Nanometer-detail cell maps with native infrared spectroscopy
Infrared vibrational spectroscopy could enable the production of high-resolution maps of molecules inside live cells and cell organelles.
A new study from Helmholtz-Zentrum Berlin (HZB) and Humboldt University (both Berlin, Germany) has reported the use of infrared (IR) vibrational spectroscopy and scattering-type near-field optical microscopy (s-SNOM) to create high-resolution molecular maps in their native, aqueous environment.
Conducting functional biological studies is challenging in dry environments, where the fixation and drying of samples can disrupt the behavior of cells and their components. However, the conditions required to analyze liquid samples, such as compression or encapsulation, can also distort cells, compromising their morphology and integrity.
Capturing 3D information in a native environment
To overcome these challenges, a team jointly led by Alexander Veber (HZB) and Janina Kneipp (Humboldt University) utilized commercially available, biocompatible and stable ultra-thin transparent membranes and a synchrotron light source, BESSY II, to record vibrational spectra of living cells, including fibroblasts.
The team carried out in-liquid IR nano imaging and spectroscopy on both fibroblasts in complete culture medium and those grown directly on silicon nitride (SiN) and silicon carbide (SiC) membranes. The membranes stabilized the samples, enabling the researchers to vary the oscillation parameters of the AFM probe without disrupting them. Bright-field transmission and reflection images were also captured. Together, this provided the team with 3D information at the nanometer range.
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“Not only were we able to visualize the nucleus and cell organelles, but we succeeded too in reading the individual contributions of proteins, nucleic acids, carbohydrates and membrane lipids based on the detected vibrational spectra,” explained Veber. “We could also vary the measurement parameters in order to control how deep into the sample we detect signals – allowing us to explore its different layers. This paves the way towards infrared nano-tomography of the cells, i.e. a detailed 3D visualization of cell structure and composition.”
A new tool in the cell biology box
The team believes that standardized 2D and 3D vibrational imaging and spectroscopy could enable faster progress in biophysics and nanomaterials, as well as new insights in cell biology.
“This method offers the possibility of analyzing biological samples and liquid-solid interfaces much more accurately than was previously possible,” concluded Veber. “In principle, we could use it to examine any type of cell, including cancer cells.”
