Droplet Probe Research Articles

Probing the interactions between asphaltenes and a PEO-PPO demulsifier at oil–water interface: Effect of temperature

HypothesisAsphaltenes are primary stabilizers in water-in-oil (W/O) emulsions that cause corrosion and fouling issues. In oil sands industry, oil/water separation processes are generally conducted at high temperatures. A high temperature is expected to impact the interactions between asphaltenes and emulsion breakers (EBs), consequently influencing demulsification performance. ExperimentsThe adsorption and interactions of asphaltenes and a PEO-PPO type EB (Pluronic F68) at the oil–water interface were investigated at various temperatures, using tensiometer, quartz crystal microbalance with energy dissipation (QCM-D), and atomic force microscopy (AFM). The effect of temperature on EB’s demulsification performance was explored through bottle tests. Additionally, demulsification mechanisms were studied using direct force measurements with the droplet probe AFM technique. FindingsDynamic interfacial tension and QCM-D results demonstrate that the PEO-PPO type EB exhibits higher interfacial activity than asphaltenes and can disrupt rigid asphaltene films at the oil–water interfaces. Elevated temperatures accelerate the displacement of adsorbed asphaltenes by EB molecules, leading to sparse interfacial films, rapid droplet coalescence, and improved demulsification efficiency (supported by AFM and bottle test results). This work provides valuable insights into interfacial interactions between asphaltenes and EB at different temperatures, enhancing the understanding of demulsification mechanisms and offering useful implications for the development of efficient EBs to enhance oil/water separation performance.

Multifunctional lipid droplet probes for observing the polarity change of ferroptosis, inflammation, fatty liver and evaluating the efficacy of drugs

BackgroundLipid droplets (LDs) polarity is intricately linked to diverse biological processes and diseases. The visualization of LDs-polarity is of vital importance but challenging due to the lack of high-specificity, high-sensitivity and large-Stokes shift probes for real-time tracking LDs-polarity in biological systems. ResultsFour D-π-A based fluorescent probes (TPA-TCF1-TPA-TCF4) have been developed by combining tricyanofuran (an electron acceptor, A) and triphenylamine (an electron donor, D) derivatives with different terminal groups. Among them, TPA-TCF1 and TPA-TCF4 exhibit excellent polar sensitivity, large Stokes shift (≥182 nm in H2O), and efficient LDs targeting ability. In particular, TPA-TCF4 is capable of monitoring the change of LDs-polarity during ferroptosis, inflammation, apoptosis of cancer cell, and fatty liver. SignificanceAll these features render TPA-TCF4 a versatile tool for pharmacodynamic evaluation of anti-cancer drugs, in-depth understanding of the biological effect of LDs on ferroptosis, and medical diagnosis of LDs-polarity related diseases.

A simple approach for effectively improving the resolution of scanning electrochemical cell microscopy

The high-resolution scanning electrochemical cell microscopy (SECCM) is a powerful tool that can directly explore the structure-property correlation of materials at nanometer scale. However, so far, the attainable maximum resolution is still restricted by the diameter of the droplet probe. Here, we report a simple and effective approach that can highly reduce the effective size of a nanopipette probe in SECCM. The effective working size was reduced to tens of nanometers by using the conventional droplet probe with an opening size of ∼129 nm through one-step oil coating. Furthermore, both the topographical and electrochemical activity of the Au nanoplate were simultaneously recorded successfully at the pixel size of sub-10 nm in the x-axis direction, meaning the potential to achieve a sub-10 nm resolution. Finally, the modified probe displays excellent applicability with acidic, neutral and alkaline electrolytes. The method retains the advantages of the droplet probe and breaks the limitation of its opening size on the SECCM imaging resolution, opening a broad avenue for both further rapid commercialization and broad applications of SECCM.

Recent advances in fluorescent probes for fatty liver imaging by detecting lipid droplets.

Fatty liver, a major health problem worldwide, is closely associated with aberrant accumulation and alteration of energy storage organelles, lipid droplets (LDs), in the disease process. Fluorescent probes with excellent optical performance, high sensitivity/selectivity and real-time monitoring have emerged as an attractive tool for the detection of LDs used in the diagnosis of fatty liver. In this review, we summarize various probes based on different response mechanisms to image LDs in the fatty liver process using different excitation imaging modes and emission wavelengths, including the visible to the near-infrared, two/three-photon, and the second near-infrared region. The perspectives and barriers associated with the reported lipid droplet (LD) probes for future development are also discussed.

Evaluation of four ground-based retrievals of cloud droplet number concentration in marine stratocumulus with aircraft in situ measurements

Abstract. Cloud droplet number concentration (Nd) is crucial for understanding aerosol–cloud interactions (ACI) and associated radiative effects. We present evaluations of four ground-based Nd retrievals based on comprehensive datasets from the Atmospheric Radiation Measurement (ARM) Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA) field campaign. The Nd retrieval methods use ARM ENA observatory ground-based remote sensing observations from a micropulse lidar, Raman lidar, cloud radar, and the ARM NDROP (Droplet Number Concentration) value-added product (VAP), all of which also retrieve cloud effective radius (re). The retrievals are compared against aircraft measurements from the fast cloud droplet probe (FCDP) and the cloud and aerosol spectrometer (CAS) obtained from low-level marine boundary layer clouds on 12 flight days during summer and winter seasons. Additionally, the in situ measurements are used to validate the assumptions and characterizations used in the retrieval algorithms. Statistical comparisons of the probability distribution function (PDF) of the Nd and cloud re retrievals with aircraft measurements demonstrate that these retrievals align well with in situ measurements for overcast clouds, but they may substantially differ for broken clouds or clouds with low liquid water path (LWP). The retrievals are applied to 4 years of ground-based remote sensing measurements of overcast marine boundary layer clouds at the ARM ENA observatory to find that Nd (re) values exhibit seasonal variations, with higher (lower) values during the summer season and lower (higher) values during the winter season. The ensemble of various retrievals using different measurements and retrieval algorithms such as those in this paper can help to quantify Nd retrieval uncertainties and identify reliable Nd retrieval scenarios. Of the retrieval methods, we recommend using the micropulse lidar-based method. This method has good agreement with in situ measurements, less sensitivity to issues arising from precipitation and low cloud LWP and/or optical depth, and broad applicability by functioning for both daytime and nighttime conditions.

Vertical Motions in Orographic Cloud Systems over the Payette River Basin. Part IV: Controls on Supercooled Liquid Water Content and Cloud Droplet Number Concentrations

Abstract This paper examines the controls on supercooled liquid water content (SLWC) and drop number concentrations (Nt,CDP) over the Payette River basin during the Seeded and Natural Orographic Wintertime Clouds: The Idaho Experiment (SNOWIE) campaign. During SNOWIE, 27.4% of 1-Hz in situ cloud droplet probe samples were in an environment containing supercooled liquid water (SLW). The interquartile range of SLWC, when present, was found to be 0.02–0.18 g m−3 and 13.3–37.2 cm−3 for Nt,CDP, with the most extreme values reaching 0.40–1.75 g m−3 and 150–320 cm−3 in isolated regions of convection and strong shear-induced turbulence. SLWC and Nt,CDP distributions are shown to be directly related to cloud-top temperature and ice particle concentrations, consistent with past research over other mountain ranges. Two classes of vertical motions were analyzed as potential controls on SLWC and Nt,CDP, the first forced by the orography and fixed in space relative to the topography (stationary waves) and the second transient, triggered by vertical shear and instability within passing synoptic-scale cyclones. SLWC occurrence and magnitudes, and Nt,CDP associated with fixed updrafts were found to be normally distributed about ridgelines when SLW was present. SLW was more likely to form at low altitudes near the terrain slope associated with fixed waves due to higher mixing ratios and larger vertical air parcel displacements at low altitudes. When considering transient updrafts, SLWC and Nt,CDP appear more uniformly distributed over the flight track with little discernable terrain dependence as a result of time and spatially varying updrafts associated with passing weather systems. The implications for cloud seeding over the basin are discussed.

Overview and statistical analysis of boundary layer clouds and precipitation over the western North Atlantic Ocean

Abstract. Due to their fast evolution and large natural variability in macro- and microphysical properties, the accurate representation of boundary layer clouds in current climate models remains a challenge. One of the regions with large intermodel spread in the Coupled Model Intercomparison Project Phase 6 ensemble is the western North Atlantic Ocean. Here, statistically representative in situ measurements can help to develop and constrain the parameterization of clouds in global models. To this end, we performed comprehensive measurements of boundary layer clouds, aerosol, trace gases, and radiation in the western North Atlantic Ocean during the NASA Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) mission. In total, 174 research flights with 574 flight hours for cloud and precipitation measurements were performed with the HU-25 Falcon during three winter (February–March 2020, January–April 2021, and November 2021–March 2022) and three summer seasons (August–September 2020, May–June 2021, and May–June 2022). Here we present a statistical evaluation of 16 140 individual cloud events probed by the fast cloud droplet probe and the two-dimensional stereo cloud probe during 155 research flights in a representative and repetitive flight strategy allowing for robust statistical data analyses. We show that the vertical profiles of distributions of the liquid water content and the cloud droplet effective diameter (ED) increase with altitude in the marine boundary layer. Due to higher updraft speeds, higher cloud droplet number concentrations (Nliquid) were measured in winter compared to summer despite lower cloud condensation nucleus abundance. Flight cloud cover derived from statistical analysis of in situ data is reduced in summer and shows large variability. This seasonal contrast in cloud coverage is consistent with a dominance of a synoptic pattern in winter that favors conditions for the formation of stratiform clouds at the western edge of cyclones (post-cyclonic). In contrast, a dominant summer anticyclone is concomitant with the occurrence of shallow cumulus clouds and lower cloud coverage. The evaluation of boundary layer clouds and precipitation in the Nliquid ED phase space sheds light on liquid, mixed-phase, and ice cloud properties and helps to categorize the cloud data. Ice and liquid precipitation, often masked in cloud statistics by a high abundance of liquid clouds, is often observed throughout the cloud. The ACTIVATE in situ cloud measurements provide a wealth of cloud information useful for assessing airborne and satellite remote-sensing products, for global climate and weather model evaluations, and for dedicated process studies that address precipitation and aerosol–cloud interactions.

Multimodal Sensing Transparent Droplet Probe for Characterization of Superhydrophobic Surfaces

Multimodal Sensing Transparent Droplet Probe for Characterization of Superhydrophobic Surfaces

Large-Eddy Simulations of Marine Boundary Layer Clouds Associated with Cold-Air Outbreaks during the ACTIVATE Campaign. Part II: Aerosol–Meteorology–Cloud Interaction

Abstract Aerosol effects on micro/macrophysical properties of marine stratocumulus clouds over the western North Atlantic Ocean (WNAO) are investigated using in situ measurements and large-eddy simulations (LES) for two cold-air outbreak (CAO) cases (28 February and 1 March 2020) during the Aerosol Cloud Meteorology Interactions over the Western Atlantic Experiment (ACTIVATE). The LES is able to reproduce the vertical profiles of liquid water content (LWC), effective radius reff and cloud droplet number concentration Nc from fast cloud droplet probe (FCDP) in situ measurements for both cases. Furthermore, we show that aerosols affect cloud properties (Nc, reff, and LWC) via the prescribed bulk hygroscopicity of aerosols () and aerosol size distribution characteristics. Nc, reff, and liquid water path (LWP) are positively correlated to and aerosol number concentration (Na) while cloud fractional cover (CFC) is insensitive to and aerosol size distributions for the two cases. The realistic changes to aerosol size distribution (number concentration, width, and the geometrical diameter) with the same meteorology state allow us to investigate aerosol effects on cloud properties without meteorological feedback. We also use the LES results to evaluate cloud properties from two reanalysis products, ERA5 and MERRA-2. Compared to LES, the ERA5 is able to capture the time evolution of LWP and total cloud coverage within the study domain during both CAO cases while MERRA-2 underestimates them.

Blue-emitting lipid droplet probes based on coumarin dye for multi-color imaging of living cells and fatty livers of mice

Lipid droplets (LDs) are highly dynamic organelles in cells and are closely related not only to intracellular lipid metabolic processes but also to various lipid metabolism disorders such as fatty liver disease, obesity, and diabetes. Since these processes are deeply associated with the dynamic behaviors between LDs and other organelles in cells, their simultaneous imaging provides valuable information on intracellular processes. Herein, we developed blue-emitting ld-specific probes (DBC30, DBC30-Bu, and DBC30-Ph) based on coumarin dye, and performed multi-color imaging of living cells and hepatic tissues of living mice using a confocal fluorescence microscope. DBC30 derivatives exhibited large molar absorption coefficients and high fluorescence quantum yields in non-polar and polar solvents. The confocal fluorescence microscopy measurements of HeLa cells pretreated with oleic acid followed by staining with DBC30 derivatives revealed that these probes selectivity stain LDs and showed blue fluorescence in LDs, allowing multi-color imaging using green and red fluorescence organelle-specific probes. Additionally, DBC30 derivatives exhibited high photostability compared with a commercially available blue-emitting ld-specific probe. We took dual-color images of the surfaces of livers following intravenous administration of DBC30 and FITC-lectin (a green fluorescent vascular endothelial marker) into normal and high-fat-diet-fed mice. Simultaneous imaging of hepatic tissues of fatty liver mice using these probes allowed the visualization of small and large LDs in hepatocytes and of the distorted sinusoidal network. Furthermore, co-staining experiments using DBC30 and the green-emitting nucleus-specific probe enabled visualization of the distribution of LDs and nuclei in hepatic tissue sections of normal and fatty livers. These results demonstrated that DBC30 is advantageous as an imaging probe for LDs in living cells and in vivo and ex vivo hepatic tissues.

A wash-free fluorescent probe with a large Stokes shift for the identification of NAFL through tracing the change of lipid droplets.

As one of the important organelles in cells, lipid droplets (LDs) are involved in various physiological processes, especially affecting the occurrence and progression of non-alcoholic fatty liver (NAFL). Therefore, it is of great significance to develop LD-specific probes with excellent biocompatibility, deep penetration and bright fluorescence. Herein, a fluorescent probe LD-HWZ was designed and synthesized based on triphenylamine and the dicyanoisophorone group. It is found that probe LD-HWZ has a large Stokes shift (Δλ = 160 nm in DMSO) and exhibits bright fluorescence in a lipid environment. In addition, biological experiments showed that LD-HWZ can localize in lipid droplets, which can be used to detect the dynamic changes of LDs. Importantly, LD-HWZ has been successfully used to discriminate NAFL tissues from normal livers. The excellent properties of probe LD-HWZ in this work are expected to shed new light on the design of lipid droplet probes for the study of fatty liver diagnosis.

Through-drop imaging of moving contact lines and contact areas on opaque water-repellent surfaces.

A myriad of natural surfaces such as plant leaves and insect wings can repel water and remain unwetted inspiring scientists and engineers to develop water-repellent surfaces for various applications. Those natural and artificial water-repellent surfaces are typically opaque, containing micro- and nano-roughness, and their wetting properties are determined by the details at the actual liquid-solid interface. However, a generally applicable way to directly observe moving contact lines on opaque water-repellent surfaces is missing. Here, we show that the advancing and receding contact lines and corresponding contact area on micro- and nano-rough water-repellent surfaces can be readily and reproducibly quantified using a transparent droplet probe. Combined with a conventional optical microscope, we quantify the progression of the apparent contact area and apparent contact line irregularity in different types of superhydrophobic silicon nanograss surfaces. Contact angles near 180° can be determined with an uncertainty as low as 0.2°, that a conventional contact angle goniometer cannot distinguish. We also identify the pinning/depinning sequences of a pillared model surface with excellent repeatability and quantify the progression of the apparent contact interface and contact angle of natural plant leaves with irregular surface topography.

Effect of different substituents on the fluorescence properties of precursors of synthetic GFP analogues and a polarity-sensitive lipid droplet probe with AIE properties for imaging cells and zebrafish.

The green fluorescent protein (GFP) is a purely natural specialty protein that has been widely used to design synthetic fluorescent probes. In the present work we designed and synthesized a series of fluorescent compounds akin to GFP precursors by a one-step method, and investigated the luminescence properties of the fluorescent compounds by varying the substituents. We presented the first systematic summary of the photophysical data including extinction coefficients and fluorescence quantum yields for this class of fluorescent dyes. We also carried out density functional theory (DFT) calculations for these dyes to investigate the effect of electronic effects due to different substituents. These studied optical properties may provide a reference for later probe design. More interestingly, we have developed a polarity-sensitive lipid droplet probe T-LD with AIE properties on this basis. The probe exhibited not only favorable pH stability and kinetic stability in terms of optical properties, but also solvent discolouration and polarity-sensitive properties, and was able to label intracellular lipid droplets. We successfully applied the probe for intracellular lipid droplet level monitoring and zebrafish imaging.

Anti-Oil-Adhesion Property of Superhydrophilic/Underwater Superoleophobic Phytic Acid-FeIII Complex Coatings

Crude oil adhesion issues are widespread in the petroleum industry, leading to inefficient production and high maintenance costs. Developing efficient antifouling materials and investigating the microscopic adhesion mechanism are of substantial significance. In the present work, a superhydrophilic/underwater superoleophobic PAFC coating with excellent antifouling properties was constructed by the coordination-driven self-assembly of phytic acid (PA) and FeCl3 (FC). The atomic force microscope (AFM) droplet probe technique was employed to elucidate the underlying mechanism of the anti-oil-adhesion property of the PAFC coating. Results showed that the PAFC modification achieved the optimum effect at a molar ratio of 1:3 between PA and FeIII. Applying a (3-aminopropyl)triethoxysilane (APTES) interlayer can effectively improve the performance of the PAFC coating on silica substrates. AFM droplet probe experiments indicated that the adhesion force between submerged micrometer-sized oil droplets and PAFC-modified substrates was significantly weaker than that with the untreated substrate. Meanwhile, the adhesion forces between oil droplets and surfaces were inversely proportional to the contact angle of the oil in water and were enhanced by higher salinity, lower collision velocity, and stronger loading force. The oil injection and wall sticking tests also confirmed the effectiveness of the PAFC modification in resisting the adhesion of crude oil.

In Vivo Simultaneous Imaging of Plasma Membrane and Lipid Droplets in Hepatic Steatosis using Red-Emissive Two-Photon Probes.

The plasma membrane, which is a phosphoglyceride bilayer at the outer edge of the cell, plays diverse and important roles in biological systems. Visualization of the plasma membrane in live samples is important for various applications in biological functions. We developed an amphiphilic two-photon (TP) fluorescent probe (THQ-Mem) to selectively monitor the plasma membrane in live samples. This probe exhibited red emission (620-700 nm), large TP absorption cross sections (δmax > 790 GM), and high selectivity to the plasma membrane. In cultured cells and in vivo hepatic tissue imaging, THQ-Mem showed bright TP-excited fluorescence (TPEF) and remarkable selectivity for the plasma membrane. Furthermore, simultaneous in vivo imaging with THQ-Mem and a TP lipid droplet probe could serve as an efficient tool to monitor morphological and physiological changes in the plasma membrane and lipid droplets.

Palladium-Catalyzed Cascade Reaction in Water to Imidazo[1,2-a]pyridazines as Switchable DSEgens, AIEgens, and ACQgens.

Dual-state emission (DSE) luminophores exhibit strong emissions in both solution and solid states, filling the gaps between aggregation-induced emissions (AIE) and aggregation-caused quenching (ACQ). However, limited design concepts and complicated synthetic strategies restrict the discovery of novel DSE molecules. Developing efficient and green methodologies to access novel DSE scaffolds via rational design remains highly desirable. In this work, we report a water-promoted Pd-catalyzed cascade reaction for the synthesis of multi-substituted imidazo[1,2-a]pyridazine derivatives with DSE properties. The intramolecular interactions of the neighboring benzene rings restrict molecular motion, leading to emissions in the solid state (quantum yield: 11 %), and the newly constructed core structure of imidazo[1,2-a]pyridazine ensures considerable planarity, allowing for emissions in solution. Further removal of the neighboring phenyl groups resulted in ACQgens, while additional methyl groups led to AIEgens. Subsequent live cell imaging investigations suggested that the novel DSEgens could serve as specific lipid droplet (LD) probes in a wide concentration range.

Lipophilic neutral iridium(III) complexes for phosphorescence imaging of lipid droplets and potential photodynamic therapy

Compared with the recently reported large number of fluorescent lipid droplet (LD) probes based on organic fluorophores, phosphorescent LD probes based on transition metal complexes are much less reported. In addition, LDs are rarely studied as targets for photodynamic therapy (PDT). In this work, two lipophilic neutral iridium(III) complexes, namely [Ir(bt)2(hpd)] (denoted as LDIr1) and [Ir(piq)2(hpd)] (denoted as LDIr2) (where Hbt = 2-phenylbenzothiazole, Hpiq = 1-penylisoquinoline, Hhpd = 3,5-heptanedione), have been synthesized and characterized. These complexes exhibit long-lived orange to red phosphorescence emission and large Stokes shifts (ca. 160 nm). They can specifically stain LDs in living A549 and HepG2 cells, showing excellent biocompatibility and favourable photostability. Complex LDIr1 has been successfully applied for monitoring of oleic acid-induced LDs accumulation in living A549 cells and in vivo imaging of larval zebrafish. Moreover, these two iridium(III) complexes can efficiently generate singlet oxygen upon visible light (425 nm) irradiation to kill cancer cells effectively by means of PDT. They display impressive high phototoxicity index (PI) values of 1087 and 263 for complexes LDIr1 and LDIr2, respectively. This study provides useful insights into rational design of new metal complex-based LD-targeted phosphorescent probes and PDT agents.

BODIPY 493 acts as a bright buffering fluorogenic probe for super-resolution imaging of lipid droplet dynamics

The need for temporal resolution and long-term stability in super-resolution fluorescence imaging has motivated research to improve the photostability of fluorescent probes. Due to the inevitable photobleaching of fluorophores, it is difficult to obtain long-term super-resolution imaging regardless of the self-healing strategy of introducing peroxide scavengers or the strategy of fluorophore structure modification to suppress TICT formation. The buffered fluorogenic probe uses the intact probes in the buffer pool to continuously replace the photobleached ones in the target, which greatly improves the photostability and enables stable dynamic super-resolution imaging for a long time. But the buffering capacity comes at the expense of reducing the number of fluorescent probes in targets, resulting in low staining fluorescence intensity. In this paper, we selected BODIPY 493, a lipid droplet probe with high fluorescence brightness, to explore the dynamic process of lipid droplet staining of this probe in cells. We found that BODIPY 493 only needs very low laser power for lipid droplet imaging due to the high molecular accumulation in lipid droplets and the high brightness, and the spatiotemporal resolution is greatly improved. More importantly, we found that BODIPY 493 also has a certain buffering capacity, which enables BODIPY 493 to be used for super-resolution imaging of lipid droplet dynamics. This work reminds researchers to coordinate the buffering capacity and brightness of fluorogenic probes.

Response of Mixed-Phase Cloud Microphysical Properties to Cloud-Seeding Near Cloud Top Over Hebei, China

On November 29, 2019, an aircraft observation during the period of cloud-seeding was carried out for a mixed-phase cloud over Xingtai, Hebei Province, China. This study investigates the response of mixed-phase cloud microphysical properties to cloud-seeding near cloud top. Before cloud seeding, the cloud droplet concentration from fast cloud droplet probe (NC_FCDP) presented a multi-peak vertical distribution structure, with a maximum concentration of 192 cm−3 at a height of 3,322 m; the maximum concentration of ice crystals from cloud imaging probe (NC_CIP) was 10 L−1, which appeared at 4,500 m in the upper part of cloud; and the peak value of liquid water content (LWC) in the cloud also appeared at 4,500 m, with a value of 0.15 g/m3. The coexistence of supercooled liquid water and ice crystals implies that they are particularly suitable for cloud seeding at the height of 4,550 m. About 7–8 min later after cloud seeding at this height, the average NC_FCDP decreased from 160.3 to 129 cm−3, and the average NC_CIP increased from 7.1 to 10 L−1. Moreover, after cloud seeding, high NC_CIP as well as larger and more ice crystals appeared almost in the same areas within the cloud, and LWC presented an obvious decreasing trend. In contrast, the concentration of small cloud droplets and LWC decreased obviously after seeding. The findings suggest that the cloud microphysical properties showed obvious responses to the artificial introduction of silver iodide, which is important for human weather modification.

Blue-Emitting Lipid Droplet Probes Based on Coumarin Dye for Multi-Color Imaging of Living Cells and Fatty Livers of Mice

Blue-Emitting Lipid Droplet Probes Based on Coumarin Dye for Multi-Color Imaging of Living Cells and Fatty Livers of Mice