Improved sealant for sample holder

Abstract: An improved sealant for a biocard or other sample holder is provided. The sealant, which comprises polymethylpentene, achieves low weight, good tensile strength, and high oxygen permeability while avoiding excessive fluid evaporation, speeding incubation times.

Description: This invention relates to an improved sealant for a sample holder; more particularly, it relates to an improved sealant for biocards and other sample holders used for analyzing biological samples and other applications. Biocards have been used to hold samples of blood or other biological samples in a spectroscopic or other automated reading machine. In such machines, a small biocard, roughly the size of a playing card, receives biological samples. The card typically holds the samples in a series of small wells, formed in the card in rows and columns. The wells of the cards are filled with appropriate reactants, which are typically dried in place. The card and reactant are then sealed tightly in some manner, typically by adhesive tape on both sides. Later the card receives a biological sample, which mixes with the reactant and may be placed under incubating conditions so that the biological agent that may be present in the sample is permitted to grow. The biological sample may be a direct patient sample, or patient material which is diluted or otherwise treated for analysis. After incubation, the samples contained in the wells are placed in front of a laser, fluorescent light or other illumination source. The content of the sample in a given well can then be deduced according to readings on the spectrum or other characteristics of the transmitted or reflected radiation. Biocards of this general type for use in these biochemical applications can for example be seen in U.S. Patent Nos. 4,318,994, 4,038,151 and others. Despite the general success of biocards in this application, there is an ongoing desire to improve the performance of the incubation process and readings on card samples. One significant aspect of the process is the way that the reactant and treated sample is sealed into the card. This is typically done using adhesive tapes made of conventional materials, such as PFA (perfluoroalkoxy) and FEP (fluorinated ethylene propylene), (which are polyfluorinated polymer films), PET (polyethylene terephthalate) and BOPP (bioxle orientated polypropylene). While materials like that have performed satisfactorily in biological sample implementations, there is an ongoing desire to make the seal, integrity and efficiency of the incubation and process greater and reliable. It is accordingly an object of the invention to provide an improved sealant for biocards and other applications. It is another object of the invention to provide an improved sealant for a biocard which fosters incubation efficiency. It is another object of the invention to provide an improved sealant for a biocard with superior oxygen permeability. It is another object of the invention to provide an improved sealant for a biocard with good transparency for illumination of the sample. The invention achieving these and other objects is a sealant for use in biocards or other analytic applications, having significantly improved incubation properties. The sealant of the invention is an optically clear material made from polymethylpentene, to which adhesive is applied for sealing the facing surfaces of the card with reliability, yet low weight and high oxygen permeability. (Although somewhat remote, reference may be made to JP-A-5096690, which discloses a bag for keeping vegetables and fruit fresh, which may comprise polymethylpentene laminated onto non-woven fabric.) The invention will now be described with reference to the drawings, in which like parts are labelled with like numbers. The drawings are briefly described below. Figure 1 illustrates a front view of a biocard, and application of an improved sealant according to the invention, to the front of the card. Figure 2 illustrates a side view of the biocard of Figure 1. Figure 3 illustrates a chart of the characteristics for the sealant according to the invention and other sealant tapes, including oxygen transmissibility and permeability. Figures 4-18 each illustrate a chart of the growth pattern of various biological agents sealed in a card using the improved sealant of the invention, and conventional tapes. Figure 19 illustrates a chart of evaporative characteristics for the improved sealant of the invention, and conventional tapes. The invention is illustrated and characteristics shown in the context of Figures 1-19. This embodiment provides an improved sealant 100 illustrated in Figure 1 in application to a biocard 110, generally in the form of adhesive-backed plastic film or membrane which can be rolled, measured, cut and otherwise easily handled when sealing reactants and samples into biocards or other sample holders. Any suitable adhesive backing, in laminate or other form, can be employed in the improved sealant of the invention. The sealant 100 is typically applied to both the front surface and rear surface of the biocard (or other sample holder), to seal the card wells which pass through the card as apertures, but could be applied to one or another side, depending on the application and sample holder used. The sealant 100 of the invention is developed from a particular form of material. That material is polymethylpentene (PMP), known commercially as "TPX" (Registered Trade Mark), and available from the Phillips and Mitsui companies. The material has been known for some time, for instance in solid plastic and sheet form. However, while PMP has been used in applications such as lining electronic circuit boards, metal casting molds for airplanes and other parts, the material has not been used as a sealant for biological or other sample analysis. General discussion of polymethylpentene as a material may be found in L.C. Lopez, G.L. Wilkes, P.M. Stricklen and S.A. White, "Synthesis, Structure, and Properties of Poly(4-Methyl-1-pentene)", J.M.S.-Rev. Macromol. Chem. Phys., C32(3&4), 301-406 (1992). The inventors have discovered that PMP material, in film form, possesses a unique combination of properties that make it particularly effective as a biocard sealant. In tape form, generally 1-2 mils (1 mil = 1/1000" = 0.00254 cm) thick, PMP exhibits good tensile strength, good handleability, excellent clarity and very light weight (having a density of approximately .8g/cubic cm). These properties all lend themselves to a particularly suitable sealant on biocards, and other applications. Figure 3 shows a table of the oxygen transmissibility and permeability of a sample card having a polymethylpentene membrane in accordance with the invention (item TPX in the table) as compared to other sealant films, including "Mylar" (Registered Trade Mark) (PET), FEP and polystyrene. Note that the oxygen transmissibility is markedly improved over the other films, at least by a factor of three over the next closest film, PFA. Note also that the oxygen permeability is also increased by at least a factor of three. However, an improved sealant incorporating PMP provides not only these, but the separate and significant advantage that the tape has much improved oxygen permeability, in the range of 4800-5000 cc/100 in 2 /24 hours/25°C/at 2 mil thickness. This is a marked advantage in the incubation of the microorganism contained in the biological sample, since by and large the microorganisms in the biological samples respond favorably, with increased growth rates, in an enhanced oxygen environment. The biological sample so developed may be a direct sample from the patient, or be patient sample which is extracted, diluted, suspended, or otherwise treated, in solution or otherwise. Figures 4-18 for example illustrate test incubations using a sampling of different biological pathogens, largely gram-negative (Gram staining technique) bacteria. The rate of growth is most illustrated segments in most time periods is significantly greater for the improved sealant of the invention, employing PMP film, than for conventional sealants as indicated. (The growth lines shown in the graphs are on a log scale.) This effect is of course related to the oxygen permeability of the improved sealant of the invention. Because the microorganism contained in the biological sample can be made to grow more quickly when sealed with the sealant 100 of the invention, more samples can be processed on a given automated reading machine in a given amount of time. It may be noted that the improved sealant of the invention has oxygen permeability of approximately 4 to 6 times that of conventional FEP and PFA films, so the bacterial or other growth environment within the wells is oxygen-rich compared to known sealing technology. While the improved sealant of the invention has the property of superior oxygen permeability, it at the same time possess adequate resistance to evaporation such that the samples lodged in the wells will not dry up during the relatively shortened incubation. The evaporative properties are for example illustrated in Figure 19, in which it can be seen that the rate of water loss for PMP sealant according to the invention exceeds that of other conventional tapes. However, the inventors have determined that the water-retention properties of the sealant 100 of the invention are still adequate to the application of biological analysis. In addition, once the incubation period is over, the good optical transparency of the sealant permits accurate fluorescent, scattering, spectroscopic or other readings of each well, because the sealant is transparent to radiation. Little reflection, absorption of other optical interference occurs, contributing to better readings. Because the improved sealant of the invention balances good strength, handleability, light weight and excellent oxygen permeability and transparency with sufficient water-retention properties, it significantly enhances the incubation phase of biocard reading and permits quicker more reliable readings. It is for instance possible to apply the improved sealant of the invention to analytic procedures which are not necessarily biological, but still benefit from the blend of properties that the inventive sealant affords.

Claims: A sample holder used for analyzing biological samples characterized in that it comprises a sealing membrane comprising polymethylpentene for providing a high oxygen transmissible and permeable barrier between the said sample holder and an atmosphere external to the said sample holder, while maintaining adequate resistance to evaporation of a test sample. A sample holder as claimed in claim 1 wherein the said sample holder has a surface and the said membrane further comprises an adhesive backing for sealing the membrane to the said surface of the sample holder. A sample holder as claimed in claim 1 or claim 2 wherein the membrane is at a thickness of 0.00508 cm (2 mils) and has an oxygen permeability of 7.44 - 7.75 x 10 4 (cm 3 /m 2 /24 hours/25°C) (4,800-5,000 (cm 3 /100 in 2 /24 hours/25°C)). A sample holder as claimed in any of claims 1 to 3 wherein it is a biocard, preferably comprising a plurality of test sample wells. A sample holder as claimed in claim 4 wherein the membrane comprises a front planar membrane and a rear planar membrane each adhesively sealed to the biocard. A sample holder used for analyzing biological samples characterized in that it comprises a sample holder body having at least one well and defining front and rear surfaces and a sealing membrane on at least one of the said front and rear surfaces of the said sample holder for providing a high oxygen transmissible and permeable barrier between the said sample holder and an atmosphere external to the said sample holder, while maintaining adequate resistance to evaporation during sample testing, the membrane comprising polymethylpentene, preferably the said membrane being sealed to both the said front and rear surfaces of the said sample holder body and/or the said membrane preferably having a thickness of 0.00508 cm (2 mils). A biological test sample card characterized in that it comprises a card body defining a plurality of test sample wells and having front and rear surfaces, and a sealing membrane applied to a portion of at least one of the said front and rear surfaces so as to cover the said test sample wells, the said membrane, which preferably has a thickness of 0.00508 cm (2 mils), comprising polymethylpentene, and the said polymethylpentene membrane preferably being applied to the said front surface and to the said rear surface of the said card, for providing a high oxygen transmissible and permeable barrier between the said test sample card and an atmosphere external to the said test sample card, while maintaining adequate resistance to evaporation of a test sample. A sample card as claimed in claim 7 wherein the said wells are arranged in an array and are loaded with reactants.

Inventors: CHEN PATRICK K, O'BEAR RAYMOND E, CHEN, PATRICK K., O'BEAR, RAYMOND E.
Applicants: BIO MERIEUX VITEK INC, BIOMERIEUX VITEK, INC.
Application year: 1996
Main classification: C12M1
IPC codes: G01N35, C12N1, G01N33, C12M1, G01N1, C12M3, B01L3