(306c) Cell Tracking Velocimetry: A Femtogram Resolution Fluorescence Cytometric Magnetometer

A magnetometer is an instrument that measures magnetism for various purposes, such as from compass in search of direction to the satellite magnetometers for surveying outer-space planets. Due to its simple mechanism, magnetism has found its use in the medical/life sciences field as well, such as magnetic resonance imaging technique, Miltenyl magnetic separation column, etc. Recently, instead of using magnetic particle conjugation like a lot of the traditional magnetic separation technique, various researchers have begun focusing on the intrinsic magnetization of biological entities. For example, Sun et al (2018) has tested the feasibility of magnetically separating unlabeled oxidized human red blood cells using microfluidic magnetic separation system. For another example, Park et al (2019) has found that glioblastoma cancer stem cells (CSCs) and non-stem tumor cells (NSTCs) have different magnetic properties due to their different iron-storage mechanism. Therefore, an ability to accurately measure/quantify the magnetic properties of biological entities has become very important.

Over the years, we have been developing an instrument referred to as the cell tracking velocimetry (CTV) which is a device that uses magnetic microfluidic channel and microscopic camera to characterize the magnetic moment of the cells. Through publications, it has been confirmed that this device can detect femtogram resolution change in iron concentration of biological entities. (Chalmers et al. 2017) With the advance in optical technology, we have been able to add a new feature into our system, to not only track the movement of the cells in dark-field/bright field optics, but to be able to differentiate multiple population among single sample by using different cell markers/optical filters. This was done by adding two motorized filter wheels in front of the light source and the camera, and programming/synchronizing the two filters so that simultaneous turn of both filters would give the same effect of switching between multiple optical filter cubes. This study will focus on using this system to detect a magnetic characteristic difference among group of cells, that has been shown in various literatures, such as the difference between apoptotic RBCs vs. healthy RBCs, iron-rich GBM CSCs vs. NSTCs and different sub-population of human monocytes.

To ensure that the added optical filters are working properly, the movement of rainbow beads (fluorescent calibration beads used in flow cytometry) was captured using the updated CTV system. The recorded image was then analyzed by an in-house analysis program, and results imply that the movement of the rainbow beads have been properly captured under all of the optical filters. To expand this study, the biological entities mentioned above will be magnetically characterized in CTV and the sub-groups among whole population will be analyzed further to be compared to that of the literature values. The expected result is that they portray the same magnetic characteristic and provide more information about their iron contents.

Most of the laboratory magnetometers for biological application, such as superconducting quantum interference device (SQUID), can measure the magnetic susceptibility of only one population at a time. However, if there are multiple population among the sample, pre-separation, such as FACS, density gradient or magnetic separation is required. The ability of the fluorescent CTV to magnetically differentiate multiple sub-groups using the already existing various surface markers in single sample can be used for various applications, such as detection of circulating tumor cells, anemia chronic disease, and many iron-related diseases. Also, the mechanism of the fluorescent CTV system could be developed into smaller scale, point-of-care medical devices as well, which will be investigated further in the near-future.