Combined optical imaging and electrical detection to characterize particles carried in a fluid

An interrogation apparatus, comprising:

• structure configured and arranged to interact with a removable microfluidic cassette to obtain an optically-based signal related to optical particle characterization of a plurality of particles carried by a fluid that can be urged to move through a channel in said cassette, said optically-based signal being extracted from a optical-interrogation location disposed along said channel;
• structure configured and arranged to interact with said removable cassette to obtain an electrically-based signal related to at least one of:
• identification of said cassette;
• a location of a fluid boundary that can be urged to move through said channel in said cassette;
• or
• characterization of one or more particles carried by said fluid;
• and
• a display element on which a result from processing one or more of said optically-based signal and said electrically-based signal may be shown.