A new method records the movement of millions of molecules in 3D in real-time, The human immunodeficiency virus, or HIV, wages war in our bodies using a strategy evolved over millions of years that turn our cellular machines against themselves.
Despite massive strides in understanding the disease, there are still important gaps. For years, scientists at the University of Utah wished there was a way to visualize how the virus and its molecules interact with human cells in real-time. So, a research group developed one.
The new method uses interferometry to capture extremely high-resolution visualizations of millions of molecules moving across viscous gels or a plasma membrane.
There are already methods that capture how molecules flow and diffuse in two dimensions. We wanted to see what is happening across the entire cellular environment.
We have very limited ways of actually going into the cell and observing how all these molecules are dancing together at the same time, We needed to generate higher-resolution methods that can look at the dynamics of biological molecules.
Cells function like an efficient office. Proteins and other molecules carry out tasks, develop products, communicate with each other and move around, even leaving their particular cell to wade into the wider world.
Molecules flow when they have a bias toward moving in a certain direction. Diffusion is when molecules move around randomly. To understand how cells or viruses function, it’s important to understand the mechanics of how they move.
The researchers used an interferometry microscope, which measures the distance that light travels over nanoscales. Molecules emit photons that travel as light waves, each with specific amplitudes and frequencies. For the experiment, the microscope split a beam of light into two beams that traveled down different paths, eventually coming back to meet each other.
These beams combine in a prism, and three separate reflections of their combination are imaged on three cameras. The interference is such that if a molecule moves 80 nanometers, its image is shifted onto a different camera. This is extremely high resolution — a human red blood cell is about 7,000 nanometers across. The researchers measured the resolution in voxels, which are pixels in three dimensions.
The researchers measured how long these light waves “remembered” each other by calculating the probability of how long the waves would retain their amplitude and frequency, called coherence. The light emitted from the same molecule will show up in the cameras with the same coherence.
They used the correlation function to figure out how the molecules were moving and in what direction. If the split light beams travel on separate paths less than 10 microns away from each other, they remember they came from the same molecule. When the light beams meet again, they’ll recombine with that knowledge. If they do not know each other, they have a 30% probability of showing up in any of the three cameras.
If they do remember each other, they have a 100% probability of showing up in one camera, but a 0% probability of showing up in the others. This method measures light emitted from millions of molecules at once, making this method ideal for studying flow and diffusion across cells and tissues.
While this method detects movement across viscous gels or plasma membranes, it is unable to create a map of particles moving across an actual cell. But, Researchers are now collaborating with researchers at ThermoFisher Scientific (FEI) in Germany to build a prototype of a microscope with much faster detectors that will be able to capture movement within living cells. They are part of a patent application for the technology and will analyze the data from the experiments.