Where a barcode is placed on a microplate is not a minor detail.
In automated systems, label position determines whether a plate can be scanned
at all — and whether its orientation can be reliably determined.
This is a recurring source of integration problems, particularly when plates
move between instruments from different vendors.
For SBS-format microplates, the four faces of the plate are referred to as
North, South, East, and West — defined relative to standard plate orientation
with A1 in the top-left corner:
- North — short face at the A-row end (near A1–A24 on a 384-well plate)
- South — short face at the last-row end (near P1–P24)
- West — long face at the column 1 side (near A1–P1)
- East — long face at the last-column side
This convention is widely used in automation specifications, integration documentation,
and vendor communications. Using it consistently avoids ambiguity when describing
label placement across instruments, teams, and workflow steps.
There is no universal standard for which face carries the barcode.
Placement varies by instrument vendor, integration partner, and established lab convention.
What matters is that the face is defined explicitly and applied consistently
across the entire workflow.
Ambiguity leads to scan failures or misreads at instruments where the expected
face is not accessible — for example, when a reader is fixed to a specific side
of a hotel or carousel.
Before specifying label placement, check the scanner accessibility for every
instrument in the workflow. A placement that works at the liquid handler may
not be readable at the plate reader or storage system.
On standard SBS plates, the short faces (North and South) are the most common
label locations because they do not interfere with the long-side gripper contact
points used by most robotic handlers.
For 384-well plates, the available label area on a short face is narrow —
typically a strip between the plate skirt and the edge of the well field.
Label height and adhesive zone must be selected to avoid:
- interference with gripper fingers on the short faces
- protrusion above the plate rim that affects stacking
- overlap with the well field that causes scanner misreads
For 1536-well plates the constraints are tighter still.
Label area is smaller, and the tolerance for misplacement is lower.
An SBS plate is symmetric along the short axis — it can be placed in a carrier
or instrument in two orientations that look identical from the outside.
If the same barcode is applied to both the North and South face,
the system can never determine which way the plate is oriented.
This is not a theoretical problem. A mirrored plate with identical barcodes
on both ends will scan correctly every time — and silently dispense into the
wrong wells every time it happens to be loaded in the flipped orientation.
The correct approach: one barcode, one face only.
If orientation verification is required, use asymmetric labeling
or a plate orientation notch combined with a sensor —
never rely on a barcode that could be read from either end.
For tube-based sample formats and some plate types, bottom-read barcodes
are an alternative to side labels.
These are read from below — typically by a rack or plate scanner with an
integrated underside reader.
WD labels eliminate the face-placement decision entirely and are less susceptible
to gripper interference. Many tube manufacturers offer pre-applied WD barcodes
that can be specified at ordering time.
For SBS plates, WD reading is less common but supported by some automation platforms.
Check instrument compatibility before committing to this approach.
Label placement on SBS plates is a system-level decision, not a labeling detail.
It must be defined before instrument integration begins — because changing it
later means relabeling plates, reconfiguring scanners, or both.