The Eye-One iO Quick Start Guide states the following cleaning instructions:
The plastic housing of the instrument may be cleaned with a damp cloth with some soap. Clean the white reference with isopropyl alcohol on a soft clean cloth. The electrostatic mat of the iO should be cleaned with Isopropyl alcohol on a clean cloth. Alkaline solvents and soap should never be used to clean the electrostatic mat.
The Quick Start Guide can be accessed at:
If the mat needs to be replaced, it will need to be returned to your local X-Rite Service Center.