As a chemistry PhD student at Harvard University, Cui did pioneering work on nanowires, using a combination of lasers and chemical vapors to cajole silicon to form tiny wires that not only conducted electrons but could also switch a current off and on like a transistor. Cui even fabricated nanowires whose switching depended on the presence of specific proteins, so they could serve as ultrasensitive biosensors in tests for early signs of prostate cancer. At Berkeley, Cui has continued to master the art of building functional devices on the nanoscale. Most recently, he has found ways to precisely link together new types of nano building blocks called nanotetrapods -- dots of material a few nanometers wide, each with four nanorods that radiate out in different directions. While other researchers have previously made nanotetrapods, Cui can link many of them together to create a web of circuitry and finely control their electrical properties. "We can get the nanotetrapods to self-assemble into whatever pattern we need," including arrays of transistors, says Cui. Because of their small size, these circuits could in theory be several times faster than the circuits in todays computer chips. By arranging nanotetrapods into branching networks, Cui has transformed them from a raw ingredient into something that might be built into real devices, such as solar cells. And because the nanotetrapods are small enough to register the presence of individual electrons, they could even take advantage of the weird quantum properties of subatomic particles, forming the basis for new types of computers that will operate thousands of times faster than todays fastest machines. While that application is many years away, Cui has already demonstrated the possibility of building new structures using the basic ingredients of nanotech.