Silk: it's stronger than Kevlar, thinner than a human hair, it's biocompatible (it doesn't trigger human immune system response), and it's produced by insects (although some new-fangled metabolically engineered bacteria
seem to be up to the task). Researchers at Tufts University have created a silk and gold biosensor
that can be implanted in the body to keep tabs on proteins and chemicals. One possible use would be to keep track of diabetic's glucose levels, notifying the patient when things go wonky. At the present time, they've only tested the antenna itself -- it was found to resonate at specific frequencies, even when implanted in several layers of muscle tissue (from a pig, mind you). For their next trick, the team will outfit the device with proteins or other molecules to monitor in-vivo chemical reactions.