The team of MIT researchers, led by Rahul Sarpeshkar and Jakub Kedzierski, reported developing a Si-based fuel cell that can break down glucose and harvest its energy. The device operates by collecting the electrons liberated during electrooxidation of glucose at the anode, while the liberated protons travel to the cathode through the solution. The subsequent reduction of protons and electrons, catalyzed at the cathode, restores the net charge neutrality in the solution (or tissue). Since glucose is present in the brain and spinal cord, including the cerebrospinal fluid, the fuel cell can operate autonomously at the implantation site, without the need for supplying the fuel. Moreover, the catalyzing agent for the anodic reaction can be produced by a bacterial biofilm, which has a self-regenerating capability (although this approach might not be suitable for humans due to the biosafety concerns). Researchers calculate that a very small fraction of available glucose will be used, therefore not impacting normal brain consumption of glucose. The prototype device was able to harvest the energy at the power density up to 100 µW/cm2, which is sufficient for operation of the ultra-low-power analog electronics that is also being developed by Dr. Sarpeshkar. Harvesting the biological energy is important for removing the batteries or inductive coils from the implanted neuroprosthetic device, and consequently shrinking its size and reducing the number of feedthoughs and leads from the device. Harvesting the energy of organic compounds, such as glucose, it just one possible method of collecting the energy from biological environment, while other groups are evaluating the absorption of light, heat and mechanical vibration.