LEGO®-inspired electrically-actuated microfluidics for on-chip protein crystallization and in situ X-ray...

X-ray crystallography has long been the workhorse technique for enabling the analysis and investigation of 3D protein structures. This understanding is crucial for deciphering protein function, including enzymatic reactions, signaling pathways, and more. The initial step in this process involves the crystallization of the target protein. In this pursuit, we have developed a microfluidic device that leverages an electrically-actuated strategy for fluid handling, built on a LEGO®-inspired architecture. This device enables on-demand control of counter-diffusive mixing by decoupling reagent loading from mixing, harnessing surface forces without necessitating pumping connections. The LEGO®-based architecture involves gold-LEGO®-electrodes (GLEs) that are snug fit into a device fabricated by photolithography and nanoimprinting. Our approach entails straightforward pipetting of crystallization reagents into the device to set up counter-diffusion crystallization, followed by the application of <1 V to trigger fluid mixing, thus creating a 'valve' that can be easily actuated using AAA batteries, all encompassed into a 150 μm thin device. Fabrication of the device using an X-ray transparent polymer allows for in situ X-ray crystallography, obviating the need for subsequent extraction and mounting of the protein crystals, and streamlining the process of protein structure determination. Using our LEGO®-based electrically-actuated protein crystallization and X-ray crystallography (LEAP-X) platform, we have successfully demonstrated the utility of the device using lysozyme, thaumatin, and proteinase K as model proteins, as well as the crystallization and in situ, room temperature structural analysis of the metalloprotein rubrerythrin as a novel target. Lastly, we propose the utility of this platform for the addition of chemical triggers for time-resolved protein crystallography.