Nitrogen-Vacancy Spins in Diamond a Possible Tool to Study Protein Diffusion and Oligomerization

Abstract

Nitrogen-Vacancy (NV) colour centres in diamond is a rapidly progressing field with promising applications ranging from quantum information to bio-imaging and sensing.1 The ability to manipulate NV electron spin optically under the ambient condition is the main driving force behind developments in nanoscale sensing techniques. In this work, we present investigations on using single NV spin to monitor diffusion dynamics of proteins. We investigate effects of spin labels interacting with NV spin and analyse protein diffusion and oligomerization. For these studies, we use a home built single NV pulsed optically-detected-magnetic-resonance (ODMR) set-up capable of handling aqueous samples. The NV spin state initialized by optical pumping and transition between states are manipulated using microwaves. Coherent control of the spin states and pulsed protocols designed to sense fluctuations were used to probe spin coherences and monitor the diffusion dynamics. Figure 1 (a,b) shows the schematic of our setup and confocal fluorescence image of NV centers created ∼ 5nm close to the surface of a diamond. Some unspecific surface adhesions tend to cause problems with reliable spin coherence signals. Lipid bilayer coated surfaces could minimize unwanted adsorption while the adhesion of the membrane to the surface is challenging. We will present some results on surface treatments that promote adhesion on diamond surfaces. Surfaces treated with oxygen, argon plasma and wet chemical routes were analysed. The result indicates differences when the molecules dispersed in chloroform and aqueous buffer respectively and dried under ambient conditions. This provides routes to achieve monolayer of lipids on the diamond surface. The lipid bilayer films serve as a platform for investigating protein diffusion, dynamics and oligomerization at a single molecule level using NV-spin sensors.