Abstract
The SBS committee on 96 well Standardiztion made it's most recent recommendations in January 1997. the Microplate manufacturers and the users have done considerable work in developing the recommendations which will in time act as a standard for the industry and be adopted as such. Three levels of compliance were defined to provide options for the microplate manufacturers, while still providing the end user and instrument designer specific details.
MP96–3 defines the (1.0) general appearance, (2.0) center to center well spacing and (3.0) external footprint, A number of plate manufacturers have either made new tools or modified existing tools to meet this conformity level. While this conformity level is the easiest to meet it also is the most important. It defines the most important dimensions for all applications.
MP96–2, in addition to the requirements of MP96–3, defines (4.0) plate height, (5.0) comer radius, (6.0) bottom outside flange, and (7.0) external clearance to the plate bottom. Meeting these dimensions has a greater impact on existing tooling since they may require major tooling changes. However, as new molding tools are created it is anticipated MP96–2 will be applied, resulting in more conformity. As the interest increases in plate Stackers, for various instruments, the dimensions of the bottom flange, defined by MP96–2 becomes more critical. The stacker mechanism uses this flange to escape the bottom plate, allowing it to drop, and still close in time to catch the next plate.
MP96–1, in addition to the requirements of MP96–3 and MP96–2, defines (8.0) sidewall ‘V’ locators. These were specifically designed for two functional purposes. The ‘V’ locators will eliminate cumulative error on multiple handling of a plate with a robotic hand. Each time the hand closes on a plate, the mating V's would position the plate within the hand at exactly the same position. The other function is to facilitate handling lidded plates on readers and other stand alone devices. Mating pins located within the V's would retain the lid and allow the plate to drop thru. Replacing the lid is accomplished by simply pushing the plate back up through the waiting lid. The V's provide the option of a simpler method of handling lidded plates.
Section 9.0 is dedicated to lid design. Here there is a conflict of interest between the plate users and the plate manufacturers. The user group specifically requested having a common lid that would fit all plates. While some application require specific functions of the lid, in most it is simply a cover, and a common lid is adequate.
The defining of a 96 well plate standard by SBS has met a real need in our industry. It would have been easier, had it been done when microplates started in the late 1960′s. We now have the opportunity to extend these standards to new plate concepts as they come to market. The 384 well plate is an excellent example. Following is the preliminary proposal for a 384 well standard. It follows the 96 well format. Some comments have already been received. They are shown. Additional comments are solicitated by all interested parties. Please address them to the author at the address shown. Those who do respond will be kept on the mailing list of comments and proposals through the adoptive stage. The intent is to publish a standard for the 384 well plate at the SBS Fall meeting.
PRELIMINARY
1.0 General
1.1 The microplate shall have 384 wells in an 16 × 24 array, as shown by Figure #1. Note: Square wells are illustrative only, and are not defined by the Standard.
1.2 The plate shall be marked showing letter A thru P located on the left hand side designating rows of wells A thru P (See Fig. 1).
1.3 The plate shall be marked with numbers 1 thru 24 left to right across the top, identifying the columns of wells 1 thru 24 (See Fig. 1).
1.4 Additional markings may be provided.
1.5 The plate shall have sufficient rigidity to allow its handling with automated mechanical means. The rigidity must be equivalent to that obtained by injection molding thermoplastics.
2.0 Center to Center Well Spacing
2.1 Well to Well Spacing
The well to well spacing in both horizontal and vertical directions is to be 0.1772 inches (4.50 mm) center to center.
The dimensions on the center to center spacing is 0.1772 inch ±0.0030 (4.50 mm ±0.08). The tolerances are not cumulative, defined as follows. Each well will be within ±0.003 inch (0.08 mm) of its theoretical centerline position of 0.1772 inch (4.50 mm), when measured on a straight line between the first and last well in that row, or column.
3.0 External Footprint
3.1 The outside dimension of the base footprint shall be as follows:
Length 5.030 inches ± 0.005 (127.76 mm ± 0.12)
Width 3.365 inches ± 0.005 (85.47 mm ± 0.12)
These dimensions are measured at the four outside corners.
Comment: Due to the larger number of smaller well openings the tolerance on the footprint dimensions have been changed to ± 0.005 inches (± 0.12mm), from the ± 0.010 inches (± 0.025) of the 96 well format.
384-Well Microplate Standardization −1/22/98
3.2 The sides and ends will be straight within ± 0.010 inch (±0.25 mm). This is defined as the maximum variation from a theoretical line connecting the applicable outside corners. When the plate width or length is measured at its point of maximum deflection, it will be as follows:
Length 5.030 inches ± 0.010 (127.76 mm ± 0.25)
Width 3.365 inches ± 0.010 (85.47 mm ± 0.25)
3.3 The centerline of the outside footprint dimensions shall coincide with the centerline of the well to well spacing.
4.0 Plate Height for Standard Wells
4.1 The plate height shall be 0.565 inches ± 0.010 (14.35 mm ±0.25). This is measured from the bottom resting plane to the top stacking surface. The top stacking surface is defined as that surface upon which another plate would rest when stacked one on another.
4.2 The maximum allowable projection above the top stacking surface is 0.030 inch (0.75 mm).
4.3 When resting on a flat surface, the top surface plane of the plate must be parallel to the resting surface within 0.010 inch (0.25 mm).
5.0 Corner Radius
5.1 The four outside corners of the plate's bottom flange shall have a minimum corner radius to the outside of 0.12 inch (3 mm), and a maximum radius of 0.19inch (5mm).
Comment: The corner radius serves as a lead in, for the plate, and is not a locator dimension. Thus a wider tolerance on the radius is allowable. This same change could be made on the 96 well standard also.
6.0 Bottom Outside Flange
6.1 The bottom outside flange, defined as dimension FH on Fig. 2, shall be 0.100 inch ± 0.010 (2.54 mm ± 0.25 mm).
6.2 The bottom flange width measured at the top of the flange, defined as dimension FW, shall be 0.060 inch −0.004 +0.020 (1.5 mm −0.1 mm +0.5mm).
Comment: A minimum flange width is essential in the design to accomodate stacker escapments. Changing the flange width to a wider tolerance of +0.020inch will provide the plate designer a wider latitude, without impacting the stacker requirements.
384-Well Microplate Standardization −1/22/98
7.0 External Clearance to the Plate Bottom
7.1 The plane of the bottom external surface of the wells, defined by the perimeter of the outside perimeter wells, shall be 0.040 inch ±0.010 (1.0 mm ± 0.25 mm) above the resting plane.
Comment: In the 96 well standard. WH is defined as 0.040 ± 0.010inches. This was to assure the bottom of one plate, when stacked on another, would clear any projections on the top surface of the bottom plate, which is limited to 0.030inches by paragraph 4.2. The reasoning behind standardizing the WH height was to define the location of the well bottom for instruments such as readers. It also provides an approximation of well depth for pipettor applications, since the plate height is defined by paragraph 4.1.
8.0 Sidewall V Locators
8.1 There shall be V shaped indentations on the ends of the plates between rows B-C and Rows N-O. Similar indentations shall be located between column 6–7 and column 18–19 on both sides
8.2 The V shaped indentation shall measure 0.200 inches (5.0 mm) at the outside opening of the bottom flange. The depth of the V shall be 0.100 inches (2.5 mm).
8.3 The Apex of the V shall be located 1.063 inches ± 0.003 (27.0 mm ± 0.08) from the horizontal and vertical direction.
8.4 The Apex of the V may have an internal radius of 0.030 inch (0.76 mm) maximum.
9.0 Lid Design
9.1 The corner of the plate at the P1 well location, shall be cut off at an angle.
9.2 The bottom of the lid, when placed on top of the plate, will have a minimum clearance of 0.200 inch (5.08 mm) between the bottom of the lid flange and the resting plane of the plate.
Comment: The interests of the users for a common lid and the interests of the plate manufacturer for brand recognition are incompatible. The disadvantage is that a plate could conform to MP384–2 in all aspects but the lid angle, and still not be able to carry that distinguishing conformity mark. The suggestion is that MP384–2A be created to cover all dimensional requirements of the standard except 9.1 and 8.0. This would provide a distinction for user specification.
384-Well Microplate Standardization −1/22/98
10.0 Plate Designation
10.1 A microplate meeting all of the dimensional requirements of this standard may be designated as MP384–1.
10.2 A microplate meeting all of the dimensional requirements of this standard, except 8.0 (Sidewall V Locators) may be designated as MP384–2.
10.3 A microplate meeting the dimensions defined in 1.0, 2.0 and 3.0 may be designated as MP384–3.
Comments: The above plate designations MP384–3, MP394–2A, MP384–2 and MP384–1 are copyrighted by the Society for BioMolecular Screening. The use of such markings on plates not conforming to the specifications defined in this standard would be a violation of that copyright.