Light-based scans tracked baculovirus infection in individual living cells

The method used cells’ own chemical signals to distinguish infected from uninfected cells without fluorescent tags.

Editorial illustration — not from the study.

The study applied optical photothermal infrared imaging and spectroscopy to living Spodoptera frugiperda Sf9 cells carrying no fluorescent reporter. Researchers examined cells 3, 6, 12 and 24 hours after baculovirus infection in a calcium fluoride sandwich setup.

Signals linked to proteins and nucleic acids provided spatial information that separated infected and uninfected cells. The measurements also captured differences between cells and showed how infection-related signals changed across the time points.

Chemical signals tracked infection

Imaging at a protein-associated band and a nucleic-acid-associated band distinguished infected from uninfected cells at each measured time point, reaching a balanced accuracy of 0.90. Point spectroscopy, which measures the chemical signal at specific locations, increased pairwise balanced accuracy to 0.94 and supported the biochemical basis of the image contrast. When the method classified cells across all four time points, overall accuracy was 0.71. Researchers also quantified differences between individual cells using a data-visualization method called UMAP, and used results across separate experimental replicates as an internal check on reproducibility.

Why label-free tracking matters

Fluorescent labels can require cells to be genetically modified and may alter the process being studied. This approach instead reads intrinsic biochemical signatures in living, unlabelled cells, offering a way to follow viral infection without a fluorescent reporter. Its ability to combine chemical information with submicron spatial resolution could help researchers examine infection-related changes within individual cells.

Evidence and caveats

The findings come from an article reporting optical photothermal infrared imaging and point spectroscopy in living Sf9 insect cells infected with baculovirus. The study included measurements at four post-infection time points and used cross-replicate reproducibility as an internal validation. The abstract describes one virus, one cell type and one experimental setup, so it does not establish how well the method would work for other viruses, cells or biological conditions. Classification across all time points was less accurate than the pairwise infected-versus-uninfected comparisons, with an overall accuracy of 0.71.

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