Optical coherence tomography complements confocal microscopy for investigation of multicellular tumour spheroids

Area of Science:

• Biomedical Optics
• Cancer Research
• Cell Biology

Background:

• Accurate optical properties, like refractive index (RI), are crucial for effective optical imaging of biological tissues.
• Understanding light propagation in tissues is essential for developing optimized imaging protocols for studying cancerous cells' response to drugs.

Purpose of the Study:

• To measure the refractive index (RI) of HCT116 multicellular spheroids using a custom spectral-domain optical coherence tomography (OCT) system.
• To investigate the effect of spheroid growth over time on their refractive indices.
• To identify immersion media that minimize refractive index mismatch for enhanced confocal microscopy of spheroids.

Main Methods:

• A custom-built spectral-domain optical coherence tomography (OCT) system was utilized for refractive index measurements.
• Multicellular spheroids of the HCT116 cell line were cultured as 3D in-vitro models.
• Two immersion media, glycerol and ScaleView-A2, were tested for their ability to match spheroid RI and improve confocal microscopy depth.

Main Results:

• Refractive index (RI) measurements of HCT116 spheroids were successfully obtained and analyzed for changes related to growth.
• ScaleView-A2, with a refractive index of 1.380, demonstrated an improved imaging depth in confocal microscopy of multicellular spheroids.
• A reduction in RI mismatch between the spheroid and immersion medium led to enhanced imaging capabilities.

Conclusions:

• Optical coherence tomography (OCT) is a valuable tool for measuring the refractive index of 3D cell cultures.
• Matching the refractive index of immersion media to spheroids significantly enhances confocal microscopy imaging depth.
• OCT shows promise as a complementary technique to microscopy for advancing cancer research and drug response studies.