Nanoparticles In Droplets Research Articles

Controlling the Shrinkage of 3D Hot Spot Droplets as a Microreactor for Quantitative SERS Detection of Anticancer Drugs in Serum Using a Handheld Raman Spectrometer.

Quantitative measurement is one of the ultimate targets for surface-enhanced Raman spectroscopy (SERS), but it suffers from difficulties in controlling the uniformity of hot spots and placing the target molecules in the hot spot space. Here, a convenient approach of three-phase equilibrium controlling the shrinkage of three-dimensional (3D) hot spot droplets has been demonstrated for the quantitative detection of the anticancer drug 5-fluorouracil (5-FU) in serum using a handheld Raman spectrometer. Droplet shrinkage, triggered by the shaking of aqueous nanoparticle (NP) colloids with immiscible oil chloroform (CHCl3) after the addition of negative ions and acetone, not only brings the nanoparticles in close proximity but can also act as a microreactor to enhance the spatial enrichment capability of the analyte in plasmonic sites and thereby realize simultaneously controlling 3D hot spots and placing target molecules in hot spots. Moreover, the shrinking process of Ag colloid droplets has been investigated using a high-speed camera, an in situ transmission electron microscope (in situ TEM), and a dark-field microscope (DFM), demonstrating the high stability and uniformity of nanoparticles in droplets. The shrunk Ag NP droplets exhibit excellent SERS sensitivity and reproducibility for the quantitative analysis of 5-FU over a large range of 50-1000 ppb. Hence, it is promising for quantitative analysis of complex systems and long-term monitoring of bioreactions.

Particle-Size-Dependent Filtration Efficiency, Breathability, and Flow Resistance of Face Coverings and Common Household Fabrics Used for Face Masks During the COVID-19 Pandemic.

During the COVID-19 pandemic, the increase in demand for protective equipment caused a global shortage and homemade barrier face coverings were recommended as alternatives. However, filtration performances of homemade face coverings have not been fully evaluated. Test methods in the ASTM standard (F3502-21) were used to evaluate filtration efficiencies (FE) and breathability (pressure drop, Δp) of face coverings and home fabric materials commonly used during the pandemic. Submicron particulates FE was measured by particle transmission through face covering samples using a Condensation Particle Counter equipped with differential mobility analyzer and electronic manometer. Flow resistance of 0.1 μm-diameter fluorescent nanoparticles in droplets was determined by measuring fluorescence intensity of residual collected at the reverse side of samples. The size-dependent FE (3–94%) and Δp (0.8–72 mmH2O) varied considerably among fabrics. Of the 16 mask types, 31.25% and 81.25% met the minimum FE and breathability standards in the ASTM F3502-21, respectively. Overall performance (qF) was highest for velcro masks (max qF = 3.36, min qF = 2.80) and lowest for Dutch wax print fabrics (max qF = 0.12, min qF = 0.03). Most of the samples resisted the flow of 0.1 µm-diameter nanoparticles in droplets. Low flow resistance was observed in bandana, neck gaiter, t-shirt I, tank top and bedspread fabrics. GSM and fabric finishing seems to affect performance. Low performances can be improved by selecting optimum-performance fabrics in the design and manufacture of barrier face coverings.Supplementary InformationThe online version contains supplementary material available at 10.1007/s41742-021-00390-6.

Co-Assembly of Colloids and Eumelanin Nanoparticles in Droplets for Structural Pigments with High Saturation.

Colloidal crystals have been used to develop structural colors. However, incoherent scattering causes the colors to turn whitish, reducing the color saturation. To overcome the problem, light-absorbing additives have been incorporated. Although various additives have been used, most of them are not compatible with a direct co-assembly with common colloids in aqueous suspensions. Here, the authors suggest eumelanin nanoparticles as a new additive to enhance the color chroma. Eumelanin nanoparticles are synthesized to have diameters of several nanometers by oxidative polymerization of precursors in basic solutions. The nanoparticles carry negative charges and do not weaken the electrostatic repulsion among same-charged polystyrene particles when they are added to aqueous suspensions. To prove the effectiveness of eumelanin as a saturation enhancer, the authors produce photonic balls through direct co-assembly of polystyrene and eumelanin using water-in-oil emulsion droplets, while varying the weight ratio of eumelanin to polystyrene. The high crystallinity of colloidal crystals is preserved for the ratio up to at least 1/50 as the eumelanin does not perturb the crystallization. The eumelanin effectively suppresses incoherent scattering while maintaining the strength of structural resonance at an optimum ratio, improving color chroma without compromising brightness.

Stomatocyte structural color-barcode micromotors for multiplex assays.

Artificial micromotors have a demonstrated value in the biomedical area. Attempts to develop this technology tend to impart micromotors with novel functions to improve the values. Herein, we present novel structural color-barcode micromotors for the multiplex assays. We found that, by rapidly extracting solvent and assembling monodispersed nanoparticles in droplets, it could form stomatocyte colloidal crystal clusters, which not only showed striking structural colors and characteristic reflection peaks due to their ordered nanoparticles arrangement, but also provided effective cavities for the integration of functional elements. Thus, the micromotors with catalysts or magnetic elements in their cavities, as well as with the corresponding structural color coding, could be achieved by using the platinum and ferric oxide dispersed pre-gel to fill and duplicate the stomatocyte colloidal crystal clusters. We have demonstrated that the self-movement of these structural color-barcode micromotors could efficiently accelerate the mixing speed of the detection sample and greatly increase the probe–target interactions towards faster and more sensitive single or multiplex detection, and the magnetism of these barcode micromotors enables the flexible collection of the micromotors, which could facilitate the detection processes. These features make the stomatocyte structural color-barcode micromotors ideal for biomedical applications.

Effect of Ammonium Perchlorate Coating on the Ignition and Combustion Characteristics of Al/JP-10 Nanofluid Fuel

ABSTRACT Aluminum (Al) nanoparticles were coated with ammonium perchlorate (AP) to obtain AP-coated Al nanoparticles with different coating amounts. The coating layers were characterized by TEM and TG. Result showed that AP formed a uniform coating layer on the surface of the Al nanoparticles. The effective coating amounts of the particles were 2.864%, 6.182%, 10.285%, and 13.182%. Al nanoparticles were added into JP-10 to obtain Al/JP-10 nanofluid fuel. A CO2 laser test system was utilized to conduct a single-droplet laser ignition experiment. Result showed that AP coating exhibited an evident promoting effect on droplet ignition combustion. With AP coating, the oxidation degree of Al nanoparticles in droplets was evidently improved, and the carbon content produced by incomplete combustion of JP-10 was also significantly diminished. This finding indicated that the AP coating was beneficial to the oxidation combustion of Al particles and JP-10 in the droplets. However, the analysis result of the combustion process of the droplet showed that the combustion intensity and temperature initially demonstrated an increasing trend and then decreased with the increase of AP content, thereby indicating that the coating amount of AP, an oxidant with relatively low calorific value, should not be extremely large to obtain the optimal combustion promotion effect.

Ignition and combustion characteristics and agglomerate evolution mechanism of aluminum in nAl/JP-10 nanofluid fuel

The ignition and combustion processes of concentrated nAl/JP-10 nanofluid fuel were studied by using a CO2 laser ignition system with online diagnosis, intermediate sampling, and offline analysis. The energy release properties of aluminum (Al) nanoparticles in droplets and the influence of oxygen content on agglomerate evolution were studied. The phase separation of liquid fuel and Al nanoparticles occurs during the combustion process of concentrated nAl/JP-10 nanofluid. The burning forms of Al nanoparticles within the droplet include local, splash out, and agglomerate burning. Among them, agglomerate burning is the primary form of energy release. During the combustion process, Al particles gradually form an Al agglomerate, and the oxidation reaction of Al nanoparticles mainly occurs after the diffusion flame disappears. Oxygen content has a significant effect on the agglomerate burning of Al nanoparticles. When oxygen content is > 10%, the Al particles are successfully ignited. When oxygen content reaches 50%, a deflagration of the agglomerate occurs, and the Al particles rapidly oxidize to completely release heat and form a dense alumina sphere.

Characterizing self-assembly and deposition behavior of nanoparticles in inkjet-printed evaporating droplets

The self-assembly and deposition mechanisms of nanoparticles in droplets on a substrate are of significant importance in many inkjet printing-based industrial applications such as microelectronics, display systems, and paint manufacturing. However, a comprehensive investigation into the velocity field of fluid and its accompanying particle transport behavior in injected droplets undergoing immediate evaporation has not been conducted. In this study, we describe the underlying mechanisms of the self-assembly and deposition behavior of nanoparticles in inkjet-printed, evaporating droplets by visualizing the internal fluid flows. We additionally characterize the relationship between the internal fluid flows and nanoparticle patterns by changing not only the wettability and temperature of the substrate, but also the chemical composition of nanoparticle suspensions. We verify that Marangoni flow generated on a hydrophobic PDMS substrate with a contact angle (CA) of >90° helps the formation of dome-shaped nanoparticle structures, while radially outward flow generated on a hydrophilic glass substrate with a CA of <10° produces either mono-layered and flat, or ring-shaped nanoparticle structures, depending on the number density of the suspension. The presented characterization results provide not only valuable mechanistic insights, but also practical guidelines for inkjet printing-based nanoparticle applications.

Numerical Models for Exact Description of in-situ Digital In-Line Holography Experiments with Irregularly-Shaped Arbitrarily-Located Particles

We present the development of a numerical simulator for digital in-line holography applications. In-line holograms of arbitrarily shaped and arbitrarily located objects are calculated using generalized Huygens-Fresnel integrals. The objects are 2D opaque or phase objects. The optical set-up is described by its optical transfer matrix. A wide variety of optical systems, involving windows, spherical or cylindrical lenses, can thus be taken into account. It makes the simulator applicable for design and description of in situ experiments. We discuss future applications of this simulator for detection of nanoparticles in droplets, or calibration of airborne instruments that detect and measure ice crystals in the atmosphere.

Interactions between Carbon Nanoparticles in a Droplet of Organic Solvent

We report the first detailed molecular dynamics study of two carbon nanoparticles (nanotubes or fullerenes) embedded in a droplet of chloroform. The carbon nanoparticles are negatively charged and are accompanied by the positive counterions of sodium. On the one hand, this setup is inspired by the carbon nanoparticle salts—“nanotubides” and “fullerides”—proposed recently as a convenient way to address the difficult problem of the dispersion of carbon nanoparticulates in the organic solvents. On the other hand, the electrospray of carbon nanoparticle suspensions has been shown to be a promising technique for the production of thin nanoparticle coatings. We explore the combination of these two approaches by using molecular simulations. We find that depending on the overall electrostatic charge balance the two nanoparticles can exist in the droplet either in the “salted-out” bound state or in a “solvent-separated” state. The latter opens up the possibility for the efficient dispersion of the nanoparticles in the charged droplet environment. We also find that depending on the charge of the nanoparticles the mother droplet may break evenly or unevenly with respect to the mass but evenly with respect to charge. The understanding of the fragmentation paths and the intermolecular interactions of the nanoparticles in droplets provides insight into the manner that the droplet chemistry can be manipulated so that effective dispersion of nanoparticulates can be achieved.

Microfluidic Generation of Droplets with a High Loading of Nanoparticles

Microfluidic approaches for controlled generation of colloidal clusters, for example, via encapsulation of colloidal particles in droplets, have been used for the synthesis of functional materials including drug delivery carriers. Most of the studies, however, use a low concentration of an original colloidal suspension (<10 wt %). Here we demonstrate microfluidic approaches for directly making droplets with moderate (10-25 wt %) and high (>60 wt %) particle concentrations. Three types of microfluidic devices, PDMS flow-focusing, PDMS T-junction, and microcapillary devices, are investigated for direct encapsulation of a high concentration of polystyrene (PS) nanoparticles in droplets. In particular, it is shown that PDMS devices fabricated by soft lithography can generate droplets from a 25 wt % PS suspension, whereas microcapillary devices made from glass capillary tubes are able to produce droplets from a 67 wt % PS nanoparticle suspension. When the PS concentration is between 0.6 and 25 wt %, the size of the droplets is found to change with the oil-to-water flow rate ratio and is independent of the concentration of particles in the initial suspensions. Drop sizes from ~12 to 40 μm are made using flow rate ratios Q(oil)/Q(water) from 20 to 1, respectively, with either of the PDMS devices. However, clogging occurs in PDMS devices at high PS concentrations (>25 wt %) arising from interactions between the PS colloids and the surface of PDMS devices. Glass microcapillary devices, on the other hand, are resistant to clogging and can produce droplets continuously even when the concentration of PS nanoparticles reaches 67 wt %. We believe that our findings indicate useful approaches and guidelines for the controlled generation of emulsions filled with a high loading of nanoparticles, which are useful for drug delivery applications.

Janus Supraparticles by Induced Phase Separation of Nanoparticles in Droplets

Biphasic Janus particles with a precisely tunable internal morphology are fabricated using a novel, versatile, and robust technique. This technique can be used in conjunction with microfluidics to produce monodisperse particles, or can be combined with bulk emulsification techniques to produce large quantities of particles. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Chemistry and Biology in Femtoliter and Picoliter Volume Droplets

The basic unit of any biological system is the cell, and malfunctions at the single-cell level can result in devastating diseases; in cancer metastasis, for example, a single cell seeds the formation of a distant tumor. Although tiny, a cell is a highly heterogeneous and compartmentalized structure: proteins, lipids, RNA, and small-molecule metabolites constantly traffic among intracellular organelles. Gaining detailed information about the spatiotemporal distribution of these biomolecules is crucial to our understanding of cellular function and dysfunction. To access this information, we need sensitive tools that are capable of extracting comprehensive biochemical information from single cells and subcellular organelles. In this Account, we outline our approach and highlight our progress toward mapping the spatiotemporal organization of information flow in single cells. Our technique is centered on the use of femtoliter- and picoliter-sized droplets as nanolabs for manipulating single cells and subcellular compartments. We have developed a single-cell nanosurgical technique for isolating select subcellular structures from live cells, a capability that is needed for the high-resolution manipulation and chemical analysis of single cells. Our microfluidic approaches for generating single femtoliter-sized droplets on demand include both pressure and electric field methods; we have also explored a design for the on-demand generation of multiple aqueous droplets to increase throughput. Droplet formation is only the first step in a sequence that requires manipulation, fusion, transport, and analysis. Optical approaches provide the most convenient and precise control over the formed droplets with our technology platform; we describe aqueous droplet manipulation with optical vortex traps, which enable the remarkable ability to dynamically "tune" the concentration of the contents. Integration of thermoelectric manipulations with these techniques affords further control. The amount of chemical information that can be gleaned from single cells and organelles is critically dependent on the methods available for analyzing droplet contents. We describe three techniques we have developed: (i) droplet encapsulation, rapid cell lysis, and fluorescence-based single-cell assays, (ii) physical sizing of the subcellular organelles and nanoparticles in droplets, and (iii) capillary electrophoresis (CE) analysis of droplet contents. For biological studies, we are working to integrate the different components of our technology into a robust, automated device; we are also addressing an anticipated need for higher throughput. With progress in these areas, we hope to cement our technique as a new tool for studying single cells and organelles with unprecedented molecular detail.

Synthesis of Light‐Diffracting Assemblies from Microspheres and Nanoparticles in Droplets on a Superhydrophobic Surface

Synthesis of Light‐Diffracting Assemblies from Microspheres and Nanoparticles in Droplets on a Superhydrophobic Surface

Cover Picture: Synthesis of Light-Diffracting Assemblies from Microspheres and Nanoparticles in Droplets on a Superhydrophobic Surface (Adv. Mater. 22/2008)

Cover Picture: Synthesis of Light-Diffracting Assemblies from Microspheres and Nanoparticles in Droplets on a Superhydrophobic Surface (Adv. Mater. 22/2008)

Slow Drying of a Spray of Nanoparticles Dispersion. In Situ SAXS Investigation

Nanoparticles confined in droplets of less than a picoliter are forced to organize in submicronic dry grains through solvent evaporation. The evolution of structures of the grains and the constituent nanoparticles during the slow drying process are investigated in situ with small-angle X-ray scattering (SAXS) for the first time. The scattering results have been explained on the basis of the equilibrium thermodynamics of the droplets in the drying tube. We demonstrate that this technique is really efficient in describing the internal arrangement of the nanoparticles inside the drying droplets. Distinction between an almost homogeneous repartition of the nanoparticles in droplets and formation of core shell like particles even in strongly polydispersed droplets can be made using SAXS.