Artist's rendition of an optode inserted into a red blood cell

These fiber-based optical nanosensors, called Optodes (as opposed to traditional, larger Electrodes) can be inserted into single cells to sense analyte levels. This technique works well, but even though the tip of the sensor may only be 100 nm in diameter, the fiber body quickly becomes larger up the taper and can create problems. Only two, or maybe three, sensors can be inserted at once into a large cell. The insertion can also damage the cell to the point that the cell's response may not be representative of its natural state.

Schematic of both Fiber-based Optode and PEBBLE nanosensors monitoring cell analytes