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Human plasminogen activator inhibitor
(PAI) ELISA Kit
This immunoassay kit allows for the in vitro quantitative determination of human PAI
concentrations in cell culture supernates, serum, plasma and other biological fluids.
Expiration date six months from the date of manufacture
FOR RESEARCH USE ONLY. NOT FOR USE IN DIAGNOSTIC PROCEDURES.
INTRODUCTION
Plasminogen activator inhibitor (PAI) is serpin family member that inhibits tissue- and
urokinase-type plaminogen activators (t-PA, u-PA). This protein appears to be an important
regulator of plasminogen activation by t-PA and extracellular proteolysis by u-PA. The
plasminogen activator proteolytic enzyme systems are important not only for fibrinolysis but
also for extracellular matrix remodeling, and have been implicated in a number of normal and
pathological processes including angiogenesis, ovulation and embryogenesis, thrombotic and
hemorrhagic disorders, connective tissue diseases, neoplasm and sepsis.
PRINCIPLE OF THE ASSAY
The microtiter plate provided in this kit has been pre-coated with an antibody specific to PAI.
Standards or samples are then added to the appropriate microtiter plate wells with a
biotin-conjugated polyclonal antibody preparation specific for PAI and Avidin conjugated to
Horseradish Peroxidase (HRP) is added to each microplate well and incubated. Then a TMB
(3,3’5, 5’ tetramethyl-benzidine) substrate solution is added to each well. Only those wells that
contain PAI, biotin-conjugated antibody and enzyme-conjugated Avidin will exhibit a change
in color. The enzyme-substrate reaction is terminated by the addition of a sulphuric acid
solution and the color change is measured spectrophotometrically at a wavelength of 450 nm ±
2 nm. The concentration of PAI in the samples is then determined by comparing the O.D. of
the samples to the standard curve.
DETECTION RANGE
1.56 ng/ml-100 ng/ml. The standard curve concentrations used for the ELISA’s were 100ng/ml,
50 ng/ml, 25 ng/ml, 12.5 ng/ml, 6.25 ng/ml, 3.12 ng/ml, 1.56 ng/ml.
SPECIFICITY
This assay recognizes recombinant and natural human PAI. No significant cross-reactivity or
interference was observed.
SENSITIVITY
The minimum detectable dose of human PAI is typically less than 0.39 ng/ml.
The sensitivity of this assay, or Lower Limit of Detection (LLD) was defined as the lowest
protein concentration that could be differentiated from zero.
MATERIALS PROVIDED
Reagent Quantity
Assay plate 1
Standard 2
Sample Diluent 1 x 20 ml
Biotin-antibody Diluent 1 x 10 ml
HRP-avidin Diluent 1 x 10 ml
Biotin-antibody 1 x 120µl
HRP-avidin 1 x 120µl
Wash Buffer
1 x 20 ml
(25×concentrate)
TMB Substrate 1 x 10 ml
Stop Solution 1 x 10 ml
STORAGE
1. Unopened test kits should be stored at 2-8°C upon receipt and the microtiter plate should be
kept in a sealed bag with desiccants to minimize exposure to damp air. The test kit may be
used throughout the expiration date of the kit. Refer to the package label for the expiration
date.
2. Opened test kits will remain stable until the expiring date shown, provided it is stored as
prescribed above.
3. A microtiter plate reader with a bandwidth of 10 nm or less and an optical density range of
0-3 OD or greater at 450nm wavelength is acceptable for use in absorbance measurement.
REAGENT PREPARATION
Bring all reagents to room temperature before use.
1. Wash Buffer If crystals have formed in the concentrate, warm up to room temperature
and mix gently until the crystals have completely dissolved. Dilute 20 ml of Wash Buffer
Concentrate into deionized or distilled water to prepare 500 ml of Wash Buffer.
2. Standard Reconstitute the Standard with 1.0 ml of Sample Diluent. This reconstitution
produces a stock solution of 100 ng/ml. Allow the standard to sit for a minimum of 15
minutes with gentle agitation prior to making serial dilutions. The undiluted standard
serves as the high standard (100 ng/ml). The Sample Diluent serves as the zero standard
(0 ng/ml).
3. Biotin-antibody Dilute to the working concentration specified on the vial label using
Biotin-antibody Diluent(1:100), respectively.
4. HRP-avidin Dilute to the working concentration specified on the vial label using
HRP-avidin Diluent(1:100), respectively.
Precaution: The Stop Solution provided with this kit is an acid solution. Wear eye, hand, face,
and clothing protection when using this material.
OTHER SUPPLIES REQUIRED
Microplate reader capable of measuring absorbance at 450 nm, with the correction
wavelength set at 540 nm or 570 nm.
Pipettes and pipette tips.
Deionized or distilled water.
Squirt bottle, manifold dispenser, or automated microplate washer.
SAMPLE COLLECTION AND STORAGE
Cell Culture Supernates Remove particulates by centrifugation and assay immediately
or aliquot and store samples at -20° C. Avoid repeated freeze-thaw cycles.
Serum Use a serum separator tube (SST) and allow samples to clot for 30 minutes
before centrifugation for 15 minutes at 1000 g. Remove serum and assay immediately or
aliquot and store samples at -20° C. Avoid repeated freeze-thaw cycles.
Plasma Collect plasma using citrate, EDTA, or heparin as an anticoagulant. Centrifuge
for 15 minutes at 1000 x g within 30 minutes of collection. Assay immediately or aliquot
and store samples at -20° C. Avoid repeated freeze-thaw cycles.
Note: Grossly hemolyzed samples are not suitable for use in this assay.
ASSAY PROCEDURE
Bring all reagents and samples to room temperature before use. It is recommended that all
samples, standards, and controls be assayed in duplicate.
1. Add 100µl of Standard, Blank, or Sample per well. Cover with the adhesive strip. Incubate
for 2 hours at 37° C.
2. Remove the liquid of each well, don’t wash.
3. Add 100µl of Biotin-antibody working solution to each well. Incubate for 1 hour at 37°C.
Biotin-antibody working solution may appear cloudy. Warm up to room temperature and
mix gently until solution appears uniform.
4. Aspirate each well and wash, repeating the process three times for a total of three washes.
Wash by filling each well with Wash Buffer (200µl) using a squirt bottle, multi-channel
pipette, manifold dispenser or autowasher. Complete removal of liquid at each step is
essential to good performance. After the last wash, remove any remaining Wash Buffer by
aspirating or decanting. Invert the plate and blot it against clean paper towels.
5. Add 100µl of HRP-avidin working solution to each well. Cover the microtiter plate with a
new adhesive strip. Incubate for 1 hour at 37° C.
6. Repeat the aspiration and wash three times as step 4.
7. Add 90µl of TMB Substrate to each well. Incubate for 30 minutes at 37°C. Keeping the
plate away from drafts and other temperature fluctuations in the dark.
8. Add 50µl of Stop Solution to each well. If color change does not appear uniform, gently
tap the plate to ensure thorough mixing.
9. Determine the optical density of each well within 30 minutes, using a microplate reader set
to 450 nm.
CALCULATION OF RESULTS
Average the duplicate readings for each standard, control, and sample and subtract the average
zero standard optical density. Create a standard curve by reducing the data using computer
software capable of generating a four parameter logistic (4-PL) curve-fit. As an alternative,
construct a standard curve by plotting the mean absorbance for each standard on the y-axis
against the concentration on the x-axis and draw a best fit curve through the points on the
graph. The data may be linearized by plotting the log of the PAI concentrations versus the log
of the O.D. and the best fit line can be determined by regression analysis. This procedure will
produce an adequate but less precise fit of the data. If samples have been diluted, the
concentration read from the standard curve must be multiplied by the dilution factor.
LIMITATIONS OF THE PROCEDURE
The kit should not be used beyond the expiration date on the kit label.
Do not mix or substitute reagents with those from other lots or sources.
It is important that the Calibrator Diluent selected for the standard curve be consistent with
the samples being assayed.
If samples generate values higher than the highest standard, dilute the samples with the
appropriate Calibrator Diluent and repeat the assay.
Any variation in Standard Diluent, operator, pipetting technique, washing technique,
incubation time or temperature, and kit age can cause variation in binding.
This assay is designed to eliminate interference by soluble receptors, binding proteins, and
other factors present in biological samples. Until all factors have been tested in the
Quantikine Immunoassay, the possibility of interference cannot be excluded.
TECHNICAL HINTS
When mixing or reconstituting protein solutions, always avoid foaming.
To avoid cross-contamination, change pipette tips between additions of each standard level,
between sample additions, and between reagent additions. Also, use separate reservoirs for
each reagent.
When using an automated plate washer, adding a 30 second soak period following the
addition of wash buffer, and/or rotating the plate 180 degrees between wash steps may
improve assay precision.
To ensure accurate results, proper adhesion of plate sealers during incubation steps is
necessary.
Substrate Solution should remain colorless until added to the plate. Keep Substrate
Solution protected from light. Substrate Solution should change from colorless to
gradations of blue.
Stop Solution should be added to the plate in the same order as the Substrate Solution. The
color developed in the wells will turn from blue to yellow upon addition of the Stop
Solution. Wells that are green in color indicate that the Stop Solution has not mixed
thoroughly with the Substrate Solution.
