Microplate Washer

Overview

A microplate washer automates the rinse steps that hold an ELISA or other plate-based immunoassay together. Between binding steps the wells are full of unbound antibody, enzyme conjugate or sample that has to be flushed away, because anything left behind raises the background and ruins the signal. Doing this by hand across a 96-well plate is slow and uneven; the washer floods and empties every well the same way, several times over, in under a minute.

The cycle is simple to state and exacting to do well: fill each well to the brim with wash buffer, let it soak if the protocol calls for it, then aspirate it down to almost nothing without disturbing the layer of captured molecules stuck to the well bottom. A good washer leaves under two microliters of residual and never scratches the coating.

How it works

The plate rides into the instrument on the Plate Carrier Stage, a single-axis carriage driven by a ball-screw that steps it one well row at a time under the head. Above it the Wash Manifold carries the working pair of needles per well: a short dispense needle that fans buffer across the wall to fill without splashing, and a long aspirate needle that reaches the bottom to draw the well dry, the whole head dropped and lifted on its own Z drive.

Buffer and vacuum come from the Fluidics. A peristaltic pump pushes wash buffer from a bottle to the dispense needles while a diaphragm vacuum pump pulls the aspirated liquid to waste, and solenoid valves switch buffers and isolate the waste line. The supply and collection are held in the Bottle Set, where level sensors flag an empty buffer or a full waste bottle before a run stalls.

Tying the cycle together, the Control Electronics sequence the stage, manifold Z axis, pump and valves through each programmed fill, soak and aspirate, with the operator setting cycles, volumes and plate format on the Operator Display.