Field Optical Microscopy Research Articles

Super-Resolution Surface-Enhanced Raman Scattering: Perspectives on the Past, Present, and Future.

Super-resolution surface-enhanced Raman scattering (SERS) allows researchers to overcome the resolution limit of far field optical microscopy and peer into electromagnetic hot spots with nanoscale resolution. By localizing the signal from single (or few) molecules on the surface of plasmonic nanoparticle aggregates, relationships between the spatial origin of the SERS signal, local electromagnetic field enhancements, and SERS intensity can be determined. This Perspective describes the successes and challenges of super-resolution SERS, from the earliest mapping of single-molecule SERS hot spots to the current state-of-the-art, while highlighting open questions and future opportunities to advance the field. Comparisons with fluorescence-based super-resolution imaging are discussed to help frame the unique challenges associated with performing SERS in the super-resolution regime.

(Invited) Near-Field Optics and Its Applications in Nanoscale Materials: A Review

In this presentation, we first offer an overview of aperture-type scanning near field optical microscopy –a family of super-resolution imaging techniques based on evanescent waves, which can be combined with atomic force microscopy and are capable of subwavelength resolution nano-optical imaging. In the second part of this review, we will discuss a few applications in which our group capitalized on the super-resolution resolving power of SNOM to design specific nano-optical and nano-photonic systems for light harvesting, resistive memory device applications and nanoscale thermo-optical management, as well as to characterize nanoscale luminescent materials. Specific case studies that will be presented include the characterization of weakly photoluminescent and curved carbon dots for memory device applications, the three-dimensional characterization of plasmon-enhanced nanophotonic devices, as well as the development of near-field thermoreflectance imaging for nanophotonic-based thermal management applications. Collectively, our study well represents the versability of SNOM as a unique super-resolution nanophotonic tool for the investigation of light-matter interaction at the nanoscale.

(Invited) Near-Field Optics and Its Applications in Nanoscale Materials: A Review

In this paper, we first offer an overview of aperture-type scanning near field optical microscopy –a family of super-resolution imaging techniques based on evanescent waves, which can be combined with atomic force microscopy and are capable of subwavelength resolution nano-optical imaging. In the second part of this review, we will discuss a few applications in which our group capitalized on the super-resolution resolving power of SNOM to design specific nano-optical and nano-photonic systems for light harvesting, resistive memory device applications and nanoscale thermo-optical management. Specific case studies that will be presented include the characterization of weakly photoluminescent and curved carbon dots for memory device applications, the three-dimensional characterization of plasmon-enhanced nanophotonic devices, as well as the development of near-field thermoreflectance imaging for nanophotonic-based thermal management applications. Collectively, our study well represents the versability of SNOM as a unique super-resolution nanophotonic tool for the investigation of light-matter interaction at the nanoscale.

A first record of alluvial gold in the Olănești and Cheia rivers, Southern Carpathians, Romania

We provide the first scientific record and the mineralogical characterization of alluvial gold in the Olănești area, Southern Carpathians, Romania, based on field evidence, optical microscopy, and XRD, BSE and EPMA data. Chemical data were acquired on 11 alluvial gold grains from the Olănești and Cheia rivers and revealed a generally continuous variation in gold and silver content with Ag ranging from 7.31 to 19.77 wt.% and Au ranging from 80.26 to 93.16 wt.%. The source of the primary native gold is inferred to be the Cu-Au Valea lui Stan and/or the Costești As-Au shear-zone-related ore deposits located towards the north and west, respectively, of the study area.

Peptide Stereochemistry Effects from pKa-Shift to Gold Nanoparticle Templating in a Supramolecular Hydrogel.

The divergent supramolecular behavior of a series of tripeptide stereoisomers was elucidated through spectroscopic, microscopic, crystallographic, and computational techniques. Only two epimers were able to effectively self-organize into amphipathic structures, leading to supramolecular hydrogels or crystals, respectively. Despite the similarity between the two peptides' turn conformations, stereoconfiguration led to different abilities to engage in intramolecular hydrogen bonding. Self-assembly further shifted the pKa value of the C-terminal side chain. As a result, across the pH range 4-6, only one epimer predominated sufficiently as a zwitterion to reach the critical molar fraction, allowing gelation. By contrast, the differing pKa values and higher dipole moment of the other epimer favored crystallization. The four stereoisomers were further tested for gold nanoparticle (AuNP) formation, with the supramolecular hydrogel being the key to control and stabilize AuNPs, yielding a nanocomposite that catalyzed the photodegradation of a dye. Importantly, the AuNP formation occurred without the use of reductants other than the peptide, and the redox chemistry was investigated by LC-MS, NMR, and infrared scattering-type near field optical microscopy (IR s-SNOM). This study provides important insights for the rational design of simple peptides as minimalistic and green building blocks for functional nanocomposites.

(Invited) Near-Field Optics and Its Applications in Nanophotonic Devices: A Review

In our presentation, we will offer an overview of aperture-type scanning near field optical microscopy (SNOM) – a family of nano-optical imaging techniques derived from scanning probe microscopy which are capable of subwavelength resolution, and the development of three dimensional (3D) SNOM methods undertaken by our group to locally image the distribution of the electromagnetic radiation in the proximity of nanoparticles and nano-objects.[1] We will discuss a few applications in which we took advantage of 3D-SNOM to design specific optical nanosystems for light harvesting device applications. Specific case studies that will be presented include the design of plasmonic thin-film solar cells enhanced by random arrays of copper nanoparticles,[2] and the use of 3D-SNOM for characterizing evanescent waveguides self-assembled from of copper nanoparticles assembled on thin films of graphene.[3] In the final part of our talk, we will we present near-field scanning thermoreflectance imaging (NeSTRI), a new pump-probe technique invented in our group (see Figure 1) in which an aperture-type SNOM is used to contactlessly determine the thermal conductivity of inhomogeneous thin films and low-dimensional systems at the nanoscale for heat-spreading and thermoelectric applications.[4,5] These examples well represent the versatility of SNOM imaging and its potential for designing an even wider family of nano-optical devices.[1] P Bazylewski, S Ezugwu, G Fanchini, Applied Sciences 7 (2017) 973[2] S Ezugwu, H Ye, G Fanchini, Nanoscale 7 (2016) 252-260[3] T Ouyang, A Akbari-Sharbaf, J Park, R Bauld, MG Cottam, G Fanchini, RSC Advances 5 (2015) 98814-98821[4] S Ezugwu, S Kazemian, DYW Choi, G Fanchini, Nanoscale 9 (2017) 4097-4106[5] S Kazemian, S Ezugwu, G Fanchini, Proc. SPIE 10926, Quantum Sensing and Nano Electronics and Photonics XVI, 109260L (1 February 2019); doi: 10.1117/12.2509828 Figure 1

Magnetic Separation of Micro Beads and Cells on a Paper-Based Lateral Flow System

Paper based lateral flow systems are widely used biosensor platforms to detect biomolecules in a liquid sample. Proteins, bacteria, oligonucleotides, and nanoparticles were investigated in the literature. In this work we designed a magnetic platform including dual magnets and tested the flow of micron size immunomagnetic particles alone and when loaded with cells on two different types of papers. The prewetting conditions of the paper and the applied external magnetic field are the two dominant factors affecting the particle and cell transport in paper. The images recorded with a cell phone, or with a bright field optical microscope were analyzed to measure the flow of particles and cells. The effect of prewetting conditions and magnetic force were measured, and it was shown that in the worst case, minimum 90% of the introduced cells reached to the edge of the paper. The paper based magnetophoretic lateral flow systems can be used for cell assays.

Complex characteristics of suevites at the B. Vanuyta river (Kara astrobleme, Russia)

Research subject. Suevites from the eastern sector of the Kara astrobleme, located in the basin of the Bolshaya Vanuyta river. Aim. To identify the suevitic type and to clarify the facial features of the suevites from the B. Vanuyta River. Materials. Hand-size samples of suevites collecteed in the basins of B. Vanuyta, Anaroga, Kara, and Sopchayu rivers, as well as samples of siltstones collected outside the Kara crater (rivers Halmeryu, Sayakha, Putyu, Anaroga and the creek Lavovyi). The samples were used for preparing polished thin sections and powder specimens for analytical works. Methods. Field observations, optical and electron scanning microscopy, and silicate analysis by the wet chemical method. Results and conclusions. The structural-textural and petrochemical features of the matrix, fragments of impact glasses, and lithoclasts of suevites from the B. Vanuyta river were characterized. The suevite matrix was found to exhibit an intensely sintered character and to be presented by feldspar, quartz, calcite, chlorite, muscovite, glauconite, and titanite. Lithoclasts include siltstones, sandstones, limestones, mudstones, and shales. Vitroclasts are characterized by angular and irregular morphology with different border patterns, and spotted, fluid, and porous textures. The similarity of the chemical composition of siltstone clusters and similar target rocks confirms the genetic relationship and the leading role of this type of target rocks in the formation of the studied suevites. The proximity in the composition of the impact glasses of the studied suevites and the glasses of type I and II suevites indicates the formation of suevite vitroclasts in the river B. Vanuyta by a similar protolith – siltstones and a clay component of the limestones. The matrix lithification character, morphology and nature of the vitroclast outlines indicate that the suevites from the B. Vanuyta river are the rocks of an aerodynamic facies formed under relatively high-temperature conditions, which structurally lie at the lower part of the detrital impactites sequence of the aerodynamic facies. The studied rocks are close to the type I suevites by the composition of the protolith and differ in the conditions of their formation. With the type II suevites, they have similar facies characteristics, but differ in the composition of the target rocks fragments. It is determined that the leading factor in the typification of suevites from the Kara astrobleme is the chemical composition, at the same time, the types can be subdivided more fractionally based on the specifics of the facies environments of their formation.

Microstructure and mechanical properties of WC–TiC–Co cemented carbides produced by spark plasma sintering (SPS) method

Cemented carbide 91 wt% WC–3 wt% TiC–6 wt% Co was sintered by spark plasma sintering at different temperatures of 1200 °C, 1300 °C, and 1400 °C and the effect of sintering temperature on the microstructure and properties of this type of composites, such as total density, apparent density, hardness, and fracture surface were measured and observed using Field Emission-Scanning Electron Microscopy, Optical Microscopy, X-ray diffractometry and mechanical test instruments. The results showed that the apparent density of the samples increased with increasing sintering temperature from 1200 to 1300 °C from 13.98 to 14.23 g/cm3, respectively. But in the sample sintered at 1400 °C, the density was reduced to 14.20 g/cm3. An increase in the fluidity of the cobalt phase and capillary pressure is the cause of the increase in density at higher temperatures, the cobalt phase has evaporated and the density has decreased slightly. Also, Vickers micro-hardness results showed that the hardness of sintered samples increased with the increase of sintering temperature. For the sample sintered at 1200 °C the hardness value of 1746.41 kgf/mm2 was obtained which increased with increasing sintering temperature from 1300 to 1400 °C from 2094.33 to 2280.97 kgf/mm2, respectively. The amount of core–shell structure [including TiC-core and (W, Ti)C-shell] increased with increasing the sintering temperature process. As a result, the hardness also increased. At the optimum sintering temperature, it was found that TiC inhibited the grain growth of tungsten carbide. In addition, as expected, the grain growth of tungsten carbide increased with increasing sintering temperatures. Examination of the fracture surface of sintered samples at different temperatures also showed that brittle fracture involves fracture.

Stability of bacteriophages in organic solvents for formulations

Bacteriophages or phages used as an alternative therapy for treating multi-drug resistant infections require formulation consideration. Current strategies to produce phage formulations involving organic solvents are based on empirical practices without a good understanding of phage stability during formulation development. In this study, we investigated the effect of common formulation organic solvents (ethanol, isopropyl alcohol, tetrahydrofuran (THF) and dimethyl sulfoxide (DMSO)) on the stability of Pseudomonas aeruginosa-specific myovirus (PEV1, PEV20) and podovirus (PEV31) phages using biological assay, transmission electron microscopy (TEM) and scattering near field optical microscopy (SNOM). The three phages were mixed with the solvents at different concentrations (25%, 50%, and 75% (v/v)) for 20 min. All phages were fully viable in the organic solvents at 25% (v/v) showing negligible titre changes. At the higher solvent concentration of 50% (v/v), the myoviruses PEV1 and PEV20 remained relatively stable (titre loss 0.4–1.3 log10), whereas the podovirus PEV31 became less stable (titre loss 0.25–3.8 log10), depending on the solvent used. Increasing the solvent level to 75% (v/v) caused increased morphological changes in TEM and decreased viability as indicated by the titre loss (0.32–7.4 log10), with DMSO being the most phage-destabilising solvent. SNOM spectra showed differences in the signal intensity and peak positions in the amide I and amide II regions, revealing altered phage proteins by the solvents. In conclusion, the choice of the solvents for phage formulation depends on both the phages and solvent types. Our results showed (1) the phages are more stable in the alcohols than DMSO and THF, and (2) the myoviruses tend to be more stable than the podovirus in the solvents. Overall, a low to moderate (25–50 % v/v) level of organic solvents (except 50% THF) can be used in formulation of the phages without a substantial titre loss.

Nanomechanical behavior of polystyrene/graphene oxide nanocomposites

The in-situ investigation of the nanomechanical features of the polymer graphene nanocomposites has become a challenging and an indispensable task to achieve the required application. Graphene oxide (GO) nanocomposites were prepared at 1.0% weight fraction of GO to reinforce polystyrene (PS) using solution blending approach. The morphology of the resulting nanocomposites was characterized by optical, scanning electron, transmission electron, atomic force, and scattering scanning near-field optical microscopies. These showed a uniform dispersion of graphene oxide nano-sheets in the PS matrix. By adopting Derjaguin–Muller–Toporov (DMT) formula, the nanomechanical properties for the cryogenically fractured surface of the composites were characterized using the traditional atomic force microscopy (AFM), peak-force quantitative nanomechanical mapping (QNM), and tip-force mode functioned with scattering scanning near–field optical microscopy (s-SNOM). Young’s modulus of the PS matrix varied around (1–2) GPa as shown by QNM and s-SNOM similar to what was reported in the literature. However, while putative GO nano-sheets were measured to have a higher elastic modulus than the surrounding matrix in Peak-Force QNM experiments, they were significantly below literature values. By using Tip-Force mode related to s-SNOM, the expected values of Young’s modulus for GO were recovered.

Experimental stability investigation of different water-in-jojoba biodiesel emulsions

Investigating the stability of water in biodiesel emulsion fuels during storage and engine operation is crucial to consider for marketing processes. This study examines the stability of water-in-Jojoba biodiesel (WJBD) emulsion that is stabilized using three commercially available surfactants, Span-80 (HLB 4.3), Tween-80 (HLB 15), Triton X-100 (HLB 13.5). The investigation involves varying the composition of the emulsions by adjusting factors such as the hydrophile lipophile balance (HLB), surfactant concentration, water concentration, mixing speed, and mixing duration, and study their effects through a bottle test. Stable emulsions are studied by bright field optical microscopy, constant shear test, and thermal loop rheology test. The research reveals that Tween-80 (HLB 15) and Span-80 (HLB 4.3) effectively yield emulsions with high relative stability. Specifically, at 5 (v%) water concentration, emulsions prepared with Tween-80 (HLB 15) demonstrate the formation of water droplets as small as 3.88 µm. Additionally, emulsions at various water concentrations are thoroughly studied. Over time, phase separation is studied by microscopic images and showed minimal coalescence after the first day for the emulsions that showed promising stability in the bottle test. To further assess the stability, the stable emulsions undergo continuous shear test, wherein a consistent pattern of stable viscosity is observed as time passed. Moreover, the thermal loop test showed minimal change in the relative microstructure of the emulsion, where the difference in the storage modulus and the loss modulus didn’t exceed 15 % and 5 %, respectively. Understanding the change in microstructure, droplet sizes, and how the emulsions behave under certain shear stresses is critical for practical applications of this fuel. Through comprehending the factors that influence the emulsion stability, this study contributes valuable insights for the successful storage and engine operation of the WJBD.

Retrieval of the Dielectric Properties of a Resonant Material in the Terahertz Region via Self-Detection Near Field Optical Microscopy

We present a numerical and analytical study of the self-detection scattering type near field optical microscopy (SD s-SNOM), a recently demonstrated technique based on a combination of self-mixing interferometry and scattering near- field microscopy. This scheme, which exploits a terahertz (THz) quantum cascade laser as both a laser source and detector, allows to investigate the optical properties of resonant materials in the THz range with resolution far beyond the diffraction limit. Our study, developed by using a modified version of the Lang-Kobayashi model, is focused on the weak feedback regime (Acket parameter <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$C ≈ 10^{-1}$</tex-math></inline-formula> ), where we derive an approximated method for the retrieval of the scattering coefficient of the SD s-SNOM configuration applied to a sample of Cesium Bromide (CsBr). These results were used in turn to derive the dielectric permittivity of the sample, reporting a good accuracy in the estimation of its phonon resonances.

Petrographic and Geochemical Inferences for Genesis of Terra Rossa: A Case Study from the Apulian Karst (Southern Italy)

Terra rossa is a reddish clay soil which is often present on the surface of limestone in regions with a Mediterranean-type climate. Its genesis is a controversial subject in terms of the origin of the parent material, from the residuum of underlying (carbonate/dolomite) bedrock in the absence/presence of an external silicate contribution (e.g., aeolian dust). Within this context the main goal of the present work was the understanding of the geochemical processes leading to the formation of the terra rossa starting from the carbonate bedrock. We report the results of a multi-method analysis on a terra rossa deposit occupying the bottom of a Quaternary karst depression on Mesozoic limestones exposed in the Murge area (Apulia Foreland, southern Italy). Geological, petrographic, textural, and chemical data were collected on karst products (reddish calcite incrustations and nodules, and fine-grained portion of terra rossa) by a detailed field mapping, optical microscopy, XRF and fusion ICP/MS analyses and by scanning electron microscope. New collected data show that the mineralogical composition of reddish incrustations and nodules is comparable, consisting of fibrous and impure calcite, detrital fragments of quartz, K-feldspar, zircon and authigenic minerals as (Mn, Ba, Ca) phases, (Al, Si, Mn, Fe, Mg, Ba, Ca) minerals, Fe-kaolinite and anatase. The prevailing minerals, instead, in the fine-grained portion of terra rossa are hematite, kaolinite, and goethite. Based on the chemical composition, and especially on REE patterns, a progressive interaction of silicate aqueous solutions (with Al, Si, Fe), containing pelite material, with the calcareous bedrock, as a source of carbonic acid, was the process driving the formation of terra rossa. Obtained results add new elements to the definition of the long-lasting question about the genetic processes responsible for the formation of terra rossa, corroborating their polygenetic origin, as result of limestone alteration in conjunction with the chemical interaction with allochthonous siliciclastic material.

Effect of a Change in the CaCl2/Pectin Mass Ratio on the Particle Size, Rheology and Physical Stability of Lemon Essential Oil/W Emulgels

A three-step (rotor-stator-microfluidization-rotor stator) protocol was used to prepare 15% lemon essential oil in water emulgels using a mixture of Tween 80 and Span 20 surfactants as low molecular mass emulsifiers and 0.4% low-methoxyl citrus peel pectin as a gelling agent. Ca2+ was used as a gel-promoting agent. Different CaCl2/pectin mass ratio values from 0.3 to 0.7 were used. Emulgels showed a microstructure consisting of oil droplets embedded in a sheared gel matrix, as demonstrated by bright field optical microscopy. Laser diffraction tests showed multimodal particle size distributions due to the coexistence of oil droplets and gel-like particles. Multiple light scattering tests revealed that the physical stability of emulgels was longer as the CaCl2/pectin mass ratio decreased and that different destabilization mechanisms took place. Thus, incipient syneresis became more important with increasing CaCl2 concentration, but a parallel creaming mechanism was detected for CaCl2/pectin mass ratio values above 0.5. Dynamic viscoelastic and steady shear flow properties of the emulgels with the lowest and highest CaCl2/pectin mass ratio values were compared as a function of aging time. The lowest ratio yielded an emulgel with enhanced connectivity among fluid units as indicated by its wider linear viscoelastic region, higher storage modulus, loss modulus and viscosity values, and more shear thinning properties than those of the emulgel formulated with the highest CaCl2/pectin mass ratio. The evolution of the dynamic viscoelastic properties with aging time was consistent with the information provided by monitoring scans of backscattering as a function of sample height.

Distinct strategy for the improvement of conductivity and electromagnetic shielding properties of MWCNTs/PLA/PBS composites: Synergistic effects of double percolation structure and UV aging

AbstractTo reveal a relationship among crystallization, conductivity and electromagnetic shielding properties of full biodegradable polymer after ultraviolet (UV) aging, polybutylene succinate (PBS)‐based composites with different weight ratios of multi‐wall carbon nanotubes (MWCNTs)/polylactic acid (PLA) /PBS masterbatch were processed via melt‐compounding approach. Morphology of the MWCNTs/PLA/PBS masterbatch prepared by Pickering emulsion method was confirmed by scanning electron microscope (SEM) and transmission electron microscope (TEM) observation. Comprehensive effects of different content of masterbatch and UV aging time on the morphology, crystallization, and electrical and electromagnetic shielding properties of MWCNTs/PLA/PBS composites were shown by Fourier transform infrared spectroscopy (FTIR), SEM, wide angle X‐ray diffraction (WAXD), differential scanning calorimeter (DSC), polarizing microscope (POM), ultra‐depth of field optical microscope, resistance tester, and vector network analyzer. Compared with PBS composite with 0.1 wt% MWCNTs, the electrical conductivity of PBS composite with the MWCNTs/PLA/PBS masterbatch increased by two orders of magnitude, and dispersed morphology for the composite showed double percolation structure. After UV aging, both MWCNTs/PBS composites and the PBS composites with the MWCNTs/PLA/PBS masterbatch, their surface presented burnt yellow and parts of flaws, while both their electrical conductivity and total electromagnetic shielding effectiveness gradually increased. Moreover, with the increasing of UV aging time, not only crystal size of these PBS‐based composites became large, but also their crystal interface became clearer. Furthermore, when UV aging time reached 528 h, the tensile strength of 0.6 M/PLA/PBS composite decreased by 12.6%, while its total electromagnetic shielding effectiveness increased by 39.8%, compared with the composite without UV aging.

Active stabilization of a pseudoheterodyne scattering scanning near field optical microscope.

Scattering scanning near-field optical microscopes (s-SNOMs) based on pseudoheterodyne detection and operating at ambient conditions typically suffer from instabilities related to the variable optical path length of the interferometer arms. These cause strong oscillations in the measured optical amplitude and phase comparable with those of the signal and, thus, resulting in dramatic artifacts. Besides hampering the comparison between the topography and the optical measurements, such oscillations may lead to misinterpretations of the physical phenomena occurring at the sample surface, especially for nanostructured materials. Here, we propose a stabilizing method based on interferometer phase control, which improves substantially the image quality and allows the correct extraction of optical phase and amplitude for both micro- and nanostructures. This stabilization method expands the measurement capabilities of s-SNOM to any slowly time-dependent phenomena that require long-term stability of the system. We envisage that active stabilization will increase the technological significance of s-SNOMs and will have far-reaching applications in the field of heat transfer and nanoelectronics.

Effect of WC nanoparticles content on the microstructure, hardness and tribological properties of Al-WC nanocomposites produced by flake powder metallurgy

Al-WC nanocomposites containing 0.1, 0.25, 0.4 and 0.6 v% of WC nanoparticles prepared by flake powder metallurgy route utilizing either cold pressing and sintering (CP–S) or hot-pressing (HP) to achieve optimum densification and hardness. The fabricated nanocomposites characterized by X-ray diffractometer (XRD), field emission scanning electron microscope (FESEM) and optical microscopy (OM). The wear rate and friction coefficient of the HP samples quantified via a pin on disk wear testing machine. The results revealed that HP samples exhibited lower porosity and higher hardness values as compared with their CP-S counterparts. Adding WC nanoparticles up to 0.4 vol% resulted in the minimum porosity and maximum hardness. Nano-WC particles addition improved wear resistance and frictional behavior of the nanocomposite and the sample containing 0.1 vol% WC exhibited superior tribological properties. SEM micrographs revealed that the wear mechanism changed from adhesive to mainly abrasive with increased content of hard nano-particles.

Determination of β-glucosidase activity using single-particle enumeration with Au@CeO2 nanoparticles.

Avisible and sensitive assay for the quantitative detection of β-glucosidase (β-glu) activity based on Au@CeO2 core-shell nanoparticles (Au@CeO2 NPs)is described. As a hydrolytic enzyme, β-glu can promote the hydrolysis of β-arbutin to hydroquinone (HQ), which can trigger the decomposition of theCeO2 shell. With the single-particle enumeration (SPE) strategy coupled withdark field optical microscopy (DFM), an obvious color alteration of single Au@CeO2 NPs during theetching process can be observed in real-time. By statistically calculating the number of the etched nanoparticles, the β-glu activity level can be quantified accurately. This assay displays a broad linear range from 0.5 to 50mU⋅mL-1 and low detection limit of 0.12mU⋅mL-1. In addition, this method was successfully used to determine β-glu in real samples and acquires satisfactory recoveries in the range of 97.1-102.0%. This study provides a visualization analysis method for β-glu, which may be helpful for monitoring other targets in the future.

Destabilization of Pickering emulsions by interfacial transport of mutually soluble solute

HypothesisPickering emulsions (PEs) once formed are highly stable because of very high desorption energies (∼107 kBT) associated with particles adsorbed to the interfaces. The destabilization of PEs is required in many instances for recovery of valuable chemicals, products and active compounds. We propose to exploit interfacial instabilities develop by the addition of different types of solutes to PEs as a route to engineer their destabilization. ExperimentsPEs stabilized by (i) spherical particles, (ii) non-spherical particles, (iii) oppositely charged particle–particle mixtures, and (iv) oppositely charged particle-polyelectrolyte mixtures are formulated. Different types of solutes are added to these highly stable PEs and the macroscopic as well as microscopic changes induced in the PEs is recorded by visual observation and bright field optical microscopy. FindingsOur results point to a simple yet robust method to induce destabilization of PEs by transiently perturbing the oil–water interface by transport of a mutually soluble solute across the interface. The generality of the method is demonstrated for different kind of solutes and stabilizers including particles of different sizes (nm to µm), shapes (sphere, spheroids, spherocylinders) and types (polystyrene, metal oxides). The method works for both oil-in-water (o/w) and water-in-oil (w/o) PEs with different kinds of non-polar solvents as oil-phase. However, the method fails when the solute is insoluble in one of the phases of PEs. The study opens up a new approach to destabilization of particle stabilized emulsions.