Strong Localized Surface Plasmon Resonance Research Articles

Confined structure regulations of molybdenum oxides for efficient tumor photothermal therapy

Molybdenum oxide nanoparticles (NPs) with tunable plasmonic resonance in the near-infrared region display superior semiconducting features and photothermal properties, which are highly related to the crystalline and defective structures such as oxygen deficiencies. However, fundamental understanding on the structure-function relationship between crystalline/defective structures and photothermal properties is still unclear. To address this, herein, we have developed an “in-situ confined oxidation-reduction” strategy to regulate the defect features of molybdenum oxide NPs in the dual-mesoporous silica nanoreactor. Especially, the effects of crystalline structure/oxygen defects of molybdenum oxides on the photothermal performances were investigated by facilely tuning the amount of molybdenum resource and the reduction temperature. As a photothermal nanoagent, the optimal defective molybdenum oxide NPs encapsulated in PEGylated porous silica nanoreactor (designated as MoO3−x@PPSNs) exhibit excellent biological stability and strong localized surface plasmon resonance effect in near-infrared absorption range with the highest photothermal conversion efficiency up to 78.7% under 808 nm laser irradiation. More importantly, the remarkable photothermal effects of MoO3−xPPSNs were comprehensively demonstrated both in vitro and in vivo. Consequently, we envision that the plasmonic MoO3−x NPs in a biocompatible porous silica nano-reactor could be used as an efficient photothermal therapy agent for photothermal ablation of tumors.

A general scattering proximity immunoassay with the formation of dimer of gold nanoparticle

In this work, we structured a colorimetric ultrasensitive detection of carcinoembryonic antigen (CEA) based on a proximity hybridization-induced gold nanoparticles (Au NPs) dimers structure. Under the dark-field microscope, this method takes advantage of the distinctive and strong distance-relative localized surface plasmon resonance (LSPR) of Au NPs and their oriented assembly. DNA served as a medium showing wonderful flexibility to label antibody and Au NPs, and tune interparticle spacing as well. Two capture probes were formed by the integration of DNA labeled antibody (DNA1-Ab1 or DNA2-Ab2) and asymmetrically assembled DNA (DNA 3 or DNA 4)- Au NPs via partly hybridization between DNA sequences. In the presence of antigen, the reaction between target protein and capture probes could trigger the generation of immunocomplex which led to the proximity hybridization of the DNA1 and DNA2, and then change the distance of interparticle to form Au NP dimers and thus showed a different color under dark-field microscope. A limit of detection of 14.25 pg/mL was obtained for the detection of CEA, which indicated a promising sensing method in clinical diagnosis of protein biomarkers.

Nanoparticles: Untying the Gordian Knot in Conventional Computed Tomography Imaging

X-ray computed tomography (CT) imaging plays an essential role in disease diagnosis due to its noninvasive, painless mode and superior penetration depth. However, the resolution of the soft tissue ...

Selective Preparation of Mo2N and MoN with High Surface Area for Flexible SERS Sensing.

γ-Mo2N and δ-MoN are the two most important molybdenum nitrides, but controllable preparation of them with high surface area has not been achieved. Herein, we achieved selective preparation of γ-Mo2N and δ-MoN. The key factor for the selective preparation of γ-Mo2N and δ-MoN is to control the crystal phase of the precursor MoO3. In H2O and NH3 mixed gas, the α-MoO3 nanoribbons are nitridated to obtain γ-Mo2N single-crystal porous nanobelts, while the h-MoO3 prisms are nitrided to obtain δ-MoN hierarchical porous columns. The corrosion effect of H2O plays a key role in the formation of single-crystal porous structure. The γ-Mo2N flexible membrane composed of the single-crystal porous nanobelts exhibits strong localized surface plasmon resonance and surface enhanced Raman scattering effect, which show highly sensitive response to polychlorinated phenol.

Controlling mid-infrared plasmons in graphene nanostructures through post-fabrication chemical doping

Engineering the doping level in graphene nanostructures to yield controlled and intense localized surface plasmon resonance (LSPR) is fundamental for their practical use in applications such as molecular sensing for point of care or environmental monitoring. In this work, we experimentally study how chemical doping of graphene nanostructures using ethylene amines affects their mid-infrared plasmonic response following the induced change in electrical transport properties. Combining post-fabrication silanization and amine doping allows to prepare the surface to support a strong LSPR response at zero bias. These findings pave the way to design highly doped graphene LSPR surfaces for infrared sensors operating in real environments.

Metal-Nitride nanocomposite thin film of nanomaze-like Cu embedded in TiN

Nanocomposite thin film has attracted tremendous research interests, owing to its great potential to achieve multifunctionality, property enhancement and tuning, as well as new physical phenomenon exploration. In this work, a new nanocomposite thin film of Cu-TiN has been designed and fabricated by pulsed laser deposition (PLD) method. The metal-nitride film exhibits interesting structure of nanomaze-like Cu nanostructure embedding into TiN matrix without apparent inter-diffusion between Cu and TiN. Such Cu-TiN nanocomposite thin film shows excellent crystallinity and highly textured growth for both Cu and TiN phases. Furthermore, interesting optical properties are obtained, for example, the real part (ε′) of the complex dielectric permittivity starts to show negative value from the wavelength of ∽450 nm, compared to the pure TiN film of ∽500 nm. In addition, strong localized surface plasmon resonance (LSPR) is observed at ∽400 nm for the Cu-TiN film, which suggests its great potential for optical device applications.

Improved visible-light driven photocatalysis by loading Au onto C3N4 nanorods for degradation of RhB and reduction of CO2

In this work, a solution-assembly technique was adopted to compose the g-C3N4 (CN) nanorods (CN1, CN2 and CN3) with a desired microstructure. Subsequently, different amounts of Au nanoparticles (NPs) with sizes ~10 nm were loaded on CN2 nanorods by an in-site reduction approach, thereby a series of plasmonic photocatalyst (CN2-A1, CN2-A2 and CN2-A3) were fabricated. The activities were investigated by photodegrading Rhodamine B (RhB) and photoreducing CO2 into CO with the irradiation of visible light, respectively. And the degradation rates of RhB over CN2-A2 photocatalyst were 97.28% in 80 min, which was 1.45 times higher than that of pure CN2 (66.90%). Moreover, without any sacrificial agents, the reduction yields of CO2 into CO by CN2-A2 photocatalyst was 3.11 μmol/g in 4 h, that was 2.46 times higher than that of CN2 (1.26 μmol/g). The improved photocatalytic performance was owning to the stronger localized surface plasmon resonance (LSPR) effect, which not only increased the utilization efficiency of visible light, but also sped up the formation and separation of photo-induced carriers. In addition, a potential charge transfer mechanism was tentatively proposed on account of as-obtained test dates.

Modulating the photoelectrochemical response of titanium dioxide (TiO2) photoelectrodes using gold (Au) nanoparticles excited at different wavelengths

Gold (Au) nanoparticles (NPs) have been widely used to modulate the photoelectrochemical current of TiO2 photoelectrodes in energy conversion and sensing systems. Understanding the different mechanisms responsible for photocurrent modulation at different frequencies is important for building optimized photoelectrochemical systems. Herein, we investigated the photocurrent magnitude at different excitation wavelengths by varying Au NP concentration at the photoelectrode surface. Under UV illumination, increasing the surface loading of Au NPs initially increased the photocurrent, and above a threshold loading level, decreased the measured photocurrent. However, under visible light excitation, increasing the Au NP surface density resulted in a steady increase in photocurrent. Mott-Schottky measurements, incident photon to current conversion efficiency measurements, and electrochemical impedance spectroscopy were used to understand the mechanisms responsible for these different observations. It was found that both current loss – due to reduced light absorption by TiO2 – and gain – due to direct charge transfer between Au and TiO2 NPs were possible under UV light. Under visible light illumination, strong light absorption and localized surface plasmon resonance of Au NPs and negligible light absorption by TiO2 NPs led to signal gain at varying Au NP surface concentrations. This bimodal signal modulation was further demonstrated in the context of biosensing using Au NP-labeled DNA barcodes, optically excited at different wavelengths. This study allows photoelectrochemical systems to be engineered for programmable signal-off, signal-on, or ratiometric biosensing combining the former sensing modes.

Single-Nanoparticle Coulometry Method with High Sensitivity and High Throughput to Study the Electrochemical Activity and Oscillation of Single Nanocatalysts.

To explore nanocatalysts with high electro-catalytic performance and less loading of precious metals, efforts have been made to develop electrochemical methods with high spatial resolution at the single nanoparticle level. Herein, a highly sensitive single-nanoparticle coulometry method is successfully developed to study the electrochemical activity and oscillation of single PtTe nanocatalysts. Based on microbattery reactions involving the formic acid electro-oxidation and the deposition of Ag on the single PtTe nanocatalyst surface, this method enables the transition from the undetectable sub-fA electric signal of the formic acid electro-oxidation into strong localized surface plasmon resonance scattering signal of Ag detected by dark-field microscopy. The lowest limiting current for a single nanocatalyst is found to be as low as 25.8 aA. Different trends of activity versus the formic acid concentration and types of activity of the single nanocatalyst have been discovered. Unveiled frequency-amplitude graph shows that the two electrochemical oscillation modes of low frequency with high amplitude and vice versa coexist in a single PtTe nanocatalyst, indicating the abundantly smooth surfaces and defects of nanocatalysts. This conducted study will open up the new avenue for further behavioral and mechanistic investigation of more types of nanocatalysts in the electrochemistry community.

Bioinspired protein corona strategy enhanced biocompatibility of Ag-Hybrid hollow Au nanoshells for surface-enhanced Raman scattering imaging and on-demand activation tumor-phototherapy

Silver-based hybrid nanoprobes for surface-enhanced Raman scattering (SERS) imaging show their tremendous potential for precise biological detection and mediated phototherapy. However, the severe toxicity induced by Ag to normal mammalian cells hinders its further application. Herein, we presented a versatile bioinspired protein corona strategy through assembling bovine serum albumin (BSA) protected Raman tag DTTC-conjugated Ag-hybrid hollow Au nanoshells (hollow AgAu-DTTC-BSA), which their silver ion release and reactive oxygen species (ROS) generation are significantly suppressed, enabling no damage to normal cells and tissues, but can be reactivated on-demand under laser-irradiation at the tumor site. These nanoshells could also produce strong localized surface plasmon resonance for efficient-stable photothermal effect and enhanced SERS activity under laser irradiation, approved by both theoretical and experimental calculations. Furthermore, the biocompatible hollow AgAu-DTTC-BSA could detect both primary tumor tissues and tiny liver metastases (~0.18 mm) in orthotopic/subcutaneous CT26 colon tumor-bearing mice models. We also demonstrate their excellent therapeutic efficacy for colorectal solid neoplasms by accurate SERS imaging-guided photothermal therapy, simultaneously assisted with toxic Ag ion and ROS. These results suggest that hollow AgAu-DTTC-BSA is promising imaging assisted photothermal agents for solid tumor theranostics and enhancing the potential of Ag-based nanoparticles for practical treatment.

Constructing Surface Plasmon Resonance on Bi2WO6 to Boost High-Selective CO2 Reduction for Methane.

Plasmonic Bi2WO6 with strong localized surface plasmon resonance (LSPR) around the 500-1400 region is successfully constructed by electron doping. Oxygen vacancies on W-O-W (V1) and Bi-O-Bi (V2) sites are precisely controlled to obtain Bi2WO6-V1 with LSPR and Bi2WO6-V2 with defect absorption. Density functional theory (DFT) calculation demonstrates that the V1-induced energy state facilitates photoelectron collection for a long lifetime, resulting in LSPR of Bi2WO6. Photoelectron trapping on V1 sites is demonstrated by a single-particle photoluminescence (PL) study, and 93% PL quenching efficiency is observed. With strong LSPR, plasmonic Bi2WO6-V1 exhibits highly selective methane generation with a rate of 9.95 μmol g-1 h-1 during the CO2 reduction reaction (CO2-RR), which is 26-fold higher than 0.37 μmol g-1 h-1 of BiWO3-V2 under UV-visible light irradiation. LSPR-dependent methane generation is confirmed by various photocatalytic results of plasmonic Bi2WO6 with tunable LSPR and different light excitations. Furthermore, the DFT-simulated pathway of CO2-RR and in situ Fourier transform infrared spectra on the surface of Bi2WO6 prove that V1 sites facilitate CH4 generation. Our work provides a strategy to obtain nonmetallic plasmonic materials by electron doping.

NIR LSPR-coupling of Ag nanorices and W18O49 nanowires: Application of LRET and SERS

Broadband plasmonic nanomaterials working in the near-infrared (NIR) region which can concentrate and transfer the low-energy NIR light in the upconversion system are desired. However, single plasmon regulation often fails to meet requirement. Herein, a new type of Ag/W18O49 binary composite film composed of a metal domain (Ag nanorices) and a semiconductor domain (W18O49 nanowires) is designed and fabricated, which exhibits a broad and strong localized surface plasmon resonance (LSPR) across visible to NIR wavelengths, arising from interactions between the two nanostructure domains. The experimental and theoretical studies demonstrate that the localized electric field is dramatically amplified due to an NIR-driven strong plasmonic coupling of LSPR. In particular, the resonance excitation of plasmonic coupling in the Ag/W18O49 composite film induces remarkable enhancement of upconversion via the LSPR effect, and simultaneously provides ultrasensitive surface-enhanced Raman scattering (SERS) by the enhanced electromagnetic field. This work demonstrates a new strategy for accurate molecular detection by assembling upconversion nanoparticles (UCNPs) on Ag/W18O49 composite film, and the so-formed NaYF4/Ag/W18O49 multilayer film can support both the quantitative detection by luminescence resonance energy transfer (LRET) and the qualitative detection by SERS.

Effects of oxidation on the localized surface plasmon resonance of Cu nanoparticles fabricated via vacuum coating

Cu is a kind of inexpensive plasmonic material but the applications based on the localized surface plasmon resonance (LSPR) of Cu nanoparticles (CuNPs) are limited. This is because CuNPs normally synthesized by chemical methods are prone to oxidization, and the absorption of Cu2O, CuO, the interband transition of electrons from 3d to 4s overlap the LSPR of CuNPs, making the LSPR of CuNPs difficult to be identified. Herein, ultra-thin Cu films composed of CuNPs were fabricated by vacuum coating where oxidization of Cu was expected weak. However, no strong LSPR in the UV–Visible absorption spectra can be seen. In order to understand the mechanism, the as-deposited ultra-thin Cu films were annealed in nitrogen, oxygen and 5% hydrogen diluted nitrogen to mimic oxygen insufficient and sufficient oxidation, and reduction ambient to obtain Cu2O, CuO and CuNPs respectively. By UV–Visible absorption spectroscopy, Field emission scanning electron microscopy, X-ray photoelectron spectroscopy, and surface enhanced Raman spectroscopy, the LSPR of CuNPs, the absorption of Cu2O, CuO/Cu(OH)2 and interband transition were identified. The absorption spectra of the as-deposited ultra-thin Cu films, and their evolutions with the annealing temperature and time were explained. Finally, the oxygen sources are analyzed.

光触发增强葡萄糖氧化酶催化活性的等离子体囊 泡用于程序化光热-饥饿疗法

Glucose oxidase (GOx)-based nanotheranostic agents hold great promise in tumor starvation and its synergistic therapy. Self-assembled plasmonic gold vesicles (GVs) with unique optical properties, large hollow cavity, and strong localized surface plasmon resonance, can be used as multi-functional nanocarriers for synergistic therapy. Herein, GOx-loaded GVs (GV-GOx) were developed for light-triggered GOx release as well as enhanced catalytic activity of GOx, achieving programmable photothermal/starvation therapy. Under near-infrared laser irradiation, the GV-GOx generated strong localized hyperthermia due to plasmon coupling effect of GVs, promoting the release of encapsulated GOx and increasing its catalytic activity, resulting in enhanced tumor starvation effect. In addition, the high photothermal effect improved the cellular uptake of GV-GOx and allowed an efficient monitoring of synergistic tumor treatment via photoacoustic/photothermal duplex imaging in vivo . Impressively, the synergistic photothermal/starvation therapy demonstrated complete tumor eradication in 4T1 tumor-bearing mice, verifying superior synergistic anti-tumor therapeutic effects than monotherapy with no apparent systemic side effects. Our work demonstrated the development of a light-triggered nanoplatform for cancer synergistic therapy.

Significant solar energy absorption of MXene Ti3C2Tx nanofluids via localized surface plasmon resonance

Efficiency is an important factor in the utilization of solar energy. Direct absorption solar energy collectors (DASCs), a new generation collector of converting solar irradiation into heat directly by nanofluids, is regarded as a promising solution for capturing solar energy with high efficiency. Both good stability and high absorption ability are crucial for nanofluids to be an ideal working fluid of DASCs. In this work, we synthesize hyperstable Ti3C2Tx-H2O nanofluids as the working fluids of DASCs and investigate its photothermal conversion performance. The results show that the maximum conversion efficiency of thin-layer Ti3C2Tx nanofluids achieves 91.9% at a very low mass fraction of 0.02 wt%, which is higher than that of multi-layer Ti3C2Tx samples. Based on the experimental results, a simulation model is built to observe the radiation energy transformation in DASCs and results show that better photothermal performance of thin-layer MXene Ti3C2Tx stems from its stronger localized surface plasmon resonance (LSPR) effect. Besides, the coupling effect and the shape of Ti3C2Tx particles also play important roles in photothermal absorption and conversion. Based on our experimental and numerical results, the Ti3C2Tx-H2O nanofluids have great potential in solar energy harvesting.

Colorimetric Detection Based on Localized Surface Plasmon Resonance for Determination of Chemicals in Urine.

Colorimetric sensors based on localized surface plasmon resonance (LSPR) have attracted much attention for biosensor and chemical sensor applications. The unique optical effect of LSPR is based on the nanostructure of noble metals (e.g., Au, Ag, and Al) and the refractive index of the environment surrounding these metal nanomaterials. When either the structure or the environment of these nanomaterials is changed, their optical properties change and can be observed by spectroscopic techniques or the naked eye. Colorimetric-probe-based LSPR provides a simple, rapid, real-time, nonlabelled, sensitive biochemical detection and can be used for point-of-care testing as well as rapid screening for the diagnosis of various diseases. Gold and silver nanoparticles, which are the two most widely used plasmonic nanomaterials, demonstrate strong and sensitive LSPR signals that can be used for the selective detection of several chemicals in biochemical compounds provided by the human body (e.g., urine and blood). This information can be used for the diagnosis of several human health conditions. This paper provides information regarding colorimetric probes based on LSPR for the detection of three major chemicals in human urine: creatinine, albumin, and glucose. In addition, the mechanisms of selective detection and quantitative analysis of these chemicals using metal nanoparticles are discussed along with colorimetric-detection-based LSPR for many other specific chemicals that can be detected in urine, such as catecholamine neurotransmitters, thymine, and various medicines. Furthermore, issues regarding the use of portable platforms for health monitoring with colorimetric detection based on LSPR are discussed.

Quasi-metal Microwave Route to MoN and Mo2C Ultrafine Nanocrystalline Hollow Spheres as Surface-Enhanced Raman Scattering Substrates.

MoN and Mo2C are important functional materials; however, due to the high activation energy barrier in their nucleation, their synthesis generally requires harsh conditions such as high temperature (>1000 °C) and high pressure (several GPa). The extreme conditions also hinder the acquisition of their ultrafine nanostructures. Herein, we report that MoN and Mo2C hollow spheres with large surface area (108.7-125.6 m2 g-1) and ultrafine nanoparticles (2-5 nm) are prepared by a quasi-metal-based microwave route under mild conditions. MoO2 hollow spheres are used as a quasi-metallic microwave absorbing medium as well as a molybdenum source and template simultaneously. The MoN and Mo2C ultrafine nanocrystalline hollow spheres exhibit strong localized surface plasmon resonance, high photothermal conversion efficiency, and strong surface-enhanced Raman scattering effects. Highly crystalline MoS2 nanosheet hollow spheres can also be obtained by this method, indicating its universality. The present work provides an effective strategy for the rapid and mild preparation of ultrafine nanocrystalline transition metal nitrides and carbides with ultrahigh activation energy.

(Invited) Manipulating Carrier Polarization in Semiconductor Nanocrystals

We investigated the role of the synthesis method and post-synthesis processing on the plasmonic properties of antimony-doped SnO2 nanocrystals. The nanocrystal samples having variable doping concentrations were prepared by coprecipitation and solvothermal methods, and subsequently thermally annealed for different durations. We found that solvothermally-synthesized Sb-doped SnO2 nanocrystals exhibit strong localized surface plasmon resonance in the near-infrared region, which is distinctly absent in the nanocrystals synthesized by the coprecipitation method. Upon thermal annealing, the plasmon absorption emerges in the nanocrystals prepared by the coprecipitation method, and increases in intensity in solvothermally-synthesized nanocrystals. Using X-ray photoelectron spectroscopy, we correlated the plasmon intensity to the oxidation of Sb3+ to Sb5+. These results demonstrate that synthesis methodology and post-synthesis treatment can dramatically influence the plasmonic properties of aliovalently-doped semiconductor nanocrystals via dopant oxidation state, and can be effectively used to design semiconductor nanocrystals with targeted plasmonic properties.

Quantifying Electrocatalytic Reduction of CO2 on Twin Boundaries

Summary A protocol relying on the use of silver nanostructures with well-defined dimensions and morphologies (e.g., nanocubes and nanowires) has been developed to differentiate and quantitatively determine the atom-specific activities of different surface atoms toward catalyzing electrochemical CO2 reduction reaction (CO2RR). The atom-specific activity of the twin-boundary edges (TBEs) is comparable to (or slightly higher than) that of the single-crystal edges (SCEs) formed from the crossing of two {100} surfaces, and it is on the order of ∼16 attoampere/atom (aA/atom) toward electrochemical CO2RR. This value is more than two orders higher than the atom-specific activity of the {100} surface atoms, i.e., ∼0.1 aA/atom. The high catalytic activity of the TBEs, which represent a class of commonly existing surface defects in stable metal nanostructures with face-centered cubic lattices, is consistent with the DFT calculations, in which the bridge-type binding configuration of COOH∗ at the TBEs stabilizes this intermediate to promote overall CO2RR.

Synergistic enhancement of photocatalytic antibacterial effects in high-strength aluminum/TiO2 nanoarchitectures

Unlike gold and silver, aluminum shows a localized surface plasmon resonance (LSPR) over a wide spectral range from ultraviolet (UV) to the visible region. Herein, we demonstrate a new process to optically couple TiO2 nanotubes (NTs) with a high-strength aluminum substrate, to achieve a synergistic enhancement of photocatalytic antibacterial effects through controlled LSPR of aluminum. The high-strength aluminum substrate was produced by tubular channel angular pressing (TCAP). Their LSPR was tailored through the formation of superficial nano-concave arrays (NCAs) with desired concave diameters. A layer of aligned TiO2 NTs was fabricated on the surface of aluminum nano-concave arrays (Al NCAs) by anodization of a thin film of titanium. When the diameter of Al NCAs reached ~80 nm, a strong LSPR near the optical bandgap of TiO2 NTs was detected, whereby a synergistic antibacterial effect to Escherichia coli (E. coli) was observed through the coupling of TiO2 NTs photocatalysis and LSPR effect of Al NCAs (80 nm) in the UV-A range. The TiO2 NTs/Al NCAs hybrid surface showed excellent resistance against scratch. The results presented here may open a door for the further development of self-cleaning medical tools based on the decontamination strategies.