A rotor assembly includes a rotor plate to rotate around a first axis, a bucket attached to the rotor plate and to rotate around a second axis, and a stop plate to rotate around the first axis between an open position and a closed position. When in the closed position, the stop plate engages the bucket to fix an angular position of the bucket relative to a plane of rotation of the rotor assembly. The rotor assembly further includes a housing for a sensor array component, the housing disposed in the bucket and including a solution inlet, a solution outlet, a transfer basin, a solution retainer disposed between the solution outlet and the transfer basin, and a collection reservoir in fluid communication with the transfer basin. The solution inlet and the solution outlet to engage ports of a flow cell of a sensor array.