Controlled morphology evolution of branched Au nanostructures and their shape-dependent catalytic and photo-thermal properties

The urchin-like gold nanoparticles/poly(ε-caprolactone)/chitosan electrospun nanofibers for antibacterial active packaging

Inspired by the natural antimicrobial effect of the topographical features of insect wings, this study prepared urchin-like gold nanoparticles (UGNPs) and deposited them on poly(ε-caprolactone) (PCL)/chitosan (P/C) electrospun nanofiber film to strengthen antibacterial activities of this active packaging. Results showed that L-Dopa was a suitable reducing agent to prepare UGNPs, and the spine length of UGNPs increased from 21.23 to 35.83 nm as the molar ratio of L-Dopa:HAuCl4 increased from 1 to 3. As the nanofiber film was immersed in the nanoparticle solution for a longer time, the UGNP content in P/C nanofibers increased. As the spine length of UGNPs and depositing UGNP content increased, the inhibition rate against S. aureus and E. coli. of P/C nanofiber film increased. In addition, P/C nanofiber film deposited with UGNPs also exhibited good thermal stability, hydrophilicity, mechanical strength, and water vapor permeability, exhibiting its potential as an antibacterial active packaging.

Hollow Cu2-xSe-based nanocatalysts for combined photothermal and chemodynamic therapy in the second near-infrared window

Chemodynamic therapy (CDT) and photothermal therapy (PTT) have gained popularity due to their non-invasive characteristics and satisfying therapeutic expectations. A Cu-based nanomaterial serving as a Fenton-like nanocatalyst for CDT together with a photothermal agent for simultaneous PTT seems to be a powerful strategy. In this work, the morphological effect of Cu2-xSe nanoparticles on CDT and PTT was systematically investigated. In particular, the hollow octahedral Cu2-xSe nanoparticles exhibited higher photothermal and chemodynamic performance than that of spherical or cubic Cu2-xSe nanoparticles in the second near-infrared (NIR-II) window. In addition, the octahedral Cu2-xSe nanoparticles were further loaded with the autophagy inhibitor chloroquine (CQ) and connected with the targeting neuropeptide Y ligand, and shown to work as a novel therapeutic platform (Cu2-xSe@CQ@NPY), holding an immense potential to achieve synergetic enhancement of CDT/PTT with a positive therapeutic outcome for breast cancer.

Recent advances in nanoflowers: compositional and structural diversification for potential applications

In recent years, nanoscience and nanotechnology have emerged as promising fields in materials science. Spectroscopic techniques like scanning tunneling microscopy and atomic force microscopy have revolutionized the characterization, manipulation, and size control of nanomaterials, enabling the creation of diverse materials such as fullerenes, graphene, nanotubes, nanofibers, nanorods, nanowires, nanoparticles, nanocones, and nanosheets. Among these nanomaterials, there has been considerable interest in flower-shaped hierarchical 3D nanostructures, known as nanoflowers. These structures offer advantages like a higher surface-to-volume ratio compared to spherical nanoparticles, cost-effectiveness, and environmentally friendly preparation methods. Researchers have explored various applications of 3D nanostructures with unique morphologies derived from different nanoflowers. The nanoflowers are classified as organic, inorganic and hybrid, and the hybrids are a combination thereof, and most research studies of the nanoflowers have been focused on biomedical applications. Intriguingly, among them, inorganic nanoflowers have been studied extensively in various areas, such as electro, photo, and chemical catalysis, sensors, supercapacitors, and batteries, owing to their high catalytic efficiency and optical characteristics, which arise from their composition, crystal structure, and local surface plasmon resonance (LSPR). Despite the significant interest in inorganic nanoflowers, comprehensive reviews on this topic have been scarce until now. This is the first review focusing on inorganic nanoflowers for applications in electro, photo, and chemical catalysts, sensors, supercapacitors, and batteries. Since the early 2000s, more than 350 papers have been published on this topic with many ongoing research projects. This review categorizes the reported inorganic nanoflowers into four groups based on their composition and structure: metal, metal oxide, alloy, and other nanoflowers, including silica, metal-metal oxide, core-shell, doped, coated, nitride, sulfide, phosphide, selenide, and telluride nanoflowers. The review thoroughly discusses the preparation methods, conditions for morphology and size control, mechanisms, characteristics, and potential applications of these nanoflowers, aiming to facilitate future research and promote highly effective and synergistic applications in various fields.

High-Yield Gold Nanohydrangeas on Three-Dimensional Carbon Nanotube Foams for Surface-Enhanced Raman Scattering Sensors

Recently, carbon nanomaterial-supported plasmonic nanocrystals used as high-performance surface-enhanced Raman scattering (SERS) substrates have attracted increasing attention due to their ultra-high sensitivity of detection. However, most of the work focuses on the design of 2-D planar substrates with traditional plasmonic structures, such as nanoparticles, nanorods, nanowires, and so forth. Here, we report a novel strategy for the preparation of high-yield Au nanohydrangeas on three-dimensional porous polydopamine (PDA)/polyvinyl alcohol (PVA)/carbon nanotube (CNT) foams. The structures and growth mechanisms of these specific Au nanocrystals are systematically investigated. PDA plays the role of both a reducing agent as well as an anchoring site for Au nanohydrangeas' growth. We also show that the ratio of surfactant KBr to the gold precursor (HAuCl4) is key to obtain these structures in a manner of high production. Moreover, the substrate of the CNT foam-Au nanohydrangea hybrid can be employed as SERS sensors and can detect the analytes down to 10-9 M.

Fabrication of Adjustable Au/Carbon Hybrid Nanozymes with Photothermally Enhanced Peroxidase Activity and Ultra-sensitivity for Glutathione Detection

Au nanozymes are extensively researched for their photothermal effect and catalytic performance, but overcoming the inherent defects of poor dispersibility and thermal stability through complementary materials will expand their prospects for biological applications. Herein, several novel CAu nanozymes were fabricated by in situ reduction of chloroauric acid on hollow carbon nanospheres (HCNs). Through regulating the number of reductions, sesame ball-shaped CAu (sCAu) with highly dispersed Au nanoparticles and diversity-shaped CAu (dCAu) were obtained. The number and morphology of loaded Au nanoparticles, absorption spectra, and hydrophilicity of CAu nanozymes were systematically characterized to demonstrate the flexibility of this novel method. The high-efficiency peroxidase-like sCAu0.3 nanozyme with hyperthermia-activated property was then screened for later bio-application. It is worth mentioning that its photothermal-promoted peroxidase-like activity could be achieved under near-infrared laser irradiation. Moreover, sCAu0.3 could specifically achieve glutathione detection in human blood samples. This method will provide a protocol for the regulation of CAu nanozymes to adapt to bio-detection applications.

Rapid controllable synthesis of branched Au superparticles: formation mechanism of toggling the growth mode and their applications in optical broadband absorption

We develop a tunable, ultrafast (5 seconds), and mass-producible seed-mediated synthesis method to prepare branched Au superparticles consisting of multiple small Au island-like nanoparticles by a wet chemical route. We reveal and confirm the toggling formation mechanism of Au superparticles between the Frank-van der Merwe (FM) growth mode and the Volmer-Weber (VW) growth mode. The key factor of this special structure is the frequent toggling between the FM (layer by layer) growth mode and the VW (island) growth mode induced by 3-aminophenol, which is continuously absorbed on the surface of newborn Au nanoparticles, leading to a relatively high surface energy during the overall synthesis process, thus achieving an island on island growth. Such Au superparticles demonstrate broadband absorption from visible to near-infrared regions due to their multiple plasmonic coupling and hence they have important applications in sensors, photothermal conversion and therapy, etc. We also exhibit the excellent properties of Au superparticles with different morphologies, such as NIR-II photothermal conversion and therapy and SERS detection. The photothermal conversion efficiency under 1064 nm laser irradiation was calculated to be as high as 62.6% and they exhibit robust photothermal therapy efficiency. This work provides insight into the growth mechanism of plasmonic superparticles and develops a broadband absorption material for highly efficient optical applications.

Near Infrared Light-to-Heat Conversion for Liquid-Phase Oxidation Reactions by Antimony-Doped Tin Oxide Nanocrystals

Effective utilization of the sunlight for chemical reactions is pivotal for dealing with the growing energy and environmental issues. So far, much effort has been focused on the development of semiconductor photocatalysts responsive to UV and visible light. However, the near infrared and infrared (NIR-IR) light occupying ∼50 % of the solar energy has usually been wasted because of the low photon energy insufficient for the band gap excitation. Antimony doping into SnO₂ (ATO) induces strong absorption due to the conduction band electrons in the NIR region. The absorbed light energy is eventually converted to heat via the interaction between hot electrons and phonons. This Concept highlights the photothermal effect of ATO nanocrystals (NCs) on liquid-phase oxidation reactions through the NIR light-to-heat conversion. Under NIR illumination even at an intensity of ∼0.5 sun, the reaction field temperature on the catalyst surface is raised 20-30 K above the bulk solution temperature, while the latter is maintained near the ambient temperature. In some reactions, this photothermal local heating engenders the enhancement of not only the catalytic activity and selectivity but also the regeneration of catalytically active sites. Further, the photocatalytic activity of semiconductors can be promoted. Finally, the conclusions and possible subjects in the future are summarized.

Multifunctional Plasmon-Tunable Au Nanostars and Their Applications in Highly Efficient Photothermal Inactivation and Ultra-Sensitive SERS Detection

The development and application in different fields of multifunctional plasmonic nanoparticles (NPs) have always been research hotspots. Herein, multi-tip Au nanostars (NSs) with an anisotropic structure were fabricated for the photothermal therapy (PTT) of bacteria and surface-enhanced Raman scattering (SERS) detection of pollutants. The size and localized surface plasmon resonance (LSPR) characteristics of Au NSs were adjusted by varying Au seed additions. In addition, photothermal conversion performance of Au NSs with various Au seed additions was evaluated. Photothermal conversion efficiency of Au NSs with optimal Au seed additions (50 μL) was as high as 28.75% under 808 nm laser irradiation, and the heat generated was sufficient to kill Staphylococcus aureus (S. aureus). Importantly, Au NSs also exhibited excellent SERS activity for the 4-mercaptobenzoic acid (4-MBA) probe molecule, and the local electromagnetic field distribution of Au NSs was explored through finite-difference time-domain (FDTD) simulation. As verified by experiments, Au NSs' SERS substrate could achieve a highly sensitive detection of a low concentration of potentially toxic pollutants such as methylene blue (MB) and bilirubin (BR). This work demonstrates a promising multifunctional nanoplatform with great potential for efficient photothermal inactivation and ultra-sensitive SERS detection.

Inorganic Nanoflowers—Synthetic Strategies and Physicochemical Properties for Biomedical Applications: A Review

Nanoflowers, which are flower-shaped nanomaterials, have attracted significant attention from scientists due to their unique morphologies, facile synthetic methods, and physicochemical properties such as a high surface-to-volume ratio, enhanced charge transfer and carrier immobility, and an increased surface reaction efficiency. Nanoflowers can be synthesized using inorganic or organic materials, or a combination of both (called a hybrid), and are mainly used for biomedical applications. Thus far, researchers have focused on hybrid nanoflowers and only a few studies on inorganic nanoflowers have been reported. For the first time in the literature, we have consolidated all the reports on the biomedical applications of inorganic nanoflowers in this review. Herein, we review some important inorganic nanoflowers, which have applications in antibacterial treatment, wound healing, combinatorial cancer therapy, drug delivery, and biosensors to detect diseased conditions such as diabetes, amyloidosis, and hydrogen peroxide poisoning. In addition, we discuss the recent advances in their biomedical applications and preparation methods. Finally, we provide a perspective on the current trends and potential future directions in nanoflower research. The development of inorganic nanoflowers for biomedical applications has been limited to date. Therefore, a diverse range of nanoflowers comprising inorganic elements and materials with composite structures must be synthesized using ecofriendly synthetic strategies.

Kinetics-Controlled Synthesis of Gold-Silver Nanosheets with Abundant in-Plane Cracking and Their Trimetallic Derivatives for Plasmon-Enhanced Catalysis

Controlled synthesis of two-dimensional noble metal nanomaterials with in-plane branching morphology has been of great research interest recently, which yet achieves limited success for AuAg-based nanocrystals. Herein, we report the...

Au Nanoflowers for Catalyzing and In Situ Surface-Enhanced Raman Spectroscopy Monitoring of the Dimerization of p-Aminothiophenol

In this work, we demonstrated a facile approach for fabrication of Au nanoflowers (Au NFs) using an amino-containing organosilane, 3-aminopropyltriethoxysilane (APTES), as a shape-directing agent. In this approach, the morphology of the Au particles evolved from sphere-like to flower-like with increasing the concentration of APTES, accompanied by a red shift in the localized surface plasmon resonance peak from 520 to 685 nm. It was identified that the addition of APTES is profitable to direct the preferential growth of the (111) plane of face-centered cubic gold and promote the formation of anisotropic Au NFs. The as-prepared Au NFs, with APTES on their surface, presented effective catalytic and surface-enhanced Raman scattering (SERS) performances, as evidenced by their applications in catalyzing the dimerization of p-aminothiophenol and monitoring the reaction process via in situ SERS analysis.

Condensed Clustered Iron Oxides for Ultrahigh Photothermal Conversion and In Vivo Multimodal Imaging

Magnetic iron oxide nanocrystals (MIONs) are established as potent theranostic nanoplatforms due to their biocompatibility and the multifunctionality of their spin-active atomic framework. Recent insights have also unveiled their attractive near-infrared photothermal properties, which are, however, limited by their low near-infrared absorbance, resulting in noncompetitive photothermal conversion efficiencies (PCEs). Herein, we report on the dramatically improved photothermal conversion of condensed clustered MIONs, reaching an ultrahigh PCE of 71% at 808 nm, surpassing the so-far MION-based photothermal agents and even benchmark near-infrared photothermal nanomaterials. Moreover, their surface passivation is achieved through a simple self-assembly process, securing high colloidal stability and structural integrity in complex biological media. The bifunctional polymeric canopy simultaneously provided binding sites for anchoring additional cargo, such as a strong near-infrared-absorbing and fluorescent dye, enabling in vivo optical and photoacoustic imaging in deep tissues, while the iron oxide core ensures detection by magnetic resonance imaging. In vitro studies also highlighted a synergy-amplified photothermal effect that significantly reduces the viability of A549 cancer cells upon 808 nm laser irradiation. Integration of such-previously elusive-photophysical properties with simple and cost-effective nanoengineering through self-assembly represents a significant step toward sophisticated nanotheranostics, with great potential in the field of nanomedicine.