U.S. patent application number 15/139738 was filed with the patent office on 2016-10-27 for method of preparing a reaction mixture and related products.
This patent application is currently assigned to Thermo Fisher Scientific Baltics UAB. The applicant listed for this patent is Thermo Fisher Scientific Baltics UAB. Invention is credited to Katja EKLIN, Jaakko KURKELA, Sanna UUSIVIRTA.
Application Number | 20160312268 15/139738 |
Document ID | / |
Family ID | 41263431 |
Filed Date | 2016-10-27 |
United States Patent
Application |
20160312268 |
Kind Code |
A1 |
KURKELA; Jaakko ; et
al. |
October 27, 2016 |
METHOD OF PREPARING A REACTION MIXTURE AND RELATED PRODUCTS
Abstract
The invention relates to a method of preparing a reaction
mixture for Polymerase Chain Reaction (PCR) assay and a solution
set for PCR. The method comprises providing a sample solution
comprising a biological sample to be amplified in said PCR assay
and first colorant providing the solution a first color, providing
a reagent solution comprising at least one other substance required
for performing said assay and second colorant providing the
solution a second color different from the first color, and mixing
the sample solution and the first reagent solution for providing a
mixed solution to be subjected to the PCR process, the mixed
solution having, due to said first and second colorants, a third
color different from the first and second colors. The invention
significantly aids in pipetting PCR assays.
Inventors: |
KURKELA; Jaakko; (Espoo,
FI) ; EKLIN; Katja; (Vantaa, FI) ; UUSIVIRTA;
Sanna; (Vantaa, FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Thermo Fisher Scientific Baltics UAB |
Vilnius |
|
LT |
|
|
Assignee: |
Thermo Fisher Scientific Baltics
UAB
Vilnius
LT
|
Family ID: |
41263431 |
Appl. No.: |
15/139738 |
Filed: |
April 27, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14195088 |
Mar 3, 2014 |
9416417 |
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15139738 |
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13499518 |
May 10, 2012 |
8663925 |
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PCT/FI2010/050772 |
Oct 4, 2010 |
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14195088 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 21/251 20130101;
G01N 2021/6439 20130101; G01N 21/78 20130101; C12Q 1/6876 20130101;
G01N 21/29 20130101; C12Q 1/6846 20130101; G01N 21/6428 20130101;
C12Q 1/686 20130101; C12Q 1/6846 20130101; C12Q 2527/125
20130101 |
International
Class: |
C12Q 1/68 20060101
C12Q001/68; G01N 21/29 20060101 G01N021/29 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 2, 2009 |
FI |
20096013 |
Claims
1-34. (canceled)
35. A method of preparing a reaction mixture for Polymerase Chain
Reaction (PCR) assay, comprising: (i) providing a first reagent
solution comprising at least one substance for performing said
assay, (ii) providing a second reagent solution comprising at least
one other substance for performing said assay, (iii) mixing the
first and second reagent solutions for providing a mixed solution
to be subjected to the PCR process, wherein the first reagent
solution contains first colorant providing the first reagent
solution a first color; the second reagent solution contains second
colorant providing the solution a second color different from the
first color; said mixing yields a mixed solution having, due to
said first and second colorants, a third color different from the
first and second colors; and wherein the third color is detected
visually.
36. The method of claim 35, further comprising providing a third
reagent solution comprising at least one further substance for
performing said assay, the third reagent solution containing a
third colorant providing the solution a fourth color different from
the first, second and third colors; and mixing the third reagent
solution with the first and second reagent solutions for providing
a mixed reagent solution having, due to said first, second and
third colorants, a fifth color different from the first, second,
third and fourth colors.
37. The method of claim 35, further comprising providing a third
reagent solution containing third colorant providing the solution a
fourth color different from the first, second and third colors; and
individually mixing the first reagent solution with said second and
third reagent solutions for obtaining first and second mixed
solutions having third and fifth colors, respectively, different
from each other and the first, second and fourth colors.
38. The method of claim 37, wherein the first reagent solution is a
PCR or qPCR master mix, the second reagent solution contains a
first set of primers and the third reagent solution contains a
second set of primers different from the first set of primers.
39. The method of claim 35, wherein the first reagent solution
comprises at least one substance for the PCR assay, which is a
polymerase, a primer, a plurality of dNTPs, a fluorescent qPCR dye,
or a probe.
40. The method of claim 39, wherein the second reagent solution
comprises at least one other substance not in the first reagent
solution and for the PCR assay, which is a polymerase, a primer, a
plurality of dNTPs, a fluorescent qPCR dye, or a probe.
41. The method of claim 40, wherein the first reagent solution
comprises a polymerase or a polymerase buffer; and the second
reagent solution comprises at least one of primers, a probe, and a
sample.
42. The method of claim 35, wherein the reaction mixture is for use
in a quantitative PCR assay.
43. The method of claim 42, wherein the reaction mixture comprises
a fluorescent agent, and wherein the absorbance peaks of the
colorants do not overlap with the emission or excitation wavelength
of the fluorescent agent or the total absorbances of the reaction
mixture at the emission or excitation wavelengths of the
fluorescent agent are less than 0.05 when measured with a 1 mm
light path.
44. The method of claim 42, wherein the mixed solution is
translucent.
45. The method of claim 42, wherein the mixed solution is
transparent.
46. The method of claim 35, wherein the first reagent solution or
the second reagent solution further comprises a biological sample
to be amplified in the PCR assay.
47. The method of claim 35, wherein the first reagent solution or
the second reagent solution is a PCR master mix, a qPCR master mix,
a PCR premix or a qPCR premix.
48. The method of claim 35, wherein the first reagent solution or
the second reagent solution further comprises a sample elution
buffer.
49. The method of claim 35, wherein the first reagent solution or
the second reagent solution further comprises a sample dilution
buffer.
50. The method of claim 35, wherein at least one of the first and
second colorants is selected from Quinoline yellow, Xylene cyanol,
Brilliant Blue, Patent Blue, Indigocarmine, Acid Red 1, m-Cresol
Purple, Cresol Red, Neutral Red, Bromocresol Green, Acid Violet 5,
Bromo phenol blue, and Orange G.
51. The method of claim 35, wherein at least one of the first
reagent solution or the second reagent solution is a
concentrate.
52. The method of claim 35, further comprising subjecting the mixed
solution to a quantitative PCR process.
53. The method of claim 38, further comprising subjecting the mixed
solution to a quantitative PCR process.
54. The method of claim 35, wherein the mixing is carried out by
pipetting the reagent solutions to one or more wells of a
microtiter strip or plate.
Description
RELATED APPLICATIONS
[0001] This application claims priority to copending U.S.
application Ser. No. 13/499,518, which is a national stage
application of PCT/FI2010/050772 filed Oct. 4, 2010, which claims
priority to Finnish application Ser. No. 20096013 filed Oct. 2,
2009, each of which is expressly incorporated by reference herein
in its entirety.
FIELD OF THE INVENTION
[0002] The invention relates to pipetting of (bio)chemical
reagents. In particular, the invention relates to a method of
pipetting of reagents to microwells for Polymerase Chain Reaction
(PCR) amplification, in particular quantitative PCR (qPCR)
amplification. In addition, the invention relates to new products
for aiding pipetting.
BACKGROUND OF THE INVENTION
[0003] When pipetting the PCR reaction, all necessary components,
i.e. reagents, can be added to the reaction tube one by one, or
preferably by first combining at least some of them as a master mix
followed by dividing this mixture to multiple samples. One of the
components that usually must be added separately is the sample
under study. The number of samples, tubes or sample wells in a
microtiter plate can be hundreds or even thousands per setup.
[0004] Adding reagents correctly, i.e. in the right order and
amount, is crucial for obtaining valid results not only in PCR but
also in many other (bio)chemical reactions. Failed experiments
result in loss of time and money. Economic importance can be huge.
This is because of waste of ingredients, plastic ware and personnel
working hours. Moreover, delays in obtaining the results of the
experiments may be significant. There have been various solutions
to this well-known problem.
[0005] There are mechanical solutions to the problem. The art
acknowledges various automated pipetting robots, multichannel
pipettes and guidance systems (e.g. Finnzymes Piko.RTM. Light
Plate, BioTx Well Aware.TM.) used with sample tubes and plates.
[0006] For several years there have also been available PCR master
mixes or buffers that contain some visible dye to help pipetting
and tracking of electrophoresis runs. These mixes typically also
have some component to increase density of the solution to help in
electrophoresis gel loading.
[0007] U.S. Pat. No. 6,942,964 discloses a product using a
pipetting aid dye which is also used as a gel loading and tracking
dye. The colorant has been incorporated with the polymerase, which
helps the user to see whether the polymerase has been pipetted to
the PCR mix or master mix. A similar product is BioLine Accuzyme
Red.
[0008] USB Corporation's RubyTaq features a polymerase including a
mixture of two dyes which are separated during the agarose gel run:
magenta (runs between 500 by [2% gels] and 1500 by [0.8% gels]) and
yellow (runs less than 10 bp).
[0009] Fermentas and Promega have also added a colorant to the
enzyme reaction buffer. Fermentas' DreamTaq.TM. Green reaction
buffer can be seen as green, but the color separates into a blue
and yellow bands during gel electrophoresis. Promega GoTaq and
GoTaq Green Mastermix behave similarly.
[0010] There are also products available where the dye added to the
polymerase is not intended to help in the electrophoresis phase.
Examples include ABgene Red.RTM. Hot.
[0011] NEB provides a product (Crimson Taq) featuring a dye Acid
red added to the DNA polymerase reaction buffer. The product also
uses 6% dextran as a density enhancer.
[0012] Qiagen's CoralLoad dye is available both as a concentrate in
a separate tube for being added to an uncolored master mix, and
also as an optional ready-made 10.times. PCR buffer. It contains
two gel tracking dyes (orange and red).
[0013] KR 2002/0045167 discloses freeze-dried PCR mixes containing
a colorant to confirm dissolution of the PCR components. U.S. Pat.
No. 6,153,412 discloses also freeze-died reaction mixtures which
are used for identifying the existence of a lyophilized PCR reagent
and to ensure complete mixing of the PCR reagent and the test
sample. U.S. Pat. No. 5,565,339, on the other hand, discloses the
use of a dye in a hot start wax, which does not dissolve into the
reaction mixture.
[0014] Absolute Blue QPCR Master Mix contains an inert blue dye to
ease pipetting in reaction set-up.
[0015] Also WO 2007/088506 discloses a dyed master mix.
[0016] Applied Biosystems has ROX passive reference dye included in
their qPCR products. The purpose of the dye is to provide a steady
fluorescence level which can be used to normalize against any non
PCR related fluorescence variation between the different reactions
and in one sample during a reaction. The method is also suggested
to normalize at least partly against deviations in pipetting
accuracy.
[0017] All but the three last ones of the products mentioned above
are suggested to be used only in traditional end point PCR. In
addition to the colorants, they typically contain a density
enhancer to get the sample material into the bottom of the gel
wells (see e.g. U.S. Pat. No. 6,942,964). Without the density
enhancer, samples would disperse into the surrounding liquid.
[0018] Colorants used in end-point PCR are generally not compatible
with quantitative PCR (qPCR). This is usually because they prevent
real-time optical measurements of the ongoing reaction. In
particular, the dyes typically have a spectrum which overlaps with
the detection wavelengths of qPCR fluorescence or their absorbance
is too high. General requirements for the dyes used include
non-inhibitory effect on the PCR reaction or stability in the
reaction pH.
[0019] An additional disadvantage of the above mentioned solutions
in which the dye is provided in the master mix or in the polymerase
is that they are not able to provide help for pipetting the samples
(i.e. in PCR the material to be amplified). Sample pipetting is,
however, the step where keeping track of the process is most
important, and most difficult.
[0020] The various mechanical systems available cannot solve the
problem entirely. They are expensive and pipetting errors cannot
always be seen visually mainly because of volume differences, which
means the error might not be detected until after obtaining failed
results.
[0021] Thus, there is a need for enhanced pipetting aids. In
particular, there is a need for such pipetting aids which can also
be applied for the sample pipetting phase.
SUMMARY OF THE INVENTION
[0022] It is an aim of the invention to provide a novel solution
for aiding pipetting during preparation of PCR assays and in
particular for making the detection of errors in various stages of
pipetting easier.
[0023] The aim of the invention is achieved by the invention as
defined in the independent claims.
[0024] In the pipetting stage of PCR assays, at least two reagent
solutions are mixed for obtaining the final mixture which is
subjected to PCR. The invention is based on the idea of coloring
the reagent solutions with different initial colorants, which, upon
mixing produce a distinguishable color different from the colors of
the initial colorants.
[0025] Thus, one can tell directly by the color of the solution,
whether it is the first reagent solution, the second reagent
solution or the mixture of these.
[0026] More specifically, the method comprises [0027] providing a
first reagent solution comprising at least one substance required
for performing the assay and a first colorant providing the
solution a first color, [0028] providing a second reagent solution
comprising at least one other substance required for performing
said assay and a second colorant providing the solution a second
color different from the first color, [0029] mixing the first and
second reagent solutions for providing a mixed solution to be
subjected to the PCR process, the mixed solution having, due to
said first and second colorants, a third color different from the
first and second colors.
[0030] In a typical application, one of the reagent solutions is a
sample solution, that is, a solution containing or intended to
receive a biological sample to be amplified in the PCR assay, and
the other of the reagent solutions contains some other at least one
other substance required for performing the assay, for example the
polymerase solution or master mix. The sample solution may be a
buffered solution (hereinafter "a sample buffer solution"). Thus, a
microwell having a first color indicates that there is only sample
solution without other reagents, e.g. master mix, in the well. A
microwell with second color indicates that master mix has been
added but there is no sample yet. Finally, a microwell with third
color implies that sample has been properly added to the master
mix. The inspection of the color can be made visually or by
automatic optical means.
[0031] In one embodiment, one of the reagent solutions is an
elution buffer, such an elution buffer used in combination with a
nucleic acid purification kit.
[0032] In one embodiment, one of the reagent solutions is a
dilution buffer used to facilitate lysis of a solid-state sample to
release nucleic acids. The reagent solution can also be used to
dilute, digest or precipitate released components before PCR. Thus,
it is possible to use the invention when pipetting direct PCR
assays.
[0033] In further embodiments, one of the reagent solutions is a
solution used in cDNA synthesis reaction, reverse transcriptase
reaction or bisulphite reaction.
[0034] In one embodiment, one of the reagent solutions is some
other solution used for preparing the sample for the PCR
process.
[0035] The invention also provides a new use of dyes for producing
two or more colored PCR reagent solutions, which are capable of
forming a mixed solution having a color distinguishable from the
initial colors of the reagent solutions.
[0036] Further embodiments are the subject of the dependent
claims.
[0037] A particular aim of the invention is to achieve a pipetting
aid solution which is compatible with quantitative PCR. This is
achieved by using such colorants and colorant concentrations which
do not significantly disturb the fluorescent processes, i.e.
excitation and emission, or optical detection used in qPCR. In
particular, the reaction mixture subjected to qPCR is transparent
or translucent at least at the qPCR excitation and emission
wavelengths. This generally means that the maximum absorbance of
the of the reaction mixture is less than 0.5, in particular less
than 0.15 (measured using 1 mm light path) and that the absorption
window of the colorant does not overlap, at least significantly,
with the excitation or emission wavelengths of the fluorescent qPCR
dye(s) or modified DNA oligonucleotide probe(s) used.
[0038] In one embodiment, a reaction mixture for quantitative PCR
is prepared, the reaction mixture comprising fluorescent dye,
primer or probe, and wherein the absorbance peaks of any of said
colorants do not overlap with the emission or excitation wavelength
of said fluorescent dye, primer or probe. If overlap exists, it
should not significantly weaken the qPCR signal, generally implying
that the total absorbance of the reaction mixture at said
wavelengths is less than 0.05, preferably less than 0.03, in
particular less than 0.1.
[0039] The invention provides considerable advantages. As the
initial solutions and the resultant solution are mutually of
different colors, one not only distinguish between the initial
solutions, but also between the initial solutions and their
mixture.
[0040] In addition, from colored solutions one can be quickly
perceive whether the solutions have been properly mixed and whether
there are significant deviations from the desired reaction
volume.
[0041] Moreover, the colors make it easier to see if there is any
liquid splashed or spilled in wrong places where they could
potentially cause contamination, microwell sealing problems etc.
Especially with adhesive sealing films applied on microtiter plates
before thermal cycling, any liquid in the sealing contact can
compromise the seal and thus the whole PCR assay.
[0042] The present invention can also be used together with the
mechanical solutions to lower their error rate even more, if the
pipetting steps performed are visualized using the colorants. When
using pipetting robots, it is possible to add a quality check step
based on optical detection after desired steps, or the volume and
color of the reagents can be quickly checked visually.
[0043] For the above reasons, dyes and other colorants used in the
present manner can help keeping track in reaction setup and
especially during loading reagents into reaction plate. Thus, the
approach provides considerable help and increased certainty for
pipetting samples.
[0044] In qPCR there is no need to load the amplified products into
a gel after a PCR reaction. Thus, a density enhancer is not needed.
Consequently, the present solutions may be free of density enhancer
or contain only minor amounts of density enhancer (i.e. less than
required for gel electrophoresis).
[0045] According to one embodiment, there is provided, in addition
to the above mentioned first and second reagent solutions, one or
more additional reagent solutions comprising additional colorants
providing the solutions different colors. The solutions are capable
of forming, on mixing, additional solutions having, due to said
additional colorants, further distinguishable colors. Thus, the
invention can be used not only for aiding the pipetting in one
particular stage of the process, e.g. pipetting of the of the
sample to master mix, but also for aiding the pipetting during
other steps, in particular the steps previous or subsequent to the
sample pipetting step.
[0046] In more detail, the method may comprise providing a third
reagent solution comprising at least one further substance required
for performing said assay, the third reagent solution containing a
third colorant providing the solution a fourth color different from
the first, second and third colors mentioned above, and mixing the
third reagent solution with the first and second reagent solutions
for providing a mixed reagent solution having, due to said first,
second and third colorants, a fifth color different from the first,
second, third and fourth colors. In particular, the first reagent
solution may be a sample, the second reaction solution the master
mix and the third reagent solution may be a primer solution. The
order of application is not essential, unless otherwise defined in
assay instructions.
[0047] Alternatively, to the above the method may comprise
providing a third reagent solution containing third colorant
providing the solution a fourth color different from the first,
second and third colors, and individually mixing the first reagent
solution with said second and third reagent solutions for obtaining
first and second mixed solutions having third and fifth colors,
respectively, different from each other and the first, second and
fourth colors. For example, the second reagent solution may contain
one set of primers and the third reagent solution may contain a
second set of primers. In this embodiment too, the colors of all
initial ingredients and all resultant mixtures are unique.
[0048] The two above mentioned embodiments can also be chained such
that the second and third reagent solutions are ultimately
individually mixed with a reagent solution which is itself prepared
by mixing at least two different colored reagent solutions. Other
kinds of combinations are possible too.
[0049] A "reagent solution" is any solution containing at least one
reagent needed or advantageously used for PCR purposes. Most
typical ingredients are polymerase, nucleotide, primer, ions,
magnesium, other salt, pH buffering agent, dNTPs or fluorescent
qPCR dye or probe, oligonucleotide, nucleic acid binding agent, a
nucleic acid template. The reagent may also be other polymerase
reaction additive, which has an influence on the polymerase
reaction or its monitoring.
[0050] The term "sample solution" covers both buffered and
non-buffered sample solutions which are still free of template or
into which the template to be amplified using PCR has already been
added, unless otherwise specified. The term "sample solution" is
covered by the term "reagent solution".
[0051] The term "master mix" refers to a mixture of all or most of
the ingredients or factors necessary for PCR to occur, typically
all except for the template and primers which are sample and
amplicon specific. Commercially available master mixes are usually
concentrated solutions. A master mix may contain all the reagents
common to multiple samples, but it may also be constructed for one
sample only. Using master mixes helps to reduce pipetting errors
and variations between samples due to differences between pipetted
volumes. It also minimizes the time spent for pipetting.
[0052] A qPCR master mix is a master mix intended for performing a
qPCR reaction. Thus, it may contain fluorescent dye or
fluorescently tagged oligonucleotide primers or probes.
[0053] The term "premix" refers to a master mix that contains all
the necessary components for a PCR reaction except for the
template.
[0054] The term "color" herein means any detectable spectral
response (of a solution) to white light in the visual range. Thus,
there is at least one wavelength range in the absorbance spectrum
of the solution which provides a colored visual appearance for the
solution (in contrast to the nearly 100% transmittance of water).
White, black, and shades of gray are herein counted as colors. As
will be shown later, an absorbance higher than about 0.01 (1 mm
light path) gives a visually perceivable color for a solution
whereas an absorbance higher than about 0.001 (1 mm light path) can
be relatively easily detected by hardware-based spectral detection
means.
[0055] The term "different colors" means that the colors are
distinguishable, preferably by the naked eye, but at least with
spectral detection means. In particular, "different colors" may
have maximum peaks in their absorption spectrum separated by at
least 30 nm. Preferably, the different colors are selected from the
groups of: red, yellow, blue or cyan, magenta, yellow and visually
distinguishable combinations and shades thereof, such as green,
orange, and violet.
[0056] The term "colorant" means any substance which is capable of
being homogeneously mixed or dissolved within a solution and
capable of giving the solution a perceivable color. According to
one embodiment, the colorant is a dye, in particular an aqueous
dye, preferably a non-oxidizing aqueous dye.
[0057] The terms "transparent" or "translucent" colorant-containing
solution refers, in particular, to a solution which has an optical
transmission window at at least some fluorescence excitation and/or
emission wavelengths that can be used for performing qPCR, the
wavelengths depending on the fluorophores, fluorescent dye(s),
and/or modified DNA oligonucleotide probe(s) contained in the
reaction mixture. Typically, the excitation wavelength is between
350 and 690 nm, in particular between 490 and 650 nm. The emission
wavelength is typically between 350 nm-730 nm, in particular 515
nm-680 nm. A transparent solution is optically essentially
non-diffusive, whereas a translucent solution passes light
diffusely.
[0058] The term "sample" refers to a solid material or a solution
that contains the nucleic acid of interest or is to be analyzed for
the presence of nucleic acid of interest.
[0059] The term "dilution buffer" refers to a solution that can be
used for sample pretreatment before PCR setup. Pretreatment can
include sample lysis for releasing nucleic acids, dilution,
binding, chemical lysis, precipitation and enzymatic digestion of
some components.
[0060] The term "preparative process" refers to any reaction,
pipetting step or pretreatment which yields a product which can in
total or in part be used as a sample in a subsequent PCR
reaction.
[0061] Typically the third color, achieved by mixing the solutions
with the first and second colorants, is a chromatic combination of
the first and second colors of the solutions. Thus, the third color
may be produced as a sum spectrum of the spectra of the first and
second colors. However, it is not excluded that the third color is
formed through a more complex process, e.g. reaction of the first
and second colorants, or due to a fluorescent process, e.g.
fluorescence resonance energy transfer (FRET), provided that the
fluorescence wavelengths differ from those of qPCR fluorophores
used.
[0062] Next, embodiments and advantages of the invention are
described in more detail with reference to the attached
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0063] FIG. 1A shows in cross-sectional view three microwells
containing colored sample buffer, colored reagent solution and
their colored mixture, respectively.
[0064] FIG. 1B shows a top view of a microtiter plate containing
empty wells and wells containing colored sample buffer, colored
reagent solution, their colored mixture and wells with optically
clear liquid.
[0065] FIGS. 2a and 2b illustrate as a flow chart exemplary ways of
carrying out the invention.
[0066] FIG. 3 shows a flow chart of the present process according
to one embodiment of the invention.
[0067] FIGS. 4a-4d show standard series obtained with master mix
and sample with (4a and 4b) and without (4c and 4d) pipetting aid
dyes.
[0068] FIGS. 5a-5d show absorbance spectra relating to a absorbance
measurement example.
[0069] FIGS. 6a-6c and 7a-7c illustrate the use of colorant in a
cDNA synthesis reaction.
DETAILED DESCRIPTION OF EMBODIMENTS
[0070] To make plate setup easier, the invention provides,
according to one embodiment, a dye combination that helps keeping
track of pipetting master mix, samples and mixing of these, in the
pipetting phase of (q)PCR process. Thus, the dyes are preferably
optimized so that they will have minimal effect on qPCR reaction
(e.g. will not influence the sample or DNA polymerase used) and
will not significantly affect optical detection of fluorescence. In
other words, the dyes used are compatible with the qPCR assay.
[0071] Typical fluorophores used for qPCR purposes include Alexa
350, FAM.TM., TET.TM., VIC.TM., JOE.TM., HEX.TM., CY.RTM.3,
TAMRA.TM., ROX.TM., Texas Red.RTM., CY.RTM.5, CY.RTM.5.5 and
Quasar.RTM.705, the emission and excitation wavelengths of which
are shown in Table 1.
TABLE-US-00001 TABLE 1 Dye Ex Em Alexa 350 350 440 FAM 494 518 JOE
520 548 VIC 538 554 HEX 535 556 Cy3 552 570 TAMRA 565 580 Cy3.5 581
596 Texas Red 583 603 ROX 585 605 Cy5 643 667 Cy5.5 675 694
Quasar705 690 705
[0072] FIG. 1A illustrates the basic principle of the invention.
The microwell 12A contains colored sample buffer 14A having a first
color (horizontal lines). The microwell 12B contains colored master
mix 14B having a second color (vertical lines). The microwell 12C
contains colored mixture of the sample buffer and colored master
mix, having a third color (horizontal and vertical lines) resulting
from the first and second colors.
[0073] FIG. 1B illustrates a microtiter plate 10 which, in addition
to the solutions shown and marked as in FIG. 1A, contains empty
wells 12 and non-colored liquid 14D having no color (dots). In
addition, there is shown a diluted reaction mixture 14E, which is
achieved by diluting the initial reaction mixture 14C with the
non-colored liquid 14D, the diluted reaction mixture having the
same basic color as the initial reaction mixture 14C, but with
increased transparency, i.e. reduced absorbance (sparse horizontal
and vertical lines). As will be described later in more detail, not
only the color, but also the degree of dilution can be monitored
according to one embodiment of the invention.
[0074] The dyes can preferably be both detected and distinguished
from each other visually, i.e. by naked eye. Thus, the different
colors are spectrally relatively densely distributed and no special
equipment is needed. However, in automatic devices utilizing
optical spectral detectors or computer vision, also colors more
finely distributed on the spectral scale can be used, without
compromising the ability to distinguish between different
colors.
[0075] According to one embodiment, the combination comprises a
blue master mix and yellow sample buffer. When mixed together these
form clearly green solution. Blue color in the plate indicates that
master mix has been added but there is no sample yet. When sample
is added color turns green. If solution in the well is yellow it
means that there is only sample without mastermix. According to one
embodiment, the blue dye comprises Xylene cyanol. According to one
embodiment, the yellow dye comprises Quinoline yellow. These dyes
have been found to be compatible with the polymerase and sample
buffer, respectively.
[0076] Other potential dyes comprise Brilliant Blue, Patent Blue,
Indigocarmine, Acid Red 1, m-Cresol Purple, Cresol Red, Neutral
Red, Bromocresol Green, Acid Violet 5, Bromo phenol blue, and
Orange G. Other potential dyes are listed in U.S. Pat. No.
6,942,964.
[0077] According to one embodiment, the dyes are strong enough to
give a visually perceivable color for the respective solutions, but
weak enough not to disturb fluorescence detection and/or weak
enough not to interfere with gel electrophoresis migration tracking
with other dyes commonly used for that purpose. For example, the
above mentioned Xylene cyanol and Quinolene yellow belong to this
group of dyes. Thus, if the colored amplified reaction mixture is
subjected to end-point gel electrophoresis analysis, the colorants
do not have an influence on the analysis. Instead of that, a
conventional loading buffer with electrophoresis dye can be added
to the amplified mixture. Moderate dyeing also maintains the
general visual appearance of the solutions transparent or
translucent.
[0078] A suitable concentration of the dye depends on the dye
itself. According to one embodiment, directed to machine-aided
color detection, the concentration of the dye in the initial
solution is adjusted to result in an absorbance of 0.001-0.5 at its
maximum absorption wavelength (1 mm light path). According to an
embodiment directed to visual color detection, the concentration of
the dye is adjusted to result in an absorbance of 0.01-0.5, in
particular 0.03-0.5, at its maximum absorption wavelength (1 mm
light path). According to a most preferred embodiment, the
absorbance is 0.03-0.15, which ensures both visual detectability of
the color and negligible or small effect on the qPCR measurement
even if the absorbance peak would slightly overlap with the qPCR
excitation and/or emission wavelengths. It is preferred, if such
overlap exists, that the total absorbance at the qPCR excitation
and/or emission wavelength is less than 0.05, preferably less than
0.03, in particular less than 0.01 (1 mm light path), regardless of
the maximum absorbance. As the two (or more) initial solutions have
differently colored dyes, there is no significant cumulative
absorbance at any particular wavelength. It should also be noted
that the above absorbances are the preferred absorbance of
solutions diluted to the desired PCR processing concentration. If
the solutions are delivered as concentrates, the preferred
absorbances are respectively higher.
[0079] According to an alternative embodiment, at least one of the
solutions is provided with dye, which is both suitable to be used
in qPCR (i.e. does not affect the fluorescence detection at the
wavelengths used) and strong enough to detected in gel
electrophoresis, and runs on an appropriate distance at the gel
with respect to the samples. Thus, a separate loading buffer is not
necessarily needed.
[0080] The sample buffer containing a dye may be delivered either
as a dilute or concentration, depending on the intended use.
[0081] FIG. 2 illustrates the general concept of pipetting a
colored sample solution (step 20) and at least one reagent solution
(step 21, optionally 22) into a single container and mixing the
solutions (step 23). The color of the mixed solution is checked
(step 24) before subjecting the mixture to PCR (step 25). It should
be noted that there may be other pipetting and processing steps
which are not shown in FIG. 2 for simplicity.
[0082] Several embodiments taking advantage of the general idea of
the invention are explained below.
[0083] According to one embodiment, there are provided a plurality
of colored sample buffer solutions, in which different colorants
are used to give the sample buffers different colors. According to
a further embodiment, mixing the plurality of colored sample
buffers with the same colored reagent mixture yields reaction
mixtures of different colors. Thus, in a multi-sample PCR assay,
one can distinguish between different samples based on the color of
the solution. For example, a yellow sample buffer and a red sample
buffer mixed with a blue master mix could give green and magenta
reaction mixtures, from which one can immediately verify not only
the proper mixing, but also the type of the sample.
[0084] According to one embodiment, there are provided a master mix
and a plurality of colored primer mixes, in which different
colorants are used to give the mixes different colors (master mix:
color 1, primer mixes: color 2 and color 3). Combining the primer
mixes with the mister mix yields still different colored mixes
(colors 4 and 6). Further, by adding a colored sample (color 7) to
the mixes obtained, distinguishable PCR solutions are obtained
(colors 8 and 9). In each case of the process, the color of the
solutions is indicative of the contents of the solution.
[0085] As illustrated in FIG. 3, according to one embodiment, there
are provided a plurality of master mixes or other premixes (steps
31, 32) which are provided with different colorants to render the
premixes differently colored (say, premix 1: color 2, premix 2:
color 3, . . . premix n: color n+1) and a sample having a further
color (color 1) (step 30). The premixes are individually mixed with
the sample (steps 33a, 33b) and the colors of the resulting
solutions are checked (steps 34a, 34b). The colors are preferably
chosen so that each combination of a premix solution and sample
solution solutions yields a unique color rendering the solutions
distinguishable from each other and the initial premix and sample
solutions. After checking (34a, 34b) the solutions are, in
principle, ready for PCR. It should be noted that there may be
other pipetting and processing steps which are not shown in FIG. 3
for simplicity.
[0086] More generally, there may be provided a plurality of initial
solutions (each containing a component needed in the PCR reaction,
e.g. polymerase, primer, ions, dNTPs or fluorescent qPCR dye or
probe, or other additives) which are provided with different
colorants to render the solutions differently colored (say,
solution 1: color 2, solution 2: color 3, . . . solution n: color
n+1) and a sample having a further color (color 1). The colors are
preferably chosen so that each combination of solutions yields a
unique color rendering the solutions distinguishable from the other
solutions.
[0087] Selected variations of the invention having high utility
value are described below.
[0088] Use of Dye in Elution Buffer
[0089] Nucleic acids for molecular biology experiments are usually
purified from complex sample material. There are various methods
for purification including methods based on extraction,
precipitation, hybridization and different modes of chromatography
or filtering etc. In most of the techniques nucleic acids are
either dissolved or eluted in selected solution. Precipitated
nucleic acids can be dissolved in a variety of solutions. When
using other method that are based on other DNA interactions there
are more requirements for the elution buffer such as suitable ionic
strength. Purification methods based on DNA binding to silica in
high ionic strength conditions are widely used. Bound DNA is eluted
from silica matrix with low ionic strength buffer or with pure
water. Many kits based on the silica binding method are available
and usually the kit contains the elution buffer. To reduce the
number of pipetting steps in the experiment workflow, the colorant
can be included in the elution buffer or the buffer provided with
the kit can be replaced with the colored buffer. By doing this, the
user does not have to add the color in a separate step.
[0090] For example, the sample buffer containing the dye can be
used as a sample elution buffer in combination with many commercial
or homebrew DNA purification kits. The elution buffer provided with
many of the available kits can be just simply replaced with the
sample buffer containing the dye. Alternatively, a small amount of
dye concentrate can be added in the elution buffer provided with
the kit without diluting the sample too much.
[0091] The other colored reagent solution may be any other solution
needed for the process, as discussed above.
[0092] Use of Dye in Dilution Buffer (Direct PCR)
[0093] New enzyme technology has made it possible to significantly
simplify sample preparation for PCR and it is even possible to put
the unpurified sample directly to the PCR. However in many
experiments the sample needs to be separated in to several
reactions and it is often preferable to be able to store some of
the sample for possible repeats or other purposes. Thus direct PCR
protocols where sample is lysed and dissolved in a special sample
buffer are very popular. In these so called dilution protocols the
dilution buffer may contain different agents that lyse the sample.
In addition to these agents a colorant can be added to the dilution
buffer to make subsequent pipetting steps easier.
[0094] The other colored reagent solution may be any other solution
needed for the process, as discussed above.
[0095] To demonstrate this embodiment, two set of extractions from
bovine milk samples were done with a kit based on DNA binding to
silica. One following the guidelines and the other set where the
elution buffer was replaced with 1.times. sample buffer with yellow
dye. Purified samples were used in qPCR and qPCR results of the
described two sets were compared. No significant difference was
observed.
[0096] Use of Dye in Reverse Transcription Reaction
[0097] Majority of real time PCR is done for gene expression
studies. In these experiments the nucleic acid of interest is RNA
and thus not directly suitable template for normal qPCR. Before
qPCR the RNA sample must be reverse transcribed before the qPCR
step. Reverse transcription and qPCR reaction can be combined and
performed subsequently in same reaction mixture. However usually
the condition is a compromise and not optimal for either of the two
reactions. In most cases it is more optimal to do separate reverse
transcription reaction and use the created cDNA as a template in a
separate qPCR reaction. In reverse transcription reaction setup
there are the same challenges of keeping track of samples during
pipetting as described for qPCR. An embodiment of the invention
describes how colorant can be used in cDNA synthesis reaction to
overcome this challenge.
[0098] The use of colorant in cDNA synthesis reaction has also been
demonstrated as follows:
[0099] Two cDNA synthesis reaction series were prepared one with
the yellow colorant, in final concentration of 10 fold compared to
the concentration instructed for the qPCR, the other without the
additional dye. HeLa total RNA dilution series with 1000 ng, 500
ng, 10 ng 1 ng, 100 pg and 10 pg dilutions were used as template.
Reactions were otherwise done according to the manual (Product
number F-470, Finnzymes). A 1.5 .mu.l aliquot of each reaction was
then used as a template in qPCR with DyNAmo SYBR Flash qPCR master
mix.
[0100] With reference to FIGS. 6a-6c and 7a-7c, two standard curves
were created, the first (FIG. 6c) representing the series with the
added dye and the other (FIG. 7c) without the dye. The results show
that cDNA synthesis can be performed in presence of colorant and
the quantitative nature of the reaction is maintained.
[0101] In practice, the dye can be brought into the reaction with
the transcriptase, with the sample, with the buffer solution or
separately as a concentrate.
[0102] Use of Dye in Bisulphite Reactions
[0103] Similarly to what is discussed above, dye can also be added
to any component taking part in a bisulphite treatment prior to
mixing the sample thereby obtained with a second reaction
solution.
[0104] As can be seen from the above examples, the dye can be
present not only when mixing the final PCR reaction mixture but
also in preparative process steps, in particular those relating to
sample preparation, such as reverse transcription reaction (e.g. in
cDNA synthesis), bisulfite reaction, sample elution or sample
dilution. These examples are not limiting and, as understood by a
person skilled in the art, the dye can be introduced also into
these reactions in various ways, for example, with the enzyme, with
reaction buffer, with the sample or separately.
[0105] As there is color present also in the preparative process
steps, pipetting of these steps is facilitated too. However,
according to a preferred embodiment, at least one colored solution
is brought when mixing the final reaction solution, e.g. with the
polymerase or master mix.
[0106] FIG. 2b illustrates, at a general level, the principle of
introducing at least one colored reagent solution (step 20') to the
process prior to at least one preparative process step 29'. The
pretreatment may involve the introduction of one or more other
substances too (step 28'). After pretreatment, the process can be
continued similarly to as explained above, by mixing the product
(or aliquot thereof) of the preparative process step with second
colored reagent solution (steps 21' and 23'), checking the color of
the mixed solution (step 24') and proceeding to (q)PCR (step
25').
[0107] Monitoring of the pipetting process is described below.
[0108] Preferably, the different colors are distinguishable by the
naked eye. However, hardware-aided optical measurements capable of
distinguishing between colors can be utilized too.
[0109] According to one embodiment, the condition of one or more
microwells to be pipetted is checked at least once during the
pipetting process automatically by optical means capable of
spectral resolution.
[0110] According to one embodiment, the condition of the microwells
is automatically checked at least two times in different stages of
the pipetting process. Preferably such checking is carried out
after every separate pipetting step.
[0111] The concentration of the colorant decreases and the color of
a colored solution become weaker due to every addition of
non-colored, i.e. optically clear, liquids. On the other hand,
addition of colored substances changes the shade of the color.
Thus, the strength and/or shade of color of a solution within a
well is indicative of the stage of pipetting. By automatic
measurement of the spectral response of the microwell(s), the
progress of the pipetting process can be monitored.
[0112] According to one embodiment, the above mentioned monitoring
is carried out using a computer program, which is adapted to
compare the measured spectral responses after the desired pipetting
steps with predefined limits for these steps. Such limits are
designed to reflect the correct shade and/or strength of the color
of the solution, taking into account the reagents added. A
microwell, for which the measured value is not within an accepted
range, is flagged incorrectly pipetted.
[0113] The detection of the color of a solution is preferably based
on absorbance measurement. The detection instrumentation, which may
be an in integral part of an automatic pipetting apparatus or a
(q)PCR thermal cycling apparatus, for example, contains absorbance
measurement means, i.e. a light source, a light detector and means
for determining the absorbance of the contents of a microwell at
least at one wavelength or wavelength range. Preferably, the
absorbance measurement means comprise a spectrophotometer. By means
of the invention, the reliability of pipetting and PCR assay can be
improved, as even small changes in shades and strengths of colors,
and thus in the contents of the wells can be detected.
[0114] According to an alternative embodiment, the detection
instrumentation is contained in a separate apparatus to which the
reaction solutions can be transferred either automatically or
manually after critical pipetting steps. In the separate apparatus,
a quick plate read is carried out before the plate is transferred
for further processing.
[0115] Thus, the invention also provides an apparatus for
monitoring pipetting, comprising means for receiving a microtiter
plate containing a plurality of microwells and means for measuring
the optical absorbance of contents of the microwells. The means for
detecting the absorbance are adapted to detect the spectral
absorbance profile of the sample (for color detection) and/or color
intensity of the sample (for dilution detection). Preferably, the
apparatus is capable of both the above mentioned functions for
being able to monitor the entire pipetting process. The optical
detection means are preferably connected to a computing unit which
analyses and stores the measured absorbances and performs a
calculation or comparison of the measurement data with pre-stored
data.
[0116] The detection instrumentation may contain a
microplate-receiving block which can be cooled for keeping the
temperature of the reactions solutions low enough. For most
hot-start polymerases cooling is not necessary.
[0117] Automatic detection is of particular assistance when the
volume of the reaction vessel is small, that is, less than 5 .mu.l,
in particular less than 1 .mu.l, as reliable visual observation of
both the color and volume of the solutions is more difficult in
these cases.
[0118] The microwells may be separate or be contained in microtiter
strips or plates of any known type. Preferably, the wells are
manufactured from transparent material, allowing the visual
inspection or spectral measurements to be carried out through the
wall of the well.
Dyeing Example
[0119] Xylene cyanol as a colorant was added to DyNAmo Flash
SYBR.RTM. green qPCR and DyNAmo Flash Probe qPCR master mixes from
(Finnzymes, Finland) in the concentration of 0.0026% (w/v). The
result was a clearly blue transparent solution. Quinolene yellow
was added to a sample buffer in the concentration of 0,00174%
(w/v). The sample buffer contained 1 mM Tris-HCl pH 8.5 and 0.1 mM
EDTA. As a result, a clearly yellow transparent solution was
obtained.
[0120] The colored sample buffer and the colored master mix were
mixed, resulting in a clearly green transparent mixture.
Amplification Example
[0121] FIGS. 4a-4d show standard series obtained with master mix
and sample with (FIGS. 4a and 4b) and without (4c and 4d) the
pipetting aid dyes of Example 1. Both series were done by
amplifying human genomic DNA sequence with DyNAmo Flash Probe
master mix according to the protocol in the product manual. Primer
sequences were ACCTCCAAACTGGCTGTAAC and ATCTCCTCCTCATTGCAAAG.
Detection was based on hydrolysis probe with a sequence
TGGCCCCTTGAAGACAGCAG. Amplicon size was 121 bp.
[0122] From the mutual similarity of the amplification curves
(FIGS. 4a and 4c) and standard curves (FIGS. 4b and 4d) can be seen
that presence of the dye does not affect the reaction efficiency or
significantly affect fluorescence intensities.
Pipetting Example:
[0123] The present invention was utilized to implement the
following pipetting sequence: [0124] A colored (blue) 2.times. mix
was thoroughly mixed with primers and probes, additives and water
for obtaining a premix for several reactions. [0125] The premix was
pipetted to several wells of a microtiter plate (15 .mu.l/well).
[0126] Colored (yellow) DNA sample solutions were pipetted onto the
premixes (5 .mu.l/well). [0127] The color of the resulting solution
was manually checked to be correct (green).
[0128] After the above steps, the resulting solution is ready to be
subjected to (q)PCR. For qPCR, the reagents are preferably
centrifuged to the bottoms of the wells.
Absorbance Measurement Examples
[0129] Absorbance of different dilutions of the dyes used in the
examples above and dilutions of existing colored master mixes were
measured and compared to visual observation to assess the visually
perceivable range in different wavelengths. The purpose was in
particular to determine visually perceivable absorbance range with
different dyes and also check if commercially available dyes would
be suitable to be used with FAM and SYBR fluorescent dyes which are
probably the most popular dyes used in qPCR.
[0130] Measurements were performed with Nanodrop ND-1000
spectrophotometer, which uses 1 mm and 0.1 mm light paths.
[0131] The results, including visual detectability of color,
absorbance maxima and absorbances of the samples as well as types
of the solutions and dyes used in the experiments are shown in
Tables 1-7 below. Tables 1-3 show the results obtained with
preferred dyes to be used with FAM or SYBR, whereas Tables 4-7 show
comparative examples obtained with commercially available colored
PCR solutions.
[0132] In the Tables, the following denotations are used: [0133]
+++ strong color [0134] ++ color easy to see [0135] + weak color
but visible in normal laboratory environment by naked eye [0136] -
color not visible in normal laboratory environment by naked eye
[0137] For cases denoted with asterisk (*), the absorbance peak was
not completely well-defined or clear.
TABLE-US-00002 TABLE 1 Absorbance Visual maximum Product Dilution
color nm (.lamda..sub.max) A .sub.(1 mm) A .sub.(1 cm) Reagent
color 500x +++ 615 Finnzymes 50x +++ 615 1.63 5x ++ 615 0.179
Xylene cyanol (XC) 1x ++ 615 0.037 0.302 0.5x + 615 0.2x - 615
0.013 0.04x 615
TABLE-US-00003 TABLE 2 Visual Product Dilution color nm
(.lamda..sub.max) A .sub.(1 mm) A .sub.(1 cm) Sample buffer 500x
+++ 413 Finnzymes 50x +++ 413 5x ++ 413 0.578 Quinolene yellow 1x
++ 413 0.124 1.163 (QY) 0.2x + 413 0.026* 0.186 0.04x - 413 0.022*
0.02x 413
TABLE-US-00004 TABLE 3 Visual Product Dilution color nm
(.lamda..sub.max) A .sub.(1 mm) A .sub.(1 cm) Colored reaction mix
1x ++ 413 0.128 Finnzymes 0.2x + 413 0.032 0.186 0.1x + 413 0.015
0.059 G7 0.04x - 413
[0138] The absorbance maxima of the solutions of Tables 1-3 are
relatively far from the fluorescent wavelengths of FAM and SYBR
dyes. The absorbance spectrum (1.times. dilution) of the reaction
mixture of Table 3 is shown in FIG. 5a. From the data is can be
concluded, that the dyes tested proved to be suitable to be used in
the initial solutions and also together in a qPCR reaction mixture
as colorants with these fluorescent dyes.
TABLE-US-00005 TABLE 4 Visual Product Dilution color nm
(.lamda..sub.max) A .sub.(1 mm) A .sub.(1 cm) Crimson Taq buffer 5x
+++ 510 1.804 NEB 1x ++ 510 0.406 0.5x ++ 510 0.213 CT 0.1x + 510
0.046 0.02x + 510 0.013* 0.01x +/- 510 0.005x - 510
[0139] The buffer of Table 4 has absorbance maximum at 510 nm which
is close to FAM and SYBR fluorescence maxima. Absorbance would
decrease qPCR signals with these dyes significantly. Thus, the use
of this mix in qPCR would not be feasible.
TABLE-US-00006 TABLE 5 Visual Product Dilution color nm
(.lamda..sub.max) A .sub.(1 mm) A .sub.(1 cm) Green GoTaq 5x +++
419 Promega 1x ++ 419 1.183 0.5x ++ 419 0.527 GT 0.1x ++ 419 0.130
0.02x + 419 0.029* 0.01x + 419 0.014* 0.005x -
[0140] The mix of Table 5 has very strong absorbance at 419 nm. As
the absorbance peaks are not very sharp it also has significant
absorbance at 495 nm (0.17 with 1 mm light path), which is the
range where FAM and SYBR dyes are excited. Absorbance would
decrease qPCR signals with these dyes. The absorbance spectrum
(1.times. dilution) is shown in FIG. 5c.
TABLE-US-00007 TABLE 6 Visual Product Dilution color nm
(.lamda..sub.max) A .sub.(1 mm) A .sub.(1 cm) Quick-Load mm 2x +++
478 1.922* NEB 1x ++ 485 1.000 0.5x ++ 485 0.516 QL 0.1x + 485
0.103 0.02x + 485 0.025 0.01x - 485 0.012* 0.005x 0.001x
0.0005x
[0141] The mix of Table 6 has very strong absorbance at 485 nm. As
the absorbance peaks are not very sharp it also has significant
absorbance at 495 nm (0.982 with 1 mm light path), which is the
range where FAM and SYBR dyes are excited. Absorbance would
decrease qPCR signals with these dyes significantly. The absorbance
spectrum (1.times. dilution) is shown in FIG. 5d.
TABLE-US-00008 TABLE 7 Visual Product Dilution color nm
(.lamda..sub.max) A .sub.(1 mm) A .sub.(1 cm) Coral Load 10x +++
Qiagen 1x ++ 475 0.407 0.5x ++ 475 0.202 CL 0.1x + 475 0.043* 0.04x
+ 475 0.018 0.02x -
[0142] The mix of Table 7 has very strong absorbance at 475 nm. As
the absorbance peaks are not very sharp it also has significant
absorbance at 495 nm (0.393 with 1 mm light path), which is the
range where FAM and SYBR dyes are excited. Absorbance would
decrease qPCR signals with these dyes significantly. The absorbance
spectrum (1.times. dilution) is shown in FIG. 5b.
[0143] Perceivable range is dependent on the wavelength but in
general color providing a absorbance above 0.01-0.1 with 1 mm light
path seems to be visually distinguishable from the clear liquid.
When absorbance is raised to 0.1-0.2, the color appears very clear
to the eye. However, sophisticated instruments are more sensitive
and thus dyes providing absorbance above 0.001 could be used when
e.g. a spectrophotometer is used for color measurement.
[0144] Use of instrument for checking the reaction setup volume by
color detection enables more diluted colors to be used for that
purpose minimizing possible negative effects that the colors might
have. For example in qPCR the range of dyes that could be used
without significantly affecting fluorescence detection would be
increased.
[0145] The embodiments and examples above and the attached drawings
are for illustrative purposes. The scope of the invention should be
evaluated on the basis of the following claims taking equivalents
into account.
* * * * *