3D projection electrophoresis for single-cell immunoblotting

While immunoassays and mass spectrometry are powerful single-cell protein analysis tools, bottlenecks remain in interfacing and throughput. Here, we introduce highly parallel, synchronous, three-dimensional single-cell immunoblots to detect both cytosolic and nuclear proteins. The novel threedimensional microfluidic device is a photoactive polyacrylamide gel with a high-density microwell array patterned on one face (x-y) for cell isolation and lysis. From each microwell, single-cell lysate is ‘electrophoretically projected’ into the 3rd dimension (z-axis), separated by size, and photo-captured for immunoprobing and three-dimensional interrogation by confocal/light sheet microscopy. Design guidelines for throughput and separation performance are informed by simulation, analyses, and deconvolution postprocessing based on physics of 3D diffusion. Importantly, separations are nearly synchronous, whereas serial analyses can impart hours of delay between the first and last cell. We achieve an electrophoresis throughput of >2.5 cells/s (70X faster than serial sampling) and perform 25 immunoblots/mm2 device area (>10X increase over previous immunoblots). A straightforward device for parallel single-cell immunoblotting, projection electrophoresis promises to advance integration of protein-level profiles into the emerging single-cell atlas of genomic and transcriptomic profiles.