Researchers map subcellular dynamics in living cells using label-free iSCAT microscopy

Researchers Develop Label-Free Imaging Method to Map Living Cell Dynamics

Researchers at Nanyang Technological University, Singapore (NTU Singapore), have developed a powerful new imaging technique that can map the inner workings of living cells without the need for any external labels or dyes. The findings were published in PhotoniX Life.

The method, a form of wide-field interferometric scattering (iSCAT) microscopy, analyzes the natural, minuscule fluctuations within a cell to reveal its state and behavior.

The core innovation lies in analyzing stochastic fluctuations in high-speed iSCAT image sequences to reveal cellular states and dynamic heterogeneity, all without external labels.

The process works by analyzing the power spectral density (PSD) of iSCAT signals over a frequency range of 30–1,250 Hz. In tests across multiple cell types, the signal consistently followed a distinct inverse-power-law relationship: S(f) = β f^(-α).

The team then translated these mathematical parameters into a visual map:

• The spectral exponent (α) and amplitude (β) were encoded into hue and value (brightness).
• The goodness-of-fit of the power law was represented as saturation.
• This created a two-dimensional spectral exponent map, effectively turning the cell's internal dynamics into a color-coded image.

The method proved remarkably effective at distinguishing between different cellular states:

• Cell Division: In HeLa cells, the maps could clearly differentiate mitotic (dividing) cells from interphase (resting) cells and could track the progression of mitosis in real time.

• Cell Death: In cells treated with hydrogen peroxide to trigger apoptosis (programmed cell death), the maps showed increased heterogeneity and distinct high-α regions closely associated with membrane blebbing, a hallmark of the dying process.

• Cancer Malignancy: When testing different subtypes of thyroid cancer, the method revealed a clear trend. The median value of α decreased with increasing malignancy: papillary carcinoma (least aggressive), follicular carcinoma, and anaplastic carcinoma (most aggressive).

This method provides an intrinsic optical readout of cellular states without labels, offering a valuable tool for longitudinal live-cell studies.

Because the technique is label-free and relies only on natural cellular activity, it is non-invasive and can be used for long-term observation. Researchers believe it could be a significant tool for:

• Mechanobiology: Studying the physical forces within cells.
• Cancer Research: Assessing malignancy without staining.
• Drug Screening: Observing real-time effects of compounds on live cells.
• Stem-Cell Therapy: Evaluating the quality and state of stem cells before transplantation.