Exploring fluorescence antibunching in solution to determine the stoichiometry of molecular complexes

Fluorescence antibunching is a well-known technique for determining the number of independent emitters per molecule or molecular complex. It was rarely applied to autofluorescent proteins due to the necessity of collecting large numbers of fluorescence photons from a single molecule, which is usually impossible to achieve with rather photolabile autofluorescent proteins. Here, we measure fluorescence antibunching on molecules in solution, allowing us to accumulate data over a large number of molecules. We use that method for determining an average stoichiometry of molecular complexes. The proposed method is absolute in the sense that it does not need any calibration or referencing. We develop the necessary theoretical background and check the method on pure dye solutions and on molecular complexes with known stoichiometry.     

Size and surface effects on the MRI relaxivity of manganese ferrite nanoparticle contrast agents

Superparamagnetic MnFe2O4 nanocrystals of different sizes were synthesized in high-boiling ether solvent and transferred into water using three different approaches. First, we applied a ligand exchange in order to form a water soluble polymer shell. Second, the particles were embedded into an amphiphilic polymer shell. Third, the nanoparticles were embedded into large micelles formed by lipids. Although all approaches lead to effective negative contrast enhancement, we observed significant differences concerning the magnitude of this effect. The transverse relaxivity, in particular r2*, is greatly higher for the micellar system compared to the polymer-coated particles using same-sized nanoparticles. We also observed an increase in transverse relaxivities with increasing particle size for the polymer-coated nanocrystals. The results are qualitatively compared with theoretical models describing the dependence of relaxivity on the size of magnetic spheres.     

The weight of author self-citations. A fractional approach to self-citation counting

The discussion about how to treat author self-citations driven by policy application and quality measurement intensified in the last years. The definition introduced by Snyder and Bonzi has — in lack of any reasonable alternative — been used in bibliometric practice for science policy purposes. This method, however, does not take into account the weight of self-citing authors among coauthors of both the cited and citing papers. The objective of the present paper is to quantify the weight of self-citations with respect to co-authorship. The analysis is conducted at two levels: at the macro level, namely, for fifteen subject fields and the most active forty countries, and at the meso level, for a set of selected research institutions.     

Safety analysis of the height control system for the Elbtunnel

A new tunnel tube crossing the river Elbe has been built in Hamburg until the end of 2002. Therefore, a new height control system was required. A computer examines the signals from light barriers and overhead sensors to detect vehicles, which try to drive into a tube with insufficient height. If necessary, it raises an alarm that blocks the road. This paper describes the application of two safety analysis techniques on this embedded system: model checking has been used to prove functional correctness with respect to a formal model. Fault tree analysis has validated the model and considered technical defects. Their combination uncovered a safety flaw, led to a precise requirement specification for the software, and showed various ways to improve system safety.     

Growth and percolation of metal nanostructures in electrode gaps leading to conductive paths for electrical DNA analysis

Metal nanostructures are promising novel labels for microarray-based biomolecular detection. Additional silver deposition on the surface-bound labels strongly enhances the sensitivity of the system and can lead to continuous metal areas, which enable an electrical readout especially for simple and robust point-of-care analyses. In this paper, atomic force microscopy (AFM) was used to study different routes of metal deposition on labelled DNA-DNA duplexes in electrode gaps. Besides the well-established metal-induced silver enhancement, a recently introduced enzymatic silver deposition was applied and proved highly specific. The in situ characterization was especially focused on the nanostructure percolation-the moment at which the nanoparticulate film becomes continuous and electrically conducting. The formation of conducting paths, continuous from one electrode to the other, was followed by complementary electrical measurements. Thereby, a percolation threshold was determined for the surface coverage with metal structures, i.e.?the required metallized area to achieve conductance. Complementary graphic simulations of the growth process and graphic 'conductance measurements' were developed and proved suitable to model the metal deposition and electrical detection. This may help to design electrode arrays and identify optimum enhancement parameters (required seed concentration and shell growth) as well as draw quantitative conclusions on the existing label (i.e.?analyte) concentration.     

Automatic determination of acoustic plate source-detector separation from one waveform

We discuss an automated procedure for determining the separation between a transient acoustic source and a detector on a plate. We use a time-estimation algorithm based on the assumption that the detected signal is represented by a small, finite number of discrete band-limited impulses. This is carried out using the MUSIC (MUltiple SIgnal Classification) algorithm in time-estimation mode to automatically estimate both the first arrival time of the lowest order antisymmetric (Ao) mode and the arrival time of the Rayleigh wave. Using the material and geometric properties of the plate and these two arrival times, we calculated the distance to the source. This technique allows the automatic determination of source-receiver separation from a single transient waveform.     

Increase in Generation of Poly-Crystalline Silicon by Atmospheric Pressure Plasma-Assisted Excimer Laser Annealing

In this work, a novel atmospheric pressure plasma-assisted excimer laser annealing method for increasing the generation efficiency of poly-crystalline silicon from amorphous silicon layers is presented. Here, both the plasma and the laser propagate coaxially in order to generate energetic synergies. The influence of different process gases and plasma discharge modes as well as the working distance were investigated. Depending on the particularly applied plasma, the crystalline area was increased by a factor of approx. 1.1 to 1.9, where the highest efficiency was observed when introducing an argon plasma beam to the annealing process.     

Thermally controlled permeation of ionic molecules through synthetic nanopores functionalized with amine-terminated polymer brushes

We present temperature-dependent ionic transport through an array of nanopores (cylindrical and conical) and a single conical nanopore functionalized with amine-terminated poly(N-isopropylacrylamide) [PNIPAAM-NH(2)] brushes. For this purpose, nanopores are fabricated in heavy ion irradiated polyethylene terephthlate (PET) membranes by a controlled chemical track-etching technique, which leads to the generation of carboxyl (COOH) groups on the pore surface. End-functionalized polymer chains are immobilized onto the inner pore walls via a 'grafting-to' approach through the covalent linkage of surface COOH moieties with the terminal amine groups of the PNIPAAM molecules by using carbodiimide coupling chemistry. The success of the chemical modification reaction is corroborated by measuring the permeation flux of charged analytes across the multipore membranes in an aqueous solution, and for the case of single conical pore by measuring the current-voltage (I-V) characteristics, which are dictated by the electrostatic interaction of the charged pore surface with the mobile ions in an electrolyte solution. The effective nanopore diameter is tuned by manipulating the environmental temperature due to the swelling/shrinking behaviour of polymer brushes attached to the inner nanopore walls, leading to a decrease/increase in the ionic transport across the membrane. This process should permit the thermal gating and controlled release of ionic drug molecules through the nanopores modified with thermoresponsive polymer chains across the membrane.     

Nano- and microstructuring of graphene using UV-NIL

In this work we demonstrate for the first time the micro-?and nanostructuring of graphene by means of UV-nanoimprint lithography. Exfoliated graphene on SiO(2) substrates, as well as graphene deposited by chemical vapor deposition (CVD) on polycrystalline nickel and copper, and transferred CVD graphene on dielectric substrates, were used to demonstrate that our technique is suitable for large-area patterning (2?×?2?cm(2)) of graphene on various types of substrates. The demonstrated fabrication procedure of micrometer as well as nanometer-sized graphene structures with feature sizes down to 20?nm by a wafer-scale process opens up an avenue for the low-cost and high-throughput manufacturing of graphene-based optical and electronic applications. The processed graphene films show electron mobilities of up to 4.6?×?10(3)?cm(2)?V (-1)?s(-1), which confirms them to exhibit state-of-the-art electronic quality with respect to the current literature.