Use of Polyacrylamide Gel Moving Boundary Electrophoresis to Enable Low-Power Protein Analysis in a Compact Microdevice

In designing a protein electrophoresis platform composed of a single-inlet, single-outlet microchannel powered solely by voltage control (no pumps, values, injectors), we adapted the original protein electrophoresis format-moving boundary electrophoresis (MBE)-to a high-performance, compact microfluidic format. Key to the microfluidic adaptation is minimization of injection dispersion during sample injection. To reduce injection dispersion, we utilize a photopatterned free-solution-polyacrylamide gel (PAG) stacking interface at the head of the MBE microchannel. The nanoporous PAG molecular sieve physically induces a mobility shift that acts to enrich and sharpen protein fronts as proteins enter the microchannel. Various PAG configurations are characterized, with injection dispersion reduced by up to 85%. When employed for analysis of a model protein sample, microfluidic PAG MBE baseline-resolved species in 5 s and in a separation distance of less than 1 mm. PAG MBE thus demonstrates electrophoretic assays with minimal interfacing and sample handling, while maintaining separation performance. Owing to the short separation lengths needed in PAG MBE, we reduced the separation channel length to demonstrate an electrophoretic immunoassay powered with an off-the-shelf 9 V battery. The electrophoretic immunoassay consumed less than 3 μW of power and was completed in 30 s. To our knowledge, this is the lowest voltage and lowest power electrophoretic protein separation reported. Looking forward, we see the low-power PAG MBE as a basis for highly multiplexed protein separations (mobility shift screening assays) as well as for portable low-power diagnostic assays.