Label-free quantification of Tacrolimus in biological samples by atomic force microscopy

In the present paper we describe an atomic force microscopy (AFM)-based method for the quantitative analysis of FK506 (Tacrolimus) in whole blood (WB) samples. Current reference methods used to quantify this immunosuppressive drug are based on mass spectrometry. In addition, an immunoenzymatic assay (ELISA) has been developed and is widely used in clinic, even though it shows a small but consistent overestimation of the actual drug concentration when compared with the mass spectrometry method. The AFM biosensor presented herein utilises the endogen drug receptor, FKBP12, to quantify Tacrolimus levels. The biosensor was first assayed to detect the free drug in solution, and subsequently used for the detection of Tacrolimus in blood samples. The sensor was suitable to generate a dose–response curve in the full range of clinical drug monitoring. A comparison with the clinically tested ELISA assay is also reported.     

Photoelectrochemical kinetics of eosin y-sensitized zinc oxide films investigated by scanning electrochemical microscopy

Eosin Y is used as a sensitizer for nanoporous zinc oxide films for prospective applications in photoelectrochemical solar cells. The kinetics of the reduction of the intermittently formed photo-oxidized dye molecules by iodide ions in the electrolyte phase was investigated by using the feedback mode of scanning electrochemical microscopy (SECM). The bulk solution phase contained triiodide as electron transfer mediator, from which the ultramicroelectrode-generated iodide ions acted as electron donors for photo-oxidized Eosin Y molecules (D(+) (ads)) at the zinc oxide sample. Effective rate constants for the dye regeneration could be extracted from the SECM approach curves. The effective rate constants at different triiodide concentrations could be related to the rate constant for the reaction of the dissolved donor with photo-oxidized Eosin Y bound to ZnO, as well as to the overall rate of the photosensitization process. For the reaction D(+) (ads) + 1.5 I(-)-->D(ads) + 0.5 I(3) (-) a rate constant of k(ox) = (1.4+/-0.8)x10(8) cm(9/2) mol(-3/2) s(-1) was determined.     

A facile preparation of nanocrystalline Mo2C from graphite or carbon nanotubes

Nanocrystalline Mo₂C powders were successfully synthesized at 500 °C by reacting molybdenum chloride (MoCl₅) with C (graphite or carbon nanotube) in metallic sodium medium. X-ray powder diffractometer (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscope (XPS) and surface area analyzer (BET method) were used to characterize the samples. Experiments reveal that the carbon source used for the carbide synthesis has a great effect on the particle size and the surface area of the samples. When micro-sized graphite was used as C source the obtained nanocrystalline Mo₂C powder consists of particles of 30∼100 nm, with a surface area of 2.311 m²/g. When carbon nanotubes were used as C source, the as-synthesized Mo₂C sample is composed of particles of 20∼50 nm, with a surface area of 23.458 m²/g, which is an order of magnitude larger than that of the carbide prepared from the graphite.     

Structural characteristics and cyclic voltammetric behaviour of Sonogel-Carbon tyrosinase biosensors. A detailed comparative study of three immobilization matrixes

Structural characteristics an cyclic voltammetry of three amperommetric biosensors based on immobilization of tyrosinase on a Sonogel-Carbon electrode for detection of phenols are described. Cyclic voltammetry was applied to study the electrochemical behaviour of the electrode and the electrochemical reaction on the electrode surface. Scanning electron microscopy, X-ray energy dispersive spectroscopy and atomic force microscopy were used for the structure characterization of the electrode surface, enzyme film and polymers coatings. The influence of additive-protective polymers, such as polyethylene glycol and perfluorinated-Nafion ion-exchanger on the surface of the biosensor were explored.     

Quantitative High Resolution Electron Microscopy

 With the resolution becoming sufficient to reveal individual atoms, HREM is now entering the stage where it can compete with X-ray methods to quantitatively determine atomic structures of materials without much prior knowledge, but with the advantage of being applicable to aperiodic objects such as crystal defects. In our view the future electron microscope will be characterised by a large versatility in experimental settings under computer control such as the illumination conditions (TEM-STEM), CBED, detecting conditions (diffraction, image, ptychography) and many other tunable parameters such as focus (g), voltage, spherical aberration (C _s ), beam tilt, etc. Since modern detectors can detect single electrons, also the counting statistics is known. The only limiting factor in the experiment will be the total number of electrons that interact with the object during the experiment due to the limitations in the exposure time or in the object damage. However, instrumental potentialities will never be exploited fully if not guided by an experimental strategy. Here intuitive guidelines can be very deceptive. For instance an image made with the best electron microscope (C _s  = 0) at the best focus (g = 0) from the best object (phase object) would show no contrast at all. Hence, questions such as what is the best C _s , focus, object thickness, etc. can only be answered properly if done using a method of experiment design.     

Imaging and Microanalysis in Environmental Scanning Electron Microscopy

A variety of gas cascade amplification and signal detection strategies have evolved for use in low vacuum and environmental scanning electron microscopy on poorly conducting specimens. These detectors have been optimized to perform well under various limitations on the range of gas pressure and working distance which may be imposed by experimental requirements. All of the detectors must produce high gains, low backgrounds, and generate a sufficient positive ion flux to the specimen to enable charge neutralization. The underlying principles of operation of each detector type are discussed, along with the range of experimental conditions appropriate to each.     

Single-detector micro-electro-mechanical scanning grating spectrometer

A compact, robust grating spectrometer based on an optimised micro-electro-mechanical grating mirror component has been developed, built, and characterised. The application of an oscillating reflection grating micro-mirror component as scanning dispersive element in a modified Czerny–Turner monochromator layout enables the design of compact grating spectrometers capable of acquiring full spectra using a single detector element. Designed for a wavelength range between 1200 and 1900 nm, the spectrometer features a spectral resolution of 10 nm with wavelength stability better than ±0.5 nm. One-hundred scan spectra can be acquired in less than one second, or spectral changes can be monitored at time a resolution of less than 10 ms. In combination with a fibre-optic interface and a typical weight of less than 1 kg, this makes this novel type of fully portable micro-electro-mechanical near-IR scanning spectrometer an interesting alternative to existing spectrometers and opens a range of new applications, in particular the detection of major and minor components in the near-IR. MEMS SG spectrometer prototype     

Electron probe microanalysis of SiO2-coated minerals: Subsurface phases in quartz

Crystal fragments of biotite, garnet, and spinel were mounted together in one block which afterwards was sawn into several pieces; each piece was coated with SiO₂ of varying thickness, up to 7.9m. Electron probe microanalysis was carried out at various accelerating voltages of the major elements present, using the non-SiO₂-coated minerals as reference standard.Calibration curves, depth below the surface versus ratios of X-ray yields, have been established with the ultimate goal to use them for a (semi)-quantification of elements present in subsurface phases in quartz, a common host mineral in rocks.     

Analytical,structural and electrical characterization of SiGe layers by electron microbeam techniques

k-ratios of Ge-L and Si-K measured at different beam energies allow to evaluate simultaneously composition and thickness of SiGe layers on a Si substrate. A simple technique applying backscattered electrons also enables estimation of composition of bulk SiGe and of composition and thickness of relatively thick (200 nm) SiGe layers on Si. Electron channeling patterns of pseudomorphic SiGe/Si structures and of pure Si substrate show no significant differences whereas in relaxed structures a smearing of the pattern with increasing density of misfit dislocations is observed. Under particular conditions the technique of the electron beam induced current permits imaging of recombination-active misfit dislocations with a spatial resolution around 0.2 m. Moreover, a repulsion of holes due to the valence-band offset in a n-Si/SiGe heterostructure was detected.     

Molecular Machines Working on Surfaces and at Interfaces

In the past ten years a great variety of artificial molecular machines have been constructed, and very interesting concepts for controlling molecular‐level movements by external inputs have been developed. Most of the studies, however, have been performed in solution, where the investigated systems contain a huge number of molecules which behave independently from one another because they cannot be addressed individually. Before such systems can find applications in many fields of technology, they must be interfaced with the macroscopic world by ordering them in some way so that they can behave coherently and can be addressed in space. The problem of obtaining ordered arrays of molecular machines can be addressed by a variety of techniques, which include deposition on surfaces, incorporation into polymers, organization at interfaces, and immobilization in membranes or porous materials. In the last few years, the development of scanning‐probe techniques has also enabled direct observation and manipulation of single molecular‐machine molecules on surfaces. Techniques of this kind have opened novel routes to the study of molecular machines, and have also contributed to better understanding the differences between movement at the macroscopic and molecular levels. This paper reviews some recent achievements in the field of molecular machines working on surfaces and at interfaces, as single molecules or ordered arrays. Hybrid natural–artificial machines are also discussed, and the working mechanism of some natural machines is illustrated for the purpose of comparison.