Multi-well device

A multi-well plate assembly has a well plate with a plurality of closed-bottom, open-top wells of substantially uniform square cross-section between the closed bottom and the open top. An insert plate is nested with the well plate and has a top wall substantially covering the open tops of the wells. Inserts project down from the top wall and into the respective wells, such that each insert is nested in a comer of the well. Access ports are formed through the insert plate for alignment with a corner of the respective well opposite the insert. The access port is formed partly through the top wall of the insert plate and partly through the sidewall of the insert.