Graphene-based microfluidics for serial crystallography

Abstract

Microfluidic strategies to enable the growth and subsequent serial crystallographic analysis of micro-crystals have the potential to facilitate both structural characterization and dynamic structural studies of protein targets that have been resistant to single-crystal strategies. However, adapting microfluidic crystallization platforms for micro-crystallography requires a dramatic decrease in the overall device thickness. We report a robust strategy for the straightforward incorporation of single-layer graphene into ultra-thin microfluidic devices. This architecture allows for a total material thickness of only ~1 μm, facilitating on-chip X-ray diffraction analysis while creating a sample environment that is stable against significant water loss over several weeks. We demonstrate excellent signal-to-noise in our X-ray diffraction measurements using a 1.5 μs polychromatic X-ray exposure, and validate our approach via on-chip structure determination using hen egg white lysozyme (HEWL) as a model system. Although this work is focused on the use of graphene for protein crystallography, we anticipate that this technology should find utility in a wide range of both X-ray and other lab on a chip applications.

A Graphene-Based Microfluidic Platform for Electrocrystallization and In Situ X-ray Diffraction

“…At this limit of 1.95 Å, the I/σ(I), or signal-to-noise level in the highest resolution shell, was above 3.0 for all of the samples, and was significantly higher for those samples prepared in the presence of an electric field, than those without ( Figure 6, Table 1). This high signal-to-noise was expected, due to the minimal contributions of the device materials to the level of background noise [45]. The size of the X-ray beam and the presence of nearby crystals limited the number of frames that could be collected from a given sample.…”

“…This work builds on our previously reported graphene-based platform for serial crystallography [45], but requires the fabrication and integration of patterned graphene electrodes, rather than simple graphene windows.…”

“…In the meantime, the challenges of such platforms lie in the need to maintain a protected sample environment, as well as minimize the interference of device materials with the subsequent X-ray analysis. To address these two issues, we recently developed a microfluidic device architecture that takes advantage of large-area sheets of graphene [45]. The use of atomically-thin graphene films minimizes the amount of material surrounding a crystal, while serving as a vapor-diffusion barrier that is stable against significant water loss over the course of weeks.…”

Microfluidics: From crystallization to serial time-resolved crystallography

“…123 This proof-of-concept work, inspired by earlier reports on the stability of graphene-wrapped crystals, 145,146 utilized windows of single-layer graphene backed by a 500 nm-thick layer of PMMA for structural stability, surrounding a microfluidic channel cut into 100 lm-thick COC. The resulting microfluidic chambers were shown to be stable against dehydration for at least two weeks and were robust enough to survive overnight shipping to the synchrotron.…”

“…The strength of the diffraction signal from a crystal is related to not only the degree of order within the crystal but also the packing density and the size of the crystal. 1,2,39,46,123 Attenuation can be calculated for a particular energy based on the exponential decay in intensity of a narrow beam of monochromatic photons from an incident intensity I 0 as it passes through a material of thickness x and density q with a mass attenuation coefficient of the material l,…”