PIPETTABLE REPLACEMENT FLUID FOR MIMICKING PIPETTABILITY OF TARGET FLUID AND RELATED METHOD

Abstract

A replacement fluid suitable to replace a target fluid, wherein the replacement fluid is different from the target fluid. The replacement fluid has pipetting characteristics substantially equivalent to the target fluid, wherein for a desired pipetted volume of the target fluid delivered by a pipette, a pipetted volume of the replacement fluid delivered by the pipette is substantially equivalent to the desired pipetted volume of the target fluid. The replacement fluid is a primary equivalent fluid having substantially similar pipetting characteristics. One or more additives may be added to the primary equivalent fluid. The one or more additives may include pipettability modifying additives and non pipettability modifying additives.

Claims

1. A replacement fluid suitable to replace a target fluid, wherein the replacement fluid is different from the target fluid, the replacement fluid comprising: a fluid having pipetting characteristics substantially equivalent to the target fluid, wherein for a desired pipetted volume of the target fluid delivered by a pipette, a pipetted volume of the replacement fluid delivered by the pipette is substantially similar to the desired pipetted volume of the target fluid.

2. The replacement fluid as claimed in claim 1, wherein the pipetted volume of the replacement fluid is within about +/−20 of the desired pipetted volume of the target fluid.

3. The replacement fluid as claimed in claim 1, wherein the replacement fluid has rheological and other properties substantially equivalent to rheological and other properties of the target fluid.

4. The replacement fluid as claimed in claim 3, wherein the rheological and other properties include viscosity, shear rate, surface tension, and contact angle.

5. The replacement fluid as claimed in claim 4, wherein the replacement fluid includes a primary equivalent fluid and one or more additives.

6. The replacement fluid as claimed in claim 5, wherein the one or more additives includes an additive that adsorbs to a surface of a pipette tip.

7. The replacement fluid as claimed in claim 5, wherein the one or more additives include one or more pipetting-modifying additives selected to modify one or more of the rheological and other properties of the primary equivalent fluid.

8. The replacement fluid as claimed in claim 7, wherein the one or more pipetting-modifying additives are selected from the group consisting of water, a water-soluble polymer, buffering salt, glycerol, sucrose, protein, lipid, and surfactant.

9. The replacement fluid as claimed in claim 5, wherein the one or more additives include one or more non-pipetting-modifying additives selected not to modify one or more of the rheological properties of the primary equivalent fluid.

10. The replacement fluid as claimed in claim 9, wherein the one or more non-pipetting-modifying additives are selected from the group consisting of stabilizing buffer, chelator, and preservative agent.

11. The replacement fluid as claimed in claim 8, wherein the replacement fluid is water and one of the one or more pipetting-modifying additives is bovine serum albumin.

12. A replacement fluid suitable to replace a target fluid to be analyzed, wherein the replacement fluid is different from the target fluid, the replacement fluid comprising: a fluid having pipetting characteristics substantially equivalent to the target fluid, wherein for a desired pipetted volume of the target fluid delivered by a pipette, a pipetted volume of the replacement fluid delivered by the pipette is substantially similar to the desired pipetted volume of the target fluid; and one or more analysis-aiding components, wherein the one or more analysis-aiding components are selected to enable analysis of the replacement fluid as though it were the target fluid.

13. The replacement fluid as claimed in claim 12, wherein the one or more analysis-aiding components are one or more absorbance or fluorescence dyes selected to enable spectroscopic analysis of the replacement fluid.

14. The replacement fluid as claimed in claim 12, wherein the replacement fluid has rheological and other properties substantially equivalent to rheological properties of the target fluid.

15. The replacement fluid as claimed in claim 14, wherein the rheological and other properties include viscosity, shear rate, surface tension, and contact angle.

16. The replacement fluid as claimed in claim 15, wherein the replacement fluid includes a primary equivalent fluid and one or more additives.

17. The replacement fluid as claimed in claim 16, wherein the one or more additives include one or more pipetting-modifying additives selected to modify one or more of the rheological and other properties of the primary equivalent fluid.

18. The replacement fluid as claimed in claim 17, wherein the one or more pipetting-modifying additives are selected from the group consisting of water, buffering salt, glycerol, sucrose, protein, lipid, water-soluble polymer, and surfactant.

19. The replacement fluid as claimed in claim 16, wherein the one or more additives include one or more non-pipetting-modifying additives selected not to modify one or more of the rheological properties of the primary equivalent fluid.

20. The replacement fluid as claimed in claim 19, wherein the one or more non-pipetting-modifying additives are selected from the group consisting of stabilizing buffer, chelator, and preservative agent.

21. The replacement fluid as claimed in claim 18, wherein the replacement fluid is water and one of the one or more pipetting-modifying additives is bovine serum albumin.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 is a graph showing the viscosity as a function of shear rate for human serum, horse serum, a first example serum substitute (called SerumSub A) and a second example serum substitute (called SerumSum B).

[0026] FIG. 2 is a graph showing a comparison of pipettability for serum solutions at 10 μL.

[0027] FIG. 3 is a graph showing a comparison of pipettability for serum solutions at 25 μL.

[0028] FIG. 4 is a graph showing a comparison of pipettability for serum solutions at 50 μL.

[0029] FIG. 5 is a graph showing a comparison of pipettability for serum solutions at 100 μL.

[0030] FIG. 6 is a graph showing a comparison of pipettability for serum solutions at 200 μL.

DETAILED DESCRIPTION OF THE INVENTION

[0031] A replacement fluid of the present invention for mimicking the pipetting characteristics of a target fluid of interest is a primary equivalent fluid having substantially similar pipettability without being the target fluid. The primary equivalent fluid may be combined with one or more pipetting modifying additives that impart chemical and physical properties of pipettability interest. There may be additional optional non pipetting modifying additives forming part of the replacement fluid. The modifying additives and the ratio of such additives in the replacement fluid are selected to generate in the replacement fluid a pipettability that is substantially the same as the pipettability of the target fluid of interest.

[0032] A first example of a replacement fluid of the present invention is a replacement fluid that mimics the pipettability of serum. A first example of a fluid replacement for serum includes water as the primary equivalent fluid, and about 6 g/L of BSA and about 4 g/L of KHP as pipettability modifying additives. Further non-pipettability modifying additives include about 4 g/L of the chelating agent ethylenediaminetetraacetic acid (EDTA) and about 0.6 g/L of the preservative Mergal (Troy Chemical, part number 100421). Yet further non-pipettability modifying additives include 1.1 g/L of copper chloride dihydrate as one spectroscopic dye, and about 0.33 g/L of Ponceau S as a second spectroscopic dye (the amount of Ponceau S depends on the spectroscopic properties needed). Further additions of hydrochloric acid and/or sodium hydroxide are made to bring the fluid to a pH of 6.

[0033] A second example of a fluid replacement for serum includes water as the primary fluid, and about 6 g/L of BSA and about 4 g/L of KHP as pipettability modifying additives. Further non-pipettability modifying additives include about 4 g/L of the chelating agent ethylenediaminetetraacetic acid (EDTA) and about 0.6 g/L of the preservative Mergal (Troy Chemical, part number 100421). Yet further non-pipettability modifying additives include about 1.1 g/L of copper chloride dihydrate as one spectroscopic dye, and about 0.08 g/L of Ponceau S as a second spectroscopic dye (the amount of Ponceau S depends on the spectroscopic properties needed). Further additions of hydrochloric acid and/or sodium hydroxide are made to bring the fluid to a pH of 6.

[0034] Test results for the first and second examples of a fluid replacement for serum include testing of rheological properties as shown in FIG. 1 and Table 1 (below). FIG. 1 is a graph showing the viscosity as a function of shear rate for human serum, horse serum, a first example serum substitute (called SerumSub A) and a second example serum substitute (called SerumSum B). An important observation from this data is how different the viscosity of water is as compared to the serum and serum-like samples. The viscosity of water remains flat and is not strongly impacted by applied shear stress. However, each serum and each serum-substitute experiences a significant decrease in viscosity as shear stress is applied (shear thinning). This shear thinning results in solution that flows more freely. Addition of the BSA and KHP to water significantly changes the viscosity and viscosity profile as compared to water, making the serum-like replacement fluids behave more like serum than like water.

[0035] Table 1 further demonstrates how additives can make rheological properties less like water, and more like serum. Table 1 provides the surface tension of human and horse sera at 59 mN/m and 52 mN/m, respectively, which is considerably lower than the surface tension of water at 75 mN/m. Adding BSA and the other named components results in surface tensions for SerumSub A and SerumSub B of 57 mN/m and 45 mN/m, which are more in line with serum than water.

TABLE-US-00001 TABLE 1 Surface tension at 5° C. for human serum, horse serum, a first example serum-like fluid and a second example serum-like fluid. Human Horse Serum Serum SerumSub A SerumSub B Water at 5° C. at 5° C. at 5° C. at 5° C. at 5° C. Surface Surface Surface Surface Surface Tension Tension Tension Tension Tension (mN/m) (mN/m) (mN/m) (mN/m) (mN/m) 58.61 51.89 56.97 45.08 74.94
The test data in FIG. 1 and Table 1 are useful in guiding which additives might be introduced to improve the rheological properties. This data proves a useful guide. However, the more important parameter to match is the pipettability of the replacement fluids. FIGS. 2-6 demonstrate pipetted volumes of various fluids including human serum, horse serum, rabbit serum, rat serum. Also included are the pipetting data for a first example of a replacement serum fluid (SerumSub A) and for a second example of a replacement serum fluid (SerumSub B). Adjusting the rheological properties is important, but only to the extent that the desired pipettability is achieved. For example, the viscosity as a function of shear rate of the SerumSub A and SerumSubB, shown in FIG. 1, are not identical to either the human or horse serum. However, they are close enough to provide a good replacement fluid for mimicking pipetting properties. This can be observed in FIGS. 2-6 by how closely the pipetted volumes of SerumSub A and SerumSub B match those same volumes for the various sera.

[0036] The present invention further includes a related method for replacing a target fluid for pipetting activities with a replacement fluid that functions substantially the same as the target fluid in terms of pipetting characteristics. A first step of the method is to determine pipetting characteristics for the target fluid. A second step is to identify one or more primary equivalent fluids that may substantially match the pipettability of the target fluid based on the identified pipetting characteristics of the target fluid. A third step is to analyze one or more rheological and/or other properties of the one or more identified primary equivalent fluids and compare them to the corresponding properties of the target fluid. The identified primary equivalent fluid(s) should be less expensive and/or more readily available as compared to the target fluid. A fourth step is optionally to introduce one or more additives to the primary equivalent fluid or fluids and evaluate adjustments made to the pipettability of the primary equivalent fluid(s) to determine mimicking of target fluid pipettability. The one or more additives may include pipettability-modifying and non-modifying additives. A fifth step of the method is to replace the target fluid with one or more selected ones of the identified primary equivalent fluids. An optional step is to carry out analysis of the primary equivalent fluid, which may include one or more spectroscopic analyses, wherein the primary equivalent fluid may include a non-modifying additive for that purpose.

[0037] While the invention has been described with respect to specific example embodiments, it is not intended to be limited to those specific embodiments. Instead, the invention covers those embodiments and all reasonable equivalents.