By Jenice Con Foo, Ph. D., Mad City Labs, Inc.
Tracking particles at the micro (10-6m) or nanoscale (10-9m) is inherently difficult due to the complexity of the systems studied, as well as the technical challenges: a blend of instrument design, photonics, modeling, and imaging.
A research group at Duke University, seeking to understand how viruses navigate the extracellular space, recently developed a real-time 4D microscopy method for single particle tracking when previous techniques proved incapable of supporting the observations they required.
A whole suite of imaging approaches exists to examine the viral infection process, starting when the virus already is bound to the tissue. However, the Duke team wanted to explore the process at an earlier stage, understanding how viruses navigate the epithelial space, through mucus and the periciliary layer. Researchers set out to build a microscope capable of observing that journey, not directly in the lungs, but in a tissue culture model that closely replicates the lungs.
The resulting instrument comprises two key elements. The first, a microscope referred to as 3D-SMART, is designed to perform active feedback tracking. It utilizes optics that rapidly drive a laser spot, in three dimensions, to “dance” around the target molecule, causing it to emit photons. The instrument collects those photons at high speed, using their arrival times to determine the exact location of the fast-moving molecule.
The instrument’s second element is a volumetric imaging scope — enabling a technique called 3D-FASTR — built around the 3D-SMART microscope. 3D-FASTR is fundamentally similar to 3D-SMART, scanning a laser in three dimensions. However, the scan is executed over a much larger range and its findings are used not to make position estimates, but to build an image.