Quantification of the concentration in a droplet formed by liquid–liquid phase separation of G-quadruplex-forming RNA

[Display omitted] •The concentration of an RNA and a peptide in a liquid droplet was quantified.•The concentration ratio in the droplet was kept when the introduced ratio was changed.•The RNA maintains G-quadruplex structure in the droplet. Liquid–liquid phase separation (LLPS), which results in the formation of highly concentrated droplets of biomolecules, is involved in various physiological phenomena. We have performed a label-free quantification of the concentration of a G-quadruplex-forming RNA and an RGG peptide in a single droplet using Raman microscopy. The concentration ratio of the RNA to the peptide within the droplet was found to maintain even when the prepared concentration ratio of these two species was varied. This result indicates that electrostatic interactions between the RNA and the peptide induced the droplet formation. It was also shown that the RNA maintains its G-quadruplex structure inside the droplets.