Total Nitric Oxide Assay Kit

ProcartaPlex multiplex assays, which are based on Luminex xMAP technology, provide a versatile platform that gives users more flexibility and a greater array of options for analyte detection. Whether you are testing for single or multiple analytes, ProcartaPlex multiplex assays deliver accurate analytical performance using efficient, easy-to-follow protocols. Each of these assays has undergone the same development, validation, manufacturing, and quality control standardization we conduct for our ELISAs. Each lot of ProcartaPlex multiplex assays as well as ELISA assays is fully qualified with the appropriate sample type (i.e., species-specific serum, plasma, and cell culture supernatants), and each lot is evaluated based on the following performance characteristics:

Specificity-each analyte is screened to make sure there is no significant cross-reactivity with other analytes in the multiplex test
Sensitivity-each analyte is evaluated for both functional sensitivity (differentiation from background) and lower limit of detection (LLOD)
Precision/accuracy-multiplex assays have good intra-assay precision (<10% CV), inter-assay precision (<10% CV), and lot-to-lot consistency (<20% CV); these values are comparable to or better than most ELISA tests
ProcartaPlex multiplex assays are regularly tested against the matching ELISAs. Therefore, you can switch easily from ProcartaPlex assays to ELISA and vice versa with reliable results. Most of our ProcartaPlex assays use the same antibody pairs as our traditional plate-based ELISAs, resulting in high correlation (R2 > 0.9) between the two assays.

Find additional tips, troubleshooting help, and resources within our Antibodies and Immunoassays Support Center.

ELISA is a simple and powerful way to quantify individual proteins specifically in complex samples. The selectivity of ELISA is achieved through the use of qualified single- or double-antibody sandwich technology, and accurate quantitation is achieved through the use of calibrated standards. ELISAs can detect low-level proteins and can be performed in a 96-well format with only 60 minutes of hands-on time. In addition, the results obtained with ELISAs are generally very reproducible. While ELISA has been established as a standard method of protein analysis, multiplexing methods that enable the measurement of multiple analytes simultaneously in a single sample address a number of specific limitations:

ELISA allows for the measurement of only one analyte at a time in a given sample, limiting investigators' increasing need to measure multiple targets in their research studies.
The low available volume of many samples being studied may limit the number of times analyses can be conducted. This is especially true in small animal research, in pediatric testing, and in microplate assays providing limited sample volumes. The ability to assay multiple analytes in a single small-volume sample enables more effective use of each sample.
Difficulties in data interpretation can arise when comparing analyte levels measured by multiple ELISAs, each assay having been performed with different sample aliquots and each susceptible to systematic errors leading to decreased precision and accuracy.
Many analytes require assays with broad dynamic ranges to avoid repeat testing or out-of-range values. Multiplex assays can be designed to have large dynamic ranges for all of the analytes, or ranges tailored to various expected analyte concentrations.

Find additional tips, troubleshooting help, and resources within our Antibodies and Immunoassays Support Center.

Here are possible causes and solutions:

Errors in pipetting the standards or samples or in subsequent steps. Always dispense into wells quickly and in the same order. Do not touch the pipette tip on the individual microwells when dispensing. Use calibrated pipettes and the appropriate tips for that device. Check for any leaks in the pipette tip.
Repetitive use of tips for several samples or different reagents. Use fresh tips for each sample or reagent transfer.
Wells have been scratched with the pipette tip or washing tips. Use caution when dispensing into and aspirating out of microwells.
Liquid transferred from well to well during incubations. Adjust the orbital shaker or check for correct rotator rpm. Peel the adhesive plate cover off carefully.
Incorrect volumes of materials dispensed into the microwells. Follow the protocol for dispensing volumes of reagents. Check calibration of the pipettes.
Standard diluted with the serum, culture medium, or other buffer. Dilute the standard with the standard diluent buffer provided in the kit.
Particulates or precipitates present in the samples. Remove any particulates/precipitates by centrifugation prior to dispensing into the assay.
Dirty microwells: visible debris within or on bottom of microwells. Inspect the microwells and invert the plate to remove debris. Wipe the bottom of the plate with an absorbent tissue after each wash step. Never insert tissue into the microwells.
“Edge effect” due to uneven temperature between the outer-edge wells and the wells in the center of the plate. Seal the plate completely with a cover during incubations, and place the plate in the center of the incubator when 37 degrees C incubation is indicated.

Find additional tips, troubleshooting help, and resources within our Antibodies and Immunoassays Support Center.

Here are possible causes and solutions:

Improper preparation of standard stock solution.Dilute the lyophilized standard as directed on the vial label, only with the standard diluent buffer or a diluent that most closely matches the matrix of your sample.
Reagents (lyophilized standard, standard diluent buffer, etc.) from different kits, with either different analytes or different lot numbers, were substituted. Never substitute any components from another kit.
Errors in pipetting the standard or in subsequent steps. Always dispense into wells quickly and in the same order. Do not touch the pipette tips on the individual microwells when dispensing. Use calibrated pipettes and the appropriate tips for that device.

Find additional tips, troubleshooting help, and resources within our Antibodies and Immunoassays Support Center.

Here are possible causes and solutions:

Reagents not at room temperature (approximately 25 plus or minus 2 degrees C) at start of assay. Allow all reagents to warm to room temperature prior to commencing the assay.
Incorrect storage of components, e.g., not stored at 2-8 degrees C. Store all components exactly as directed in the protocol and on labels.
Anti-rabbit IgG HRP or streptavidin-HRP working solution made more than 15 minutes before use in assay. Use the diluted anti-rabbit IgG HRP or streptavidin-HRP within 15 minutes of dilution.
Expired reagents.Check expiration dates upon receipt of kit and use the kit prior to expiration.
Plate read at incorrect wavelength. The correct wavelength to read ELISAs using the TMB substrate is 450 nm.
TMB solution lost activity. Ensure that the TMB solution is clear before it is dispensed into the plate wells. A blue color and/or the presence of particulate matter indicate that the product is contaminated. Please contact Technical Support if this problem is noted. To avoid contamination, we recommend that the quantity required for an assay be dispensed into a previously unused disposable trough for pipetting. Discard any TMB solution left in the trough and do not put it back in the bottle. Avoid contact between the TMB solution and items containing metal ions. Do not cover your plates with aluminum foil or aluminum-coated Mylar sheets because this can cause color development in the absence of HRP.
Attempt to measure analyte in a matrix for which the ELISA assay is not optimized. Contact Technical Support when using alternative sample types.
Wells have been scratched with pipette tip or washing tips. Use caution when dispensing into and aspirating out of microwells.
Incorrect chromogen or stop solution used. Use only the chromogen and stop solution supplied with the kit.
Standard diluent buffer added to all wells rather than the designated wells. Follow the protocol and only add the standard diluent to the designated wells and to the samples where it is required, or to samples producing signals greater than that of the highest standard.
Use of buffer containing azide, which is not compatible with HRP. Avoid the use of azide in the assay.

Find additional tips, troubleshooting help, and resources within our Antibodies and Immunoassays Support Center.