Wendel Wohlleben

Quantum control of energy flow in light harvesting

Coherent light sources have been widely used in control schemes that exploit quantum interference effects to direct the outcome of photochemical processes. The adaptive shaping of laser pulses is a particularly powerful tool in this context: experimental output as feedback in an iterative learning loop refines the applied laser field to render it best suited to constraints set by the experimenter. This approach has been experimentally implemented to control a variety of processes, but the extent to which coherent excitation can also be used to direct the dynamics of complex molecular systems in a condensed-phase environment remains unclear. Here we report feedback-optimized coherent control over the energy-flow pathways in the light-harvesting antenna complex LH2 from Rhodopseudomonas acidophila, a photosynthetic purple bacterium. We show that phases imprinted by the light field mediate the branching ratio of energy transfer between intra- and intermolecular channels in the complexs donor–acceptor system. This result illustrates that molecular complexity need not prevent coherent control, which can thus be extended to probe and affect biological functions.

Testing Metal‐Oxide Nanomaterials for Human Safety

Nanomaterials can display distinct biological effects compared with bulk materials of the same chemical composition. The physico-chemical characterization of nanomaterials and their interaction with biological media are essential for reliable studies and are reviewed here with a focus on widely used metal oxide and carbon nanomaterials. Available rat inhalation and cell culture studies compared to original results suggest that hazard potential is not determined by a single physico-chemical property but instead depends on a combination of material properties. Reactive oxygen species generation, fiber shape, size, solubility and crystalline phase are known indicators of nanomaterials biological impact. According to these properties the summarized hazard potential decreases in the order multi-walled carbon nanotubes >> CeO(2), ZnO > TiO(2) > functionalized SiO(2) > SiO(2), ZrO(2), carbon black. Enhanced understanding of biophysical properties and cellular effects results in improved testing strategies and enables the selection and production of safe materials.

Acute and chronic effects of nano- and non-nano-scale TiO2 and ZnO particles on mobility and reproduction of the freshwater invertebrate Daphnia magna

Among the emerging literature addressing the biological effects of nanoparticles, very little information exists, particularly on aquatic organisms, that evaluates nanoparticles in comparison to non-nanocounterparts. Therefore, the potential effects of nano-scale and non-nano-scale TiO(2) and ZnO on the water flea, Daphnia magna, were examined in 48-h acute toxicity tests using three different test media, several pigment formulations--including coated nanoparticles--and a variety of preparation steps. In addition, a 21-d chronic Daphnia reproduction study was performed using coated TiO(2) nanoparticles. Analytical ultracentrifugation analyses provided evidence that the nanoparticles were present in a wide range of differently sized aggregates in the tested dispersions. While no pronounced effects on D. magna were observed for nano-scale and non-nano-scale TiO(2) pigments in 19 of 25 acute (48-h) toxicity tests (EC50>100 mg L(-1)), six acute tests with both nano- and non-nano-scale TiO(2) pigments showed slight effects (EC10, 0.5-91.2 mg L(-1)). For the nano-scale and non-nano-scale ZnO pigments, the acute 48-h EC50 values were close to the 1 mg L(-1) level, which is within the reported range of zinc toxicity to Daphnia. In general, the toxicity in the acute tests was independent of particle size (non-nano-scale or nano-scale), coating of particles, aggregation of particles, the type of medium or the applied pre-treatment of the test dispersions. The chronic Daphnia test with coated TiO(2) nanoparticles demonstrated that reproduction was a more sensitive endpoint than adult mortality. After 21d, the NOEC for adult mortality was 30 mg L(-1) and the NOEC for offspring production was 3 mg L(-1). The 21-d EC10 and EC50 values for reproductive effects were 5 and 26.6 mg L(-1), respectively. This study demonstrates the utility of evaluating nanoparticle effects relative to non-nano-scale counterparts and presents the first report of chronic exposure to TiO(2) nanoparticles in D. magna.

Cytotoxicity screening of 23 engineered nanomaterials using a test matrix of ten cell lines and three different assays

BackgroundEngineered nanomaterials display unique properties that may have impact on human health, and thus require a reliable evaluation of their potential toxicity. Here, we performed a standardized in vitro screening of 23 engineered nanomaterials. We thoroughly characterized the physicochemical properties of the nanomaterials and adapted three classical in vitro toxicity assays to eliminate nanomaterial interference. Nanomaterial toxicity was assessed in ten representative cell lines.ResultsSix nanomaterials induced oxidative cell stress while only a single nanomaterial reduced cellular metabolic activity and none of the particles affected cell viability. Results from heterogeneous and chemically identical particles suggested that surface chemistry, surface coating and chemical composition are likely determinants of nanomaterial toxicity. Individual cell lines differed significantly in their response, dependent on the particle type and the toxicity endpoint measured.ConclusionIn vitro toxicity of the analyzed engineered nanomaterials cannot be attributed to a defined physicochemical property. Therefore, the accurate identification of nanomaterial cytotoxicity requires a matrix based on a set of sensitive cell lines and in vitro assays measuring different cytotoxicity endpoints.

Not ready to use – overcoming pitfalls when dispersing nanoparticles in physiological media

Industrial nanoparticles are not developed to be compatible with in vitro cell culture assays which are carried out in isotonic solutions at physiological pH and often in the presence of proteins. The tendency of nanoparticles to deagglomerate or agglomerate is strongly sensitive to these parameters. The state of agglomeration and the protein corona bear an important influence on the level of toxic effects via the change of transport mechanisms and surface coating. Here we rigorously characterized the interaction of nanoparticles with physiological media for in vitro nanotoxicology experiments. Beyond adsorption of proteins on metal oxide and polymeric nanoparticles, we quantified nanoparticle deagglomeration due to adsorbing proteins acting as protection colloids. We report on previously neglected, but indispensable testing of sterility and measures to ensure it. Our findings result in a checklist of pre-requirements for dispersion of nanoparticles in physiological media and for reliable attribution of potential toxic effects.

Estimating the effective density of engineered nanomaterials for in vitro dosimetry

The need for accurate in vitro dosimetry remains a major obstacle to the development of cost-effective toxicological screening methods for engineered nanomaterials. An important key to accurate in vitro dosimetry is the characterization of sedimentation and diffusion rates of nanoparticles suspended in culture media, which largely depend upon the effective density and diameter of formed agglomerates in suspension. Here we present a rapid and inexpensive method for accurately measuring the effective density of nano-agglomerates in suspension. This novel method is based on the volume of the pellet obtained by bench-top centrifugation of nanomaterial suspensions in a packed cell volume tube, and is validated against gold-standard analytical ultracentrifugation data. This simple and cost-effective method allows nanotoxicologists to correctly model nanoparticle transport, and thus attain accurate dosimetry in cell culture systems, which will greatly advance the development of reliable and efficient methods for toxicological testing and investigation of nano-bio interactions in vitro.

Application of short-term inhalation studies to assess the inhalation toxicity of nanomaterials

BackgroundA standard short-term inhalation study (STIS) was applied for hazard assessment of 13 metal oxide nanomaterials and micron-scale zinc oxide.MethodsRats were exposed to test material aerosols (ranging from 0.5 to 50 mg/m3) for five consecutive days with 14- or 21-day post-exposure observation. Bronchoalveolar lavage fluid (BALF) and histopathological sections of the entire respiratory tract were examined. Pulmonary deposition and clearance and test material translocation into extra-pulmonary organs were assessed.ResultsInhaled nanomaterials were found in the lung, in alveolar macrophages, and in the draining lymph nodes. Polyacrylate-coated silica was also found in the spleen, and both zinc oxides elicited olfactory epithelium necrosis. None of the other nanomaterials was recorded in extra-pulmonary organs. Eight nanomaterials did not elicit pulmonary effects, and their no observed adverse effect concentrations (NOAECs) were at least 10 mg/m3. Five materials (coated nano-TiO2, both ZnO, both CeO2) evoked concentration-dependent transient pulmonary inflammation. Most effects were at least partially reversible during the post-exposure period.Based on the NOAECs that were derived from quantitative parameters, with BALF polymorphonuclear (PMN) neutrophil counts and total protein concentration being most sensitive, or from the severity of histopathological findings, the materials were ranked by increasing toxic potency into 3 grades: lower toxic potency: BaSO4; SiO2.acrylate (by local NOAEC); SiO2.PEG; SiO2.phosphate; SiO2.amino; nano-ZrO2; ZrO2.TODA; ZrO2.acrylate; medium toxic potency: SiO2.naked; higher toxic potency: coated nano-TiO2; nano-CeO2; Al-doped nano-CeO2; micron-scale ZnO; coated nano-ZnO (and SiO2.acrylate by systemic no observed effect concentration (NOEC)).ConclusionThe STIS revealed the type of effects of 13 nanomaterials, and micron-scale ZnO, information on their toxic potency, and the location and reversibility of effects. Assessment of lung burden and material translocation provided preliminary biokinetic information. Based upon the study results, the STIS protocol was re-assessed and preliminary suggestions regarding the grouping of nanomaterials for safety assessment were spelled out.

Optimal control of ground-state dynamics in polymers

Coherent control of the vibrational dynamics in crystalline polydiacetylene is demonstrated by tailoring the Stokes pulse of a coherent anti-Stokes Raman scattering (CARS) setup in a feedback-controlled self-learning loop. The feedback signal is derived from the spectral distribution of the CARS signal. Controlled excitation of one mode and simultaneous extinction of all other modes with high efficiency is demonstrated. In addition, the relative phases of the three normal modes have been controlled allowing excitations of local modes and suggesting the possibility of ground state reaction control.

Interaction of metal oxide nanoparticles with lung surfactant protein A

The alveolar lining fluid (ALF) covering the respiratory epithelium of the deep lung is the first biological barrier encountered by nanoparticles after inhalation. We here report for the first time significant differences for metal oxide nanoparticles to the binding of surfactant protein A (SP-A), the predominant protein component of ALF. SP-A is a physiologically most relevant protein and provides important biological signals. Also, it is involved in the lungs immune defence, controlling e.g. particle binding, uptake or transcytosis by epithelial cells and macrophages. In our study, we could prove different particle-protein interaction for eight different nanoparticles, whereas particles of the same bulk material revealed different adsorption patterns. In contrast to other proteins as bovine serum albumin (BSA), SP-A does not seem to significantly deagglomerate large agglomerates of particles, indicating different adsorption mechanisms as in the well-investigated model protein BSA. These findings may have important consequences for biological fate and toxicological effects of inhaled nanomaterials.

Multidimensional analysis of nanoparticles with highly disperse properties using multiwavelength analytical ultracentrifugation.

The worldwide trend in nanoparticle technology toward increasing complexity must be directly linked to more advanced characterization methods of size, shape and related properties, applicable to many different particle systems in science and technology. Available techniques for nanoparticle characterization are predominantly focused on size characterization. However, simultaneous size and shape characterization is still an unresolved major challenge. We demonstrate that analytical ultracentrifugation with a multiwavelength detector is a powerful technique to address multidimensional nanoparticle analysis. Using a high performance optical setup and data acquisition software, information on size, shape anisotropy and optical properties were accessible in one single experiment with unmatched accuracy and resolution. A dynamic rotor speed gradient allowed us to investigate broad distributions on a short time scale and differentiate between gold nanorod species including the precise evaluation of aggregate formation. We report how to distinguish between different species of single-wall carbon nanotubes in just one experiment using the wavelength-dependent sedimentation coefficient distribution without the necessity of time-consuming purification methods. Furthermore, CdTe nanoparticles of different size and optical properties were investigated in a single experiment providing important information on structure-property relations. Thus, multidimensional information on size, density, shape and optical properties of nanoparticulate systems becomes accessible by means of analytical ultracentrifugation equipped with multiwavelength detection.