The implantable WPI's MicroImplant oxygen microsensor has a tiny probe tip of 50 ??m, an open fiber length of 5 mm and a sheath diameter of 900 ??m.
An implanted probe (IMP), the MicroImplant fiber optic oxygen sensor has a jacket diameter of 900 µm, an exposed fiber length of 5 mm, and a probe tip size of 50 µm. Crabs, fish, and soil were all successfully implanted with the IMP sensor.
You can also visit site of the manufacturer.