A wireless system-on-chip with integrated antenna, power harvesting and biosensors is presented that is small enough, 200µm × 200µm × 100µm, to allow painless injection. Small device size is enabled by: a 13µm × 20µm 1nA current reference; optical clock recovery; low voltage inverting dc-dc to enable use of higher quantum efficiency diodes; on-chip resonant 2.4GHz antenna; and array scanning reader. In-vivo power and data transfer is demonstrated and linear glucose concentration recordings reported.