Synthesis of Anisotropic Concave Gold Nanocuboids with Distinctive Plasmonic Properties

Gold nanoparticles have attracted considerable attention owing to their appealing plasmonic properties that have found applications in sensing, imaging, and energy harvesting. In the present article, we report the synthesis of anisotropic concave Au nanocuboids using a seeded growth method controlled by a seed concentration. Unlike conventional nonconcave counterparts which typically present two fundamental plasmonic modes (transverse and longitudinal modes), our experimental measurements and theoretical analysis show that the anisotropic concave Au nanocuboid has three plasmonic resonances. Theoretical calculations based on a finite element method confirm that the third resonance is a transverse “edge” mode, which is enhanced by the sharpened edges of the concave surfaces. This third resonance is found to be separated from the conventional broad transverse mode band. Because of the separation of the resonance mode, the quality-factor of the original transverse mode shows nearly a 3-fold enhancement

Fluorescent pH Sensor Based on Ag@SiO₂ Core–Shell Nanoparticle

We have demonstrated a novel method for the preparation of a fluorescence-based pH sensor by combining the plasmon resonance band of Ag core and pH sensitive dye (HPTS). A thickness-variable silica shell is placed between Ag core and HPTS dye to achieve the maximum fluorescence enhancement. At the shell thickness of 8 nm, the fluorescence intensity increases 4 and 9 times when the sensor is excited at 405 and 455 nm, respectively. At the same time, the fluorescence intensity shows a good sensitivity toward pH value in the range of 5–9, and the ratio of emission intensity at 513 nm excited at 455 nm to that excited at 405 nm versus the pH value in the range of 5–9 is determined. It is believed that the present pH sensor has the potential for determining pH real time in the biological sample

Janus Polymer/Carbon Nanotube Hybrid Membranes for Oil/Water Separation

A robust and simple method is provided to fabricate Janus polymer/carbon nanotube (CNT) hybrid membranes for oil/water separation. Starting from CNT membranes formed by dispensing, hydrophobic poly­(styrene) (PS) and hydrophilic poly­(<i>N</i>,<i>N</i>-dimethylaminoethyl methacrylate) (PDMAEMA) were grated from different sides of the photoactive CNT membranes via self-initiated photografting and photopolymerization (SIPGP) to achieve Janus polymer/CNTs hybrid membranes. The obtained membranes have excellent oil/water selectivity in the removal of oil from water. Moreover, they can effectively separate both surfactant-stabilized oil-in-water and water-in-oil emulsions because of the anisotropic wettability of the membranes

Light-Triggered Reversible Self-Assembly of Gold Nanoparticle Oligomers for Tunable SERS

A photoresponsive amphiphilic gold nanoparticle (AuNP) is achieved through the decoration of AuNP with hydrophilic poly­(ethylene glycol) (PEG) and hydrophobic photoresponsive polymethacrylate containing spiropyran units (PSPMA). Owing to the photoresponsive property of spiropyran units, the amphiphilic AuNPs can easily achieve the controllable assembly/disassembly behaviors under the trigger by light. Under visible light, spiropyran units provide weak intermolecular interactions between neighbored AuNPs, leading to isolated AuNPs in the solution. While under UV light irradiation, spiropyran units in the polymer brushes transform into merocyanine isomer with conjugated structure and zwitterionic state, promoting the integration of adjacent AuNPs through π–π stacking and electrostatic attractions, further leading to the formation of Au oligomers. The smart reversible AuNP oligomers exhibited switchable plasmonic coupling for tuning surface-enhanced Raman scattering (SERS) activity, which is promising for the application of SERS based sensors and optical imaging

Reaction-Driven Self-Assembled Micellar Nanoprobes for Ratiometric Fluorescence Detection of CS₂ with High Selectivity and Sensitivity

The detection of highly toxic CS₂, which is known as a notorious occupational hazard in various industrial processes, is important from both environmental and public safety perspectives. We describe here a robust type of chemical-reaction-based supramolecular fluorescent nanoprobes for ratiometric determination of CS₂ with high selectivity and sensitivity in water medium. The micellar nanoprobes self-assemble from amphiphilic pyrene-modified hyperbranched polyethylenimine (Py-HPEI) polymers with intense pyrene excimer emission. Selective sensing is based on a CS₂-specific reaction with hydrophilic amino groups to produce hydrophobic dithiocarbamate moieties, which can strongly quench the pyrene excimer emission via a known photoinduced electron transfer (PET) mechanism. Therefore, the developed micellar nanoprobes are free of the H₂S interference problem often encountered in the widely used colorimetric assays and proved to show high selectivity over many potentially competing chemical species. Importantly, the developed approach is capable of CS₂ sensing even in complex tap and river water samples. In addition, in view of the modular design principle of these powerful micellar nanoprobes, the sensing strategy used here is expected to be applicable to the development of various sensory systems for other environmentally important guest species

Real-Time in Situ Investigation of Supramolecular Shape Memory Process by Fluorescence Switching

Shape memory hydrogels (SMHs) that take advantage of supramolecular chemistry cross-links to fix temporary shapes at room temperature are newly developed important shape memory polymers. It is thus highly desirable to explore in detail the in situ formation and real-time spatial distribution of temporary supramolecular cross-links in SMH systems, which can provide more in-depth information about the shape memory mechanism and promote the fabrication of new SMHs. However, related study still remains very challenging. We herein report the development of a special SMH system that involves fluorescent alginate–Eu³⁺ complexes as switching cross-links. Its coordination-triggered supramolecular shape memory/recovery processes and dynamics could be directly visualized by a high-contrast fluorescence imaging method. Remarkably, this efficient and sensitive fluorescence study enables real-time in situ monitoring of the process, in which Eu³⁺ ions gradually diffuse into the hydrogel sample and chelate with alginate to form the Eu³⁺–Alg temporary cross-links. Furthermore, a theoretical model correlating the fluorescence intensities of the SMH system with their shape memory effect (SME) was successfully established, which allows the facile and accurate prediction of both the shape memory and recovery ratios on the basis of quantitative emission spectral results. These details disclosed in this study will thus deepen the understanding of supramolecular shape memory process and mechanisms and accelerate the development of new practical shape memory hydrogels in the future

Nanohole-Array Induced Metallic Molybdenum Selenide Nanozyme for Photoenhanced Tumor-Specific Therapy

Deficient catalytic sensitivity to the tumor microenvironment is a major obstacle to nanozyme-mediated tumor therapy. Electron transfer is the intrinsic essence for a nanozyme-catalyzed redox reaction. Here, we developed a nanohole-array-induced metallic molybdenum selenide (n-MoSe2) that is enriched with Se vacancies and can serve as an electronic transfer station for cycling electrons between H2O2 decomposition and glutathione (GSH) depletion. In a MoSe2 nanohole array, the metallic phase reaches up to 84.5%, which has been experimentally and theoretically demonstrated to exhibit ultrasensitive H2O2 responses and enhanced peroxidase (POD)-like activities for H2O2 thermodynamic heterolysis. More intriguingly, plenty of delocalized electrons appear due to phase- and vacancy-facilitated band structure reconstruction. Combined with the limited characteristic sizes of nanoholes, the surface plasmon resonance effect can be excited, leading to the broad absorption spectrum spanning of n-MoSe2 from the visible to near-infrared region (NIR) for photothermal conversion. Under NIR laser irradiation, metallic MoSe2 is able to induce out-of-balance redox and metabolism homeostasis in the tumor region, thus significantly improving therapeutic effects. This study that takes advantage of phase and defect engineering offers inspiring insights into the development of high-efficiency photothermal nanozymes

Light-Controlled Shrinkage of Large-Area Gold Nanoparticle Monolayer Film for Tunable SERS Activity

The two-dimensional (2D) monolayer gold nanoparticle (Au NP) film is of significant interest and importance in both fundamental and practical applications including optoelectronic devices, sensing, catalysis, and surface-enhanced Raman spectroscopy (SERS). Because of the weak physical interaction, the conventional monolayer Au NP film fabricated at the oil–water interface was unstable, easily breakable, and difficultly transferred. In the present work, we report on a simple and effective chemical cross-linking strategy at the air–water interface to achieve a large-scale monolayer gold nanoparticle film with intelligently tunable size of nanogaps, and excellent free-standing and easily transferable properties. In our strategy, acrylamide, a polymerizable molecule, was first modified on the surface of Au NPs for subsequent self-assembly into a monolayer film at the liquid–liquid interface. Through photopolymerization of acrylamide, a chemically cross-linked film was formed with closely packed nanoparticles, highly macroscopic uniformity, and excellent free-standing property, which allowed it to be easily transferred from the air–water interface onto various solid substrates while maintaining its integrity. It is interesting to find that the macroscopic film underwent an <i>in situ</i> shrinkage under irradiation of UV-light, and its area shrinkage ratio is close to 55% (equal to 2.2 times) of that from non-cross-linked counterparts. More importantly, UV-light-controlled <i>in situ</i> shrinkage of the Au NP film would lead to intelligently, precisely tuned nanogaps less than 0.5 nm between neighboring Au NPs for maximal amplification of SERS signals, and the macroscopic uniformity of the films ensured the reproducible performance of SERS signals, providing an ideal candidate for SERS applications

Biodegradable PLA Nonwoven Fabric with Controllable Wettability for Efficient Water Purification and Photocatalysis Degradation

Although many bioinspired superwetting materials with excellent capability for oil/water separation have been constructed, functional surfaces combining effective separation property, biodegradability, and easy-controllability are still highly desired. In this work, a facile strategy to realize the controllable wettability on the polylactic acid (PLA) nonwoven fabric has been developed; the resulting superwetting PLA nonwoven fabrics exhibit high absorption capacity and high selectivity in oil/water separation. Moreover, the superhydrophilic PLA nonwoven fabric possesses excellent simultaneous photocatalysis degradation of water-miscible toxic organic pollutants. With the versatility and biodegradability, these advanced PLA nonwoven fabrics may provide effective solutions to oily water treatment

Engineering Gold Nanoparticles in Compass Shape with Broadly Tunable Plasmon Resonances and High-Performance SERS

We present the uniform and high-yield synthesis of a novel gold nanostructure of compass shape composed of a Au sphere at the central and two gradually thinning conical tips at the opposed poles. The Au compass shapes were synthesized through a seed-mediated growth approach employing a binary mixture of cetyltrimethylammonium bromide (CTAB) and sodium oleate (NaOL) as the structure-directing agents. Under the condition of single surfactant (CTAB), the spherical seeds tend to grow into larger spherical Au nanoparticles (NPs); while the spherical seeds favor the formation of Au compass shaped NPs using two mixed surfactants (CTAB/NaOL). The reaction kinetics clearly shows a growth mechanism of Au compass shaped NPs. Interestingly, due to their anisotropic structure, Au compass shaped NPs show two distinctive plasmonic resonances, similar to those from Au nanorods. Particularly, the longitudinal surface plasmon resonances of Au compass shaped NPs exhibit a broadly tunable range from 600 to 865 nm. In addition, the obtained Au compass shaped NPs can be self-assembled into a two-dimensional monolayer with closely packed and highly aligned NPs, which results in periodic arrays of overlapped Au tips, generating hot spots for high-performance surface-enhanced Raman scattering