Learning about cells by examining how they scatter light
Looking inside the cell without opening it
When light hits an obstacle, its scattering pattern reveals information regarding the internal structure of the obstacle. If that obstacle is a cell, the scattering pattern might indicate whether the cell is healthy or cancerous. But studying and categorizing different cells’ light-scattering properties is no small task.
Now, with help from a National Institute of General Medical Sciences grant, Jun Qing Lu, PhD, assistant professor of physics at East Carolina University, and her colleagues are studying cellular light response using a promising mathematical approach called the finite-difference time-domain method (FDTD).
“We’re looking inside the cell without opening it. If there are any changes, we should be able to see them from the outside,” says Lu.
In the past, researchers used various approximation methods to study how light scatters from cells, but these simplified approaches can only provide limited information about highly-symmetric homogeneous bodies. Since cells are irregular in both shape and contents, a different approach was needed. “FDTD can handle any kind of shape or structure,” Lu says. “But it’s very computationally intensive.”
FDTD has been around for a while, but it has been applied to biology only within the last few years. It’s a numerical modeling technique that can be applied to interactions between electromagnetic waves and objects whose structural details are small compared to the wavelength of light. “Inside and in the vicinity of the target object, divide your space into a 3-D grid system and divide time into small steps,” Lu says. “When the light hits the object, the electric and magnetic field distributions at each point in the grid space are calculated for each time step. Then put everything together to calculate the scattering pattern.”
With about a million grid points, about two thousand time steps, and six finite difference equations for each grid point, it’s clear why the process requires lots of computational power. If you also want to see how the light scattering changes with different cell types or the same cell in a different life stage, that requires even more power. “Parallel computing makes it faster,” Lu says.
Lu and her colleagues work side by side doing computational modeling and experimental work. “I’m a theoretician,” Lu says. “But I have scientists by my side doing experiments. So far, the models match reality pretty well.”
Thus far, Lu’s group has been studying light scattering by individual cells. Eventually, they will use the FDTD technique to do tissue studies—with hopes of distinguishing tumor from non-tumor. “People are showing lots of interest in this method,” says Lu. “It’s the right direction to pursue.”