The results of surface activating agents on cell recovery in microfluidic devices

KM Brown, R Barua, DE
Thomas, KE Degen, DM Keck, AR Hyler. The results of surface activating agents on cell recovery in microfluidic devices. Microscale Separations and Bioanalysis, Tallahassee, FL. May 2023. 

The CytoR1™ Platform is a unique label-free benchtop platform that integrates custom microfluidic devices (CytoChips™). Each CytoChip design generates a specific nonuniform electrical field via dielectrophoresis (DEP) that leverages unique electrokinetic properties for sorting, filtering, enriching, and recovering cell subpopulations from heterogeneous samples. To create electrical fields, a safe, repeatable, and consistent connection from the CytoGenerator (power amplifier and signal generator) to the electrodes is required. Further, the electrode material on the CytoChips determines the performance of electrical field gradients. Here, we evaluate multiple electrode interfacing systems as well as two electrode materials to determine a user-friendly and efficient experimental setup for electrokinetic-based sorting.

Methods: Here, we evaluate three configurations of the CytoChip Interfacing System (CIS) providing electrical connection from the CytoGenerator to the CytoChip electrodes. The first is a top-down screw (TDS) where pogo pins directly clamp onto the device. The second considers mechanical power screws (MPS) where the screw raises or lowers pogo pins for more flexibility. Finally, we consider gold-coated needles (GN) inserted into the side of the chip. The time to repeatably setup the interfacing methods was evaluated. In addition to comparing CIS mechanisms, we evaluate two electrode materials, liquid 10X PBS (15 S/m) and a solid fusible alloy (19,231 S/m), to evaluate the field gradient produced in one CytoChip configuration. Experimental characterizations with visual confirmation across frequencies of 10kHz-15MHz were performed to determine the response of murine ovarian cancer cells to varying field gradients and extract where the cells begin experiencing positive DEP.

Results & Conclusions: The approximate CIS setup times for repeatable connectivity were (minutes): TDS 3.20, MPS 2.28 and GN 2.98. The MPS system is fastest to assemble, and we also note that the GN system has exposed metal parts leaving the user more vulnerable to high voltage exposure. For the electrode materials, a positive DEP force for cancer cells is observed for 10x PBS between 50kHz to 800kHz and fusible metal between 25kHz to 5MHz. Fusible metal’s conductivity is two orders of magnitude higher producing greater field strength. This effect causes the cells to experience positive DEP forces at wider ranges of frequency. In conclusion, the MPS-driven CIS showed improved repeatability and reduced time for setup for CytoChip interfacing and use on the CytoR1 Platform for cell sorting. Further, a solid fusible alloy maximizes DEP force responses. Future work will investigate additional configurations and materials to increase sorting efficiencies and effectiveness.