The suction parameter enhances the friction factors as well as heat transfer rate. Moreover, the friction factor in the radial direction and heat transfer enrich for the first solution and moderate for the second outcome due to the augmentation , while the trend of the friction factor in the radial direction is changed only in the case of stretching for both branches.

Effect of non-uniform heating on thermal performance of an enclosure filled with nanofluid

The influence of non-uniform temperature during convective transport in a closed enclosure is examined numerically. This system works using a water-based nanofluid where Cu is used as colloidal suspension of nanoparticles. The numerical simulation is performed in a Computational Fluid Dynamics software constructed using finite volume discretization technique. The investigation is executed in a bottom wall heated (BWH) enclosure by controlling Rayleigh number (Ra) for different heating profiles. The BWH is carried using uniform, parabolic, and linear temperature profiles. For all the cases investigated, the mean temperature of the bottom wall is fixed. The transfer of energy by the convection process is calculated using the Nusselt number. Flow visualizations through streamlines and isotherms reveal that the thermal convection is minimum for uniform temperature and maximum for linear temperature profiles. The irreversibility evolved during different heating profiles is measured with entropy generation (EG). The results reveal that the EG is minimum for uniform heating and maximum for parabolic heating. Further, EG increases with an increase in Ra. The present study can provide useful insights for designing thermal devices.

Ferrofluids and bio-ferrofluids: looking back and stepping forward.

Ferrofluids investigated along for about five decades are ultrastable colloidal suspensions of magnetic nanoparticles, which manifest simultaneously fluid and magnetic properties. Their magnetically controllable and tunable feature proved to be from the beginning an extremely fertile ground for a wide range of engineering applications. More recently, biocompatible ferrofluids attracted huge interest and produced a considerable increase of the applicative potential in nanomedicine, biotechnology and environmental protection. This paper offers a brief overview of the most relevant early results and a comprehensive description of recent achievements in ferrofluid synthesis, advanced characterization, as well as the governing equations of ferrohydrodynamics, the most important interfacial phenomena and the flow properties. Finally, it provides an overview of recent advances in tunable and adaptive multifunctional materials derived from ferrofluids and a detailed presentation of the recent progress of applications in the field of sensors and actuators, ferrofluid-driven assembly and manipulation, droplet technology, including droplet generation and control, mechanical actuation, liquid computing and robotics.

Nano-Au particle decorated poly-(3-amino-5-hydroxypyrazole) coated carbon paste electrode for in-vitro detection of valacyclovir

A versatile reusable electrochemical biosensor has been formulated by using colloidal gold nanoparticle (AuNPs) suspension and conducting polymer poly-(3-amino-5-hydroxypyrazole (poly-AHP) modified carbon paste electrode (AuNPs/poly-AHP/CPE) for detection of an important anti-viral drug valacyclovir (VAL). A thin film of poly-AHP incorporated with homogeneous distribution of AuNPs on the surface of carbon paste electrode is fabricated stepwise by applying one by one. An electrochemical potentiodynamic polymerization of AHP was followed by a potentiostatic electrodissolution–induced deposition of AuNPs on poly-AHP. The sensor surface has been characterized by scanning electron microscopy (SEM), energy dispersive X-Ray spectroscopy (EDX), X-ray powder diffraction (XRD) and UV–visible spectroscopy for surface topological/morphological characteristics. Electrochemical efficiency of the present sensor system towards the detection of VAL is explored by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV) and hydrodynamic steady-state current–time analysis, and the fabricated AuNPs/poly-AHP/CPE is recognized as a capable sensor system for electrochemical determination of VAL. Applying DPV under optimized conditions, the anodic peak current exhibited a linear relationship against VAL over the range of 5–80 nM with a detection limit of as low as 1.9 nM and an analysis time of 15 s. Under hydrodynamic conditions mimicking flow-cell analysis, the low detection limit was as low as 2.5 nM (S/N > 4) with rapid analysis time of mere 5 s. Selective determination of VAL was performed in the presence of dopamine and serotonin. Practical utility of the AuNPs/poly-AHP film sensor has been demonstrated for the detection of VAL directly from artificial urine, pharmaceutical formulations and diluted human serum with good recovery limits.

Antibacterial Effect of Colloidal Suspensions Varying in Silver Nanoparticles and Ions Concentrations.

A lot of effort has been dedicated recently to provide a better insight into the mechanism of the antibacterial activity of silver nanoparticles (AgNPs) colloidal suspensions and their released silver ionic counterparts. However, there is no consistency regarding whether the antibacterial effect displayed at cellular level originates from the AgNPs or their ionic constitutes. To address this issue, three colloidal suspensions exhibiting different ratios of AgNPs/silver ions were synthesized by a wet chemistry method in conjunction with tangential flow filtration, and were characterized and evaluated for their antimicrobial properties against two gram-negative, Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa), and two gram-positive, Staphylococcus aureus (S. aureus) and Staphylococcus epidermidis (S. epidermidis), bacterial strains. The produced samples contained 25% AgNPs and 75% Ag ions (AgNP_25), 50% AgNPs and 50% Ag ions (AgNP_50), and 100% AgNPs (AgNP_100). The sample AgNP_100 demonstrated the lowest minimum inhibitory concentration values ranging from 4.6 to 15.6 ppm for all four bacterial strains, while all three samples indicated minimum bactericidal concentration (MBC) values ranging from 16.6 ppm to 62.5 ppm against all strains. An increase in silver ions content results in higher bactericidal activity. All three samples were found to lead to a significant morphological damage by disruption of the bacterial cell membranes as analyzed by means of scanning electron microscopy (SEM). The growth kinetics demonstrated that all three samples were able to reduce the bacterial population at a concentration of 3.1 ppm. SEM and growth kinetic data underline that S. epidermidis is the most sensitive among all strains against the investigated samples. Our results showed that all three AgNPs colloidal suspensions exhibited strong antibacterial properties and, thus, they can be applied in medical devices and antimicrobial control systems.

Effect of nanoparticles on the performance of polymer/surfactant flooding for enhanced oil recovery: A review

It is well known that approximately 30% of Original Oil in Place (OOIP) is produced by water flooding. Therefore, to improve the residual oil recovery, the Enhanced Oil Recovery (EOR) methods are applied. Chemical flooding, as a promising EOR technique, has encountered some challenges in achieving its objectives, including the high cost of chemicals and its poor performance under oil and gas reservoir harsh conditions. Chemical nanofluids, as engineered colloidal suspensions of nanoparticles (NPs) in chemical-based fluids, have been recently discovered to address these challenges. This study comprehensively reviews the positive effects of NPs on the performance of polymer and surfactant flooding found in the literature. In addition, the enhancement of oil recovery through the use of disparate polymers and surfactants in combination with different NPs is investigated to bring the most potential NPs to researchers’ attention for future studies. It was concluded that NPs have great potential to improve rheological properties of polymers, and interfacial tension (IFT) between displacing and displaced fluid is reduced more than polymer and surfactant alone by adding NPs to the chemical solutions. Moreover, in the presence of NPs, the wettability of reservoir rock is altered towards more water-wet medium. NPs are also reported to have the ability to decrease the surfactant adsorption on porous media to some extent. Furthermore, the remaining challenges and possible future trends in this regard are reflected in the present paper. The collective review of the results presented in this study helps researchers to have a better understanding of NPs’ effects on Chemical Enhanced Oil Recovery (CEOR).

Freedericksz transition in ferronematic liquid crystal under weak anchoring conditions

Freedericksz effect is investigated theoretically for a ferronematic liquid crystal, which is a colloidal suspension of ferromagnetic nanoparticles in a nematic fluid. Considering a splay type Freedericksz geometry, weak anchoring conditions are assumed at the cell boundaries. The specific nature of this anchoring reveals a rich variety of stable ferronematic phases, which include uniform, distorted and saturated states. Apart from weak anchoring conditions at the cell boundaries, soft planar anchoring is assumed for the mesogenic molecules at the surface of a nanoparticle. The interplay between these two anchoring phenomena along with Frank type elastic theory determine the values of Freedericksz threshold between various ferronematic states. It is found that compared to relatively strong anchoring for the mesogens both at the cell boundaries and at the surface of the nanoparticles, weak anchoring significantly reduces the Freedericksz threshold field. Landau theory is then utilized to understand the nature of transition between different ferronematic states. Based on the phenomenon of segregation effect, these transitions are found to be either first order or second order in nature. The present theory is also extended to non-ferromagnetic nanoparticles and significant reduction in Freedericksz threshold is obtained. Finally, these results are corroborated with experimental findings.

Determination of the Size Distribution of Metallic Colloids from Extinction Spectroscopy.

In this paper, we explore the ability of extinction spectroscopy to characterize colloidal suspensions of gold nanoparticles (Au NPs). We demonstrate that the Au NPs’ size distribution can be deduced by analyzing their extinction spectra using Mie theory. Our procedure, based on the non-negative least square algorithm, takes advantage of the high sensitivity of the plasmon band to the Au NP size. In addition, this procedure does not require any a priori information on the Au NP size distribution. The Au NPs’ size distribution of monomodal or bimodal suspensions can be satisfactorily determined from their extinction spectra. Finally, we show that this characterization tool is compatible with in situ measurement and allows following the change in NPs’ radii during laser exposure.

Green and Scalable Preparation of Colloidal Suspension of Lignin Nanoparticles and Its Application in Eco-friendly Sunscreen Formulations.

Lignin nanoparticles (LNPs) are applied in several industrial applications. The nanoprecipitation of LNPs is fast and inexpensive but currently still limited to the use of hazardous organic solvents, making it difficult to apply them on a large scale. Here, we report a scalable nanoprecipitation procedure for the preparation of colloidal lignin nanoparticles (cLNPs) by the use of the green solvents dimethylisosorbide and isopropylidene glycerol. Irrespective of the experimental conditions, cLNPs showed higher UV absorbing properties and radical scavenging activity than parent LNPs and raw lignin. cLNPs were successively used in the preparation of eco-friendly sunscreen formulations (SPF 15, 30, and 50+, as evaluated by the COLIPA assay), which showed high UV-shielding activity even in the absence of synthetic boosters (microplastics) and physical filters (TiO2 and ZnO). Biological assays on human HaCaT keratinocytes and human skin equivalents demonstrated the absence of cytotoxicity and genotoxicity, associated with an optimal protection of the skin from UV-A damage.

Transparent silica aerogel slabs synthesized from nanoparticle colloidal suspensions at near ambient conditions on omniphobic liquid substrates

This paper presents a novel sol-gel method to synthesize large and thick silica aerogel monoliths at near ambient conditions using a commercial aqueous solution of colloidal silica nanoparticles as building blocks. To achieve slabs with high visible transmittance and low thermal conductivity, the method combines the strategies of (i) synthesizing gels on an omniphobic perfluorocarbon liquid substrate, (ii) aging at temperatures above room temperature, and (iii) performing solvent exchange with a low-surface-tension organic solvent prior to ambient drying. The omniphobic liquid substrates were used to prevent cracking and ensure an optically-smooth surface, while nanoparticle building blocks were small (<10 nm) to limit volumetric light scattering. Gels were aged at temperatures between 25 and 80 °C for up to 21 days to make them stronger and stiffer and to reduce shrinkage and cracking during ambient drying. Ambient drying was achieved by first exchanging water in the gel pores for octane, followed by drying in an octane-rich atmosphere to decrease capillary forces. The synthesized nanoparticle-based silica aerogel monoliths had thicknesses up to 5 mm, diameters up to 10 cm, porosities exceeding 80%, and thermal conductivities as low as 0.08 W m−1 K−1. Notably, the slabs featured visible transmittance exceeding 75% even for slabs as thick as 5 mm. The as-synthesized aerogel monoliths were exposed to TMCS vapor to induce hydrophobic properties resulting in a water contact angle of 140° that prevented water infiltration into the pores and protected the aerogels from water damage. This simple synthesis route conducted at near ambient conditions produces hydrophobic aerogel monoliths with promising optically transparent and thermally insulating properties that can be adhered to glass panes for window insulation and solar-thermal energy conversion applications.

Sensitivity Enhancement in the Colorimetric/Spectroscopic Determination of Lysozyme Concentration in Nanomolar Level with Colloidal Citrat e Capped Au@Ag Core-shell Nanoparticles

Background: Lysozyme level in body fluids is a significant indicator of various diseases. Cheap and simple colorimetric detection of lysozyme, in biological sample, by gold and silver nanoparticles is a field of interest of nanoparticle research for more than a decade. Objective: We report here an attempt to improve the sensitivity part of the colorimetric lysozyme detection process by using citrate capped gold-silver core-shell nanoparticles without any functionalization. Methods: Performance of gold-silver core-shell nanoparticles in determining of lysozyme concentration in water is done using colorimetric/spectroscopic technique. Gold nanoparticles, silver nanoparticles and mixed colloidal suspension of gold and silver nanoparticles, for comparison have also been studied. Selectivity study has been performed through spectroscopic analysis, red-greenblue colour component analysis and fractal dimension analysis of the nanoparticles interacted with several low and high isoelectric point proteins. Results: Gold-silver core-shell nanoparticles showed higher sensitivity for a wider range of lysozyme concentration compared to gold and silver nanoparticles prepared by us or reported in literature. Gold nanoparticles showed higher sensitivity compared to the core-shell nanoparticles, but for a narrow concentration range of lysozyme. For silver nanoparticles and the mixed nanoparticle system, both sensitivity and range of determination of lysozyme concentration were much smaller compared to the core-shell nanoparticles. Core-shell nanoparticles showed better selectivity compared to gold nanoparticles in identifying aquatic solution of lysozyme from that of other proteins. Conclusion: Gold-silver core-shell nanoparticles have higher sensitivity in determining wide range of lysozyme concentration in water compared to gold and silver nanoparticles reported in literature.

Effect of Ultralow Concentrated Reduced Graphene Oxide Nanofluid on Radiator Performance

Abstract Nanocoolants are engineered colloidal suspensions of nanoparticles in a conventional coolant (water–ethylene glycol). Use of metals and metallic oxide nanofluids at concentrations greater than 0.01 vol % has been studied in greater detail compared to functionalized graphene nanofluids. In the present work, an experimental investigation is carried out on an automobile radiator by changing the conventional coolant to reduced graphene oxide (RGO) nanocoolant. The present study focuses on the effect of ultralow nanoparticle concentration (0.002–0.006 vol %), Reynolds number of hot coolant (80–170), Reynolds number of air (210–270), and inlet temperature of hot coolant (40 °C and 60 °C). The effect of these parameters on the performance of the radiator is measured in terms of convective heat transfer coefficient (CHTC), Nusselt number, friction factor, and effectiveness. Results indicate that at 0.006 vol % concentration, there is a maximum increase of 100.5% and 111%, respectively, in CHTC and effectiveness, besides a reduction in friction factor. RGO nanocoolant offers great scope for reducing the radiator size and increasing its performance.

Light Confinement with Structured Beams in Gold Nanoparticle Suspensions

We carry out an experimental campaign to investigate the nonlinear self-defocusing propagation of singular light beams with various complex structures of phase and intensity in a colloidal suspension of gold nanoparticles with a plasmonic resonance near the laser wavelength (532nm). Studying optical vortices embedded in Gaussian beams, Bessel vortices and Bessel-cosine (necklace) beams, we gather evidence that while intense vortices turn into two-dimensional dark solitons, all structured wavepackets are able to guide a weak Gaussian probe of different wavelength (632.8 nm) along the dark core. The probe confinement also depends on the topological charge of the singular pump.

Co-Encapsulation of Methylene Blue and PARP-Inhibitor into Poly(Lactic-Co-Glycolic Acid) Nanoparticles for Enhanced PDT of Cancer.

The development of resistance against photodamage triggered by photodynamic therapy (PDT) is ascribed mainly to the cellular redox defenses and repair. If the tumor tissue is not promptly eliminated by the first few PDT sessions, PDT-resistance can be favored, challenging the efficacy of the treatment. Although the mechanism of PDT resistance is still unclear, in vitro assays have evidenced that it can be developed through the PARP damage-repair signaling pathway. Therefore, inhibition of poly(adenosine diphosphate (ADP)-ribose) polymerase (PARP) has the potential to increase PDT efficacy. This work reports on the synthesis of a controlled release system of a photosensitizer, methylene blue (MB) and a PARP-inhibitor, the veliparib. MB and veliparib were co-encapsulated in poly(lactic-co-glycolic acid) (PLGA) nanoparticles (VMB-NPs). A colloidal stable aqueous suspension of nanoparticles was obtained. The average hydrodynamic diameter was 90 nm and a narrow size distribution was obtained, with a polydispersity index (PDI) of 0.08. The release kinetics of MB and veliparib from VMB-NPs showed an initial burst of 8.7% and 58.3% release of the total amounts of MB and veliparib respectively, in the first 6 h, and a delayed release of up to 11.3% and 70%, in 19 days, for MB and veliparib, respectively. The VMB-NPs showed no cytotoxicity in the dark but the viability of B16F10-Nex2 cells decreased by 36% when the cells were irradiated (102 J/cm2, 660 nm) and treated with VMB-NPs containing 1.0 µM of MB and 8.3 µM of veliparib. Considering the increased photoactivity even at low MB and veliparib concentrations and the absence of cytotoxicity in dark, the co-encapsulation of MB and veliparib was shown to be a promising strategy to improve the PDT efficacy.

Opal-based terahertz optical elements fabricated by self-assembly of porous SiO2 nanoparticles.

In this paper, we study artificial opals as a promising material platform for terahertz (THz) optics. Materials were synthesized using self-assembly of porous SiO2 nanoparticles and annealing at different temperatures to further tune their optical properties. Two distinct approaches for the fabrication of bulk THz optics from these novel materials were considered. First, THz cylindrical lenses of identical geometry but different refractive indices and focal lengths were produced using standard mechanical processing of opals, in order to highlight their compatibility with conventional technologies of bulk optics fabrication. Second, a THz axicone was made via direct sedimentation of aqueous colloidal suspension of SiO2 nanoparticles in the mold of geometry inverse to that of a desired optical shape, followed by annealing and polishing. The second approach has an advantage of being considerably less labor intensive, while capable of obtaining optical elements of complex geometries. Thus fabricated bulk THz optical elements were studied experimentally using continuous-wave THz imaging, and the results were compared with 2D and 3D numerical predictions based on the finite-difference time-domain and finite-element frequency-domain methods. Our findings highlight technological robustness of the developed THz optical material platform and, thus, open the door for creating a variety of bulk THz optical elements of complex shapes and widely-tunable optical performance.