In just over a decade since its discovery, research on graphene has exploded due to a number of potential applications in electronics, materials, and medicine. In its water-soluble form of graphene oxide, the material has shown promise as a biosensor due to its preferential absorption of single-stranded polynucleotides and fluorescence quenching properties. The rational design of these biosensors, however, requires an improved understanding of the binding thermodynamics and ultimately a predictive model of sequence-specific binding. Toward these goals, here we directly measured the binding of nucleosides and oligonucleotides to graphene oxide nanoparticles using isothermal titration calorimetry and used the results to develop molecular models of graphene-nucleic acid interactions. We found individual nucleosides binding KD values lie in the submillimolar range with binding order of rG < rA < rC < dT < rU, while 5mer and 15mer oligonucleotides had markedly higher binding affinities in the range of micromolar and submicromolar KD values, respectively. The molecular models developed here are calibrated to quantitatively reproduce the above-mentioned experimental results. For oligonucleotides, our model predicts complex binding features such as double-stacked bases and a decrease in the fraction of graphene stacked bases with increasing oligonucleotide length until plateauing beyond ∼10-15 nucleotides. These experimental and computational results set the platform for informed design of graphene-based biosensors, further increasing their potential and application.

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their dysregulation in disease. However, the molecular mechanisms that drive these phase transitions, the biophysical properties of the resulting droplets, and the way their properties impact biological function, remain poorly understood. Here, we focus on LAF-1, an essential DEAD-box RNA helicase associated with P granules in the C. elegans germline. We find that purified LAF-1 can phase separate into liquid droplets at near physiological (low mM) concentrations. LAF-1 droplet formation is driven by its disordered N-terminal RGG domain, which is both necessary and sufficient for droplet formation. We combine microrheology, FRAP, and single molecule imaging approaches to reveal the local viscoelastic properties and molecular dynamics inside the droplets. Our results provide mechanistic and structural insight into the phase transition-driven assembly of liquid-like organelles, and suggest that the biophysics of intracellular phase separation can sensitively control molecular dynamics and function.