Plasmon Amplification Research Articles

A novel non-catalytic plasmonic immunoabsorbant assay amplification mechanism

The amplification of signals is dependent upon enzyme/ catalyst. Enzyme activity, specificity, pH condition, enzyme linkers, stability, storage and efficiency are some very important factors that can eventually affect the detection results. We aimed to amplify signals without the assistance of enzyme/ catalyst so that the strategy can be used in the wide range of signal detection including immune-assay. Silver nanocrystals (Ag NCs) grown from self-nucleation are used as chromogens due to their strong plasmon band at ∼ 400 nm. During 140 s of reaction time in presence of 6.10 mM CTAB and 0.61 mM of AgNO3, the 0.57 mM of Ascorbic acid allows Ag over growth on antibody-tagged gold nanospheres (10±0.5 nm) that competes silver atoms from the self-nucleation growth and thus affects the growth kinetics of the latter. By utilizing the opened kinetic window, sensitive detection has been achieved from 6.67 × 10–14 M (1 pg) to 3.33 × 10–9 M (50 ng) using human IgG as a model protein. The non-catalytic plasmonic immunoabsorbant assay we developed herein adds a new possibility of plasmonic NPs for sensitive detection. The detection slope and resolution is higher and better than those via signal amplification through the assistance of enzymes/ catalysts. This work supports the concept that nanoparticles mediated reactions are sensitive enough that they have the potential to go independently without enzymes/ catalyst assistance.

Plasmon scattering at a junction in double-layer two-dimensional electron gas plasmonic waveguide

Abstract The scattering of plasmons at a junction within a double-layer two-dimensional electron gas plasmonic waveguide is studied via a full electromagnetic method. The dispersion relation is derived by utilizing the transfer matrix method and can be extended to the situation of an arbitrary number of layers. By numerically solving the dispersion equations, both the acoustic and optical plasmon modes are identified in this double layer system, and the unstable plasmon modes arising from plasmon coupling in different layers are discussed elaborately. Subsequently, the total fields are expanded with eigenmodes and matched at the interface to analyze the scattering characteristics at the junction. The results indicate that the total power of the plasmon mode is amplified when the electron fluid flows from a high concentration region to a low concentration region, and the amplification is more evident at a higher drift velocity. Additionally, we address the scattering of unstable plasmons caused by the two-stream instability and find that the transmitted plasmons are excited intensively at the incidence of the growing plasmon, leading to the plasmon amplification. The detailed examination of plasmon scattering at junction is the prerequisite for studying more complex structures of terahertz plasmonic devices and comprehending the corresponding amplification mechanism.

Asymmetric Polarization in a Rough Multilayer: Towards the Discrimination of Enantiomer Pairs.

Chirality plays a significant part in many vital processes, and to further our level of understanding, there is a steadily growing interest in enhancing the yield of enantioselective processes. Here, a multilayer with etched grooves is activated in a Kretschmann geometry and consists of alternating platinum Pt, silica SiO2, and silicon Si, as well as a silver Ag layer. Due to the production process, the groove surface exhibits a micrometric roughness, characterized by a typical vibrational mode at ω = 96 MHz. The mode is attributed to a localized acoustic vibration and has been detected as a transmitted signal. The outcomes of the inquiry include plasmonic amplification of the transmitted signal and its wavevector-less nature; in addition, it is shown that the signal is depolarized in reference to the incident beam because of the rough surface. When the Kretschmann scheme is combined with the depolarization brought on by the roughness, a built-in asymmetry results in a higher optical flux of spectrum photons in the depolarized plane than the co-polarized plane, resulting in distinct, enantioselective, and solely polarization-dependent spectral contrast. In conclusion, enantioselectivity is demonstrated for the D,L-penicillamine.

Effect of electron–phonon interactions on a three-level QD-based spaser: linear and quadratic potentials

Abstract In this article, we study the effect of electron–phonon interaction on a spaser (surface plasmon amplification by stimulated emission of radiation) system consisting of a metal nanoparticle surrounded by a large number of quantum dots (QDs). Usually, the effect of electron–phonon interaction is neglected in the spaser-related literature. However, gain media, in this case QDs, attributed by the large Raman scattering cross-section, exhibit stronger electron–phonon interaction. In the present work, we investigate the effects of electron–phonon interaction on a three-level QD-based spaser. We consider two types of interaction potentials, linear and quadratic, and analyse their effects individually. First, we focus on the linear electron–phonon interaction that perturbs the electrons present in the excited state. This yields a periodic steady-state number of localized surface plasmons (LSPs). The accompanying analytic solution reveals that the population inversion of the gain medium depends on the linear potential strength (Frohlich constant) but does not affect the threshold of spaser considerably for the given numerical parameters. In addition to the LSP, phonons are generated during this process, the temporal dynamics of which are also presented here. Initially, the number of phonons exhibit decaying periodic oscillations, whose amplitude depends on the strength of the electron–phonon interaction. Under continuous pumping, at later times, the number of phonons reaches a steady-state value, which may find potential applications in the realization of continuous phonon nanolasers. Furthermore, the effect of the quadratic potential is investigated phenomenologically by increasing the excited-state decay rate. This results in numerous LSPs and an intense spaser spectrum.

A comparative study of coherent and incoherent drives in a four-level quantum dot–based spaser

Abstract In this article, we theoretically investigate a spaser (surface plasmon amplification by stimulated emission of radiation) comprising a spherical silver nanoparticle surrounded by a four-level gain medium of quantum dots. The spaser system is pumped coherently and incoherently with the same excitation rate, and the characteristics of the resultant coherent localized surface plasmon (LSP) mode are compared for the two pumping scenarios. We provide a detailed analytical expression for the steady state and demonstrate that the incoherent pump is more suitable for the continuous spaser mode. The reason is better understood by studying the temporal evolution of the number of LSPs N n , where the LSP oscillation starts earlier for an incoherent drive and relaxes to a steady state with a large value of N n . At a large pump rate, the spaser curve shows saturation. In addition, we have found that the resonance peak of the spaser field is independent of coherent and incoherent pumping, whereas the peak amplitude of the field depends on the pump rate.

Surface acoustic wave actuated plasmonic signal amplification in a plasmonic waveguide

Enhancement of nanoscale confinement in the subwavelength waveguide is a concern for advancing future photonic interconnects. Rigorous innovation of plasmonic waveguide-based structure is crucial in designing a reliable on-chip optical waveguide beyond the diffraction limit. Despite several structural modifications and architectural improvements, the plasmonic waveguide technology is far from reaching its maximum potential for mass-scale applications due to persistence issues such as insufficient confined energy and short propagation length. This work proposes a new method to amplify the propagating plasmons through an external on-chip surface acoustic signal. The gold–silicon dioxide (Au-SiO2) interface, over Lithium Niobate (LN) substrate, is used to excite propagating surface plasmons. The voltage-varying surface acoustic wave (SAW) can tune the plasmonic confinement to a desired signal energy level, enhancing and modulating the plasmonic intensity. From our experimental results, we can increase the plasmonic intensity gain of 1.08 dB by providing an external excitation in the form of SAW at a peak-to-peak potential swing of 3 V, utilizing a single chip.

Light concentration and electron transfer in plasmonic-photonic Ag,Au modified Mo-BiVO4 inverse opal photoelectrocatalysts.

Plasmonic photocatalysis based on metal-semiconductor heterojunctions is considered a key strategy to evade the inherent limitations of poor light harvesting and charge separation of semiconductor photocatalysts. It can be profitably combined with three-dimensional photonic crystals (PCs) that offer an ideal scaffold for loading plasmonic nanoparticles and a unique architecture to intensify photon capture. In this work, Mo-doped BiVO4 inverse opals were applied as visible light-responsive photonic hosts of Ag and/or Au plasmonic nanoparticles in order to exploit the synergy of plasmonic and photonic amplification effects with interfacial charge transfer for the photoelectrocatalytic degradation of recalcitrant pharmaceutical contaminants under visible light. Photoelectrochemical evaluation indicated a major contribution from hot spot-assisted local field enhancement, most pronounced for Ag/Mo-BiVO4 PCs due to the spectral overlap of the localized surface plasmon resonance with the electronic absorption and blue-edge slow photon region of Mo-BiVO4 PCs, in contrast to weak plasmonic sensitization effects for the Au-modified PCs. The diverse band alignment at the metal-semiconductor interfaces resulted in the enhanced photoelectrocatalytic degradation of tetracycline broad spectrum antibiotic by Ag/Mo-BiVO4 and the refractory ibuprofen drug by (Ag,Au)/Mo-BiVO4, attributed to the enhanced charge separation by electron transfer toward Ag nanoparticles. Combination of visible light activated semiconductor PCs and plasmonic nanoparticles with suitable band alignment and photonic band gap may provide a versatile approach for the rational design of efficient plasmonic-photonic photoeletrocatalysts.

A plasmonic MNAzyme signal amplification strategy for quantification of miRNA-4739 breast cancer biomarker

A major challenge in the 21st century is the development of point-of-care diagnostic tools capable to detect and quantify disease biomarkers in a straightforward, affordable, sensitive, and specific manner. The remarkable plasmonic properties of gold nanoparticles (AuNPs) have promoted their use for development of simple methodologies for nucleic acid detection in combination with a variety of oligonucleotides amplification techniques. Here, assemblies of AuNPs with Multicomponent Nucleic Acid enzymes (MNAzymes) has been successfully used in the design of a highly sensitive and simple bioassay for rapid spectroscopic detection and quantification of miRNA-4739 in blood samples. The miRNA selected is a doxorubicin chemoresistant biomarker in breast cancer which overexpression promotes the proliferation, progression, and survival of cancer cells. In this work, two alternatives experimental designs, based on use of MNAzymes and AuNPs, have been optimized and applied for sensitive miRNA-4739 quantification: one based on a traditional direct measurement of wavelength shift and a second non-conventional simple approach based on isolation and measurement of free nanoparticles absorbance. Improvement in sensitivity and, higher measurement accuracy and precision were achieved with the second approach. The developed bioassay provides a detection limit as low as 7 pmolL−1 for miRNA-4739 quantification and performed satisfactory selectivity and well practical applicability by analysis of the miRNA-4739 in blood, demonstrating that the proposed strategy is a promising and suitable spectroscopic method for breast cancer diagnosis thought liquid biopsy of circulating tumoral cells.

Ultrafast Plasmonic Nucleic Acid Amplification and Real-Time Quantification for Decentralized Molecular Diagnostics.

Point-of-care real-time reverse-transcription polymerase chain reaction (RT-PCR) facilitates the widespread use of rapid, accurate, and cost-effective near-patient testing that is available to the public. Here, we report ultrafast plasmonic nucleic acid amplification and real-time quantification for decentralized molecular diagnostics. The plasmonic real-time RT-PCR system features an ultrafast plasmonic thermocycler (PTC), a disposable plastic-on-metal (PoM) cartridge, and an ultrathin microlens array fluorescence (MAF) microscope. The PTC provides ultrafast photothermal cycling under white-light-emitting diode illumination and precise temperature monitoring with an integrated resistance temperature detector. The PoM thin film cartridge allows rapid heat transfer as well as complete light blocking from the photothermal excitation source, resulting in real-time and highly efficient PCR quantification. Besides, the MAF microscope exhibits close-up and high-contrast fluorescence microscopic imaging. All of the systems were fully packaged in a palm size for point-of-care testing. The real-time RT-PCR system demonstrates the rapid diagnosis of coronavirus disease-19 RNA virus within 10 min and yields 95.6% of amplification efficiency, 96.6% of classification accuracy for preoperational test, and 91% of total percent agreement for clinical diagnostic test. The ultrafast and compact PCR system can decentralize point-of-care molecular diagnostic testing in primary care and developing countries.

Dual-Enhanced Plasmonic Biosensing for Point-of-Care Sepsis Detection.

Rapid, sensitive, simultaneous quantification of multiple biomarkers in point-of-care (POC) settings could improve the diagnosis and management of sepsis, a common, potentially life-threatening condition. Compared to high-end commercial analytical systems, POC systems are often limited by low sensitivity, limited multiplexing capability, or low throughput. Here, we report an ultrasensitive, multiplexed plasmonic sensing technology integrating chemifluorescence signal enhancement with plasmon-enhanced fluorescence detection. Using a portable imaging system, the dual chemical and plasmonic amplification enabled rapid analysis of multiple cytokine biomarkers in 1 h with sub-pg/mL sensitivities. Furthermore, we also developed a plasmonic sensing chip based on nanoparticle-spiked gold nanodimple structures fabricated by wafer-scale batch processes. We used the system to detect six cytokines directly from clinical plasma samples (n = 20) and showed 100% accuracy for sepsis detection. The described technology could be employed in rapid, ultrasensitive, multiplexed plasmonic sensing in POC settings for myriad clinical conditions.

Single-shot multi-channel plasmonic real-time polymerase chain reaction for multi-target point-of-care testing.

Plasmonic nucleic acid amplification tests demand high-throughput and multi-target detection of infectious diseases as well as short turnaround time and small size for point-of-care molecular diagnostics. Here, we report a multi-channel plasmonic real-time reverse-transcription polymerase chain reaction (mpRT-qPCR) assay for ultrafast and on-chip multi-target detection. The mpRT-qPCR system features two pairs of plasmonic thermocyclers for rapid nanostructure-driven amplification and microlens array fluorescence microscopes for in situ multi-color fluorescence quantification. Each channel shows a physical dimension of 32 mm, 75 mm, and 25 mm in width, length, and thickness. The ultrathin microscopes simultaneously capture four different fluorescence images from two PCR chambers of a single cartridge at a single shot exposure per PCR cycle of four different excitation light sources. The experimental results demonstrate a single assay result of high-throughput amplification and multi-target quantification for RNA-dependent RNA polymerase, nucleocapsid, and human ribonuclease P genes in SARS-CoV-2 RNA detection. The mpRT-PCR increases the number of tests four times over the single RT-PCR and exhibits a short detection time of 15 min for the four RT-PCR reactions. This point-of-care molecular diagnostic platform can reduce false negative results in clinical applications of virus detection and decentralize healthcare facilities with limited infrastructure.

Concept of terahertz waveguide plasmon amplifier based on a metal groove with active graphene

We propose a concept of terahertz waveguide plasmon amplifier based on a metal groove with active graphene. It is shown that the power amplification factor of the longitudinal-section magnetic (LSM) waveguide plasmon (normalized to its wavelength) near the cut-off frequency of this mode can exceed the amplification factor of the transverse magnetic (TM) plasmon in a layered graphene structure by more than four orders of magnitude for the same frequency. This is caused by the increase of the LSM plasmon wavelength near the cut-off frequency, smaller energy velocity of the LSM mode, and greater energy release from graphene for the LSM plasmon due to stronger lateral confinement of the LSM waveguide plasmon as compared to the TM plasmon in a layered graphene structure. We show that the enhancement of the LSM plasmon amplification factor near the cut-off frequency is a stronger effect than that due to screening of graphene.

SPASER as Nanoprobe for Biological Applications: Current State and Opportunities

AbstractSince the concept of surface plasmon amplification by stimulated emission of radiation (SPASER) was proposed in 2003, great progresses have been made on two kinds of plasmonic nanolasers, namely SPASER device and SPASER nanoparticle. In comparison, SPASER nanoparticle, with ultra‐narrow emission line, small size, and good biocompatibility, is a kind of promising luminescent nanoprobe and has a bright application prospect in biomedical imaging and sensing. Hence, it is gradually becoming an attractive research hotspot in the world. However, as the research on SPASER nanoparticle is still in its infancy, there are still lots of problems to be solved before it is widely applied. In this paper, the latest research advances of SPASER nanoparticles and their biological applications are reviewed. Besides existing problems, challenges and opportunities of SPASER nanoparticles as next generation luminescent nanoprobes are discussed as well.

Development of surface plasmon polariton-based nanolasers

Overcoming the optical diffraction limit and reducing the size of optoelectronic integrated circuits have become requirements for the rapidly increasing demand for data transmission and novel functionality. These goals can be achieved by applying a surface plasmon mode that can attain subwavelength confinement. In this Tutorial, we discuss the operation principle and development of the surface plasmon amplification of the stimulated emission of radiation and the newly developed plasmonic nanolasers that play essential roles in reducing system sizes. Nanowire-type surface plasmon polariton (SPP) nanolasers with semiconductor–insulator–metal structures were developed and integrated with graphene, which offers numerous advantages to SPP nanolasers. Furthermore, the electrical modulation mechanism of nanolasers on graphene–insulator–metal (GIM) platform was also verified, which can recognize integrated SPP detectors. Therefore, we propose using an integrated plasmonic circuit on the GIM platform to provide multiple functionalities in a compact footprint.

Engineering chiral plasmonic nanostructures for gain-assisted plasmon amplification and tunable enhancement of circular dichroism

We have demonstrated that the SPASER configuration can provide giant chiroptical enhancements in plasmonic nano assemblies within the lasing threshold which can be harnessed for highly efficient chiral sensing or imaging of complex biological environments.

Design of a nanocomposite with gold nanoparticles as the core and casein-templated gold nanoclusters as the shell with ultra-low protein corona for enhanced photodynamic therapy

The photodynamic therapy efficiency of AuNPs-CS-AuNCs can be well enhanced by the synergy effect of CS-AuNCs and AuNPs which is due to the surface plasmonic amplification and energy transfer from AuNPs to AuNCs.

Coherence Between Different Propagating Surface Plasmon Polariton Modes Excited by Quantum Mechanical Tunnel Junctions

AbstractCoherence between different surface plasmon polariton (SPP) modes excited by inelastically tunneling electrons in biased metal–insulator–metal tunnel junctions (MIM‐TJs) is demonstrated. By employing a dedicated SPP stripe waveguide with MIM‐TJ, an effective double‐slit configuration similar to the Young's experiment is realized for an electrically biased SPP source. The spatial correlation between different SPP modes originates from a single inelastic tunneling event and leads to strong interference in the far‐field, observed as alternate bright and dark fringes in the Fourier plane. The measured fringe‐spacing inversely follows the stripe waveguide length, with upper limit dictated by the SPP propagation length, confirming the SPP mediated spatial correlation. Finite difference time domain simulations support the experimental findings. Also, the experimental and simulation results unambiguously demonstrate the two‐step plasmonic decay process in plasmonic MIM‐TJs. The results presented here provide a simple and robust demonstration of the inherent coherence existing between different decay channels (plasmons and photons) of the inelastically tunneling electrons and can be exploited for plasmonic applications with tailored spatial coherence with implications in plasmon amplification and quantum information processing.

Optical amplification by surface-plasmon-resonant Au grating substrates: Monolayer MoS2 with 170-fold second harmonic generation and 3-fold (off-resonance) Raman scattering

Nanoplasmonics is a potential game-changer in the development of next-generation on-chip photonic devices and computers, owing to the geometrically controlled and amplified linear and nonlinear optical processes. For instance, it resolves the limited light-matter interaction of the unique two-dimensional (2D) crystalline materials like semiconducting monolayer molybdenum disulfide (1L-MoS 2 ). Metal grating (MG) substrates excel at this because their surface plasmons (SPs) can lead to stark field confinement near the surface. This work studies optical amplification of 1L-MoS 2 on the gold (Au) MG substrate, which was designed to operate in a glycerol environment with SP resonance (SPR) at 850 nm excitation wavelength. Its design was verified by simulated and experimental reflectances, and topographically inspected by atomic force microscopy (AFM). Two advanced imaging modalities, second harmonic generation (SHG) and confocal Raman microscopy (CRM) were used to evaluate its 170-fold SHG on- and 3-fold CRM off-resonance optical amplifications, respectively. Some MoS 2 -to-grating adhesion issues due to trapped liquid showed as image nonuniformities. Possible improvements to limitations like surface roughness were also discussed. These Au MG substrates can boost conventional linear and nonlinear backscattering microscopies because they are tunable in the visible and near-infrared range by selecting geometry, metal, and environment. • Plasmonic optical amplification study of monolayer MoS 2 on Au/Si-grating substrate. • 170× on- and 3× off-resonance gains in second harmonic generation and Raman signals. • These nanogratings can boost both linear and nonlinear backscattering microscopies. • Tune by geometry, metal, and environment within the visible and near-infrared range. • Improve light-matter interaction (with less power and less light-induced damage).

Charge carriers drift induced THz amplification in dual-layer graphene structure

The terahertz plasmon amplification in structure based on graphene with spatial dispersion of its hydrodynamic conductivity is investigated theoretically. The spatial dispersion of graphene conductivity is related to accounting of charge carriers pressure forces and direct current in graphene. It was shown that the real part of graphene conductivity becomes negative at THz frequency range due to direct electric current in graphene.

Paving the Way for Tunable Graphene Plasmonic THz Amplifiers

This study reviews recent advances in room-temperature coherent amplification of terahertz (THz) radiation in graphene, electrically driven by a dry cell battery. Our study explores THz light–plasmon coupling, light absorption, and amplification using a current-driven graphene-based system because of its excellent room temperature electrical and optical properties. An efficient method to exploit graphene Dirac plasmons (GDPs) for light generation and amplification is introduced. This approach is based on current-driven excitation of the GDPs in a dual-grating-gate high-mobility graphene channel field-effect transistor (DGG-GFET) structure. The temporal response of the DGG-GFETs to the polarization-managed incident THz pulsation is experimentally observed by using THz time-domain spectroscopy. Their Fourier spectra of the transmitted temporal waveform through the GDPs reveals the device functions 1) resonant absorption at low drain bias voltages below the first threshold level, 2) perfect transparency between the first and the second threshold drain bias levels, and 3) resonant amplification beyond the second threshold drain bias voltage. The maximal gain of 9% is obtained by a monolayer graphene at room temperatures, which is four times higher than the quantum limit that is given when THz photons directly interact with electrons. The results pave the way toward tunable graphene plasmonic THz amplifiers.