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.     

Optofluidic Platform for Real‐Time Monitoring of Live Cell Secretory Activities Using Fano Resonance in Gold Nanoslits

An optofluidic platform for real‐time monitoring of live cell secretory activities is constructed via Fano resonance in a gold nanoslit array. Large‐area and highly sensitive gold nanoslits with a period of 500 nm are fabricated on polycarbonate films using the thermal‐annealed template‐stripping method. The coupling between gap plasmon resonance in the slits and surface plasmon polariton Bloch waves forms a sharp Fano resonance with intensity sensitivity greater than 11 000% per refractive index unit. The nanoslit array is integrated with a cell‐trapping microfluidic device to monitor dynamic secretion of matrix metalloproteinase 9 (MMP‐9) from human acute monocytic leukemia cells in situ. Upon continuous lipopolysaccharide (LPS) stimulation, MMP‐9 secretion is detected within 2 h due to ultrahigh surface sensitivity and close proximity of the sensor to the target cells. In addition to the advantage of detecting early cell responses, the sensor also allows interrogation of cell secretion dynamics. Furthermore, the average secretion per cell measured using our system well matches previous reports while it requires orders of magnitude less cells. The optofluidic platform may find applications in fundamental studies of cell functions and diagnostics based on secretion signals.     

Directing Gold Nanoparticles into Free‐Standing Honeycomb‐Like Ordered Mesoporous Superstructures

2D mesoporous materials fabricated via the assembly of nanoparticles (NPs) not only possess the unique properties of nanoscale building blocks but also manifest additional collective properties due to the interactions between NPs. In this work, reported is a facile and designable way to prepare free‐standing 2D mesoporous gold (Au) superstructures with a honeycomb‐like configuration. During the fabrication process, Au NPs with an average diameter of 5.0 nm are assembled into a superlattice film on a diethylene glycol substrate. Then, a subsequent thermal treatment at 180 °C induces NP attachment, forming the honeycomb‐like ordered mesoporous Au superstructures. Each individual NP connects with three neighboring NPs in the adjacent layer to form a tetrahedron‐based framework. Mesopores confined in the superstructure have a uniform size of 3.5 nm and are arranged in an ordered hexagonal array. The metallic bonding between Au NPs increases the structural stability of architected superstructures, allowing them to be easily transferred to various substrates. In addition, electron energy‐loss spectroscopy experiments and 3D finite‐difference time‐domain simulations reveal that electric field enhancement occurs at the confined mesopores when the superstructures are excited by light, showing their potential in nano‐plasmonic applications.     

Single-layer graphene-based surface plasmon resonance sensor with dynamic evanescent field enhancement for biomarker study

ABSTRACT

In this work, we have developed a kind of single-layer graphene-based surface plasmon resonance (SLG-SPR) biosensor to detect C-reactive protein (CRP) and Prostate-specific antigen (PSA). In the experiment of testing CPR, the results obtained revealed that the changes in resonance wavelength of SLG-SPR biosensors are higher than that of the gold-film based SPR (Au-SPR) biosensors. Moreover, for the experiment of testing PSA, due to the dynamic evanescent field enhancement produced by a strong electric field coupling between the localized SPR (LSPR) of AuNPs and SPR of single-layer graphene-based film (SLG-film) that further amplify the evanescent field signal. We verified the SLG-SPR biosensors exhibited higher sensitivity than the Au-SPR biosensors and the SLG-SPR biosensor exceeded the traditional biosensor detection limit. Accordingly, the SLG-SPR biosensor based on dynamic optical enhancement can realize high sensitivity detection of low concentration biomarkers and can be applied to most of the trace biomarkers in theory.     

Dominance of Plasmonic Resonant Energy Transfer over Direct Electron Transfer in Substantially Enhanced Water Oxidation Activity of BiVO4 by Shape‐Controlled Au Nanoparticles

The performance of plasmonic Au nanostructure/metal oxide heterointerface shows great promise in enhancing photoactivity, due to its ability to confine light to the small volume inside the semiconductor and modify the interfacial electronic band structure. While the shape control of Au nanoparticles (NPs) is crucial for moderate bandgap semiconductors, because plasmonic resonance by interband excitations overlaps above the absorption edge of semiconductors, its critical role in water splitting is still not fully understood. Here, first, the plasmonic effects of shape‐controlled Au NPs on bismuth vanadate (BiVO₄) are studied, and a largely enhanced photoactivity of BiVO₄ is reported by introducing the octahedral Au NPs. The octahedral Au NP/BiVO₄ achieves 2.4 mA cm^?2 at the 1.23 V versus reversible hydrogen electrode, which is the threefold enhancement compared to BiVO₄. It is the highest value among the previously reported plasmonic Au NPs/BiVO₄. Improved photoactivity is attributed to the localized surface plasmon resonance; direct electron transfer (DET), plasmonic resonant energy transfer (PRET). The PRET can be stressed over DET when considering the moderate bandgap semiconductor. Enhanced water oxidation induced by the shape‐controlled Au NPs is applicable to moderate semiconductors, and shows a systematic study to explore new efficient plasmonic solar water splitting cells.     

LSPR生物传感器在临床医学检测应用中的研究进展

肿瘤标志物在人类医学及恶性肿瘤的早期诊断、治疗监测及预后评估方面具有重要作用。目前血清肿瘤标志物的检测方法主要有放射免疫法(RIA),酶联免疫吸附法(ELISA)及化学发光免疫法(CLEIA)等,这些方法各自存在放射性污染、操作繁琐、检测时间长、价格昂贵等缺点,限制了血清肿瘤标志物在临床医学及肿瘤检测中的应用。新近出现的基于局域表面等离子体共振效应(LSPR)的传感器因在生物医学检测领域极具优势而成为研究热点。基于局域表面等离子体共振效应的生物传感器,利用贵金属纳米结构对周围介质环境变化敏感的基本原理,可将生物分子吸附引发的金属纳米颗粒外界介质折射率的改变转化为可测量的LSPR峰值吸收波长有规律的移动以实现对传感器表面样品的检测,具备检测灵敏度高、特异性好、免标记、设备便携、成本低的优点,具备临床检测潜力。但到目前为止,利用此传感器检测与疾病及肿瘤相关的肿瘤标志物的类似研究报道较少。在本文中,我们针对LSPR生物传感器的传感原理、国内外的研究进展以及我们在此方面的主要研究成果进行了综述。

     

Gold/WO<Subscript>3</Subscript> nanocomposite photoanodes for plasmonic solar water splitting

A facile electron-charging and reducing method was developed to prepare Au/WO₃ nanocomposites for plasmonic solar water splitting. The preparation method involved a charging step in which electrons were charged into WO₃ under negative bias, and a subsequent reducing step in which the stored electrons were used to reductively deposit Au on the surface of WO₃. The electron-charged WO₃ (c-WO₃) exhibited tunable reducibility that could be easily controlled by varying the charging parameters, and this property makes this method a universal strategy to prepare metal/WO₃ composites. The obtained Au/WO₃ nanocomposite showed greatly improved photoactivity toward the oxygen evolution reaction (OER) when compared with WO₃. After Au decoration, the OER photocurrent was improved by a percentage of over 80% at low potentials (<0.6 V vs. SCE), and by a percentage of over 30% at high potentials (>1.0 V vs. SCE). Oxygen evolution measurements were performed to quantitatively determine the Faraday efficiency for OER, which reflected the amount of photocurrent consumed by water splitting. The Faraday efficiency for OER was improved from 74% at the WO₃ photoanode to 94% at the Au-8/WO₃ composite photoanode, and this is the first direct evidence that the Au decoration significantly restrained the anodic side reactions and enhanced the photoelectrochemical (PEC) OER efficiency. The high photoactivity of the composite photoanode toward OER was ascribed to the plasmon resonance energy transfer (PRET) enhancement and the catalytic enhancement of Au nanoparticles (NPs).

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