The need for cellular and molecular sensors and actuators

Summary form only given. Systems biology may present the ultimate micro and nanoengineering challenge: a single mammalian cell requires at least a hundred-thousand variables and equations to describe its dynamic state, cell-cell interactions are critical to system function, and some organs have a billion interacting cells. At present, biologists might record five dynamic intracellular variables simultaneously from a single cell - typically through fluorescent imaging. Historically, the assumption has been that it is sufficient to hold all but a few variables constant and make a limited number of measurements. In a realm of highly interconnected, distributed nonlinear networks, measurements made in this way cannot adequately capture system dynamics. The growing interest in nanobiology and nanomedicine is spawning extensive activity in artificial nanosensors that include ligand-gated ion channels, fluorescent nanocrystal reporters that bind to targeted sites, nanofibers that can deliver DNA, and metal nanoshells that can provide localized heating. The engineering challenges that must be met for nanoscience to make a broad impact in basic research in biology and medicine include techniques to record and control multiple dynamic variables in single cells; nanosensors that report the local environment rather than just position; and addressable nanoactuators that control more than just conductance or temperature.