Surface Regulation Towards Stimuli‐Responsive Luminescence of Ultrasmall Thiolated Gold Nanoparticles for Ratiometric Imaging

The surface chemistry of the ultrasmall thiolated gold nanoparticles (AuNPs, < 3.0 nm) plays key roles in both governing the intrinsic emission and establishing interfaces surrounded by various amine‐containing biomolecules in the biomedical applications such as imaging, targeting, and diagnostics. However, a fundamental understanding of the surface ligand's role in the stimuli‐responsive emissions of AuNPs toward the amine molecules is currently lacking. Here, through investigation of the thiolate surface and exotic amine structures, it is discovered that the nucleophilic amines tend to closely bind the electrophilic gold surface, generating a high‐energy stimuli‐responsive emission from the low‐energy intrinsically emitting AuNPs. Both the intrinsic and stimuli‐responsive emissions show a unique amine concentration‐dependent ratiometric pattern for quantitative assessments of important biogenic amines in the biological samples. This discovery opens a new pathway to the design of stimuli‐responsive AuNPs, and would promote more experimental and theoretical research on the application‐driven surface engineering for advanced biological applications.     

Improved Hydrogen Production of Au–Pt–CdS Hetero‐Nanostructures by Efficient Plasmon‐Induced Multipathway Electron Transfer

The design of new functional materials with excellent hydrogen production activity under visible‐light irradiation has critical significance for solving the energy crisis. A well‐controlled synthesis strategy is developed to prepare an Au–Pt–CdS hetero‐nanostructure, in which each component of Au, Pt, and CdS has direct contact with the other two materials; Pt is on the tips and a CdS layer along the sides of an Au nanotriangle (NT), which exhibits excellent photocatalytic activity for hydrogen production under light irradiation (λ > 420 nm). The sequential growth and surfactant‐dependent deposition produce the three‐component Au–Pt–CdS hybrids with the Au NT acting as core while Pt and CdS serve as a co‐shell. Due to the presence of the Au NT cores, the Au–Pt–CdS nanostructures possess highly enhanced light‐harvesting and strong local‐electric‐field enhancement. Moreover, the intimate and multi‐interface contact generates multiple electron‐transfer pathways (Au to CdS, CdS to Pt and Au to Pt) which guide photoexcited electrons to the co‐catalyst Pt for an efficient hydrogen reduction reaction. By evaluating the hydrogen production rate when aqueous Na₂SO₃–Na₂S solution is used as sacrificial agent, the Au–Pt–CdS hybrid exhibits excellent photocatalytic activity that is about 2.5 and 1.4 times larger than those of CdS/Pt and Au@CdS/Pt, respectively.     

A Universal Platform for Macromolecular Deliveryinto Cells Using Gold Nanoparticle Layers via the Photoporation Effect

Although promising, it is challenging to develop a simple and universal method for the high‐efficiency delivery of biomacromolecules into diverse cells. Here, a universal delivery platform based on gold nanoparticle layer (GNPL) surfaces is proposed. Upon laser irradiation, GNPL surfaces show such good photothermal properties that absorption of the laser energy causes a rapid increase in surface temperature, leading to enhanced membrane permeability of the cultured cells and the diffusion of macromolecules into the cytosol from the surrounding medium. The high‐efficiency delivery of different macromolecules such as dextran and plasmid DNA into different cell types is achieved, including hard‐to‐transfect mouse embryonic fibroblasts (mEFs) and human umbilical vein endothelial cells (HUVECs), while cell viability is well maintained under optimized irradiation conditions. The platform vastly outperforms the leading commercial reagent, Lipofectamine 2000, especially in transfecting hard‐to‐transfect cell lines (plasmid transfection efficiency: ≈53% vs ≈19% for mEFs and ≈44% vs ≈8% for HUVECs). Importantly, as the gold nanoparticles (GNPs) constituting the GNPL are firmly immobilized together, the potential cytotoxicity caused by endocytosis of GNPs is effectively avoided. This platform is reliable, efficient, and cost‐effective with high‐throughput and broad applicability across different cell types, opening up an innovative avenue for high‐efficiency intracellular delivery.     

Robust Superlubricity of Gold–Graphite Heterointerfaces

Noncommensurate 2D interfaces hold great promise toward low friction and nanoelectromechanical applications. For identical constituents, the crystals interlock at specific rotational configurations leading to high barriers for slide. In contrast, nonidentical constituents comprising different lattice parameters should enable robust superlubricity for all rotational configurations. This is however not the case for gold–graphite interfaces, as both theory and experiments show scaling behavior of the sliding force as a function of the interface contact area. By simulating the sliding force for gold–graphite interfaces, this work shows that the origin for high force barriers at special angular configurations is a result of commensurability between the moiré structure and the contact geometry. Consequently, this paper suggests new geometries that can potentially overcome such commensurability effects to enable robust superlubricity.     

Self‐Assembly of Mechanoplasmonic Bacterial Cellulose–Metal Nanoparticle Composites

Nanocomposites of metal nanoparticles (NPs) and bacterial nanocellulose (BC) enable fabrication of soft and biocompatible materials for optical, catalytic, electronic, and biomedical applications. Current BC–NP nanocomposites are typically prepared by in situ synthesis of the NPs or electrostatic adsorption of surface functionalized NPs, which limits possibilities to control and tune NP size, shape, concentration, and surface chemistry and influences the properties and performance of the materials. Here a self‐assembly strategy is described for fabrication of complex and well‐defined BC–NP composites using colloidal gold and silver NPs of different sizes, shapes, and concentrations. The self‐assembly process results in nanocomposites with distinct biophysical and optical properties. In addition to antibacterial materials and materials with excellent senor performance, materials with unique mechanoplasmonic properties are developed. The homogenous incorporation of plasmonic gold NPs in the BC enables extensive modulation of the optical properties by mechanical stimuli. Compression gives rise to near‐field coupling between adsorbed NPs, resulting in tunable spectral variations and enhanced broadband absorption that amplify both nonlinear optical and thermoplasmonic effects and enables novel biosensing strategies.     

Shape‐Controlled Synthesis of Polyhedral Nanocrystals and Their Facet‐Dependent Properties

Growth of inorganic polyhedral nanocrystals with excellent morphology control presents significant synthetic challenges, especially when the development of synthetic schemes to make nanocrystals with systematic shape evolution is desired. Nanocrystals with fine size and shape control facilitate formation of their self‐assembled packing structures and offer opportunities for examination of their facet‐dependent physical and chemical properties. In this Feature Article, recent advances in the synthesis of nanocrystals with systematic shape evolution are highlighted. The reaction conditions used to achieve this morphology change offer insights into the growth mechanisms of nanocrystals. A novel class of polyhedral core–shell heterostructures fabricated using structurally well‐defined nanocrystal cores is also presented. Facet‐dependent photocatalytic activity, molecular adsorption, and catalytic and electrical properties of nanocrystals have been examined and are discussed. Nanomaterials with enhanced properties and functionality may be obtained through continuous efforts in the synthesis of nanocrystals with well‐defined structures and investigation of their plane‐selective properties.     

Concentrations of native and gold defects in HgCdTe from first principles calculations

We have studied the defect formation energies of the various native (vacancies, interstitials, and antisites) and Au defects in Hg_1−xCd_xTe using density functional-based total energy calculations with ultrasoft pseudo-potentials. These studies are important for infrared (IR) detection technology where the device performance can be severely degraded because of defects. To calculate formation energies, we modeled the neutral and charged defects using supercells containing 64 atoms. From the formation energies, we have determined the defect concentrations as a function of stoichiometry and temperature. We find the prevalent neutral defects to be Au at the Hg site (Au_Hg ), Hg vacancies (V_Hg ), and Te antisites (Te_Hg ). We have also explicitly studied charged defects and have found Te _Hg ²⁺ , Au _Hg ¹⁻ , V _Hg ¹⁻ , V _Hg ²⁻ , and V _Te ²⁺ to have low formation energies. We have identified Au_Hg to be the prevalent Au defect, having concentrations several orders of magnitude greater than the other Au defects. We find that the charge state of V_Hg is primarily (1−) or (2−) depending on the electronic chemical potential.     

Controlled Folding of 2D Au–Polymer Brush Composites into 3D Microstructures

Microscale, quasi‐2D Au–polymer brush composite objects are fabricated by a versatile, controllable process based on microcontact printing followed by brush growth and etching of the substrate. These objects fold into 3D microstructures in response to a stimulus: crosslinked poly(glycidyl methacrylate) (PGMA) brushes fold on immersion in MeOH, and poly(methacryloxyethyl trimethylammonium chloride) (PMETAC) brushes fold on addition of salt. Microcages and microcontainers are fabricated. A multistep microcontact printing process is also used to create sheets of Au–PGMA bilayer lines linked by a PGMA film, which fold into cylindrical tubes. The bending of these objects can be predicted, and hence predefined during the synthesis process by controlling the parameters of the gold layer, and of the polymer brush.     

基于介电泳机理的金纳米颗粒传感器装配方法

研究了一种基于介电泳机理的金纳米颗粒传感器装配方法。在分析介电泳工作原理的基础上,利用Comsol Multiphysics仿真软件,对平面微电极条件下所产生的空间电场进行了建模仿真,研究了金纳米粒子极化模型及相关介电泳频谱特性。设计加工了基于光刻标准工艺和引线键合技术的平面微电极阵列,构建了具有三维位移平台和视频监控装置的介电泳装配实验平台。以250nm金颗粒为实验对象,在理论分析基础上,完成了在微电极阵列上的介电泳组装实验研究,并通过电特性测量验证了组装结果。实验结果表明:金纳米颗粒的介电泳组装效果与介质溶液的电导率、电场频率和幅度、金纳米粒子浓度、电极间隙及作用时间有关,在适宜的条件下,采用介电泳技术可实现对金纳米颗粒的有效操控和纳米器件装配,该方法为纳米传感器的制造提供了一种有效途径。