A cell’s nucleus-to-cytoplasm (N:C) ratio is a histological metric used to stage malignant disease. Current N:C assessment methods, such as optical microscopy, are time-consuming, subjective, and low-throughput. Here, we compare the N:C ratios of prostate cancer (PC-3) cells measured by a novel microfluidic PhotoAcoustic Flow Cytometer (PAFC) to those obtained using an Imaging Flow Cytometer (IFC). PC-3 cells were stained with DRAQ-5 nuclear dye and divided into populations measured using the PAFC and IFC. The PAFC consisted of a microfluidic device integrated with a singleelement ultrasound transducer (375 MHz central frequency) and a sub-nanosecond pulsed laser (532 nm). Individual cells were 3D flow-focused through the overlapping focal region of the ultrasound and laser pulses. PAFC estimation of the cell and nucleus diameters were determined through power spectra fitting of backscattered US waves and emitted PA waves to established theoretical models. An ImageStreamX® IFC was used to acquire brightfield and fluorescent images of individual cells, which were masked, gated, and used to assess the cell (brightfield) and nucleus (fluorescence) diameter to validate the PAFC measurements. The average cell and nucleus diameters determined using the PAFC (n = 388) were 18.8 ± 3.3 μm and 14.3 ± 2.9 μm, respectively. The corresponding values from the IFC (n = 4651) were 18.3 ± 2.2 μm and 12.2 ± 1.9 μm. The N:C ratio (calculated as the ratio of the nucleus diameter to cell diameter) was 0.77 ± 0.10 using the PAFC and 0.67 ± 0.07 using the IFC. Our novel PAFC device has the potential to be used for circulation tumor cell detection using the N:C ratios of cells.

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Joseph A. Sebastian, Vaskar Gnyawali, Lianne Ho Yan So, Michael J. Moore, Scott S. H. Tsai, and Michael C. Kolios, "Measuring the nucleus-to-cytoplasmic ratio in PC-3 cells using photoacoustic flow cytometry and imaging flow cytometry," Proc. SPIE 10878, Photons Plus Ultrasound: Imaging and Sensing 2019, 108782H (Presented at SPIE BiOS: February 06, 2019; Published: 27 February 2019); https://doi.org/10.1117/12.2506434.