Literature Seminar – Contrast allows us to distinguish an object from its background. In biological electron microscopy it is challenging to see the details inside of cells due to the relatively similar atomic makeup of all biomolecular building blocks. To remedy this, molecular species of interest are often “tagged” in order to provide contrast, typically with a heavy metal particle. Subsequently, tags of differential elemental compositions can be distinguished by several means such as electron energy loss spectroscopy (EELS). By measuring how electrons interact uniquely with different elements, it is possible to map where these elements are localized in an image. Within a cellular electron micrograph, this means that several molecular species can be simultaneously localized at the unparalleled resolution afforded by electron microscopy. While core electrons are often used for elemental analysis in an EELS spectrum, few of these incident electrons will reach the detector resulting in a small signal to noise ratio. By moving to a different area in an EELS spectrum, where signal is acquired from electrons further from the nucleus, higher signal to noise is achieved. This comes with some drawbacks which can be accounted for using alternative sample acquisition techniques or by chemometric methods, the details of which will be presented in this talk. Nascent methods of elemental mapping will advance high resolution biological electron microscopy and enable the next generation of inquiry into subcellular biology.