An investigation into methodologies for the modification of contact angle for MX crystallography

C. Burton, M. Prince, P. Topham, P. Docker D. Axford, A. Orville G. Evans, J. Kay, D. Stuart
Aston University,
United Kingdom

Keywords: MX crystallography, sample environments, service microfluidics, hydrophobic

Summary:

This paper describes a detailed investigation into a range of surface modifications for manipulating the hydrophobicity of X-ray compatible materials for the application of surface microfluidics. With traditional microfluidics, as the scale of a fluid channel reduces, the hydrostatic pressures required to overcome flow resistance increase. This is initially often due to adverse surface wetting properties of the channel. The same forces responsible for arresting flow in this way can however be used to control microfluidic flows on the surface of a chip by appropriate patterning the surface with hydrophilic regions to encourage wetting, and hydrophobic regions to prevent wetting in areas where it is not desired. By using surface micro fluidics in this way many of the inherent complications arising from enclosed microfluidics are eliminated along with the often expensive processing routes to produce them. The viability of surface patterned microfluidics for macro molecular crystallography is entirely governed by access to surface treatment methodologies which enable the surface contact angle to be selectively controlled. This paper evaluates a number of hydrophobic surface modifications for the development of surface microfluidic protein crystal slurry manipulation systems for the application of MX crystallography. This paper will detail the process of reviewing and benchmarking the static contact angle of a number of X-ray compatible microfluidic substrate by way of sessile droplet methods. These materials will then be patterned with the techniques investigated and the contact angles revisited. The work continues evaluating recently introduced techniques to capture micro crystal slurries, diffraction testing taking place at the Diamond Light Source, a third generation light source in the United Kingdom. One of the outcomes to be realized from this work is the ability to accurately array samples on a surface prior to x-ray interrogation. Such an array could take the form of a 2D microwell plate. Surface devices could have a variety of applications suitable for some of the maturing technologies used to introduce sample to an X-ray beam, for example depositing sample into Kapton loops for serial approaches or for the arrays to be acoustically launched into a beam for more parallel methodologies. Of greater interest to the authors is the possibility to interrogate sample whilst sat in these arrays and the reason the substrate materials selected were themselves X ray compatible. We believe the results from this study will lead to new and exciting advances in sample manipulation initially for the MX community but also for the X ray community at large.