If researchers can understand how viruses assemble, they may be able to design drugs that prevent viruses from forming in the first place. Unfortunately, how exactly viruses self-assemble has long remained a mystery because it happens very quickly and at very small length-scales. Now, there is a system to track nanometer-sized viruses at sub-millisecond time scales. The method, developed by researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences, is the first step towards tracking individual proteins and genomic molecules at high speeds as they assemble to create a virus.