Search

The characterization of dispersions, suspensions, and emulsions is important in a wide range of scientific applications and industries. Samples can consist of different materials and a wide range of particle sizes and concentrations. A single particle sizing and counting instrument with a dynamic detection range of ≥ 6 decades has been developed to detect single nano- and microparticles in aqueous suspensions based on light scattering measured in two directions. Hydrodynamic focusing is employed for particle separation and to provide stable conditions for light scattering detection. This gives the advantage of size resolution in the nm range, allowing, e.g., number based size distributions, classification of nanomaterials, determination of particle agglomerates, developments for dispersion stability analysis, or cutoff of filter media. In addition, concentration determination is based on sample volume measurement with < 20 nl measurement uncertainty. We present results of particle detection in a size range from approximately above 40 nm for gold nanoparticles to 8 μm for polystyrene particles using a prototyped instrument of the LUMiSpoc® series produced by LUM GmbH. The data obtained demonstrate the advantages of single-particle detection, particularly for characterizing polydisperse systems, such as precise particle sizing in the nanometer range through light scattering intensity based on Mie scattering theory. In addition, we present particle concentration data based on the integrated measurement of sample volume, which allows particle concentration to be determined with an uncertainty of 2.5% (95% confidence interval). To achieve such small uncertainties, dilution series measurements must be used to correct for coincidence losses and particle adhesion. [ABSTRACT FROM AUTHOR]

We demonstrate controlled modification of the fluorescence and energy transfer properties of Photosystem I (PSI) – one of the most important light harvesting systems – by using a newly developed approach to produce optical subwavelength microcavities for cryogenic temperature issues. The experiments were carried out on PSI from the cyanobacterium Arthrospira platensis as it shows a broad and structured fluorescence emission. By changing the distance between the cavity forming mirrors, the electromagnetic field mode structure around PSI is varied affecting the emission and energy transfer properties, which allows us to selectively enhance signals of resonant emitters and suppress off-resonant emission. By comparing the experimental data with simulations, we are able to show how excitation transfer within PSI is affected by the microcavity. The ability to control the energy transfer within such efficient energy converters as photosynthetic proteins can establish the opportunity for enhancing the efficiencies of bio-solar applications. The defined control of the resonance conditions by microcavities makes them a preferable tool to study the effects of additional electromagnetic modes on the energy transfer in any coupled multi-chromophore system. The resonator geometry excludes the direct contact of the proteins with any surface. Possible quenching or denaturation of the complexes close to metal surfaces is still an insuperable obstacle for studies with proteins and nanostructures, which can be avoided by resonators. [ABSTRACT FROM AUTHOR]

The construction of a microscope with fast sample transfer system for single-molecule spectroscopy and microscopy at low temperatures using 2D/3D sample-scanning is reported. The presented construction enables the insertion of a sample from the outside (room temperature) into the cooled (4.2 K) cryostat within seconds. We describe the mechanical and optical design and present data from individual Photosystem I complexes. With the described setup numerous samples can be investigated within one cooling cycle. It opens the possibility to investigate biological samples (i) without artifacts introduced by prolonged cooling procedures and (ii) samples that require preparation steps like plunge-freezing or specific illumination procedures prior to the insertion into the cryostat. [ABSTRACT FROM AUTHOR]

Abstract: The interaction between glycerol and photosystem I (PSI) was investigated using low temperature single-molecule spectroscopy. PSI complexes were dissolved in three different solutions: in buffer solution, in 66% glycerol/buffer solution, and in 66% glycerol/buffer solution that was afterwards diluted by buffer; the final glycerol concentration was <1‰. Mean fluorescence spectra and intercomplex heterogeneity of PSI complexes in 66% glycerol/buffer solution and in the re-diluted solution show high similarity, but differ from complexes in buffer solution indicating that the glycerol concentration is not the determining factor modifying the spectral properties. However, the exposure of PSI to a high glycerol concentration during sample preparation affects PSI and the effect is maintained if glycerol is removed from the solution. [Copyright &y& Elsevier]