Plasmonic Nanomaterials Research Articles

Wet-Chemical Electro-Plasmonic Modulation of Metasurfaced Cell-Electrode Interfaces for Effective and Selective Entropic Killing of Cancer Cells.

Surface plasmons (SPs) of metallic nanostructures excited by optical ways have been extensively utilized for versatile sensing, biomedical, catalysis, and energy conversion applications. Nevertheless, utilizing the electrically excited plasmonic field (effect) of metallic nanostructures (and electrodes) in wet-chemical conditions, for catalytic and energy conversion, especially for potential biological and biomedical applications, is still poorly studied. Herein, we report a conceptual and biocompatible wet-chemical platform and approach to utilize the electrically excited plasmonic field (effect) of metasurfaced plasmonic electrodes (without light irradiation) for cell fate regulation on electrode surfaces. By using self-assembled two-dimensional (2D) ordered-plasmonic AuNP- or Au@SiO2 NP-nanomembrane as a metasurfaced electrode, the cancer cells cultured on it can be selectively and effectively killed (due to the enhanced stimulus current and related entropic effects) via wet-chemical electro-plasmonic modulation (WC-EPM) of the cell-electrode interfaces. Biological conformational and configurational entropic change information from the cell membrane during the WC-EPM of the cell-electrode interface has also been revealed by label-free in situ surface-enhanced Raman spectroscopy. The developed approach and results can be guides for the WC-EPM regulation of biological interfaces to achieve cell fate regulation and disease treatment and is also constructive for the design of 2D plasmonic nanomaterials and devices for efficient electrochemical energy conservation and biomedical applications.

Plasmonic metal/semiconductor hybrid nanomaterials for solar to chemical energy conversion

Plasmonic nanomaterials are sources of light, heat and electrons at nanometer scale. Given the outstanding performance in harvesting and converting solar energy under visible light irradiation, hybrid nanomaterials with plasmonic activity have recently emerged as a new class of advanced photocatalysts. Because of the enhanced charge-separation at hybrid interfaces, the hybrids usually exhibit higher catalytic activity compared with their monometallic counterparts. Here, we review the recent progress on synthesis of plasmonic hybrid nanomaterials and their applications in photocatalysis, including H2 production, CO2 reduction and N2 fixation. We hope this review will give systematic and valuable reference on plasmonic solar to chemical energy conversion.

Quantum Tunneling Induced Optical Rectification and Plasmon-Enhanced Photocurrent in Nanocavity Molecular Junctions.

Molecular junctions offer the opportunity for downscaling optoelectronic devices. Separating two electrodes with a single layer of molecules accesses the quantum-tunneling regime at low voltages (<1 V), where tunneling currents become highly sensitive to local nanometer-scale geometric features of the electrodes. These features generate asymmetries in the electrical response of the junction which combine with the incident oscillating optical fields to produce optical rectification and photocurrents. Maximizing photocurrents requires accurate control of the overall junction geometry and a large confined optical field in the optimal location. Plasmonic nanostructures such as metallic nanoparticles are prime candidates for this application, because their size and shape dictate a consistent junction geometry while strongly enhancing the optical field from incident light. Here we demonstrate a robust lithography-free molecular optoelectronic device geometry, where a metallic nanoparticle on a self-assembled molecular monolayer is sandwiched between planar bottom and semitransparent top electrodes, to create molecular junctions with reproducible morphology and electrical response. The well-defined geometry enables predictable and intense plasmonic localization, which we show creates optical-frequency voltages ∼ 30 mV in the molecular junction from 100 μW incident light, generating photocurrent by optical rectification (>10 μA/W) from only a few hundred molecules. Quantitative agreement is thus obtained between DC- and optical-frequency quantum-tunneling currents, predicted by a simple analytic equation. By measuring the degree of junction asymmetry for different molecular monolayers, we find that molecules with a large DC rectification ratio also boost zero-bias electrical asymmetry, making them good candidates for sensing and energy harvesting applications in combination with plasmonic nanomaterials.

Chiral Plasmonic Triangular Nanorings with SERS Activity for Ultrasensitive Detection of Amyloid Proteins in Alzheimer's Disease.

Chiral plasmonic nanomaterials have attracted unprecedented attention due to their broad applications in biomedicine, negative refractive index, and chiral sensing. Here, using a wet-chemistry process, chiral triangular Au nanorings are fabricated with a platinum (Pt) framework (l/d-Pt@Au triangular nanorings, named l/d-Pt@Au TNRs). The l/d-Pt@Au TNRs exhibit strong optical activity with a g-factor of 0.023 and can be used effectively for the discrimination of enantiomers due to selective resonance coupling between the induced electric and magnetic dipoles associated with enantiomers and the chiral plasmonic TNRs, also known as the surface-enhanced Raman scattering-chiral anisotropy (SERS-ChA) effect. The chiral d-Pt@Au TNRs represent a label-free SERS platform that can be applied to detect Aβ monomers and fibrils, the hallmarks of Alzheimer's disease (AD), achieving a limit of detection (LOD) down to 0.045 × 10-12 m and 4 × 10-15 m for 42-residue-long amyloid-β (Aβ42 ) monomer and fibrils, respectively. Furthermore, chiral d-Pt@Au TNRs can also be successfully carried out to detect Aβ42 proteins in AD patients with ultrahigh levels of sensitivity, thus allowing picogram quantities of Aβ42 proteins to be identified. This research opens up an avenue for the use of chiral plasmonic nanomaterials as ultrasensitive SERS substrates to early diagnosis of protein-misfolding diseases.

Plasmonic Gold Nanomaterials as Photoacoustic Signal Resonant Enhancers for Cysteine Detection.

The development of photoacoustic systems is important for the real-time detection of cysteine (Cys), a biothiol in biological systems that serves as a significant biomarker for human health. Advanced photoacoustic (PA) signals with colloidal plasmonic Au nanomaterials rely on the efficient conversion of light to energy waves under moderately pulsed laser irradiation. In this study, we synthesized Cys-capped Au nanorods (Au@Cys NRs) and Cys-capped Au nanoparticles (Au@Cys NPs) through a conjugate of three Cys concentrations (10, 100, and 1000 μM). These plasmonic Au nanomaterials can be used as a PA resonance reagent due to their maximum localized surface plasmon resonance (LSPR) absorption bands at 650 nm and 520 nm in Au NRs and Au NPs, respectively. Subsequently, the PA signals were noticeably increased proportionally to the concentrations in the Au@Cys NRs and Au@Cys NPs under 658 nm and 520 nm laser irradiation, respectively, according to our portable photoacoustic system. Furthermore, PA signal amplitudes in Cys detection are boosted by ~233.01% with Au@Cys NRs and ~102.84% with Au@Cys NPs enhancement, compared to free Cys, according to ultrasound transducers at frequencies of 3 MHz.

Core-Shell Plasmonic Nanomaterials toward: Dual-Mode Imaging Analysis of Glutathione and Enhanced Chemodynamic Therapy.

A simple process, rich information, and intelligent response are the goals pursued by cancer diagnosis and treatment. Herein, we developed a core-shell plasmonic nanomaterial (Au@MnO2-DNA), which consisted of a AuNP core with an outer shell MnO2 nanosheet decorated with fluorophore modified DNA, to achieve the aforementioned aims. On the basis of the unique optical properties of plasmonic nanoparticles and the oxidability of the shell MnO2, scattering signal and fluorescence (FL) signal changes were both related to the expression level of glutathione (GSH), for which a dual-mode imaging analysis was successfully achieved on single optical microscope equipment with one-key switching. Meanwhile, the product of Mn2+ from the reaction between MnO2 and GSH not only served as a smart chemodynamic agent to initiate Fenton-like reaction for achieving chemodynamic therapy (CDT) of cancer cells but also relieved the side effect of intracellular GSH in cancer therapy. Therefore, the core-shell plasmonic nanomaterials with dual modal switching features and diagnostic properties act as excellent probes for achieving bioanalysis of aberrant levels of intracellular GSH and simultaneously activating the CDT of cancer cells based on the in situ reactions in cancer cells.

Metal oxides as electrocatalysts for water splitting: On plasmon‐driven enhanced activity

AbstractMany technological approaches have been searched in order to overcome the main challenges concerning the world energy crisis and global environmental issues. Among them, plasmon‐driven photoelectrochemical reactions towards water electrolysis attract great attention due to their capacity to efficiently harvest solar energy. Synergism between tunable optical features and catalysts active sites of plasmonic nanomaterials gives rise to a singular perspective for photochemical processes. Through resonant photonic excitation, hot carriers’ motion facilitates the charge transfer process on the catalyst surface for chemical reactions. In this minireview, recent experimental research with emphasis on water splitting reactions have been summarized with the purpose of understanding the mechanistic hot electrons generation and transfer on the plasmonic noble metal nanoparticles (MNPs) and transition metal oxides (MOs) heterostructures. Examples of plasmonic nanomaterials are highlighted and compared for both water electrolysis semi reactions. Finally, this work concludes by describing the remaining challenges and gives some perspectives regarding the promising future of plasmon‐driven reactions investigations.

Design criteria to fabricate plasmonic gold nanomaterials for surface-enhanced Raman scattering (SERS)-based biosensing

The discovery of noble metal plasmonic nanoparticles (PNPs) has introduced surface-enhanced Raman scattering (SERS) as a highly sensitive and specific bioanalytical technique with greater potential in point-of-need disease diagnosis. This Tutorial provides an overview of the principles governing a gold PNP-based biosensor design for sensitive and reliable SERS-based detection of disease biomarkers. First, we will highlight the optical transducer properties of PNPs, the principles of SERS, the benefits of SERS detection, and the modes of SERS for biomarker detection. The analytical performance (sensitivity and specificity) and the reliability (accuracy and reproducibility) of a SERS biosensor are mainly dictated by (i) the chemical and optical transducer properties of PNPs, (ii) the functional nano interface, where the interaction(s) between PNPs and target biomolecules take place, and (iii) SERS data acquisition and evaluation metrics. Maintaining a balance between SERS signal enhancement and reproducibility is critical for advancing the field deployment of SERS technologies. However, the reproducibility of SERS biosensors is often overlooked in lieu of the assay sensitivity. Consequently, next, we will discuss the systematic optimization strategies for fabricating gold PNPs as SERS substrates and designing their functional interface to design SERS biosensors with sufficient sensitivity, specificity, and reproducibility. We will highlight the choice of PNPs and their integration into biosensing platforms depending on the mode of SERS detection. Last, we will discuss the SERS data acquisition and performance evaluation as an integral part of the SERS biosensors development workflow.

Plasmon-Coupled Directional Emission from Soluplus-Mediated AgAu Nanoparticles for Attomolar Sensing Using a Smartphone

Although there are numerous techniques for the synthesis of plasmonic (metallic Ag and Au) nanomaterials, eco-friendly and biocompatible methodologies that present diverse applications in nanophotonics and biomedical domains are seldom reported. Soluplus is a graft copolymer of polyvinyl caprolactam–polyvinyl acetate–polyethylene glycol and is extensively used for improving the solubility and bioavailability of poorly water-soluble drugs. However, the utility of their amphiphilic chemical structure, strong UV-light absorbing, and bifunctional properties of the polymer matrix as well as its role as a solubilizer have not been explored for rapid synthesis of plasmonic bimetallic nanohybrids. Although a variety of nanoparticles (NPs) have been studied for surface plasmon-coupled emission (SPCE) spectroscopic applications, AgAu nanohybrids have not been examined in the subject platform hitherto. In this article, we demonstrate a synthesis route for obtaining AgNPs, AuNPs, and AgAu nanohybrids using soluplus as both the reducing and capping agent in a simple UV-light induced one-pot rapid technique. These hybrid nanomaterials were interfaced with propagating surface plasmon polaritons from a 50 nm Ag thin film to understand the plasmonic coupling phenomenon in spacer, cavity, and extended cavity nanoconfigurations. The obtained AgAu nanohybrids aided in addressing the three major long-standing challenges in SPCE technology development, namely, (i) unavoidable quenching in the presence of AuNPs, (ii) chemical instability in AgNPs, and (iii) intrinsic ohmic losses in plasmonic NPs. In addition to overcoming the above-mentioned caveats, unaccustomed >1200-fold sharply directional and polarized SPCE enhancements were achieved using AgAu nanohybrids. The multifold nanogaps generated in AgAu nanohybrid sustained multiple hotspots catering to attomolar sensitivity of the SPCE reporter molecule, rhodamine B (RhB). The proposed methodology to obtain dequenched as well as augmented SPCE enhancements is of utmost utility in biophysicochemical sensor development.

Magneto-optical methods for magnetoplasmonics in noble metal nanostructures

The use of magneto-optical techniques to tune the plasmonic response of nanostructures—magnetoplasmonics—is a hot topic in active plasmonics, with fascinating implications for several plasmon-based applications and devices. In this exciting field, plasmonic nanomaterials with strong optical response to magnetic fields are desired, which is generally challenging to achieve with pure noble metals. To overcome this issue, several efforts have been carried out to design and tailor the magneto-optical response of metal nanostructures, mainly by combining plasmonic and magnetic materials or using ferromagnetic materials able to sustain a plasmonic response. However, despite their weak magneto-optical response, noble metals are a valuable model system allowing an accurate rationalization of magnetoplasmonic effects based on the interaction of magnetic fields with charge carriers. In addition, the emerging class of non-magnetic plasmonic heavily doped semiconductors is showing great potential for high performance magnetoplasmonics in the infrared range. In this Tutorial, the most common magneto-optical experimental methods employed to measure these effects are introduced, followed by a review of the major experimental observations that are discussed within the framework of an analytical model developed for the rationalization of magnetoplasmonic effects. Different materials are discussed, from noble metals to heavily doped semiconductors.

Synthesis of Two-Dimensional Plasmonic Molybdenum Oxide Nanomaterials by Femtosecond Laser Irradiation

Synthesis of Two-Dimensional Plasmonic Molybdenum Oxide Nanomaterials by Femtosecond Laser Irradiation

Paper-based plasmonic substrates as surface-enhanced Raman scattering spectroscopy platforms for cell culture applications.

The engineering of advanced materials capable of mimicking the cellular micro-environment while providing cells with physicochemical cues is central for cell culture applications. In this regard, paper meets key requirements in terms of biocompatibility, hydrophilicity, porosity, mechanical strength, ease of physicochemical modifications, cost, and ease of large-scale production, to be used as a scaffold material for biomedical applications. Most notably, paper has demonstrated the potential to become an attractive alternative to conventional biomaterials for creating two-dimensional (2D) and three-dimensional (3D) biomimetic cell culture models that mimic the features of in vivo tissue environments for improving our understanding of cell behavior (e.g. growth, cell migration, proliferation, differentiation and tumor metastasis) in their natural state. On the other hand, integration of plasmonic nanomaterials (e.g. gold nanoparticles) within the fibrous structure of paper opens the possibility to generate multifunctional scaffolds equipped with biosensing tools for monitoring different cell cues through physicochemical signals. Among different plasmonic based detection techniques, surface-enhanced Raman scattering (SERS) spectroscopy emerged as a highly specific and sensitive optical tool for its extraordinary sensitivity and the ability for multidimensional and accurate molecular identification. Thus, paper-based plasmonic substrates in combination with SERS optical detection represent a powerful future platform for monitoring cell cues during cell culture processes. To this end, in this review, we will describe the different methods for fabricating hybrid paper-plasmonic nanoparticle substrates and their use in combination with SERS spectroscopy for biosensing and, more specifically, in cell culture applications.

Light Capture and Energy Conversion in Plasmonic-Polymeric Hybrid Nanoelectrodes

Plasmonic nanomaterials have absorption cross-sections exceeding other classes of materials but dephase quickly into their dielectric environment. In this work, plasmonic-polymeric nanoantenna-reactor systems are hybridized to increase the electron-hole pair lifetime through interfacial redistribution. The electron-hole pair can then be extracted to drive catalysis as the selected polymeric acceptor, a metallophthalocyanine, has been shown to catalysis O2 and CO2 reduction efficiently. Single particle spectroelectrochemistry was used to characterize the energy transfer efficiencies of the hybrid structures by recording the surface plasmon resonance energy linewidth change during in situ polymerization. The electrochemical polymerization is selective and photoenhanced on the surface of the gold nanorods. We complement resonance energy transfer efficiencies calculated from single particle changes in linewidth with calculations from excitation polarization-dependent photoluminescence measurements. Non-radiative energy transfer efficiencies up to 50% are achieved for plasmonic-polymeric nano-antenna reactors. The understanding of interfacial transfer pathways between plasmonic-polymeric materials will lead to control and tunability of scalable hybrid nanoelectrodes.

Plasmonic Carbonaceous Nanotemplates for Microplastics Raman Detection

Plasmonic Carbonaceous Nanotemplates for Microplastics Raman Detection

Agarose hydrogel doped with gold nanobipyramids(AuNBPs@AG)as colorful height readout device for sensing hydrogen peroxide in complex sample matrix

The portable and instrument-free sensing device for quantitative detection is of significant applications in resource constrained countries and regions. Here, a colorful height readout device formed by agarose hydrogel doped with gold nanobipyramids (AuNBPs@AG) is developed for the determination of hydrogen peroxide (H2O2) content. The responsive mechanism is based on H2O2 guided etching of AuNBPs, which causes the plasmon-mediated color change of the AuNBPs@AG hydrogel filled in plexiglass tube from top to bottom. We demonstrate the height of color-changed hydrogel is quantitatively related to the concentration of H2O2. The agarose hydrogel, as the carrier material for loading AuNBPs, guarantees the stability of AuNBPs and promotes the separation of complex samples. The method shows a good linear relationship in four ranges of H2O2 concentrations of 20 − 100 μM, 200 − 1000 μM, 1 − 10 mM and 10 − 100 mM. Compared with previous methods, using this inexpensive and easy to operate device for H2O2 detection can effectively reduce the interference of the color background, overcome the problem of the nanoparticles aggregation, and eliminate the need for expensive and sophisticated detection instruments. The practicality of the method is demonstrated via the analysis of commercial products such as contact lens solution and hair dye with satisfactory results. Our work provides a novel path for developing the height-readout quantitative devices with integrating hydrogels and plasmonic nanomaterials.

Self-energized organic-inorganic hybrid composite for surface enhanced Raman spectroscopy

In this study, we integrate plasmonic metal nanomaterials with a piezoelectric polyvinylidene fluoride (PVDF) polymer and lithium niobate (LiNbO3) based composite to form an all-solid-state flexible self-energized sensor. We demonstrate that following the application of a load, the film enhances the surface-enhanced Raman spectroscopy (SERS) signal of an analyte molecule up to 14 times. The piezoelectric β-phase of PVDF in the film is optimized through the introduction of multi-walled carbon nanotubes and post-fabrication UV irradiation annealing. Additionally, the SERS signal enhancement can be further increased by the application of in situ UV light irradiation of the sample, resulting in the generation of photoexcited electrons from LiNbO3 microparticles introduced into the composite. Both the application of a mechanical displacement and the UV light-induced charge generation result in an improved charge transfer between the film and an analyte molecule. The piezoelectric PVDF/LiNbO3 film has been shown to be a suitable SERS platform for the detection of important biological molecules, demonstrating the potential of the substrate for fast on-site detection applications.

Probing the Intracellular Bio-Nano Interface in Different Cell Lines with Gold Nanostars.

Gold nanostars are a versatile plasmonic nanomaterial with many applications in bioanalysis. Their interactions with animal cells of three different cell lines are studied here at the molecular and ultrastructural level at an early stage of endolysosomal processing. Using the gold nanostars themselves as substrate for surface-enhanced Raman scattering, their protein corona and the molecules in the endolysosomal environment were characterized. Localization, morphology, and size of the nanostar aggregates in the endolysosomal compartment of the cells were probed by cryo soft-X-ray nanotomography. The processing of the nanostars by macrophages of cell line J774 differed greatly from that in the fibroblast cell line 3T3 and in the epithelial cell line HCT-116, and the structure and composition of the biomolecular corona was found to resemble that of spherical gold nanoparticles in the same cells. Data obtained with gold nanostars of varied morphology indicate that the biomolecular interactions at the surface in vivo are influenced by the spike length, with increased interaction with hydrophobic groups of proteins and lipids for longer spike lengths, and independent of the cell line. The results will support optimized nanostar synthesis and delivery for sensing, imaging, and theranostics.

Plasmonic Core–Shell Nanomaterials and their Applications in Spectroscopies

AbstractPlasmonic core–shell nanostructures have attracted considerable attention in the scientific community recently due to their highly tunable optical properties. Plasmon‐enhanced spectroscopies are one of the main applications of plasmonic nanomaterials. When excited by an incident laser of suitable wavelength, strong and highly localized electromagnetic (EM) fields are generated around plasmonic nanomaterials, which can significantly boost excitation and/or radiation processes that amplify Raman, fluorescence, or nonlinear signals and improve spectroscopic sensitivity. Herein, recent developments in plasmon‐enhanced spectroscopies utilizing core–shell nanostructures are reviewed, including shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS), plasmon‐enhanced fluorescence spectroscopy, and plasmon‐enhanced nonlinear spectroscopy.

Optical nanomaterials with focus on rare earth doped oxide: A Review

Optical nanomaterials (ONMs) have attracted significant attention of the global research community owing to their several superior advantages. Some of the ONMs depict negligible photobleaching, bright emission, large electron-hole overlap integral, ease of coating on any surface, large Stoke/Antistoke shifts, higher photostabilites, easy to incorporate inside human body etc. These properties make them technologically highly efficient which helps in minimizing the global issue of energy crisis and improving the standard of living of common man. Several aspects of ONMs such as plasmonic nanomaterials, quantum dots, photonic crystals, and rare earth doped nanoparticles have been discussed. For covering various categories of luminescent nanomaterials (LNMs) based on composition, a brief introduction and importance of metal nanoclusters, carbon nano dots, organic-inorganic nanocomposites, and metal doped nanoparticles have been also included. This review article gives very concise overview of rare earth doped oxide nanoparticles covering several important aspects such as rare earth ion (RE) as dopant, oxide-based host, nanophosphors etc. The importance of LNMs, their advantages as well as drawbacks are also highlighted. Technologically important types of RE doped oxide nanoparticles pertaining to downconversion, upconversion, persistence and radioluminescence are also explained and covered in detail in this review article. Several recent applications involving LNMs in bioimaging, solar cell, thermal sensor, biosensor, anti-counterfeiting etc are explained. In the last section of the review, a comparison between nano and bulk rare earth doped oxide LNMs are discussed in terms of several photophysical properties such as dopant local symmetry, Stark splitting, emission intensity, luminescence lifetime, host to dopant energy transfer, quantum yield etc. Finally, this review article is concluded with summary, outlook, challenges, and future scope on the use of LNMs. Several important aspects of LNMs with focus on RE doped oxide nanoparticles have been covered in this review article which will help general readers in their further research, in this important area, for development of both fundamental sciences and applications involving LNMs.

Responsive Plasmonic Nanomaterials for Advanced Cancer Diagnostics.

Plasmonic nanostructures, particularly of noble-metal Au and Ag, have attracted long-lasting research interests because of their intriguing physical and chemical properties. Under light excitation, their conduction electrons can form collective oscillation with the electromagnetic fields at particular wavelength, leading to localized surface plasmon resonance (LSPR). The remarkable characteristic of LSPR is the absorption and scattering of light at the resonant wavelength and greatly enhanced electric fields in localized areas. In response to the chemical and physical changes, these optical properties of plasmonic nanostructures will exhibit drastic color changes and highly sensitive peak shifts, which has been extensively used for biological imaging and disease treatments. In this mini review, we aim to briefly summarize recent progress of preparing responsive plasmonic nanostructures for biodiagnostics, with specific focus on cancer imaging and treatment. We start with typical synthetic approaches to various plasmonic nanostructures and elucidate practical strategies and working mechanism in tuning their LSPR properties. Current achievements in using responsive plasmonic nanostructures for advanced cancer diagnostics will be further discussed. Concise perspectives on existing challenges in developing plasmonic platforms for clinic diagnostics is also provided at the end of this review.