Coherent Controllable Transport of a Surface Plasmon Coupled to a Plasmonic Waveguide with a Metal Nanoparticle-Semiconductor Quantum Dot Hybrid System

Plasmonics - By using the real-space method, the switching of a single plasmon interacting with a hybrid nanosystem composed of a semiconductor quantum dot (SQD) and a metallic nanoparticle (MNP)...     

Plasmonic Effect on the Optical Properties in a Hybrid V-Type Three-Level Quantum Dot-Metallic Nanoparticle Nanosystem

We investigated theoretically the exciton–plasmon coupling effects on the population dynamics and the absorption properties of a hybrid nanosystem composed of a metal nanoparticle (MNP) and a V-type three-level semiconductor quantum dot (SQD), which are created by the interaction with the induced dipole moments in the SQD and the MNP, respectively. Excitons of the SQD and the plasmons of the MNP in such a hybrid nanosystem could be coupled strongly or weakly to demonstrate novel properties of the hybrid system. We also find that the gain happens in such a hybrid system, because of the coherent interaction between the SQD and the MNP. Our results show that the non-linear optical response of the hybrid nanosystem can be greatly enhanced or depressed due to the exciton–plasmon couplings.     

Synthesis of Cd-free InP/ZnS Quantum Dots Suitable for Biomedical Applications

Fluorescent nanocrystals, specifically quantum dots, have been a useful tool for many biomedical applications. For successful use in biological systems, quantum dots should be highly fluorescent and small/monodisperse in size. While commonly used cadmium-based quantum dots possess these qualities, they are potentially toxic due to the possible release of Cd²⁺ ions through nanoparticle degradation. Indium-based quantum dots, specifically InP/ZnS, have recently been explored as a viable alternative to cadmium-based quantum dots due to their relatively similar fluorescence characteristics and size. The synthesis presented here uses standard hot-injection techniques for effective nanoparticle growth; however, nanoparticle properties such as size, emission wavelength, and emission intensity can drastically change due to small changes in the reaction conditions. Therefore, reaction conditions such temperature, reaction duration, and precursor concentration should be maintained precisely to yield reproducible products. Because quantum dots are not inherently soluble in aqueous solutions, they must also undergo surface modification to impart solubility in water. In this protocol, an amphiphilic polymer is used to interact with both hydrophobic ligands on the quantum dot surface and bulk solvent water molecules. Here, a detailed protocol is provided for the synthesis of highly fluorescent InP/ZnS quantum dots that are suitable for use in biomedical applications.     

Design Principles of FRET‐Based Dye‐Sensitized Solar Cells with Buried Quantum Dot Donors

In this article, the physics of FRET is demonstrated for an architecture of dye‐sensitized solar cells, in which the quantum dot “antennas” that serve as donors are incorporated into the solid titania electrode, providing isolation from electrolyte quenching, and potentially increased photostability. The energy transferred to the dye acceptor from the quantum dot donor, in addition to the direct light absorption by the dye, finally induce dye excitation and electron injection to the metal oxide semiconductor electrode. We use time‐resolved photoluminescence measurements to directly show achievement of FRET efficiencies of up to 70%, corresponding to over 80% internal quantum efficiency when considering radiative energy transfer as well. The various parameters governing the FRET efficiency and the requirements for high efficiency FRET‐based cells are discussed. Since both buried donors inside the electrode and donors solubilized in the electrolyte have both been shown to achieve high energy transfer efficiencies, and as the two methods take advantage of different available volumes of the electrode to introduce donors providing the excess absorption, synergy of the two methods is highly promising for achieving panchromatic absorption within a thin electrode.     

Annexin A5-conjugated quantum dots with a paramagnetic lipidic coating for the multimodal detection of apoptotic cells

Apoptosis, or programmed cell death, plays an important role in the etiology of a variety of diseases, including cancer. Visualization of apoptosis would allow both early detection of therapy efficiency and evaluation of disease progression. To that aim we developed a novel annexin A5-conjugated bimodal nanoparticle. The nanoparticle is composed of a quantum dot that is encapsulated in a paramagnetic micelle to enable its use both for optical imaging and MRI. Multiple recombinant human annexin A5 protein molecules were covalently coupled to the nanoparticle for targeting. In this study the specificity of the annexin A5-conjugated nanoparticles for apoptotic cells was demonstrated both with fluorescence microscopy and MRI, which confirms its potential for the detection of apoptosis with both imaging modalities in vivo.     

Imaging neuronal structure dynamics using 2‐photon super‐resolution patterned excitation reconstruction microscopy

Visualizing fine neuronal structures deep inside strongly light‐scattering brain tissue remains a challenge in neuroscience. Recent nanoscopy techniques have reached the necessary resolution but often suffer from limited imaging depth, long imaging time or high light fluence requirements. Here, we present two‐photon super‐resolution patterned excitation reconstruction (2P‐SuPER) microscopy for 3‐dimensional imaging of dendritic spine dynamics at a maximum demonstrated imaging depth of 130 μm in living brain tissue with approximately 100 nm spatial resolution. We confirmed 2P‐SuPER resolution using fluorescence nanoparticle and quantum dot phantoms and imaged spiny neurons in acute brain slices. We induced hippocampal plasticity and showed that 2P‐SuPER can resolve increases in dendritic spine head sizes on CA1 pyramidal neurons following theta‐burst stimulation of Schaffer collateral axons. 2P‐SuPER further revealed nanoscopic increases in dendritic spine neck widths, a feature of synaptic plasticity that has not been thoroughly investigated due to the combined limit of resolution and penetration depth in existing imaging technologies.      

Photoluminescence Quenching in Quantum Emitter,Metallic Nanoparticle,and Graphene Hybrids

We have developed a theory for photoluminescence quenching and plasmonic properties in hybrid nanosystems made from three nanosystems such as a quantum emitters, metallic nanoparticles, and graphene. The metallic nanoparticles and graphene have surface plasmons which couple with probe photons and create surface plasmon polaritons. Therefore, the excitons in the quantum emitters interact with surface plasmon polaritons via the dipole-dipole interaction. Due to this interaction, energy is exchanged between the nanosystems. The second quantized formulation and the quantum density matrix method have been used to calculate photoluminescence and the radiative and non-radiative decay processes in the presence of dipole-dipole interaction. We have compared our theory with experiments of two and three nanosystems, and a good agreement between theory and experiments is achieved. It has been found that the photoluminescence quenching in hybrid systems not only occurs through the direct non-radiative energy transfer from the quantum emitter to the metal nanoparticle and to graphene but also occurs through the indirect non-radiative energy transfer from quantum emitter to the metal nanoparticle via graphene and from the quantum emitter to graphene via metal nanoparticle. These are interesting findings and they can be used to fabricate nanoswitches and nanosensors for medical applications.     

Quantum nature of photon signal emitted by Xanthoria parietina and its implications to biology

The properties of living systems are usually described in the semi-classical framework that makes phenomenological division of properties into four classes--matter, psyche, soft consciousness and hard consciousness. Quantum framework provides a scientific basis of this classification of properties. The scientific basis requires the existence of macroscopic quantum entity entangled with quantum photon field of a living system. Every living system emits a photon signal with features indicating its quantum nature. Quantum nature of the signal emitted by a sample of X. parietina is confirmed by analysing photo count distributions obtained in 20000 measurements of photon number in contiguous bins of sizes of 50, 100, 200, 300 and 500 ms. The measurements use a broadband detector sensitive in 300-800 nm range (Photo count distributions of background noise and observed signal are measured similarly. These measurements background noise corrected squeezed state parameters of the signal. The parameters are signal strength expressed in counts per bin, r = 0.06, theta = 2.76 and phi = 0.64. The parameters correctly reproduce photo count distribution of any bin size in 50 ms-6 s range. The reproduction of photo count distributions is a credible evidence of spontaneous emission of photon signal in a quantum squeezed state for macroscopic time by the sample. The evidence is extrapolated to other living systems emitting similar photon signals. It is suggested that every living system is associated with a photon field in squeezed state. The suggestion has far reaching implications to biology and provides two ways of observing and manipulating a living system--either through matter or field or a combination of the two. Some implications and possible scenarios are elaborated.     

Mechanically mediated electron transfer in model metallo-enzyme interfaces

In this paper, we develop a physical analysis of charge transfer in the model 'metallo-enzyme' complex which consists of a synthetic redox-addressed assembly (a 'reaction center') hybridized with a quantum dot (a gold nanoparticle) and attached via molecular bridge (a spacer) to the electrode. This artificial system allows us to model electronic transduction in experimental redox ezyme-gold nanoparticle hybrid structure recently reported by Xiao et al. [Xiao, Y., Patolsky, F., Katz, E., Hainfeid, J.F., Willner, I., 2003. Science 299, 1877-1881]. We consider a photosensitive spacer that allows us to control the conductivity of the bridge by light. In this paper we will focus on a special type of nanoelectro-mechanical processes in this system and investigate single electronic effects in there.     

Hydrolytic enzymes conjugated to quantum dots mostly retain whole catalytic activity

BackgroundTagging a luminescent quantum dot (QD) with a biological like enzyme (Enz) creates value-added entities like quantum dot–enzyme bioconjugates (QDEnzBio) that find utility as sensors to detect glucose or beacons to track enzymes in vivo. For such applications, it is imperative that the enzyme remains catalytically active while the quantum dot is luminescent in the bioconjugate. A critical feature that dictates this is the quantum dot–enzyme linkage chemistry. Previously such linkages have put constraints on polypeptide chain dynamics or hindered substrate diffusion to active site, seriously undermining enzyme catalytic activity. In this work we address this issue using avidin–biotin linkage chemistry together with a flexible spacer to conjugate enzyme to quantum dot.MethodsThe catalytic activity of three biotinylated hydrolytic enzymes, namely, hen egg white lysozyme (HEWL), alkaline phosphatase (ALP) and acetylcholinesterase (AChE) was investigated post-conjugation to streptavidin linked quantum dot for multiple substrate concentrations and varying degrees of biotinylation.ResultsWe demonstrate that all enzymes retain full catalytic activity in the quantum dot–enzyme bioconjugates in comparison to biotinylated enzyme alone. However, unlike alkaline phosphatase and acetylcholinesterase, the catalytic activity of hen egg white lysozyme was observed to be increasingly susceptible to ionic strength of medium with rising level of biotinylation. This susceptibility was attributed to arise from depletion of positive charge from lysine amino groups after biotinylation.ConclusionsWe reasoned that avidin–biotin linkage in the presence of a flexible seven atom spacer between biotin and enzyme poses no constraints to enzyme structure/dynamics enabling retention of full enzyme activity.General significanceOverall our results demonstrate for the first time that streptavidin–biotin chemistry can yield quantum dot enzyme bioconjugates that retain full catalytic activity as native enzyme.     

Resonant Broadband Field Enhancement in Cylindrical Plasmonic Structure Surrounded by Perovskite Environment

We demonstrate the optical response of metal nanoparticles and their interaction with organic-inorganic perovskite (methyl ammonia lead halide (CH₃NH₃PbI₃)) environment using discrete dipole approximation (DDA) simulation technique. Important optical properties like absorption, scattering, and electric field calculations for metal nanoparticle using different geometry have been analyzed. The metal nanoparticles embedded in the perovskite media strongly support surface plasmon resonances (SPRs). The plasmonic interaction of metal nanoparticles with perovskite matrix is a strong function of MNP’s shape, size, and surrounding environment that can manipulate the optical properties considerably. The cylindrical shape of MNPs embedded in perovskite environment supports the SPR which is highly tunable to subwavelength range of 400–800 nm. Wide range of particle sizes has been selected for Ag, Au, and Al spherical and cylindrical nanostructures surrounded by perovskite matrix for simulation. The chosen hybrid material and anisotropy of structure together make a complex function for resonance shape and width. Among all MNPs, 70-nm spherical silver nanoparticle (NP) and cylindrical Ag NP having diameter of 50 nm and length of 70 nm (aspect ratio 1.4) generate strong electric field intensity that facilitates increased photon absorption. The plasmonic perovskite interaction plays an important role to improve the absorption of photon inside the thin film perovskite environment that may be applicable to photovoltaics and photonics.

     

Plasmonic Effects of Dual-Metal Nanoparticle Layers for High-Performance Quantum Dot Solar Cells

To improve quantum dot solar cell performance, it is crucial to make efficient use of the available incident sunlight to ensure that the absorption is maximized. The ability of metal nanoparticles to concentrate incident sunlight via plasmon resonance can enhance the overall absorption of photovoltaic cells due to the strong confinement that results from near-field coupling or far-field scattering plasmonic effects. Therefore, to simultaneously and synergistically utilize both plasmonic effects, the placement of different plasmonic nanostructures at the appropriate locations in the device structure is also critical. Here, we introduce two different plasmonic nanoparticles, Au and Ag, to a colloidal PbS quantum dot heterojunction at the top and bottom interface of the electrodes for further improvement of the absorption in the visible and near-infrared spectral regions. The Ag nanoparticles exhibit strong scattering whereas the Au nanoparticles exhibit an intense optical effect in the wavelength region where the absorption of light of the PbS quantum dot is strongest. It is found that these dual-plasmon layers provide significantly improved short-circuit current and power conversion efficiency without any form of trade-off in terms of the fill factor and open-circuit voltage, which may result from the indirect contact between the plasmonic nanoparticles and colloidal quantum dot films.

     

Bioconjugation of CdTe quantum dot for the detection of 2,4-dichlorophenoxyacetic acid by competitive fluoroimmunoassay based biosensor

Quantum dots (QD) are semiconductor fluorescent nanoparticles, which can be made use of for environmental monitoring with high sensitivity. In view of the alarming levels of pesticides and herbicides being used in agriculture practices, there is a need for their rapid, sensitive and specific detection in food and environmental samples, as pesticides and herbicides are harmful to living beings even at trace levels. Present study was carried out to develop a reliable and rapid method for analysis and detection of 2,4-D (herbicide) using cadmium telluride quantum dot nanoparticle (CdTe QD). Fluoroimmunoassay based on the fluorescent property of quantum dot was used along with immunoassay to detect 2,4-D. CdTe capped with mercaptopropionic acid, was conjugated using N-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride (EDC) and a coupling reagent like N-hydroxysuccinimide (NHS) to alkaline phosphatase (ALP) which was in turn conjugated to 2,4-D molecule. Anti 2,4-D-IgG antibodies were immobilized in an immunoreactor column using Sepharose CL-4B as an inert matrix. The detection of 2,4-D was carried out by fluoroimmunoassay-based biosensor using competitive binding between conjugated 2,4-D-ALP-CdTe and free 2,4-D with immobilized anti 2,4-D antibodies in an immunoreactor column. It was possible to detect 2,4-D upto 250pgmL(-1). Present study also emphasizes on the resonance energy transfer between ALP and CdTe QD as a result of bioconjugation, which can be used for future biosensor development based on quantum dot-biomolecular interactions.     

Ultra‐sensitive,rapid gold nanoparticle‐quantum dot plexcitonic self‐assembled aptamer‐based nanobiosensor for the detection of human cardiac troponin I

Acute myocardial infarction (AMI) is one of the leading causes of death throughout the world. Usual methods for detecting AMI are expensive, time‐consuming and using blood samples as biological samples. Therefore, creating an ultra‐fast, sensitive and non‐invasive diagnostic test is necessary. Herein, a novel ultra‐sensitive, fluorescent, plasmon‐exciton coupling hybrid of a gold nanoparticle‐quantum dot (PQ)‐based aptamer nanobiosensor is presented for the detection of human cardiac troponin I (cTnI), the golden biomarker of AMI, and a preclinical test is performed within saliva. The binding of the cTnI protein to aptamer leads to a fluorescence enhancement of the plexcitonic hybrid system. The response range of this nanobiosensor is 0.4–2500 fM and the limit of detection is 0.3 fM. It seems that this novel design of nanobiosensor in the form of the PQ plexcitonic hybrid system can presents new opportunities for nanobiosensor progress.     

Neurexin/Neuroligin Interaction Kinetics Characterized by Counting Single Cell-Surface Attached Quantum Dots

We report what to our knowledge is a new method to characterize kinetic rates between cell-surface-attached adhesion molecules. Cells expressing specific membrane receptors are surface-labeled with quantum dots coated with their respective ligands. The progressive diminution in the total number of surface-diffusing quantum dots tracked over time collectively reflects intrinsic ligand/receptor interaction kinetics. The probability of quantum dot detachment is modeled using a stochastic analysis of bond formation and dissociation, with a small number of ligand/receptor pairs, resulting in a set of coupled differential equations that are solved numerically. Comparison with the experimental data provides an estimation of the kinetic rates, together with the mean number of ligands per quantum dot, as three adjustable parameters. We validate this approach by studying the calcium-dependent neurexin/neuroligin interaction, which plays an important role in synapse formation. Using primary neurons expressing neuroligin-1 and quantum dots coated with purified neurexin-1β, we determine the kinetic rates between these two binding partners and compare them with data obtained using other techniques. Using specific molecular constructs, we also provide interesting information about the effects of neurexin and neuroligin dimerization on the kinetic rates. As it stands, this simple technique should be applicable to many types of biological ligand/receptor pairs.     

Application of Solanum lycopersicum (tomato) hairy roots for production of passivated CdS nanocrystals with quantum dot properties

Semiconductor quantum dot particles have a wide range of applications in medicine, bioassays, computing and photovoltaics. Biological synthesis is an attractive approach for mass production of quantum dots as cells have the capacity to passivate the particles with organic ligands. In this work, hairy roots of Solanum lycopersicum (tomato) were used to produce CdS nanoparticles with quantum dot properties. Treatment of the roots with 100 μM Cd during the mid-growth phase of batch culture elicited cellular responses for Cd detoxification without affecting root growth. A combination of freeze-drying and freeze-thawing of the roots was used to extract Cd from the biomass; anion-exchange chromatography was then applied to selectively remove metal–phytochelatin complexes. Size-fractionation using gel filtration allowed the recovery of phytochelatin-capped Cd- and inorganic sulphide-containing nanoparticles displaying the size and size-dependent optical/electronic properties of CdS quantum dots. At 4–10 nm in diameter, these particles fluoresced at wavelengths corresponding to blue-violet on the colour spectrum and exhibited a high level of photostability with prolonged excitation. Whereas 69% of the Cd extracted from the roots was associated with phytochelatin peptides, the maximum yield of CdS nanocrystals with quantum dot properties was 1.4% of the total Cd taken up into the biomass. This work demonstrates a new culture-based approach for the biosynthesis of metallo-organic semiconductor quantum dots using hairy roots.     

Quantum Theory of Surface Plasmon Polaritons: Planar and Spherical Geometries

A quantum theory of retarded surface plasmons on a metal–vacuum interface is formulated, by analogy with the well-known and widely exploited theory of exciton-polaritons. The Hamiltonian for mutually interacting instantaneous surface plasmons and transverse electromagnetic modes is diagonalized with recourse to a Hopfield–Bogoljubov transformation, in order to obtain a new family of modes, to be identified with retarded plasmons. The interaction with nearby dipolar emitters is treated with a full quantum formalism based on a general definition of modal effective volumes. The illustrative cases of a planar surface and of a spherical nanoparticle are considered in detail. In the ideal situation of absence of dissipation, as an effect of the conservation of in-plane wavevector, retarded plasmons on a planar surface represent true stationary states (which are usually called surface plasmon polaritons), whereas retarded plasmons in a spherical nanoparticle, characterized by frequencies that overlap with the transverse electromagnetic continuum, become resonances with a finite radiative broadening. The theory presented constitutes a suitable full quantum framework for the study of nonperturbative and nonlinear effects in plasmonic nanosystems.     

Coherent Control of Two-Dimensional Optical Absorption in a Quantum Dot Nanostructure

We investigate the two-dimensional (2D) optical absorption spectrum in a semiconductor quantum dot nanostructure driven by two orthogonal standing-wave lasers. It is found that, due to the position-dependent quantum interference effect, the 2D optical absorption spectrum can be easily controlled via adjusting the system parameters. Thus, our scheme may provide some technological applications in solid-state optoelectronics.     

Engineering imaging probes and molecular machines for nanomedicine

Nanomedicine is an emerging field that integrates nanotechnology, biomolecular engineering, life sciences and medicine; it is expected to produce major breakthroughs in medical diagnostics and therapeutics. Due to the size-compatibility of nano-scale structures and devices with proteins and nucleic acids, the design, synthesis and application of nanoprobes, nanocarriers and nanomachines provide unprecedented opportunities for achieving a better control of biological processes, and drastic improvements in disease detection, therapy, and prevention. Recent advances in nanomedicine include the development of functional nanoparticle based molecular imaging probes, nano-structured materials as drug/gene carriers for in vivo delivery, and engineered molecular machines for treating single-gene disorders. This review focuses on the development of molecular imaging probes and engineered nucleases for nanomedicine, including quantum dot bioconjugates, quantum dot-fluorescent protein FRET probes, molecular beacons, magnetic and gold nanoparticle based imaging contrast agents, and the design and validation of zinc finger nucleases (ZFNs) and TAL effector nucleases (TALENs) for gene targeting. The challenges in translating nanomedicine approaches to clinical applications are discussed.     

Dipole Decay Rates Engineering via Silver Nanocones

A full control of the interaction between confined plasmons and point sources of radiation is a central issue in molecular plasmonics. In this paper, a theoretical contribution towards a physical understanding on the localized surface plasmons excited into metallic nanocones by a point dipole is given. A numerical approach based on the discrete dipole approximation is applied to determine the modifications of the dipole decay rates for varying geometrical parameters of the dipole-metal nanoparticle system. Results declare the centrality of the cone aperture to control the plasmon resonances and to handle the effects it induces on the lifetime of a point emitter. A full spectral tuning of the resonances in the decay rates can be achieved by operating on a unique spatial degree of freedom: by tailoring the aperture alone, total decay rates 10⁵ times higher than the free-space value can be obtained at short distances from the metal in a large region of the spectral range. Quite unexpectedly, size dependence of the antenna is found to have a marginal role if only a lifetime manipulation is desired. It becomes, instead, a crucial aspect of the problem when large quantum yields are required. Results presented in this work shed light on spontaneous emission modification due to interaction with plasmonic nanocones of different shapes and are relevant for a number of applications in the fields of nanoplasmonics and fluorescence microscopy.