This project focused on Node-pore sensing (NPS) to probe and screen single cells and in particular, identify circulating endothelial cells (CECs) in blood. NPS relies on measuring a series of current subpulses produced as a cell traverses across a microfluidic channel that has been segmented by “nodes.”  The subpulses are a result of the insulating cell displacing by volume the conducting media in the channel—the volume displaced is different in the segment vs. node.  The magnitude of the subpulses correspond to the cell size and the sub-pulse duration, to the cell transit time across the segment between two nodes.  If the segments between the nodes are coated with antibodies, specific interactions between cell-surface markers with those antibodies would result in the cell taking longer to pass through those segments (and the duration of the subpulses would be subsequently longer) than through a segment coated with an isotype control.  

Intellectual Merit:  Over the course of this project, we advanced the NPS technology in two different ways:  first in terms of the device and integration into a point-of-care platform; and second in terms of the analysis.

            NPS can be thought of in terms ofradar/telecommunications systems in which the goal is to detect the unique electrical current signature generated as cells pass through the NPS device.  Under the funded project, we applied concepts from these disciplines to design our NPS device such that would enable high-throughput detection. We encoded our devices with Barker codes, which are a specific set of 1’s and 0’s.  Their properties are ideal for NPS, as they can separate different overlapping signals. Such overlapping signals are known as “coincidence” events, and occur when two or more cells pass through in the NPS channel simultaneously.  Coincidence events commonly occur in traditional flow cytometry and removed from analysis.  We successfully showed that we could differentiate 3-5 cells transiting our NPS devices simultaneously.  Moreover, we also showed that we could perform real-time analysis of cells with Barker coding. 

           During the project period, we also significantly advanced NPS by inserting a “contraction” channel whose width is narrower than a cell diameter in between a sequence of node-pores.  In so doing, we are now able to mechanically phenotype cells. Specifically, we are able to characterize multiple mechanical properties of that cell: diameter, resistance to compressive deformation, transverse deformation under constant strain, and recovery time after deformation.  We have recently demonstrated that mechano-NPS can distinguish malignant vs. non-malignant immortal epithelial cell lines and measure deformability changes in the cell cytoskeleton due to drugs. Our future task is to use this method to distinguish CECs.  Overall, the key advancement of our next-generation NPS is the fact that we have now obviated the use of antibodies, making our device far simpler to use and appropriate for long-term storage. 

            In addition to the work described above, we achieved a major milestone in terms of successfully creating a compact benchside/point-of-care platform (POC) to perform NPS measurements.  We delivered this platform to City of Hope in Spring 2018, and we have set up another platform in a separate research group at UC Berkeley. 

Broader Impact:  Over the duration of this project, the PI, Sohn, was actively involved with outreach with middle-school children.  She hosted 25 students from the Johns Hopkins Center for Talented Youth Programin September 2015, and with her lab, demonstrated the basics of microfluidics. The 25 students learned soft-lithography and made and tested microfluidic devices.  Sohn answered their questions on career paths and described the focus of this NSF-funded project.  In Summer 2016 and 2018, Sohn participated in the Girls in Engineeringsummer camp at UC Berkeley as the “Lead Faculty” in one of the weekly modules.  She gave an overall introduction to engineering to the middle-school girls enrolled that week and also described her research.  Moreover, Sohn answered the girls’ many questions about engineering, her career path, and her passion for research.  Finally, Sohn has served as a judge for the BioE High School Competition (BioEHSC™), which is sponsored by the Berkeley Bioengineering Honor Society and held on campus in April 2017 and 2018.  BioEHSC™ is a team-based research and design competition which has students focus on identifying a problem in medicine or biology and proposing a solution.  As judge, Sohn listened to 5-10 teams who focused on solutions involving medical devices/platforms and ranked these teams based on their design and the potential impact it would have on the chosen problem.

Last Modified: 11/18/2018
Modified by: Lydia L Sohn