Visualization of Charge Dynamics when Water Droplets Bounce on a Hydrophobic Surface

Visualizing the motion of water droplets and understanding their electrification behavior holds significance for applications related to droplet transport, self-cleaning, and anti-icing/deicing and for providing a comprehensive explanation of the solid–liquid triboelectrification mechanism. Here, by constructing microcolumnar structures on the polytetrafluoroethylene surface, a water droplet-based single electrode triboelectric nanogenerator was fabricated for visualizing charge dynamics when a water droplet bounces on a hydrophobic surface. The motion state of the water droplet is closely linked to its electrification behavior through the integration of a high-speed camera and an ammeter. The electrification behavior stemming from the bounce of the water droplet is dynamically captured in real-time. The results show that the magnitude and polarity of the electrical signal have strong dependence on the motion state of the water droplet. For instance, when a water droplet approaches or moves away from the substrate in a single direction, a unipolar electrical signal is generated. However, when the water droplet reaches its limit in the initial motion direction, it signifies a static equilibrium state, resulting in the electrical signal being at zero. Furthermore, we examine the impact of factors such as impact speed, drop contact area, contact line spreading/retraction speed, and impact angle on electrification. Finally, based on the close relationship between poly­(ethylene oxide) (PEO) droplet bounce dynamics and electrical signals, the bouncing details of PEO droplets with different concentrations are tracked by electrical signals. This study digitally presents the whole process of droplet bounce in situ and provides a means for monitoring and tracking droplet movement

Visualization of Charge Dynamics when Water Droplets Bounce on a Hydrophobic Surface

Visualizing the motion of water droplets and understanding their electrification behavior holds significance for applications related to droplet transport, self-cleaning, and anti-icing/deicing and for providing a comprehensive explanation of the solid–liquid triboelectrification mechanism. Here, by constructing microcolumnar structures on the polytetrafluoroethylene surface, a water droplet-based single electrode triboelectric nanogenerator was fabricated for visualizing charge dynamics when a water droplet bounces on a hydrophobic surface. The motion state of the water droplet is closely linked to its electrification behavior through the integration of a high-speed camera and an ammeter. The electrification behavior stemming from the bounce of the water droplet is dynamically captured in real-time. The results show that the magnitude and polarity of the electrical signal have strong dependence on the motion state of the water droplet. For instance, when a water droplet approaches or moves away from the substrate in a single direction, a unipolar electrical signal is generated. However, when the water droplet reaches its limit in the initial motion direction, it signifies a static equilibrium state, resulting in the electrical signal being at zero. Furthermore, we examine the impact of factors such as impact speed, drop contact area, contact line spreading/retraction speed, and impact angle on electrification. Finally, based on the close relationship between poly­(ethylene oxide) (PEO) droplet bounce dynamics and electrical signals, the bouncing details of PEO droplets with different concentrations are tracked by electrical signals. This study digitally presents the whole process of droplet bounce in situ and provides a means for monitoring and tracking droplet movement

Inhibitation of Cellular Toxicity of Gold Nanoparticles by Surface Encapsulation of Silica Shell for Hepatocarcinoma Cell Application

Nanotechnology, as a double-edged sword, endows gold nanoparticles (GNPs) more “power” in bioimaging and theragnostics, whereas an outstanding issue associated with the biocompatibility of GNPs should also be addressed. Especially for the silica-coated gold nanospheres (GNSs) and gold nanorods (GNRs), there is increasing attention to explore the application, because the surface silica encapsulation has been proved to be an alternative strategy for other organic surface coatings. However, among those reports there are very limited publications to focus on the toxicity of silica-coated GNSs and GNRs. Besides, the existing detoxification methods via surface chemistry on GNPs greatly improve the biocompatibility but still undergo challenges for high dose (>100 pM) demand and long-term stability. Here, we demonstrated a straightforward, low-cost, universal strategy for the surface chemistry on GNPs via silica encapsulating. Different size, shape, dose, and surface capping of GNPs for the nanotoxicity test have been carefully discussed. After silica encapsulating, the detoxification for all GNPs presents significantly from HepG2 cell proliferation results, especially for the GNRs. This new straightforward strategy will definitely rationalize the biocompatibility issue of GNPs and also provide potential for other surface chemistry methodology in biomedical fields

Novel Au Catalysis Strategy for the Synthesis of Au@Pt Core–Shell Nanoelectrocatalyst with Self-Controlled Quasi-Monolayer Pt Skin

Design of catalytically active Pt-based catalysts with minimizing the usage of Pt is a major issue in fuel cells. Herein, for the first time, we have developed a Au catalytic reduction strategy to synthesize a Au@Pt core–shell electrocatalyst with a quasi-monolayer Pt skin spontaneously formed from the gold surface catalysis. In the presence of presynthesized gold nanocrystals (used as the catalyst and Au seeds) and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer (used as reductant), under the Au surface catalysis, platinum ions can be reduced and deposited on the gold nanocrystals to form a Pt skin surface with a quasi-monatomic thickness. In the present strategy, Pt ions can be reduced only under the catalysis of gold surface and thus when the surface of Au NPs is covered by a monatomic Pt layer, the reduction reaction of Pt ions will be spontaneously turned off. Therefore, the significant advantage of this synthesis strategy is that the formation of quasi-monolayer Pt skin surface can be self-controlled and is completely free of controlling the dosage of platinum ions and the size distribution of Au cores. The synthesized Au@Pt core@shell structure exhibited enhanced electrocatalytic activities for oxygen reduction reaction and methanol oxidation reaction, which are 6.87 and 10.17 times greater than those of Pt/C catalyst, respectively. The present study provides a new strategy for obtaining high-performance bimetallic/multimetallic electrocatalysts with high utilization of precious metals

Near Infrared Light Sensitive Ultraviolet–Blue Nanophotoswitch for Imaging-Guided “Off–On” Therapy

Photoswitchable materials are important in broad applications. Recently appeared inorganic photoswitchable upconversion nanoparticles (PUCNPs) become a competitive candidate to surmount the widespread issue of the organic counterparts photobleaching. However, current PUCNPs follow solely Yb³⁺/Nd³⁺ cosensitizing mode, which results in complex multilayer doping patterns and imperfectness of switching in UV–blue region. In this work, we have adopted a new strategy to construct Nd³⁺ free PUCNPsNaErF₄@NaYF₄@NaYbF₄:0.5%Tm@NaYF₄. These PUCNPs demonstrate the superior property of photoswitching. A prominent UV–blue emission from Tm³⁺ is turned on upon 980 nm excitation, which can be completely turned off by 800 nm light. The quasi-monochromatic red upconversion emission upon 800 nm excitationa distinct feature of undoping NaErF₄ upconversion systemendows the PUCNPs with promising image-guided photoinduced “off–on” therapy in biomedicine. As a proof-of-concept we have demonstrated the imaging-guided photodynamic therapy (PDT) of cancer, where 800 nm excitation turns off the UV–blue emission and leaves the emission at 660 nm for imaging. Once the tumor site is targeted, excitation switching to 980 nm results in UV–blue emission and the red emission. The former is used to induce PDT, whereas the latter is to monitor the therapeutic process. Our study implies that this upconversion photoswitching material is suitable for real-time imaging and image-guided therapy under temporal and spatial control

Ultrastrong Absorption Meets Ultraweak Absorption: Unraveling the Energy-Dissipative Routes for Dye-Sensitized Upconversion Luminescence

Dye sensitization is becoming a new dimension to highly improve the upconversion luminescence (UCL) of lanthanide-doped upconversion nanoparticles (UCNPs). However, there is still a lack of general understanding of the dye–UCNPs interactions, especially the confused large mismatch between the inputs and outputs. By taking dye-sensitized NaYF₄:Yb/Er@NaYF₄:Nd UCNPs as a model system, we not only revealed the in-depth energy-dissipative process for dye-sensitized UCL but also confirmed the first ever experimental observation of the energy back transfer (EBT) in the dye-sensitized UCL. Furthermore, this energy-dissipative EBT restricted the optimal ratio of dyes to UCNP. By unearthing all of the energy loss behind the EBT, energy transfer, and energy migration processes, this paper sheds light on the further design of effective dye-sensitized nanosystems for UCL or even downconversion luminescence

Covalently Assembled NIR Nanoplatform for Simultaneous Fluorescence Imaging and Photodynamic Therapy of Cancer Cells

A highly efficient multifunctional nanoplatform for simultaneous upconversion luminescence (UCL) imaging and photodynamic therapy has been developed on the basis of selective energy transfer from multicolor luminescent NaYF₄:Yb³⁺,Er³⁺ upconversion nanoparticles (UCNPs) to photosensitizers (PS). Different from popular approaches based on electrostatic or hydrophobic interactions, over 100 photosensitizing molecules were covalently bonded to every 20 nm UCNP, which significantly strengthened the UCNP–PS linkage and reduced the probability of leakage/desorption of the PS. Over 80% UCL was transferred to PS, and the singlet oxygen production was readily detected by its feature emission at 1270 nm. Tests performed on JAR choriocarcinoma and NIH 3T3 fibroblast cells verified the efficient endocytosis and photodynamic effect of the nanoplatform with 980 nm irradiation specific to JAR cancer cells. Our work highlights the promise of using UCNPs for potential image-guided cancer photodynamic therapy