A novel RNA sensor based on dynamics of oligonucleotide-functionalized Janus particles driven by rotational diffusion

PCR tests are used to diagnose infections caused by high-risk viruses and infectious bacteria, including novel coronaviruses. However, the current methods are problematic because of their long testing time and operational complexity. In this study, we focused on rotational Brownian motion that changes microscopically. We developed a new biosensor that is specific, quick, and facile for detecting target DNA/RNA by photographing the rotational Brownian motion of oligonucleotide probe-modified Janus particles under a microscope and analyzing the diffusivity, which is the degree of motion. The Stokes–Einstein–Debye relationship shows the rotational diffusivity of the particles is inversely proportional to the particle size cubed. For Janus particles, which emit fluorescence on only half of their surface, the rotational diffusivity corresponds to the correlation time, which is the correlation intensity per elapsed time of the flashing signal obtained from the rotational Brownian motion of the particles. In the presence of the target RNA, Janus particles captured the RNA, leading to the formation of Janus particle-RNA complexes and an increase in particle volume, which increased the correlation time. The correlation time of the Janus particle-target RNA complexes increased with increasing target RNA concentrations.