Search

Depto. de Química Física, Fac. de Ciencias Químicas, pub

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., Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

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., Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

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 and enable the study of molecular dynamics with unprecedented precision., Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

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 flat spectral response of dielectric silica nanoparticles simplifies the choice of illumination wavelength., Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

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 microfluidic devices. We systematically monitored the evolution of the plasmon scattering signal from thousands of single nanoparticles in parallel, from different gold nanorod batches, prepared by both, silver-assisted and silver-free seeded growth. By varying the experimental conditions, we confirmed the presence of a silver surface layer for nanorods prepared by the silver-assisted method. Although the silver layer is initially protected by the surfactant CTAB, it gets oxidized as soon as CTAB desorbs because of a reduced concentration in the flowing solution., Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

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., Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

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 same gold nanoparticles using scanning electron microscopy. Our method of estimating individual particle dimensions from spectroscopic data reduces the error in plasmonic sensing experiments by as much as 30%., Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

Single-particle plasmon spectroscopy has become a standard technique to detect and quantify the presence of unlabeled macromolecules. Here, we extend this method to determine their exact distance from the plasmon sensors with sub-nanometer resolution by systematically varying the sensing range into the surrounding by adjusting the size of the plasmonic nanoparticles. We improved current single-particle plasmon spectroscopy to record continuously for hours the scattering spectra of thousands of nanoparticles of different sizes simultaneously with 1.8 s time resolution. We apply this technique to study the interaction dynamics of bacterial Min proteins with supported lipid membranes of different composition. Our experiments reveal a surprisingly flexible operating mode of the Min proteins: In the presence of cardiolipin and membrane curvature induced by nanoparticles, the protein oscillation occurs on top of a stationary MinD patch. Our results reveal the need to consider membrane composition and local curvature as important parameters to quantitatively understand the Min protein system and could be extrapolated to other macromolecular systems. Our label-free method is generally easily implementable and well suited to measure distances of interacting biological macromolecules, Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

Single-particle plasmon spectroscopy has become a standard technique todetect and quantify the presence of unlabeled macromolecules. Here, we extend thismethod to determine their exact distance from the plasmon sensors with sub-nanometerresolution by systematically varying the sensing range into the surrounding by adjustingthe size of the plasmonic nanoparticles. We improved current single-particle plasmonspectroscopy to record continuously for hours the scattering spectra of thousands ofnanoparticles of different sizes simultaneously with 1.8 s time resolution. We apply thistechnique to study the interaction dynamics of bacterial Min proteins with supportedlipid membranes of different composition. Our experiments reveal a surprisinglyflexibleoperating mode of the Min proteins: In the presence of cardiolipin and membranecurvature induced by nanoparticles, the protein oscillation occurs on top of a stationaryMinD patch. Our results reveal the need to consider membrane composition and localcurvature as important parameters to quantitatively understand the Min protein system and could be extrapolated to othermacromolecular systems. Our label-free method is generally easily implementable and well suited to measure distances ofinteracting biological macromolecules

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., European Commission, Agencia Estatal de Investigación (España), Johannes Gutenberg University Mainz (Alemania), Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub