Scientists have successfully captured vivid images of biomolecules within single live cells in water for the first time using infrared (IR) transmission imaging. This IR technique allows researchers to accurately measure the mass of crucial biomolecules, including proteins, inside a cell. Utilizing straightforward components, this method could greatly expedite developments in biomanufacturing, cell therapy, and drug creation.
To foster rapid advancements in biotechnology, particularly in the creation of vital drug treatments, scientists are working on faster, more precise, and more accessible ways to examine biomolecules in living cells.
At the National Institute of Standards and Technology (NIST), researchers have unveiled a new approach that employs infrared (IR) light to generate clear images of biomolecules within cells. Previously, this was a challenge due to water’s propensity to absorb infrared radiation. This innovative method mitigates water’s interference with IR-based measurements, enabling scientists to quantify essential biomolecules in cells, such as proteins that regulate cellular activities. The capacity to observe changes in live cells may accelerate progress in biomanufacturing, cell therapy, drug development, and more.
Their research findings have been published in Analytical Chemistry.
Infrared radiation is the light spectrum just beyond visible light. Although we can’t see IR light, we can sense it as heat. In IR microscopy, the material of interest absorbs radiation from various wavelengths in the infrared spectrum. Scientists quantify and analyze this IR absorption spectrum to produce a set of “fingerprints” that can identify specific molecules and chemical structures. However, water, the most prevalent molecule both inside and outside cells, significantly absorbs infrared light, obscuring the absorption signals from other biomolecules within the cells.
A helpful analogy to grasp this optical masking effect is to envision an airplane flying overhead while the Sun shines brightly. It’s challenging to see the airplane without assistance since the Sun overpowers the view, but using a specialized Sun-blocking filter makes it easy to spot the airplane in the sky.
“In the spectrum, water absorbs infrared so strongly that we needed to distinguish the absorption spectrum of proteins from the overwhelming water background; thus, we designed the optical system to unveil the water contributions and highlight the protein signals,” explained NIST chemist Young Jong Lee.
Lee pioneered a patented technique that employs an optical component to counteract water absorption in IR. This method, known as solvent absorption compensation (SAC), was applied with a custom-built IR laser microscope to observe fibroblast cells, which are responsible for forming connective tissue. Over a 12-hour observation period, researchers successfully identified collections of biomolecules (proteins, lipids, and nucleic acids) at various stages of the cell cycle, such as during cell division. While this duration may seem extensive, the method ultimately proves to be quicker than existing alternatives, which require extensive beam time at large synchrotron facilities.
This innovative method, termed SAC-IR, is label-free, meaning it doesn’t necessitate any dyes or fluorescent markers that could harm cells and yield inconsistent results across different laboratories.
The SAC-IR approach enabled NIST researchers to quantify the absolute mass of proteins, nucleic acids, lipids, and carbohydrates within a cell. This technique has the potential to lay the groundwork for standardizing biomolecule measurement methods in cells, which could be invaluable in fields like biology, medicine, and biotechnology.
“In cancer cell therapies, for instance, when immune cells from a patient are modified to better recognize and eliminate cancer cells before being reintroduced to the patient, it is crucial to consider, ‘Are these cells safe and effective?’ Our technique can provide additional insights into the biomolecular changes within cells to evaluate their health,” stated Lee.
Other promising applications include utilizing cells for drug screening—either in discovering new drugs or assessing the safety and effectiveness of drug candidates. For instance, this method could evaluate the potency of new drugs by measuring absolute concentrations of diverse biomolecules across a large number of individual cells or analyze how various cell types respond to the drugs.
The researchers aim to enhance the technique for more accurate measurement of additional key biomolecules, including DNA and RNA. This advancement could also yield in-depth answers to fundamental queries in cell biology, such as identifying which biomolecular signatures correspond to cell viability—indicating if a cell is alive, dying, or dead.
“Some cells are stored in a frozen state for months or even years before being thawed for future use. We do not yet fully comprehend how to thaw cells for optimal viability. With our new measurement capabilities, we may improve processes for freezing and thawing cells by examining their infrared spectra,” mentioned Lee.
