Shape-dependent thermo-plasmonic effect of nanoporous gold at the nanoscale for ultrasensitive heat-mediated remote actuation

Multifunctional SERS Substrate for Simultaneous Detection of Multiple Contaminants and Photothermal Removal of Pathogenic Bacteria

In this work, a boric-acid-modified Fe3O4@Au@BA-MOF composite material as a multifunctional SERS substrate was ingeniously constructed for detecting both pathogens and antibiotics as well as photothermally inactivating the pathogens. Through improving the dispersity and stability of gold nanoparticles (Au NPs), leveraging the specificity of boric acid (BA) groups in recognizing cis-diol structures, and the ability of SERS technology to provide unique fingerprint spectra of targets, the sensitive and stable detection of pathogens and antibiotics was achieved. Compared with Au NPs and Fe3O4@Au, the SERS enhancement factor of Fe3O4@Au@BA-MOF was 4.31 × 106, which was about 400 times and 16 times higher than the former two, respectively. Among the existing work, the limit of detection for pathogens was lower or comparable, and it exhibited good stability, maintaining consistent performance for 23 days. Additionally, this substrate achieved efficient photothermal inactivation of pathogens under both near-infrared light and natural light excitation. Within 8 min of near-infrared light irradiation, the bactericidal rates for Staphylococcus aureus and Escherichia coli reach 100% and 99.3%, respectively.

Mesoporous carbon hemispheres integrated with Fe-Gd nanoparticles for potential MR/PA imaging-guided photothermal therapy

Asymmetric carbon has emerged as an important material to enrich morphologies as well as enhance functions for bioapplications. Here, asymmetric mesoporous carbon hemispheres (CHS) integrated with γ-Fe2O3 and GdPO4 (Fe-Gd) nanoparticles are proposed and prepared for potential imaging-guided photothermal therapy (PTT). Interestingly, Fe-Gd/CHS contributes to an almost 1.5 times enhancement in light harvesting and photothermal conversion efficiency as compared with its corresponding spherical analogue. The possible underlying mechanism is discussed in view of the unique asymmetric structure-featured carbon. Further identification of the inherited photoacoustic (PA) and magnetic resonance (MR) imaging properties leads to the consequent in vivo evaluation of its imaging and PTT performances, which demonstrates its capability as a function-integrated system for potential theranostics.

Incorporating Chaotropic/Kosmotropic Chemistries onto Plasmonic Nanoheater to Boost Steam Generation Beyond its Photothermal Property

Photothermal steam generation promises decentralized water purification, but current methods suffer from slow water evaporation even at high photothermal efficiency of ≈98%. This drawback arises from the high latent heat of vaporization that is required to overcome the strong and extensive hydrogen bonding network in water for steam generation. Here, light-to-vapor conversion is boosted by incorporating chaotropic/kosmotropic chemistries onto plasmonic nanoheater to manipulate water intermolecular network at the point-of-heating. The chaotropic-plasmonic nanoheater affords rapid light-to-vapor conversion (2.79 kg m-2  h-1  kW-1 ) at ≈83% efficiency, with the steam generation rate up to 6-fold better than kosmotropic platforms or emerging photothermal designs. Notably, the chaotropic-plasmonic nanoheater also lowers the enthalpy of water vaporization by 1.6-fold when compared to bulk water, signifying that a correspondingly higher amount of steam can be generated with the same energy input. Simulation studies unveil chaotropic surface chemistry is crucial to disrupt water hydrogen bonding network and suppress the energy barrier for water evaporation. Using the chaotropic-plasmonic nanoheater, organic-polluted water is purified at ≈100% efficiency, a feat otherwise challenging in conventional treatments. This study offers a unique chemistry approach to boost light-driven steam generation beyond a material photothermal property.

Photothermal Nanomaterials: A Powerful Light-to-Heat Converter

All forms of energy follow the law of conservation of energy, by which they can be neither created nor destroyed. Light-to-heat conversion as a traditional yet constantly evolving means of converting light into thermal energy has been of enduring appeal to researchers and the public. With the continuous development of advanced nanotechnologies, a variety of photothermal nanomaterials have been endowed with excellent light harvesting and photothermal conversion capabilities for exploring fascinating and prospective applications. Herein we review the latest progresses on photothermal nanomaterials, with a focus on their underlying mechanisms as powerful light-to-heat converters. We present an extensive catalogue of nanostructured photothermal materials, including metallic/semiconductor structures, carbon materials, organic polymers, and two-dimensional materials. The proper material selection and rational structural design for improving the photothermal performance are then discussed. We also provide a representative overview of the latest techniques for probing photothermally generated heat at the nanoscale. We finally review the recent significant developments of photothermal applications and give a brief outlook on the current challenges and future directions of photothermal nanomaterials.

Nanoporous Gold Ring-Integrated Photothermal Intraocular Lens for Active Prevention of Posterior Capsular Opacification

Posterior capsular opacification (PCO) is the leading complication after cataract surgery, and is mainly induced by the proliferation and migration of residual lens epithelial cells (LECs). Although numerous attempts have been made to reduce the incidence of PCO, this complication remains a critical challenge in postoperative visual recovery. This study aims to report a functionalized intraocular lens (R-IOL) with a region-confined photothermal effect for the active prevention of PCO after implantation. The outer rim of R-IOL (non-optical area) is decorated with a nanoporous gold (NPG) ring, which can effectively eliminate the LECs around R-IOL, ultimately inhibiting the migration of LECs from the periphery to the visual axis center in the initial stage, and preventing the subsequent PCO. Furthermore, the mechanism of LECs elimination can be attributed to apoptosis induced by mild photothermal therapy. After in vivo implantation for 30 days, PCO is rarely observed in the R-IOL group, whereas the considerably higher incidence of PCO (75%) is found in the pristine IOL (P-IOL) group. The region-confined photothermal effect based on NPG not only provides an active strategy to effectively prevent PCO, but also introduces new opportunities for the treatment of undesirable hyperplasia.

Complete surface reconstruction of nanoporous gold during CH4 pyrolysis

The catalytic activity and selectivity of metallic nanocatalysts can be controlled using physical and chemical methods to tune the exposed crystal facets. Nanoporous metals (NPMs) have unique bicontinuous structures, large specific surface areas, and high catalytic activities, and are widely used in the field of heterogeneous catalysis. However, owing to the complex surface topography of NPMs, it is difficult to regulate their exposed crystal facets over a large area. In this study, nanoporous gold (NPG) is successfully prepared with a complete regular surface that exposes the Au {111} and {100} facets through a methane pyrolysis reaction. The results of high-spatial and -temporal resolution in situ experiments and theoretical calculations indicate that C species significantly weaken the interaction between surface Au atoms with low coordination numbers and their surrounding atoms, which results in the migration and recombination of surface atoms. This research fundamentally clarifies the reconstruction mechanism of porous materials during methane pyrolysis and provides a theoretical basis for the targeted regulation of exposed NPM surfaces.

Materials as Machines

Machines are systems that harness input power to extend or advance function. Fundamentally, machines are based on the integration of materials with mechanisms to accomplish tasks-such as generating motion or lifting an object. An emerging research paradigm is the design, synthesis, and integration of responsive materials within or as machines. Herein, a particular focus is the integration of responsive materials to enable robotic (machine) functions such as gripping, lifting, or motility (walking, crawling, swimming, and flying). Key functional considerations of responsive materials in machine implementations are response time, cyclability (frequency and ruggedness), sizing, payload capacity, amenability to mechanical programming, performance in extreme environments, and autonomy. This review summarizes the material transformation mechanisms, mechanical design, and robotic integration of responsive materials including shape memory alloys (SMAs), piezoelectrics, dielectric elastomer actuators (DEAs), ionic electroactive polymers (IEAPs), pneumatics and hydraulics systems, shape memory polymers (SMPs), hydrogels, and liquid crystalline elastomers (LCEs) and networks (LCNs). Structural and geometrical fabrication of these materials as wires, coils, films, tubes, cones, unimorphs, bimorphs, and printed elements enables differentiated mechanical responses and consistently enables and extends functional use.

Plasmonic nanosponges filled with silicon for enhanced white light emission

Plasmonic nanosponges are a powerful platform for various nanophotonic applications owing to extremely high local field enhancement in metallic nanopores. The filling of the nanopores with high-refractive index semiconductors (e.g. Si, Ge, GaP, etc.) opens up opportunities for the enhancement of nonlinear effects in these materials. However, this task remains challenging due to the lack of knowledge on the integration process of metal and high-index semiconductor components in such nanoobjects. Here, we investigate metal-dielectric nanoparticles fabricated from bilayer Si/Au films by the laser printing technique via a combination of theoretical and experimental methods. We reveal that these hybrid nanoparticles represent the Au sponge-like nanostructure filled with Si nanocrystallites. We also demonstrate that the Au net provides strong near-field enhancement in the Si grains increasing the white light photoluminescence in the hybrid nanostructures compared to uniform Si nanoparticles. These results pave the way for engineering the internal structure of the sponge-like hybrid nanoparticles possessing white light luminescence and control of their optical properties on demand.

Plasmonic-induced overgrowth of amorphous molybdenum sulfide on nanoporous gold: An ambient synthesis method of hybrid nanoparticles with enhanced electrocatalytic activity

Hybrid materials of earth abundant transition metal dichalcogenides and noble metal nanoparticles, such as molybdenum sulfide (MoS_x) and gold nanoparticles, exhibit synergistic effects that can enhance electrocatalytic reactions. However, most current hybrid MoS_x-gold synthesis requires an energy intensive heat source of >500 °C or chemical plating to achieve deposition of MoS_x on the gold surface. Herein, we demonstrate the direct overgrowth of MoS_x over colloidal nanoporous gold (NPG), conducted feasibly under ambient conditions, to form hybrid particles with enhanced electrocatalytic performance toward hydrogen evolution reaction. Our strategy exploits the localized surface plasmon resonance-mediated photothermal heating of NPG to achieve >230 °C surface temperature, which induces the decomposition of the (NH₄)₂MoS₄ precursor and direct overgrowth of MoS_x over NPG. By tuning the concentration ratio between the precursor and NPG, the amount of MoS_x particles deposited can be systematically controlled from 0.5% to 2% of the Mo/(Au + Mo) ratio. Importantly, we find that the hybrid particles exhibit higher bridging and an apical S to terminal S atomic ratio than pure molybdenum sulfide, which gives rise to their enhanced electrocatalytic performance for hydrogen evolution reaction. We demonstrate that hybrid MoS_x-NPG exhibits >30 mV lower onset potential and a 1.7-fold lower Tafel slope as compared to pure MoS_x. Our methodology provides an energy- and cost-efficient synthesis pathway, which can be extended to the synthesis of various functional hybrid structures with unique properties for catalysis and sensing applications.