WO2001083109A2

WO2001083109A2 - Low wavelength uv transparent vessels and method for making same

Info

Publication number: WO2001083109A2
Application number: PCT/US2001/013647
Authority: WO
Inventors: Jeffrey Conroy; Vladimir Pismenny; James W. Wishart
Original assignee: Dynex Technologies, Inc.
Priority date: 2000-04-28
Filing date: 2001-04-27
Publication date: 2001-11-08
Also published as: WO2001083109A3; AU2001257360A1

Abstract

An article of manufacture (18), such as a microplate or cuvette (20), for screening liquids and/or biological substances and compounds at very low UV radiation, i.e., as low as about 190 nm. The devices of the invention (18) may be integrally formed from a UV transparent material or may comprise a rigid body fitted with a UV transparent liner. Methods for making the devices (18) of the invention are also disclosed.

Description

Low Wavelength UV Transparent Vessels and Method For

Making Same

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention is directed to the field of laboratory equipment and, more particularly, to a new low wavelength UV transparent vessel for examining biological materials, and a method for making those vessels.

2. Description of the Related Art

For many years, scientists working in the life sciences have used microtiter plates (usually clear polystyrene) for absorbance measurements of sample liquids. There has always been a need to conduct absorbance measurements of samples in the ultraviolet

(UV) region and in many cases in the deep UV (with a wavelength of less than about 260 nm) . These needs were accommodated by using the only material known to be suitable, i.e., quartz, but quartz is relatively expensive which limits its usefulness.

More recently, the need for UV absorbance measurements has been accommodated by producing UV transparent microplates . Some of these plates use special UV materials (for example, Low UV Plexiglas) which are transparent to UV light and therefore give relatively good sample readings at about 270 nm and in some cases down to about 220 nm. One manner of producing such UV transparent plates is by attaching, as with an adhesive, a thin film of UV transparent material to the bottom of a plastic body having plural holes therein which define wells, thereby forming a microplate wherein the bottoms of the wells are defined by the UV transparent film. The UV transparent film may comprise the same material as the main body or it may be of a different material. While the result is a microplate suitable for absorbance measurements in the UV range, physical attachment of the film to the main body results in performance drawbacks. For example, because the attachment of the film to the body is not always complete, sample liquid may leak from one well to another, resulting in cross contamination of neighboring wells. Also, the use of adhesives to bond the film to the body may itself cause contamination of sample liquids or an undesired reaction of the adhesive with the sample. Further, some of these new plates do not have sufficient physical and chemical resistance to handle highly reactive sample liquids or samples requiring thermal cycling. For example, the materials used to make some of these micrόplates results in plates having very low temperature limits or plates that will not withstand chemical reagents commonly used in the laboratory. Furthermore, none of the UV transparent plastic plates currently available are suitable for spectroscopic measurements using UV radiation below about 220 nm because they are not optically transparent at such short wavelengths. Even if measurements could be recorded, they would be obscured by high background noise. Therefore, even today, if one needs accurate absorption readings in the range of 200-220 nm, a quartz plate is used because quartz is one of the very few materials that is optically transparent in that wavelength range. As stated, however, quartz plates are expensive, which renders them unsuitable for most applications . SUMMARY OF THE INVENTION

The present invention is for microplates and other vessels, such as cuvettes, which exhibit optical transparency to low UV radiation comparable to quartz, but which can be manufactured at a small fraction of the cost. The invention also includes methods of manufacturing such devices . The devices of the invention are particularly suited for use in conducting spectroscopic examination of fluid samples, and more particularly to microplates and other vessels suitable for the spectroscopic examination of fluid samples using low wavelength UV light, i.e., as low as about 190 nm.

The present invention relies, in part, on the recognition and selection of materials which are suitable for fabricating the devices of the present invention, are relatively inexpensive, and have optical characteristics, especially transmission, comparable to quartz at low wavelength UV light, possess excellent physical and chemical stability. The result is a low cost, mass-producible laboratory- device ideally suited for spectroscopic analysis of fluids over a broad range of wavelengths, including low wavelength UV light.

Two embodiments of a microplate in accordance with the present invention are disclosed hereinbelow. However, it will be appreciated that other devices, such as cuvettes, may be fabricated using the teachings of this disclosure, and that such devices will also enjoy the benefits described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, wherein like reference numerals delineate similar elements throughout the general views : Figure la is a side view, partly in section and partly in schematic, of a mold for making a microplate in accordance with a first embodiment of the invention, prior to the formation of the microplate; Figure lb is a side view, partly in section and partly in schematic, of the mold of Fig. la, after the formation of the microplate;

Figure 2 is a perspective of a flexible microplate manufactured in accordance with the invention;

Figure 3 is a side view, shown partly in section of a clipper cutter for trimming the microplate of Figure 2;

Figure 4a is a side view, partly in section and partly in schematic, of a mold for making a microplate in accordance with a second embodiment of the invention, prior to the formation of the microplate;

Figure 4b is a side view, partly in section and partly in schematic, of the mold of Fig. 4a, after the formation of the microplate;

Figure 5a is a side view, shown in section, of a portion of a rigid microplate formed in accordance with the second embodiment of the invention;

Figure 5b is a detail of a well of the microplate of Figure 5a, shown in section; and

Figure 6 is a side view, shown in section, of a clipper cutter for trimming the microplate of Figure 5a .

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

A first embodiment of a microplate in accordance with the invention, particularly suited for small scale laboratory use, comprises a flexible, unitary plate of UV transparent material for absorbance readings . A second microplate embodiment comprises a rigid body having a UV transparent liner, and this embodiment, owing to its greater rigidity, is suitable for robotic manipulations and stacking with other plates. The UV transparent material utilized in these embodiments is optically transparent at low UV wavelengths, i.e., lower than 220 nm, and as low as about 190 nm. The material may be a fluoropolymer, for example a copolymer of tetrafluoroethylene and ethylene, ■ sold, for example by DuPont High Performance Materials, Circleville, Ohio, under the brand name TEFZEL^®.

Both embodiments demonstrate excellent physical and chemical stability as well as optical transmission comparable with quartz in the low UV range, which makes the devices of the invention particularly suited for spectroscopic analysis using UV light, and especially UV light at about 190 nm to about 220 nm. Method For Making A Flexible Microplate

Figure la is a side view of a thermal forming process suitable for fabricating a flexible microplate according to the present invention. As shown, a thin film 10, comprised of^' a material that is at least substantially transparent to low UV light, for example TEFZEL^®, is initially positioned above a mold 12, the mold being shaped as a microplate having multiple open- bottom wells 14 and a series of ports 16 coupled to a vacuum source (not shown) . Film 10, which is supported at its periphery, is heated by thermoelement heaters 18 (shown in schematic) disposed above and below the film. Film 10 is heated to about its melting point, which in the case of TEFZEL^®, a preferred material, is about 520°F. Once the film begins to soften, the lower thermoelement 18 is removed and film 10 is lowered onto the surface of mold 12. As shown, a vacuum is drawn between film 10 and mold 12 through ports 16 to facilitate conforming film 10 to the contour of mold 12 (see Figure lb) . After film 10 cools, it is separated from mold

12. , Figure 2 shows a finished molded product 18 after excess material at the periphery of the molded product has been cut away. As shown, the film retains the shape of mold 12, i.e., the shape of a microplate having multiple wells 20 suitable for spectroscopic analysis. The resulting microplate, being thin, is somewhat flexible and therefore is most appropriate for small scale laboratory use. It will be appreciated that the resulting microplate is integrally formed of a single piece of material, having a low UV transparency, preferably TEFZEL^®.

Figure 3 shows a method for cutting away the excess material at the periphery of the molded product 18. As shown, for this purpose thin film microplate 18 is supported on a holder 20 having a shape complementary to the microplate, whereupon the excess material is cut away using cutters 22 affixed to a steel rule die 24 on a "clicker die" press, by movement in the direction shown by arrows 26. Though only two cutters 22 are shown, it will be appreciated that additional cutters 22 may be added to cut away the excess material on all four sides of the molded product. Alternatively, only two cutters 22 may be used, with the product being cut once, rotated 90°, and then cut again. Other methods for cutting away the excess material are well known in the art and may be used.

It will be appreciated that the resulting microplate 18 is suitable for spectroscopic analysis of a plurality of fluid samples, and that the unique properties of the material from which the microplate is fabricated make it specially suited to spectroscopic analysis at low UV wavelengths, i.e., down to about 190 nm. While Figs . la and lb depict manufacture of a single microplate, it will be appreciated that multiple microplates may be manufactured simultaneously if a suitable mold is provided, and that if a single sheet of thin film is used, the resulting plural microplates may be separated by cutting through the film between the microplates. Thereafter, the excess material on each plate can be cut away as described above, and it will be appreciated that this process may also be modified to accommodate the simultaneous processing of multiple microplates.

Process For Making A Rigid Microplate

The thin film microplate described above may not be useful in all applications. The thin product 18 of Figs la and lb may bend if used with robotic arms, which tend to exert forces greater than imparted by manual manipulation of the microplate. To satisfy the requirements of these applications, it is necessary to manufacture a microplate which has a grater structural rigidity than the above-described thin film microplate. One way to do that would be simply make a microplate which is thicker in the body and/or end region, while maintaining a thin film in the bottom of the wells . That may not satisfy all applications, however, and an even more rigid microplate may be required. Figure 4a shows a side view of a thermoforming process for making a rigid microplate 25 suitable for robotic manipulation. As shown, film 26, which is made of a material that is substantially transparent to low wavelength UV light, such as TEFZEL^®, is positioned above a body 28, which itself sits on top of a mold base 30. Body 28, which is preformed as a microplate with open- bottom wells 32, may comprise^' any material, such as nylon, which is capable of withstanding the forming temperatures and is sufficiently rigid to withstand the forces in the intended application. As with the embodiment of Figs. 1-3, thermoelement heaters 34, disposed above and below film 26, heat film 26 to about its melting point, i.e. about 520°F in the case of TEFZEL^®. Once film 26 begins to soften, the lower thermoelement 34 is removed, and film 26 is lowered onto the surface of body 28. As shown, a vacuum is drawn between film 26, body 28 and mold base 30 through vacuum ports 34 to facilitate molding of film 26 to the contour of body 28 (Figure 4b) . Once film 26 cools, it forms a thin lining of UV transparent film 26 covering the outside surfaces of body 28 including the inner walls of wells 30 and defining the bottom of the plurality of wells 36 in body 28. The resulting combination of body 28 with thin film liner 26 molded thereon comprises a rigid microplate 25 in accordance with the invention. The molding technique described above results in an excellent cohesion between body 28 and film 26, thereby avoiding the leakage and contamination problems common with adhesively bonded liners.

After film 26 cools sufficiently, microplate 25, comprising body 28 and molded film 26, is removed from mold base 30 whereupon excess film 40 at the periphery of microplate 25 is cut away. Figure 5a shows finished microplate 25 having wells 38, as it looks after it is removed from the mold but before the cutting operation, showing some excess film 40. As shown in Figure 5a, formed rigid microplate 25 includes a body 28. with film 26 covering the top surface thereof, and forming the sole bottom 44 of microplate 42. This is shown in the detail of Figure 5b which shows a single well 38 whose walls are formed by body 28 with a layer of film 26 thereon. Film 26 forms the sole structural bottom 44 of well 38, thereby providing a low UV transparent well for observing materials which may be placed in wells 38. Figure 6 shows an apparatus which may be used to cut away excess film at the periphery of rigid microplate 25. As with the embodiment of Figs. 1-3, cutters 46 affixed to a steel rule die 48 on a "clicker press" may be used, though any other method suitable for cutting away the excess material may also be employed. As shown, the cut is preferably made on a shoulder 50 of microplate 42 such that the thin film terminates just inside the outer edge of the body 28 and excess film 40 may be removed. It will be apparent that the microplate of Fig. 5 has a rigidity, provided by body 28, which renders the microplate suitable for robotic manipulation. Yet, because the bottoms 44 of wells 38 are defined solely by film 26, the microplate, like microplate 16 of the embodiment of Figs. 1-3, is suitable for spectroscopic analysis of multiple fluids samples at low UV wavelengths, i.e., as low as about 190 nm. As with the embodiment of Figs. 1-3, it will be appreciated that the processes for manufacturing and trimming the microplate of Fig. 5 may be modified to accommodate mass manufacture.

While two microplates formed in accordance with the present invention are shown and described, it will be apparent that still other devices are within the contemplation of the present invention. For example, a cuvette, i.e., a single-well device, can be formed according to the present invention. A cuvette could be molded from a thin film of TEFZEL^® or, alternatively, rigidity may be imparted by first forming a rigid cuvette-shaped body from, for example, nylon, and then molding thereon a thin film liner comprising, for example, TEFZEL^® . In the latter event, the rigid body could be formed with openings in its side walls which, once covered by the TEFZEL^® film, would render the resulting cuvette suitable for use with spectrophotometers employing radiation aligned with the thin film windows .

Although TEFZEL^® is described as the preferred material for the well bottoms, another material can be used provided it is transparent or at least substantially transparent to the wavelength light that is to be used in analyzing samples placed in the device, such as x-ray or visible light.

It will also be appreciated that the inventive rigid microplate may be formed in different ways. For example, the softened film could be placed on the top of the microplate, and then forced into the wells of body 28 by increasing the air pressure above film 26, thereby "blowing" film 26 into the bottom of wells 38. Alternatively, the film could be stamped or pressed into its shape in any other well-known fashion, so long as the supporting body has sufficient rigidity to withstand the rigors of the environment in which it is intended for use and the rigors of the selected manufacturing process.

Thus, while there have been shown and described and pointed out fundamental novel features of the present invention as applied to a preferred embodiment thereof, it will be understood . that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the present invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Substitutions of elements from one described embodiment to another are also fully intended and contemplated. It is also to be understood that the drawings are not necessarily drawn to scale but that they are merely conceptual in nature. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

Claims

1. A vessel for holding material to be observed by means of low wavelength UV light, said vessel comprising: a well having a bottom and at least one wall; and at least one of said bottom and said at least one wall being formed of a fluoropolymer which is substantially transparent to said low wavelength UV light.

2. The vessel of claim 1, wherein said fluoropolymer is a copolymer of tetrafuoroethylene and ethylene .

3. The vessel of claim 1, further comprising a plurality of wells, each having a bottom and at least one wall, wherein at last one of said bottom and said at least one wall of each of said plurality of wells is formed of said fluropolymer .

4. A microplate for holding material to be observed by light at a predetermined frequency, comprising: a plurality of wells for holding said material; a plate for supporting said plurality of wells; wherein said plurality of wells are formed at least in part of a fluoropolymer which is substantially transparent to said ^' light at ^' said predetermined frequency.

5. The microplate of claim 4, wherein said predetermined frequency is a low wavelength UV.

6. The microplate of claim 4, wherein said fluoropolymer is a copolymer of tetrafuoroethylene and ethylene .

7. The microplate of claim 4, wherein said plurality of wells and .said plate are formed unitarily as a single piece of said fluoropolymer .

8. The microplate of claim 4, wherein said plurality of wells are formed at least in part of a film of said fluoropolyme .

9. The microplate of claim 8, wherein said plate is made of a material different from that of said film.

10. The microplate of claim 9, wherein said material different from that of said film is a rigid plastic.

11. The microplate of claim 10, wherein said rigid plastic is nylon.

12. The microplate of claim 10, wherein said rigid plastic has a melting point higher than that of said film

13. A method of forming a microplate for holding material to be observed at a predetermined frequency, comprising the steps of: softening a film of a plastic which is substantially transparent to said predetermined frequency; placing said film of said plastic on a mold having a plurality of wells formed therein; applying a differential pressure to said mold and to said film, to draw said film onto said mold and into said wells; cooling said film to harden said film so that said film retains the form of said wells; and removing said film of said low UV transparent material from said mold.

14. The method of claim 13, wherein said step of removing said film takes place after said step of cooling.

15. The method of claim 13, wherein a plate having a plurality of apertures formed therein is placed on said mold before said film is drawn therethrough, and wherein said film is urged by said differential pressure through said apparatus in said plate into said wells of said mold.

16. The method of claim 15, wherein said plate is made of a material different from that of said film

17. The method of claim 16, wherein said material different from that of said film is a rigid plastic .

18. The method of claim 17, wherein said rigid plastic is nylon.

19. The method of claim 18, wherein said rigid plastic has a melting point higher than that of said film.