Uniform Gold Nanostructure Formation via Weakly Adsorbed Gold Films and Thermal Annealing for Reliable Localized Surface Plasmon Resonance-Based Detection of DNase-I

Deoxyribonuclease-I (DNase-I), a representative endonuclease, is an important biomarker for the diagnosis of infectious diseases and cancer progression. However, enzymatic activity decreases rapidly ex vivo, which highlights the need for precise on-site detection of DNase-I. Here, a localized surface plasmon resonance (LSPR) biosensor that enables the simple and rapid detection of DNase-I is reported. Moreover, a novel technique named electrochemical deposition and mild thermal annealing (EDMIT) is applied to overcome signal variations. By taking advantage of the low adhesion of gold clusters on indium tin oxide substrates, both the uniformity and sphericity of gold nanoparticles are increased under mild thermal annealing conditions via coalescence and Ostwald ripening. This ultimately results in an approximately 15-fold decrease in LSPR signal variations. The linear range of the fabricated sensor is 20–1000 ng mL⁻¹ with a limit of detection (LOD) of 127.25 pg mL⁻¹, as demonstrated by spectral absorbance analyses. The fabricated LSPR sensor stably measured DNase-I concentrations from samples collected from both an inflammatory bowel disease (IBD) mouse model, as well as human patients with severe COVID-19 symptoms. Therefore, the proposed LSPR sensor fabricated via the EDMIT method can be used for early diagnosis of other infectious diseases.     

Simple and Rapid High‐Yield Synthesis and Size Sorting of Multibranched Hollow Gold Nanoparticles with Highly Tunable NIR Plasmon Resonances

Branched gold nanoparticles with sharp tips are considered excellent candidates for sensing and field enhancement applications. Here, a rapid and simple synthesis strategy is presented that generates highly branched gold nanoparticles with hollow cores and a ca.100% yield through a simple one‐pot seedless reaction at room temperature in the presence of Triton X‐100. It is shown that multibranched hollow gold nanoparticles of tunable dimensions, branch density and branch length can be obtained by adjusting the concentrations of the reactants. Insights into the formation mechanism point toward an aggregative type of growth involving hollow core formation first, and branching thereafter. The pronounced near‐infrared (NIR) plasmon band of the nanoparticles is due to the combined contribution from hollowness and branching, and can be tuned over a wide range (≈700–2000 nm). It is also demonstrated that the high environmental sensitivity of colloidal dispersions based on multibranched hollow gold nanoparticles can be boosted even further by separating the nanoparticles into fractions of given sizes and improved monodispersity by means of a glycerol density gradient. The possibility to obtain highly monodisperse multibranched hollow gold nanoparticles with predictable dimensions (50–300 nm) and branching and, therefore, tailored NIR plasmonic properties, highlights their potential for theranostic applications.     

High Spatial Resolution Mapping of Localized Surface Plasmon Resonances in Single Gallium Nanoparticles

Plasmonics has emerged as an attractive field driving the development of optical systems in order to control and exploit light–matter interactions. The increasing interest around plasmonic systems is pushing the research of alternative plasmonic materials, spreading the operability range from IR to UV. Within this context, gallium appears as an ideal candidate, potentially active within a broad spectral range (UV–VIS–IR), whose optical properties are scarcely reported. Importantly, the smart design of active plasmonic materials requires their characterization at high spatial and spectral resolution to access the optical fingerprint of individual nanostructures, attainable by transmission electron microscopy techniques (i.e., by means of electron energy‐loss spectroscopy, EELS). Therefore, the optical response of individual Ga nanoparticles (NPs) by means of EELS measurements is analyzed, in order to spread the understanding of the plasmonic response of Ga NPs. The results show that single Ga NPs may support several plasmon modes, whose nature is extensively discussed.     

真空镀膜法制备纳米铝颗粒膜及其表面等离激元共振特性研究

采用直流磁控溅射镀膜技术制备了纳米铝颗粒膜,并尝试通过两种方式获得纳米铝的表面等离激元共振吸收峰,一种是先在室温石英基底上沉积纳米铝,再进行真空退火;另一种是在热石英基底上沉积纳米铝。用透射电镜和扫描电子显微镜、X-射线光电子谱、紫外-可见吸收光谱表征了样品的形貌和晶态结构、成份和吸收特性。采用比对的方式,研究了基底温度、沉积时间对两种方法制备的纳米铝表面等离激元共振的影响。结果表明,先沉积纳米铝,再进行真空退火,不能获得表面等离激元共振吸收峰,而在热基底上沉积纳米铝,可以获得明显的表面等离激元共振吸收峰。通过调控沉积时间和沉积温度实现了纳米铝表面等离激元共振峰从紫外光区到可见光区的可控移动。而且,研究发现对于平均厚度大于3 nm的纳米铝薄膜,由于纳米铝氧化具有自限性,其表面等离激元共振特性在空气中稳定且主要取决于纳米铝颗粒的团聚度。本研究对理解纳米铝表面等离激元共振特性及其应用具有指导意义。     

Reproducible Enhancement of Fluorescence by Bimetal Mediated Surface Plasmon Coupled Emission for Highly Sensitive Quantitative Diagnosis of Double‐Stranded DNA

Plasmonic enhancement of fluorescence from SYBR Green I conjugated with a double‐stranded DNA (dsDNA) amplicon is demonstrated on polymerase chain reaction (PCR) products. Theoretical computation leads to use of the bimetallic (Au 2 nm–Ag 50 nm) surface plasmons due to larger local fields (higher quality factors) than monometallic (Ag or Au) ones at both dye excitation and emission wavelengths simultaneously, optimizing fluorescence enhancement with surface plasmon coupled emission (SPCE). Two kinds of reverse Kretschmann configurations are used, which favor, in signal‐to‐noise ratio, a fluorescence assay that uses optically dense buffer such as blood plasma. The fluorescence enhancement (12.9 fold at maximum) with remarkably high reproducibility (coefficient of variation (CV) < 1%) is experimentally demonstrated. This facilitates credible quantitation of enhanced fluorescence, however unlikely to obtain by localized surface plasmons. The plasmon‐induced optical gain of 46 dB due to SPCE‐active dye molecules is also estimated. The fluorescence enhancement technologies with PCR enables LOD of the dsDNA template concentration of ≈400 fg µL^?1 (CV < 1%), the lowest ever reported in DNA fluorescence assay to date. SPCE also reduces photobleaching significantly. These technologies can be extended for a highly reproducible and sufficiently sensitive fluorescence assay with small volumes of analytes in multiplexed diagnostics.     

Growth of Silver Nanowires from Controlled Silver Chloride Seeds and Their Application for Fluorescence Enhancement Based on Localized Surface Plasmon Resonance

A “Polyol” method has granted low‐cost and facile process‐controllability for silver‐nanowire (Ag‐NW) synthesis. Although homogenous and heterogeneous nucleation and growth during Ag‐NW synthesis are possible using polyol methods, heterogeneous nucleation and growth of Ag NW guarantees highly selective growth of nanostructures using silver chloride (AgCl) seeds, which provides a stable source of chloride ions (Cl?) and thermodynamic reversibility. In this paper, a microdroplet has been adopted to synthesize uniform AgCl seeds with different diameter that are used for seed‐mediated Ag‐NW synthesis. The concentration of two precursors (AgNO₃ and NaCl) in the droplets is modulated to produce different sizes of AgCl seeds, which determines the diameter and length of Ag NWs. The process of the seed‐mediated growth of Ag NWs has been monitored by observing the peak shift in the time‐resolved UV–vis extinction spectrum. Furthermore, the distinct plasmonic property of Ag NWs for transverse and longitudinal localized‐surface‐plasmon‐resonance (LSPR)‐mediated fluorescence enhancement is utilized. The high aspect ratio and sharp tips work as simple antennas that induce the enhanced fluorescence emission intensity of a fluorophore, which can be applied in the fields of biological tissue imaging and therapy.     

GSH、L-Cys和6-MP诱导纳米金聚集行为的分析与应用

利用纳米金的表面等离子共振吸收光谱研究了谷胱甘肽(GSH)、L半胱氨酸(L-Cys)和6-巯基嘌呤(6-MP)3种巯基化合物与纳米金作用的机理.结果表明,3种巯基化合物均能诱导纳米金聚集导致其表面等离子共振吸收峰红移.聚集后的纳米金对介质环境(如溶液极性)的变化较敏感,其吸收峰随着加入分析物的极性变化有规律地红移,并且吸光度也线性下降.可根据波长的红移或吸光度变化确立定量关系,可望用于分析对象的定量检测.     

Controllable Fabrication of Au Nanocups by Confined‐Space Thermal Dewetting for OCT Imaging

Here, this study reports a novel confined‐space thermal dewetting strategy for the fabrication of Au nanocups with tunable diameter, height, and size of cup opening. The nanocup morphology is defined by the cup‐shaped void space created by a yolk–shell silica template that spontaneously takes an eccentric configuration during annealing. Thermal dewetting of Au, which is sandwiched between the yolk and shell, leads to the desired nanocup morphology. With strong scattering in near infrared, the Au nanocups exhibit superior efficiency as contrast agents for spectral‐domain optical coherence tomography imaging. This confined‐space thermal dewetting strategy is scalable and general, and can be potentially extended to the synthesis of novel anisotropic nanostructures of various compositions that are difficult to produce by conventional wet chemical or physical methods, thus opening up opportunities for many new applications.