Elemental/molecular Imaging Techniques
LA-ICP-MS (see members)
In LA-ICP-MS, direct solid sampling of inorganic and organic materials is possible with subsequent real-time ICP-MS detection of most elements of the periodic table (Figure 1). The microbeam capabilities of the laser enable microanalysis (beam diameter, 1-250 μm) for spatial resolution purposes (surface mapping and depth profiling) in the low μg g-1 range for most elements of the periodic table. In practice a (flat) sample is placed in a chamber where ablation takes place and particles are released as a fine, dense aerosol. The aerosol is then transported to the ICP-MS by an argon or helium carrier gas, followed by ionization in the plasma, extraction of ions into the quadrupole mass spectrometer and separation according to their mass-to-charge ratios. The merits of this techniques for elemental imaging have been recognized in many fields already (materials synthesis and application, environmental analysis, geology, conservation and archeology, biology and botanics, forensics, metallurgy, etc.).
Figure 1: LA-ICP-MS instrumentation. (New Wave Research UP-213 interfaced with Agilent 7500ce and Cetac Analyte G2 ArF 193 nm Eximer laser interfaced with Agilent 7900)
Figure 2: 2D and 3D imaging principles.
Imaging of elemental signatures in samples is achieved through multiple parallel line scans on the surface (2D) or laser drilling on a virtual grid on the surface (3D); for imaging principles see Figure 2. The 2D mapping approach is fundamentally different from the 3D approach: i) 2D maps are generated from high-repetition rate laser ablation along the lines and relatively long ICP-MS acquisition times, resulting in lateral information (e.g., 100 μm x 100 μm pixels), and ii) 3D maps are generated from low-repetition rate laser ablation on the grid (50 pulses Hz per grid point at 1 Hz) and extremely short ICP-MS acquisition times, followed by peak integration and extraction of depth maps along the z-axis, resulting in lateral and depth-related information (e.g., 90 μm x 90 μm x 0.15 μm voxels). Read more
PIXE (see members)
Elemental mapping of biological tissues has been identified in the early days of nuclear microprobe developments as one of the most promising applications of high-energy focused ion beams (see Figure 1).
Figure 1. Focused high-energy ion beam at JSI. Applications: Biomedicine, geology, fusion, metallurgy, micromachining, ecology
Due to improvements of the accelerators, ion lenses and detectors, micro-PIXE became a technique of choice for tissue elemental mapping in the cases, where high elemental sensitivity, high lateral resolution and quantitative nature of the elemental analysis need to be combined for tissue analysis (see Figure 2).
Figure 2. Micro-PIXE on biological tissue at JSI, JSI micro-PIXE setup
Combined with Elastic Backscattering Spectrometry (EBS) and Scanning Transmission Ion Microscopy (STIM), providing light element composition and tissue thickness, micro-PIXE elemental maps could be quantified without a need of reference materials. Micro-PIXE is currently available to complement biomedical research together with several similar techniques, such as micro-X-ray fluorescence (micro-XRF) spectroscopy at synchrotron radiation facilities and table-top method of laser ablation with inductively coupled plasma mass spectrometry (LA-ICP-MS). Read more.
Synchrotron-related Techniques (see members)
Synchrotron light is the electromagnetic radiation emitted when electrons, moving at velocities close to the speed of light, are forced to change direction under the action of a magnetic field. Although natural synchrotron radiation from charged particles spiralling around magnetic-field lines in space is as old as the stars—for example the light we see from the Crab Nebula, short-wavelength synchrotron radiation generated by relativistic electrons in circular accelerators is only a half-century old.
Figure 1. European Synchrotron Radiation Facility (ESRF) Grenobe
The first observation, literally since it was visible light that was seen, occurred at the General Electric Research Laboratory in Schenectady, New York in 1947. The first generation synchrotron facilities were originally constructed as particle accelerators for the high energy physics community to conduct experiments on the fundamental properties of matter. Soon after their commissioning it was realized that large quantities of electromagnetic radiation, including X-rays, were produced.
In the 60 years since, SR has become a premier research tool for the study of matter in all its variety, and dedicated facilities around the world were built and constantly evolved to provide this light in ever more useful forms. There are approximately 50 synchrotron facilities located throughout the world and access to such research institutions is accomplished by competitive general user proposals. In most cases, beam-time at these tax-payer funded facilities is free, resulting in travel costs as the primary expense. Read more.
Links to synchrotron facilities:
ESRF, Grenoble, France; http://www.esrf.eu/ (Figure 1)
Elettra, Trieste, Italy; http://www.elettra.trieste.it/
DESY, Hamburg, Germany; http://photon-science.desy.de/
CLS, Saskatoon, Canada; http://www.lightsource.ca/
SEM-EDX (see members)
High resolution scanning electron microscope (SEM, Carl Zeiss, Model SUPRA 35 VP) equipped with an energy dispersive X-ray spectrometer (EDX, Oxford Instruments, Model Inca 400)
Morphological Imaging Techniques
SEM (see members)
See above at SEM-EDX.
Optical microscopy (see members)
Inverted optical microscope (Nikon, Model Eclipse) equipped with a digital camera.
AFM (see members)
Atomic force microscope (AFM, Veeco Instruments, Model MultiMode V Scanning Probe Microscope + NanoScope V Control Station) and atomic force microscope (AFM, Agilent Technologies, Model Agilent 5500 Scanning Probe Microscope).