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Human Vascular Endothelial Cell Growth Factor(VEGF165)
ELISA Kit
Catalog No. CSB-E13100h
(96T)
l This immunoassay kit allows for the in vitro quantitative determination of human VEGF165 concentrations in serum, plasma and other biological fluids.
l Expiration date six months from the date of manufacture
l FOR RESEARCH USE ONLY. NOT FOR USE IN DIAGNOSTIC PROCEDURES.
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INTRODUCTION
The broad term ’VEGF’ covers a number of proteins from two families, that result from alternate splicing of mRNA from a single, 8-exon, VEGF gene. The two different families are referred to according to their terminal exon (exon 8) splice site - the proximal splice site (denoted VEGFxxx) or distal splice site (VEGFxxxb). In addition, alternate splicing of exon 6 and 7 alters their heparin-binding affinity, and amino acid number (in humans: VEGF121, VEGF121b, VEGF145, VEGF165, VEGF165b, VEGF189, VEGF206; the rodent orthologs of these proteins contain one fewer amino acid). These domains have important functional consequences for the VEGF splice variants, as the terminal (exon 8) splice site determines whether the proteins are pro-angiogenic (proximal splice site, expressed during angiogenesis) or anti-angiogenic (distal splice site, expressed in normal tissues). In addition, inclusion or exclusion of exons 6 and 7 mediate interactions with heparan sulfate proteoglycans (HSPGs) and neuropilin co-receptors on the cell surface, enhancing their ability to bind and activate the VEGF receptors (VEGFRs).
PRINCIPLE OF THE ASSAY
The microtiter plate provided in this kit has been pre-coated with an antibody specific to VEGF165. Standards or samples are then added to the appropriate microtiter plate wells with a HRP-conjugated antibody preparation specific for VEGF165 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 VEGF165, HRP-conjugated antibody 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 VEGF165 in the samples is then determined by comparing the O.D. of the samples to the standard curve.
DETECTION RANGE
0.156 ng/ml-10 ng/ml. The standard curve concentrations used for the ELISA’s were 10 ng/ml, 5 ng/ml, 2.5 ng/ml, 1.25 ng/ml, 0.625 ng/ml, 0.313 ng/ml, 0.156ng/ml.
SPECIFICITY
This assay recognizes recombinant and natural human VEGF165. No significant cross-reactivity or interference was observed.
SENSITIVITY
The minimum detectable dose of human VEGF165 is typically less than 0.04 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
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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. 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 for 30min.
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 Centrifuge the standard vial at 6000-10000rpm for 30s. Reconstitute the Standard with 1.0 ml of Sample Diluent. This reconstitution produces a stock solution of 10 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 (10 ng/ml). The Sample Diluent serves as the zero standard (0 ng/ml). Prepare fresh for each assay. Use within 4 hours and discard after use.
3. HRP-antibody Dilute to the working concentration using HRP-antibody Diluent(1:100), respectively. The suggested 100-fold dilution can be achieved by adding 10 uL HRP-antibody to 990uL of HRP-antibody Diluent for 1ml working solution.
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
l 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. Centrifuge the sample again after thawing before the assay. Avoid repeated freeze-thaw cycles.
l Plasma Collect plasma using citrate, EDTA, or heparin as an anticoagulant. Centrifuge for 15 minutes at 1000 g within 30 minutes of collection. Assay immediately or aliquot and store samples at -20°C. Centrifuge the sample again after thawing before the assay. 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. All the reagents should be added directly to the liquid level in the well. The pipette should avoid contacting the inner wall of the well.
1. Add 100μl of Standard, Blank, or Sample per well. Cover with the adhesive strip. Incubate for 30min at 37°C.
2. 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.
3. Add 100μl of HRP -antibody working solution to each well. Incubate for 30min at 37°C. HRP-antibody working solution may appear cloudy. Warm up to room temperature and mix gently until solution appears uniform.
4. Repeat the aspiration and wash five times as before.
5. Add 90μl of TMB Substrate to each well. Incubate for 10-30 minutes at 37°C. Keeping the plate away from drafts and other temperature fluctuations in the dark.
6. Add 50μl of Stop Solution to each well when the first four wells containing the highest concentration of standards develop obvious blue color. If color change does not appear uniform, gently tap the plate to ensure thorough mixing.
7. Determine the optical density of each well within 30 minutes, using a microplate reader set to 450 nm.
CALCULATION OF RESULTS
Using the professional soft "Curve Exert 1.3" to make a standard curve is recommended, which can be downloaded from our web.
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 VEGF165 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.
