Module 1 : Introduction

Lecture 2 : Modern Approaches in Bioanalysis and Bioassays

In electron microscopy (discussed in lectures 17 and 18), the electrons are accelerated by applying a very high accelerating voltage. The wavelength of the electron beam is inversely proportional to the square root of the accelerating voltage, and wavelengths smaller than 0.5 nm can be generated. This provides around three orders of magnitude improvement in
resolution. Scanning electron microscopy (SEM) scans the specimen and provides surface information of the specimen. In transmission electron microscopy (TEM), electrons penetrate into the sample and the transmitted electrons generate the image. TEM, therefore, provides information about the internal structures of the specimen. Both SEM and TEM generally require staining of the specimen with a heavy atom. There have been several advancements in transmission electron microscopy, cryo-electron microscopy (Cryo-EM) is perhaps the most noted one. Cryo-EM allows the imaging of hydrated samples, does not require any staining and can provide resolutions between 5-10 Å making the method useful in studying the structures of biomacromolecules. Advent of scanning probe microscopy, especially the atomic force microscopy (discussed in lecture 19), could make it possible doing imaging in solution with resolutions comparable to electron microscope.