Microscopy Solutions Blog

A Quantitative Investigation of Biological Materials using EELS

Gatan has produced a poster demonstrating how electron energy loss spectroscopy (EELS) can be a valuable tool to obtain compositional information from biological samples.

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Introduction
EELS is the analysis of the energy distribution of the electrons that have passed through a thin sample and have interacted with it inelastically. EELS is a powerful technique capable of providing chemical and electronic information from particular areas in the sample. Spatial information can be obtained using two different approaches: the first method is to combine EELS with a scanning transmission electron microscope (STEM) where the electron probe is scanned across a selected area in the sample and an EELS spectrum is collected point-by-point across the scan giving a Spectrum Image (SI). The second method is to use Energy Filtering Transmission Electron Microscopy (EFTEM). EFTEM utilizes a special spectrometer that has the capability to filter the energy of the electrons that have interacted with the spectrometer with the specimen. Concentrating on a particular ionisation edge it is possible to build up images that show a two-dimensional distribution of a particular element.

 

Why EELS for Biological materials?
Unstained biological materials are traditionally difficult to analyse in the TEM as they show very little contrast and more importantly they are quite sensitive to the electron beam. The sample can be easily damaged by the electron beam if extra care is not taken while performing the experiment. Biological materials are almost entirely composed of carbon and in some areas they show other elements in small concentrations. EELS is very well suited to study such materials given its high sensitivity to light elements and collection efficiency.

Conclusions
EELS has proved to be a valuable tool to obtain compositional information from biological samples. In addition to the composition, EELS can also give insight in to the chemistry unveiling the nature of the chemical bonds and different oxidation states.This information is important in order to understand how the elements chemically interact with each other. Damage can be also avoided thanks to the capability of the GIF Quantum to acquire EELS spectra at a rate of over 1000 spectra per seconds. Thus, large data sets can be acquired in a very short time.

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