Cytotoxicity of Metal and Semiconductor Nanoparticles Indicated by Cellular Micromotility

In the growing field of nanotechnology, there is an urgent need to sensitively determine the toxicity of nanoparticles since many technical and medical applications are based on controlled exposure to particles, that is, as contrast agents or for drug delivery. Before the in vivo implementation, in vitro cell experiments are required to achieve a detailed knowledge of toxicity and biodegradation as a function of the nanoparticles' physical and chemical properties. In this study, we show that the micromotility of animal cells as monitored by electrical cell-substrate impedance analysis (ECIS) is highly suitable to quantify in vitro cytotoxicity of semiconductor quantum dots and gold nanorods…

Single Particle Plasmon Sensors as Label-Free Technique To Monitor MinDE Protein Wave Propagation on Membranes.

We use individual gold nanorods as pointlike detectors for the intrinsic dynamics of an oscillating biological system. We chose the pattern forming MinDE protein system from Escherichia coli (E. coli), a prominent example for self-organized chemical oscillations of membrane-associated proteins that are involved in the bacterial cell division process. Similar to surface plasmon resonance (SPR), the gold nanorods report changes in their protein surface coverage without the need for fluorescence labeling, a technique we refer to as NanoSPR. Comparing the dynamics for fluorescence labeled and unlabeled proteins, we find a reduction of the oscillation period by about 20%. The absence of photoble…

LbL multilayer capsules: recent progress and future outlook for their use in life sciences.

In this review we provide an overview of the recent progress in designing composite polymer capsules based on the Layer-by-Layer (LbL) technology demonstrated so far in material science, focusing on their potential applications in medicine, drug delivery and catalysis. The benefits and limits of current systems are discussed and the perspectives on emerging strategies for designing novel classes of therapeutic vehicles are highlighted. © 2010 The Royal Society of Chemistry.

Angular Trapping of Anisometric Nano-Objects in a Fluid

We demonstrate the ability to trap, levitate, and orient single anisometric nanoscale objects with high angular precision in a fluid. An electrostatic fluidic trap confines a spherical object at a spatial location defined by the minimum of the electrostatic system free energy. For an anisometric object and a potential well lacking angular symmetry, the system free energy can further strongly depend on the object's orientation in the trap. Engineering the morphology of the trap thus enables precise spatial and angular confinement of a single levitating nano-object, and the process can be massively parallelized. Since the physics of the trap depends strongly on the surface charge of the objec…

Detecting Intruders on the Nanoscale

Mammalian cell growth on gold nanoparticle-decorated substrates is influenced by the nanoparticle coating

In this work, we study epithelial cell growth on substrates decorated with gold nanorods that are functionalized either with a positively charged cytotoxic surfactant or with a biocompatible polymer exhibiting one of two different end groups, resulting in a neutral or negative surface charge of the particle. Upon observation of cell growth for three days by live cell imaging using optical dark field microscopy, it was found that all particles supported cell adhesion while no directed cell migration and no significant particle internalization occurred. Concerning cell adhesion and spreading as compared to cell growth on bare substrates after 3 days of incubation, a reduction by 45% and 95%, …

En-Face differential absorption optical coherence tomography with gold nanorods as the contrast agent

A new variety of nanoparticles showing unique and characteristic optical properties, appeals for its use as contrast agents in medical imaging. Gold nanospheres, nanorods and nanoshells with a silica core are new forms of promising contrast agents which can be tuned to specific absorption or scattering characteristics within the near-infrared (NIR) spectrum ranging from 650 - 1300 nm. They have the ability to be used for both image enhancement and as photosensitive markers due to their well designable scattering and absorption properties. Furthermore, their strong optical absorption permits treatment of malignant cells by photoablation processes, induced when heating them with a matched lig…

Growth of gold tips onto hyperbranched CdTe nanostructures

Momentum Distribution of Electrons Emitted from Resonantly Excited Individual Gold Nanorods.

Electron emission by femtosecond laser pulses from individual Au nanorods is studied with a time-of-flight momentum resolving photoemission electron microscope (ToF k-PEEM). The Au nanorods adhere to a transparent indium–tin oxide substrate, allowing for illumination from the rear side at normal incidence. Localized plasmon polaritons are resonantly excited at 800 nm with 100 fs long pulses. The momentum distribution of emitted electrons reveals two distinct emission mechanisms: a coherent multiphoton photoemission process from the optically heated electron gas leads to an isotropic emission distribution. In contrast, an additional emission process resulting from the optical field enhanceme…

Absorption Properties of Metal–Semiconductor Hybrid Nanoparticles

The optical response of hybrid metal-semiconductor nanoparticles exhibits different behaviors due to the proximity between the disparate materials. For some hybrid systems, such as CdS-Au matchstick-shaped hybrids, the particles essentially retain the optical properties of their original components, with minor changes. Other systems, such as CdSe-Au dumbbell-shaped nanoparticles, exhibit significant change in the optical properties due to strong coupling between the two materials. Here, we study the absorption of these hybrids by comparing experimental results with simulations using the discrete dipole approximation method (DDA) employing dielectric functions of the bare components as input…

Protein-membrane interaction probed by single plasmonic nanoparticles.

We present a nanosized and addressable sensor platform based on membrane coated plasmonic particles and show unequivocally the covering with lipid bilayers as well as the subsequent detection of streptavidin binding to biotinylated lipids. The binding is detected on membrane covered gold nanorods by monitoring the spectral shift by fast single particle spectroscopy (fastSPS) on many particles in parallel. Our approach allows for local analysis of protein interaction with biological membranes as a function of the lateral composition of phase separated membranes.

Light-controlled one-sided growth of large plasmonic gold domains on quantum rods observed on the single particle level

We create large gold domains (up to 15 nm) exclusively on one side of CdS or CdSe/CdS quantum rods by photoreduction of gold ions under anaerobic conditions. Electrons generated in the semiconductor by UV stimulation migrate to one tip where they reduce gold ions. Large gold domains eventually form; these support efficient plasmon oscillations with a light scattering cross section large enough to visualize single hybrid particles in a dark-field microscope during growth in real time.

Microfluidic continuous flow synthesis of rod-shaped gold and silver nanocrystals

We present a continuous flow synthesis of gold and silver nanorods allowing tailored design of particles with desired shapes and online monitoring of particle growth.

Self-Assembly of Amphiphilic Nanocrystals

Amphiphilic hybrid materials are formed from polymer-coated semiconductor nanoparticles that simulate a surfactant-like response (see picture). The strength and density of the surface coating are the key assembling forces driving a transition from single particles to cylindrical or vesicular superstructures.

Synthesis of Au-CdS@CdSe Hybrid Nanoparticles with a Highly Reactive Gold Domain.

We propose a novel route to synthesize semiconductor–gold hybrid nanoparticles directly in water, resulting in much larger gold domains than previous protocols (up to 50 nm) with very reactive surfaces which allow further functionalization. This method advances the possibility of self-assembly into complex structures with catalytic activity toward the reduction of nitro compounds by hydrides. The large size of these gold domains in hybrid particles supports efficient light scattering at the plasmon resonance frequency, making such structures attractive for single-particle studies.

Mechanical properties of MDCK II cells exposed to gold nanorods

Background: The impact of gold nanoparticles on cell viability has been extensively studied in the past. Size, shape and surface functionalization including opsonization of gold particles ranging from a few nanometers to hundreds of nanometers are among the most crucial parameters that have been focussed on. Cytoxicity of nanomaterial has been assessed by common cytotoxicity assays targeting enzymatic activity such as LDH, MTT and ECIS. So far, however, less attention has been paid to the mechanical parameters of cells exposed to gold particles, which is an important reporter on the cellular response to external stimuli.Results: Mechanical properties of confluent MDCK II cells exposed to go…

Comparative evaluation of the impact on endothelial cells induced by different nanoparticle structures and functionalization

In the research field of nanoparticles, many studies demonstrated a high impact of the shape, size and surface charge, which is determined by the functionalization, of nanoparticles on cell viability and internalization into cells. This work focused on the comparison of three different nanoparticle types to give a better insight into general rules determining the biocompatibility of gold, Janus and semiconductor (quantum dot) nanoparticles. Endothelial cells were subject of this study, since blood is the first barrier after intravenous nanoparticle application. In particular, stronger effects on the viability of endothelial cells were found for nanoparticles with an elongated shape in compa…

Plasmonic nanosensors reveal a height dependence of MinDE protein oscillations on membrane features

6 p.-4 fig.

The role of halide ions in the anisotropic growth of gold nanoparticles: a microscopic, atomistic perspective

We provide a microscopic view of the role of halides in controlling the anisotropic growth of gold nanorods through a combined computational and experimental study. Atomistic molecular dynamics simulations unveil that Br− adsorption is not only responsible for surface passivation, but also acts as the driving force for CTAB micelle adsorption and stabilization on the gold surface in a facet-dependent way. The partial replacement of Br− by Cl− decreases the difference between facets and the surfactant density. Finally, in the CTAC solution, no halides or micellar structures protect the gold surface and further gold reduction should be uniformly possible. Experimentally observed nanoparticle'…

Novel plasmonic sensor design using plasmon-induced transparency

We introduce a novel sensor concept in the field of plasmonics, namely plasmon-induced transparency sensors. These sensors combine localized particle plasmon resonances with extremely small sensing volume with excellent sharp spectral resonances that show a good respose to refractive index changes of the surrounding environment. The principle is based on the plasmonic analog of electromagnetically induced transparency (EIT) between a radiative dipole and a nonradiative quadrupole antenna. This effect yields a spectrally narrow resonance within a broad localized particle plasmon resonance in the near-infrared spectral region [1, 2]. Using deposition of biotin and streptavidin, we demonstrate…

CTAB Stabilizes Silver on Gold Nanorods

We present a study that allows us to explain the chemical changes behind the often observed but so far ununderstood drift of the plasmon resonance of chemically prepared gold nanorods in microfluid...

Self-assembly of small gold colloids with functionalized gold nanorods.

We present a general strategy to stabilize gold nanorod suspensions with mono- and bifunctional polyethylene glycol (PEG) and to attach a controlled number of nanoparticles or biomolecules. Characterization by gel electrophoresis, transmission electron microscopy (TEM), and optical dark-field microscopy show the specific binding of functionalized nanorods to their target while avoiding nonspecific binding to substrates, matrices, and other particles. Such nanorods are well suited for self-assembly of nanostructures and single-molecule labeling.

Gold Nanorods as Plasmonic Sensors for Particle Diffusion.

Plasmonic gold nanoparticles are normally used as sensor to detect analytes permanently bound to their surface. If the interaction between the analyte and the nanosensor surface is negligible, it only diffuses through the sensor’s sensing volume, causing a small temporal shift of the plasmon resonance position. By using a very sensitive and fast detection scheme, we are able to detect these small fluctuations in the plasmon resonance. With the help of a theoretical model consistent with our detection geometry, we determine the analyte’s diffusion coefficient. The method is verified by observing the trends upon changing diffusor size and medium viscosity, and the diffusion coefficients obtai…

Plasmonic Nanosensors for the Determination of Drug Effectiveness on Membrane Receptors.

We demonstrate the potential of the NanoSPR (nanoscale surface plasmon resonance sensors) method as a simple and cheap tool for the quantitative study of membrane protein–protein interactions. We use NanoSPR to determine the effectiveness of two potential drug candidates that inhibit the protein complex formation between FtsA and ZipA at initial stages of bacterial division. As the NanoSPR method relies on individual gold nanorods as sensing elements, there is no need for fluorescent labels or organic cosolvents, and it provides intrinsically high statistics. NanoSPR could become a powerful tool in drug development, drug delivery, and membrane studies.

Single Unlabeled Protein Detection on Individual Plasmonic Nanoparticles

The ultimate detection limit in analytic chemistry and biology is the single molecule. Commonly, fluorescent dye labels or enzymatic amplification are employed. This requires additional labeling of the analyte, which modifies the species under investigation and therefore influences biological processes. Here, we utilize single gold nanoparticles to detect single unlabeled proteins with extremely high temporal resolution. This allows for monitoring the dynamic evolution of a single protein binding event on a millisecond time scale. The technique even resolves equilibrium coverage fluctuations, opening a window into Brownian dynamics of unlabeled macromolecules. Therefore, our method enables …

Toxicity of gold-nanoparticles: Synergistic effects of shape and surface functionalization on micromotility of epithelial cells

Nanoparticle exposure is monitored by a combination of two label-free and non-invasive biosensor devices which detect cellular shape and viscoelasticity (quartz crystal microbalance), cell motility and the dynamics of epithelial cell-cell contacts (electric cell-substrate impedance sensing). With these tools we have studied the impact of nanoparticle shape on cellular physiology. Gold (Au) nanoparticles coated with CTAB were synthesized and studied in two distinct shapes: Spheres with a diameter of (43 ± 4) nm and rods with a size of (38 ± 7) nm × (17 ± 3) nm. Dose-response experiments were accompanied by conventional cytotoxicity tests as well as fluorescence and dark-field microscopy to v…

Enhanced Thermal Stability of Gold and Silver Nanorods by Thin Surface Layers

Using in situ transmission electron microscopy, we find that a carbon shell governs the morphological transitions of gold and silver nanorods upon heating. Encapsulated Ag nanorods show a surprising nonuniform sublimation behavior starting from one side and leaving behind the shell. Uncovered gold nanorods transform their shape to spheres well below the bulk melting temperature through surface diffusion, which is prevented by a thin carbon shell.

Particle Plasmons as Dipole Antennas: State Representation of Relative Observables

The strong interactions between light and plasmons (in metal nanoparticles) allow to observe chemical and physical processes on and around the particle on nanometer length scales as well as they al...

Mapping the polarization pattern of plasmon modes reveals nanoparticle symmetry.

We study the wavelength and polarization dependent plasmon resonances of single silver and gold nanorods, triangles, cubes, and dimers with a novel single particle spectroscopy method (RotPOL). In RotPOL, a rotating wedge-shaped polarizer encodes the full polarization information of each particle within one image. This reveals the symmetry of the particles and their plasmon modes, allows analyzing inhomogeneous samples and the monitoring of particle shape changes during growth in situ.

Multiplexed plasmon sensor for rapid label-free analyte detection.

Efficient and cost-effective multiplexed detection schemes for proteins in small liquid samples would bring drastic advances to fields like disease detection or water quality monitoring. We present a novel multiplexed sensor with randomly deposited aptamer functionalized gold nanorods. The spectral position of plasmon resonances of individual nanorods, monitored by dark-field spectroscopy, respond specifically to different proteins. We demonstrate nanomolar sensitivity, sensor recycling, and the potential to upscale to hundreds or thousands of targets.

Highly Sensitive plasmonic silver nanorods

We compare the single-particle plasmonic sensitivity of silver and gold nanorods with similar resonance wavelengths by monitoring the plasmon resonance shift upon changing the environment from water to 12.5% sucrose solution. We find that silver nanoparticles have 1.2 to 2 times higher sensitivity than gold, in good agreement with simulations based on the boundary-elements-method (BEM). To exclude the effect of particle volume on sensitivity, we test gold rods with increasing particle width at a given resonance wavelength. Using the Drude-model of optical properties of metals together with the quasi-static approximation (QSA) for localized surface plasmons, we show that the dominant contrib…

Plasmonic Focusing Reduces Ensemble Linewidth of Silver-Coated Gold Nanorods

Silver coating gold nanorods reduces the ensemble plasmon line width by changing the relation connecting particle shape and plasmon resonance wavelength. This change, we term "plasmonic focusing", leads to less variation of resonance wavelengths for the same particle size distribution. We also find smaller single particle linewidth comparing resonances at the same wavelength but show that this does not contribute to the ensemble linewidth narrowing.

Interfacial States Cause Equal Decay of Plasmons and Hot Electrons at Gold-Metal Oxide Interfaces.

We compare the decay of plasmons and "conventional" hot electrons within the same series of gold/metal oxide interfaces. We found an accelerated decay of hot electrons at gold-metal oxide interfaces with decreasing band gap of the oxide material. The decay is accelerated by the increased phase space for electron scattering caused by additional interfacial states. Since plasmons decay faster within the same series of gold-metal oxide interfaces, we propose plasmons are able to decay into the same interfacial states as hot electrons. The similarity of plasmon damping to conventional hot electron decay implies that many classical surface analysis techniques and theoretical concepts are transfe…

Plasmonic-photonic hybrid cavity for tailored light-matter coupling

We propose and demonstrate a hybrid cavity system in which metal nanoparticles are evanescently coupled to a dielectric photonic crystal cavity using a nanoassembly method. While the metal constituents lead to strongly localized fields, optical feedback is provided by the surrounding photonic crystal structure. The combined effect of plasmonic field enhancement and high quality factor (Q ≈ 900) opens new routes for the control of light-matter interaction at the nanoscale.

The role of halide ions in the anisotropic growth of gold nanoparticles: a microscopic, atomistic perspective† †Electronic supplementary information (ESI) available: Solvation structure of halides, electrostatic potentials at the interface, halide ions on the Au(111) surface in water, density profiles and electrostatic potential profiles for different CTAB/CTAC systems and conversion of the plasmon shift to the layer thickness. See DOI: 10.1039/c6cp01076h Click here for additional data file.

We provide a microscopic view of the role of halides in controlling the anisotropic growth of gold nanorods through a combined computational and experimental study.

Nanoassembled plasmonic-photonic hybrid cavity for tailored light-matter coupling.

We propose and demonstrate a hybrid cavity system in which metal nanoparticles are evanescently coupled to a dielectric photonic crystal cavity using a nanoassembly method. While the metal constituents lead to strongly localized fields, optical feedback is provided by the surrounding photonic crystal structure. The combined effect of plasmonic field enhancement and high quality factor (Q approximately 900) opens new routes for the control of light-matter interaction at the nanoscale.

Selbstorganisation amphiphiler Nanokristalle

Amphiphile Hybridmaterialien bestehen aus polymerbeschichteten Halbleiternanopartikeln, die ein stark tensidahnliches Verhalten aufweisen (siehe Bild). Die Starke und Dichte der Oberflachenbeschichtung sind die treibenden Organisationskrafte hinter dem Ubergang von isolierten Partikeln zu zylindrischen oder vesikularen Uberstrukturen.

Plasmonic Core–Satellite Assemblies as Highly Sensitive Refractive Index Sensors

Highly sensitive and spectrally tunable plasmonic nanostructures are of great demand for applications such as SERS and parallel biosensing. However, there is a lack of such nanostructures for the midvisible spectral regions as most available chemically stable nanostructures offer high sensitivity in the red to far red spectrum. In this work, we report the assembly of highly sensitive nanoparticle structures using a hydroxylamine mediated core–satellite assembly of 20 nm gold nanoparticle satellites onto 60 nm spherical gold cores. The average number of satellites allows tuning the plasmon resonance wavelength from 543 to 575 nm. The core–satellite nanostructures are stable in pH ranges from…

Plasmon damping depends on the chemical nature of the nanoparticle interface

Damping of gold nanorod plasmons by surface-adsorbed molecules is best explained by scattering off adsorbate-induced dipoles.

A new approach to assess gold nanoparticle uptake by mammalian cells: combining optical dark-field and transmission electron microscopy.

Toxicological effects of nanoparticles are associated with their internalization into cells. Hence, there is a strong need for techniques revealing the interaction between particles and cells as well as quantifying the uptake at the same time. For that reason, herein optical dark-field microscopy is used in conjunction with transmission electron microscopy to investigate the uptake of gold nanoparticles into epithelial cells with respect to shape, stabilizing agent, and surface charge. The number of internalized particles is strongly dependent on the stabilizing agent, but not on the particle shape. A test of metabolic activity shows no direct correlation with the number of internalized par…

Planar metamaterial analogue of electromagnetically induced transparency for plasmonic sensing.

We experimentally demonstrate a planar metamaterial analogue of electromagnetically induced transparency at optical frequencies. The structure consists of an optically bright dipole antenna and an optically dark quadrupole antenna, which are cut-out structures in a thin gold film. A pronounced coupling-induced reflectance peak is observed within a broad resonance spectrum. A metamaterial sensor based on these coupling effects is experimentally demonstrated and yields a sensitivity of 588 nm/RIU and a figure of merit of 3.8.

Organization into Higher Ordered Ring Structures Counteracts Membrane Binding of IM30, a Protein Associated with Inner Membranes in Chloroplasts and Cyanobacteria.

The IM30 (inner membrane-associated protein of 30 kDa), also known as the Vipp1 (vesicle-inducing protein in plastids 1), has a crucial role in thylakoid membrane biogenesis and maintenance. Recent results suggest that the protein binds peripherally to membranes containing negatively charged lipids. However, although IM30 monomers interact and assemble into large oligomeric ring complexes with different numbers of monomers, it is still an open question whether ring formation is crucial for membrane interaction. Here we show that binding of IM30 rings to negatively charged phosphatidylglycerol membrane surfaces results in a higher ordered membrane state, both in the head group and in the inn…

Single Out-of-Resonance Dielectric Nanoparticles as Molecular Sensors.

Light scattering from single nanoparticles and nanostructures is a commonly used readout method for nanosensors. Increasing the spectral sensitivity of resonant nanosensors to changes in their local surrounding has been the focus of many studies. Switching from spectral to intensity monitoring allows one to investigate nonresonant or out-of-resonance dielectric nanoparticles. Here, we systematically compared such dielectric silica nanoparticles with plasmonic gold nanorods by deriving analytical expressions and by performing experiments. The experiments show a similar sensitivity for the detection of an adsorbate layer for both particle types, which is in good agreement with theory. The fla…

Evaluation of Nanoparticles as Contrast Agent for Photoacoustic Imaging in Living Cells

Au@MnO-“Nanoblumen” - Hybrid-Nanokomposite zur selektiven dualen Funktionalisierung und Bildgebung

In j ngster Vergangenheit hat das Interesse f r die Entwicklung von Hybrid-Nanostrukturen, die sich aus verschiedenen Materialien zusammensetzen, in erheblichem Mase zugenommen. Es wurde berichtet, dass die Zusammenf hrung verschiedener Nanomaterialien, die ihrerseits spezifische optische, magnetische oder elektronische Eigenschaften aufweisen, zu Kompositen aus mehreren dieser Komponenten, deren individuelle Eigenschaften ver ndern oder sogar verbessern k nnen. Durch gezielte Optimierung der Struktur und der Grenzfl chenwechselwirkung innerhalb der Nanokomposite k nnte eine breite Basis f r zuk nftige Technologien geschaffen werden, beispielweise f r die synchrone Biomarkierung, Proteintre…

Synthesis of rod-shaped gold nanorattles with improved plasmon sensitivity and catalytic activity.

We prepared rod-shaped gold nanorattles solid gold nanorods surrounded by a thin gold shell using a galvanic replacement process starting with silver-coated gold nanorods. These structures are very promising candidates for catalytic applications and optimized plasmon sensors. They combine the advantages of rods (low plasmon resonance frequency, large polarizability, small damping) with the high surface area of hollow structures. The plasmon sensitivity to changes in the dielectric environment is up to 50% higher for gold nanorattles compared to gold nanorods with the same resonance frequency and 6x higher than for plasmons in spherical gold nanoparticles. The catalytic activity measured for…

Chemical Interface Damping Depends on Electrons Reaching the Surface.

Metallic nanoparticles show extraordinary strong light absorption near their plasmon resonance, orders of magnitude larger compared to nonmetallic nanoparticles. This "antenna" effect has recently been exploited to transfer electrons into empty states of an attached material, for example to create electric currents in photovoltaic devices or to induce chemical reactions. It is generally assumed that plasmons decay into hot electrons, which then transfer to the attached material. Ultrafast electron-electron scattering reduces the lifetime of hot electrons drastically in metals and therefore strongly limits the efficiency of plasmon induced hot electron transfer. However, recent work has revi…

Phase separated Cu@Fe3O4 heterodimer nanoparticles from organometallic reactants

Cu@Fe3O4 heteroparticles with distinct morphologies were synthesized from organometallic reactants. The shape of the magnetic domains could be controlled by the solvent and reaction conditions. They display magnetic and optical properties that are useful for simultaneous magnetic and optical detection. After functionalization, the Cu@Fe3O4 heterodimers become water soluble. The morphology, structure, magnetic and optical properties of the as-synthesized heterodimer nanoparticles were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), mossbauer spectroscopy, superconducting quantum interference device (SQUID) magnetometry, and dark field imaging. A special a…

Au@MnO nanoflowers: hybrid nanocomposites for selective dual functionalization and imaging.

Recently, the development of hybrid nanostructures consisting of various materials has attracted considerable interest. The assembly of different nanomaterials with specific optical, magnetic, or electronic properties to multicomponent composites can change and even enhance the properties of the individual constituents. Specifically tuning the structure and interface interactions within the nanocomposites has resulted in novel platforms of materials that may lead the way to various future technologies, such as synchronous biolabeling, protein separation and detection, heterogeneous catalysis, and multimodal imaging in biomedicine. Of the various kinds of nanomaterials, gold nanorods show an…

Plasmonic Nanosensors for the Label-Free Imaging of Dynamic Protein Patterns.

We introduce a new approach to monitor the dynamics and spatial patterns of biological molecular assemblies. Our molecular imaging method relies on plasmonic gold nanoparticles as point-like detectors and requires no labeling of the molecules. We show spatial resolution of up to 5 μm and 30 ms temporal resolution, which is comparable to wide-field fluorescence microscopy, while requiring only readily available gold nanoparticles and a dark-field optical microscope. We demonstrate the method on MinDE proteins attaching to and detaching from lipid membranes of different composition for 24 h. We foresee our new imaging method as an indispensable tool in advanced molecular biology and biophysic…

Warhead Reactivity Limits the Speed of Inhibition of the Cysteine Protease Rhodesain.

Viral and parasitic pathogens rely critically on cysteine proteases for host invasion, replication, and infectivity. Their inhibition by synthetic inhibitors, such as vinyl sulfone compounds, has emerged as a promising treatment strategy. However, the individual reaction steps of protease inhibition are not fully understood. Using the trypanosomal cysteine protease rhodesain as a medically relevant target, we design photoinduced electron transfer (PET) fluorescence probes to detect kinetics of binding of reversible and irreversible vinyl sulfones directly in solution. Intriguingly, the irreversible inhibitor, apart from its unlimited residence time in the enzyme, reacts 5 times faster than …

Plasmonic Nanosensors for Simultaneous Quantification of Multiple Protein–Protein Binding Affinities

Most of current techniques used for the quantification of protein-protein interactions require the analysis of one pair of binding partners at a time. Herein we present a label-free, simple, fast, and cost-effective route to characterize binding affinities between multiple macromolecular partners simultaneously, using optical dark-field spectroscopy and individual protein-functionalized gold nanorods as sensing elements. Our NanoSPR method could easily become a simple and standard tool in biological, biochemical, and medical laboratories.

Gold Nanoparticle Growth Monitored in situ Using a Novel Fast Optical Single-Particle Spectroscopy Method

Size- and shape-dependent optical properties of gold nanorods allow monitoring their growth using a novel fast single-particle spectroscopy (fastSPS) method. FastSPS uses a spatially addressable electronic shutter based on a liquid crystal device to investigate particles randomly deposited on a substrate, orders of magnitude faster than other techniques. We use fastSPS to observe nanoparticle growth in situ on a single-particle level and extract quantitative data on nanoparticle growth.

Probing the Size Effect of Co2FeGa-SiO2@C Nanocomposite Particles Prepared by a Chemical Approach

In this contribution, we report the chemical synthesis of carbon coated, silica supported Co2FeGa (Co2FeGa-SiO2@C) nanocomposite particles. The particle size of Co2FeGa particles can be tuned by varying the amount of silica supports. The dependences of the crystal structure and magnetic properties on particle size have been investigated by synchrotron radiation based X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) spectroscopy, transmission electron microscope (TEM), 57Fe Mossbauer spectroscopy, and superconducting quantum interference device (SQUID). The superparamagnetic critical size of Co2FeGa Heusler nanoparticles is found to be ∼17 nm by correlating the TEM derived par…

Structural and mechanistic insights into the interaction of the circadian transcription factor BMAL1 with the KIX domain of the CREB-binding protein

JBC papers in press xx, 16604-16619 (2019). doi:10.1074/jbc.RA119.009845

Potassium Triggers a Reversible Specific Stiffness Transition of Polyethylene Glycol

We use plasmon rulers made from two connected gold nanoparticles to monitor the conformation and stiffness of single PEG molecules and their response to cations. By observing equilibrium fluctuations of the interparticle distance, we obtain the spring constants or stiffness of the connecting single-molecule tether with pico-Newton sensitivity. We observe a transition of the PEG molecules’ extension and stiffness above about 1.2 mM K+ ion concentration which is specific to potassium ions. Molecular dynamics simulations reveal the formation of crown-like structures as the most likely molecular mechanism responsible for this specific effect.

Narrowing the Plasmonic Sensitivity Distribution by Considering the Individual Size of Gold Nanorods

The plasmonic nanoparticle sensitivity, sensing volume, and the signal-to-noise ratio are strongly dependent on the nanoparticle dimensions. It is difficult to chemically produce or purify nanoparticles with a size variation of less than 10%. This size variation induces a systematic error in sensing experiments that can be reduced when the exact size of each individual nanoparticle is known. In this work, we show how the size of gold nanorods can be estimated directly from the optical spectra of single nanoparticles by using the increase of radiation damping with the nanoparticle size. We verify our approach by comparing these spectrally estimated sizes with the precise sizes of exactly the…

Conformational dynamics of a single protein monitored for 24 hours at video rate

We use plasmon rulers to follow the conformational dynamics of a single protein for up to 24 h at a video rate. The plasmon ruler consists of two gold nanospheres connected by a single protein linker. In our experiment, we follow the dynamics of the molecular chaperone heat shock protein 90 (Hsp90), which is known to show “open” and “closed” conformations. Our measurements confirm the previously known conformational dynamics with transition times in the second to minute time scale and reveals new dynamics on the time scale of minutes to hours. Plasmon rulers thus extend the observation bandwidth 3–4 orders of magnitude with respect to single-molecule fluorescence resonance energy transfer a…

Liquid crystalline phases from polymer functionalised semiconducting nanorods

The orientation of semiconducting nanomaterials is a hot topic in optoelectronic applications. Liquid crystallinity offers the potential to orient inorganic anisotropic nanorods, if they can be solubilised sufficiently as realised by polymer functionalisation. In this work we functionalised TiO2, SnO2, ZnO and CdTe nanorods with PMMA, PS and PDEGMEMA (poly(diethylene glycol monomethyl ether) methacrylate) diblock copolymers containing anchor groupsvia grafting-to. The block copolymers were synthesised by RAFT polymerisation (PDI ≈ 1.2) via reactive ester diblock copolymers, which were functionalised later with anchor units polymer-analogously. The surface coverage of the nanorods (determine…

Implantable Sensors Based on Gold Nanoparticles for Continuous Long-Term Concentration Monitoring in the Body.

Implantable sensors continuously transmit information on vital values or biomarker concentrations in bodily fluids, enabling physicians to survey disease progression and monitor therapeutic success. However, currently available technologies still face difficulties with long-term operation and transferability to different analytes. We show the potential of a generalizable platform based on gold nanoparticles embedded in a hydrogel for long-term implanted biosensing. Using optical imaging and an intelligent sensor/reference-design, we assess the tissue concentration of kanamycin in anesthetized rats by interrogating our implanted sensor noninvasively through the skin. Combining a tissue-integ…

Quantitative Optical Trapping of Single Gold Nanorods

We report a quantitative analysis of the forces acting on optically trapped single gold nanorods. Individual nanorods with diameters between 8 and 44 nm and aspect ratios between 1.7 and 5.6 were stably trapped in three dimensions using a laser wavelength exceeding their plasmon resonance wavelengths. The interaction between the electromagnetic field of an optical trap and a single gold nanorod correlated with particle polarizability, which is a function of both particle volume and aspect ratio.

Plasmonic Silver Nanorod Sensitivity: Experiment and Simple Theoretical Treatment

We compare the plasmonic sensitivity of silver and gold nanorods with similar resonance wavelengths by monitoring the plasmon resonance shift of single noble metal nanorods upon changing the environment from water to sucrose solution. We find that silver nanorods have 1.2 to 2 times higher sensitivity than gold in good agreement with simulations based on the boundary-elements-method (BEM). To exclude the effect of particle volume on sensitivity, we test gold rods with increasing particle width at a given resonance wavelength. Using the Drude-model of optical properties of metal together with the quasi-static approximation (QSA) for localized surface plas-mons, we show that the dominant cont…

Intensity-Based Single Particle Plasmon Sensing.

Plasmon sensors respond to local changes of their surrounding environment with a shift in their resonance wavelength. This response is usually detected by measuring light scattering spectra to determine the resonance wavelength. However, single wavelength detection has become increasingly important because it simplifies the setup, increases speed, and improves statistics. Therefore, we investigated theoretically how the sensitivity toward such single wavelength scattering intensity changes depend on the material and shape of the plasmonic sensor. Surprisingly, simple equations describe this intensity sensitivity very accurately and allow us to distinguish the various contributions: Rayleigh…

Separation of Nanoparticles by Gel Electrophoresis According to Size and Shape

We demonstrate the separation of gold and silver nanoparticles according to their size and shape by agarose gel electrophoresis after coating them with a charged polymer layer. The separation is monitored optically using the size- and shape-dependent plasmon resonance of noble metal particles and confirmed by transmission electron microscopy (TEM). Electrophoretic mobilities are quantitatively explained by a model based on the Henry formula, providing a theoretical framework for predicting gel mobilities of polymer coated nanoparticles.

Plasmonic Nanosensors for the Label-Free Imaging of Dynamic Protein Patterns

Additional data to support our work on "Plasmonic Nanosensors for the Label-Free Imaging of Dynamic Protein Patterns" published in the Journal of Physical Chemistry Letters (DOI: 10.1021/acs.jpclett.0c01400) Movies: - S1: MinVideo_EColi.mp4 - S2: MinVideo_DOPC_DOPG_CL.mp4 - S3: MinVideo_DOPC_DOPG.mp4 Audio Files: - S1: MinSound_EColi.mp4 - S2: MinSound_DOPC_DOPG_CL.mp4 - S3: MinSound_DOPC_DOPG.mp4