Improved Probe Technique Captures Chemical Differences Between Individual Cells

Cells positioned next to each other within the same tissue are not chemically uniform. Each carries its own subtly distinct chemical signature, a form of hidden individuality that can point to how diseases originate and progress. Researchers from the University of Osaka have now built a technique sensitive enough to detect this cell-by-cell variation within tissue, achieving what the team describes as unprecedented precision and stability.

Shifts in a cell’s chemical composition can signal the emergence and advance of disorders such as neurodegenerative diseases, so studying these changes at the smallest possible scale matters. Mass spectrometry imaging (MSI) using ambient sampling and electrospray ionization (ESI) has previously been used for this purpose. In ESI-based MSI, a small probe delivers solvent to a cell, detaching molecules that become charged and are then separated and counted by a mass spectrometer. Since mammalian cells can measure as little as 10 micrometers, the imaging method needs to produce pixel sizes smaller than that.

As Takao Yasuda, lead author of the study published in Analytical Chemistry, explains, “One issue with mass spectrometry imaging is that, as we focus on smaller and smaller regions within the cell, we require increasingly high sensitivity and stability.” To tackle this, the team refined an ESI-based MSI system called tapping-mode scanning probe ESI (t-SPESI), originally developed by corresponding author Yoichi Otsuka. In this process, a very fine fused silica probe repeatedly taps the cell, alternately delivering solvent and drawing out components for analysis—a motion that allows use of minimal solvent but demands high sensitivity and stability.

Otsuka notes two limiting factors: “the long pathway between the probe and the mass spectrometer, and the tendency for cell components to adhere to the probe surface over time.”

The researchers addressed the first by miniaturizing the analytical apparatus, cutting device mass by 45% and ion pathway length by 56%, which more than doubled signal intensity. To reduce sample adhesion and improve long-term stability, they coated the silica probe with a fluorine-containing chemical, functioning much like a nonstick coating.

Testing the system on mouse brain tissue, the team visualized lipid distributions—including lipid classes previously linked to Alzheimer’s and Parkinson’s disease—at a pixel size of 5 micrometers, matching fine tissue structures, while maintaining stability. The researchers expect that examining cells within tissue using this method will offer insights for disease research and treatment, and that further optimization, such as adjusting probe size, could yield further performance gains for studying disease mechanisms.