# Self-Mixing Interferometry-Based Micro Flow Cytometry System for Label-Free Cells Classification
## 4 Results and Discussion
### Human Living Cell Discrimination  
After calibration, the measurements were also performed using two different types of human living cells, MCF7 and 293, that were suspended in phosphate-buffered saline (PBS) for maintaining cell activity. The liquids were expected to have a similar composition with the normal clinically relevant samples in commercial CF measurement. The concentration of each suspension was about \(5\times 10^{4}\) per milliliter. The bursts induced by each cell type were shown in Figure 10, indicating a comparable signal amplitude level with the PS beads. However, the cell bursts of the two types cells were quite different as compare to the PS beads-induced bursts. Most of those obtained with the MCF7 cells exhibited quite irregular fringe amplitude distribution and the envelope was no longer Gaussian-shaped. The bursts from 293 cells mostly presented single dominating fringe. The probable explanation is that the cell membrane surface is not as smooth as the beads, the random defects results in such fringe arrangement irregularity that can be observed in Figure 10a.  
The statistic correlation results of SMI signal amplitude and size parameter \(K\) from cells population samples were depicted in Figure 11. Similar to what was observed for the PS particles, there were two clusters of dots in the figure coinciding with the two cell types. However, the clusters overlapped significantly, with a large distribution dispersion, especially in the case of MCF7 cells.  
Histogram plots of the size parameter \(K\) and the signal amplitude of the measurement are shown in Figure 12. The size parameter \(K\) distribution remains reliable for cell types discrimination as two groups of cells can be recognized in Figure 12a. The CV values of \(K\) distribution were 52% and 17%, were dramatically larger than those of PS particles, resulting in a lower sensing accuracy. The broadening of  
Figure 11: Scatter plot of the detection results obtained from MCF7 cells (in red); 293 cells (in blue).  
Figure 10: The SMI bursts of individual human living cells: (**a**) MCF7 cells; (**b**) 293 cells.  
the distribution from the cells as compared with the PS beads is likely attributed to the considerable cell morphologic dispersion. Another possible explanation is that during the measurement, the cell samples contained some apoptosis cells or aggregations of which the sizes were different than the normal living cells. Nevertheless, the results indicated the mean measured dimension of the MCF is bigger than 293, which is coherent with the data from the reference 28. However, the mean \(K\) value ratio between two cells \(\mu\)2/\(\mu\)1 is around 4 which is much higher than the realistic cell dimension ratio 15 \(\mu\)m/11 \(\mu\)m. Thus, in cell size characterization measurement, our system can only discriminate the cell type while not providing accurate cell sizing. The amplitude distribution of both cells is quite confusing in Figure 12b and such a larger amplitude dispersion can probably be attributed to the variable cell reflectivity impacting the modulation index \(m\).