Frequently Asked Questions

Q.  What is a unit?

A.  One Unit is the quantity of antibody or conjugate which when diluted as recommended provides sufficient reagent to test one sample in duplicate wells using 100ul volumes per well.

Please note that other suppliers often refer to product size in test wells. Therefore when comparing suppliers always remember that 1 Neogen unit = 2 test wells.


Q.  What is a reagent set?

A.  A Reagent Set contains all of the antibodies and antibody - enzyme conjugates that are required to detect the selected pathogen. Thus a DAS ELISA Reagent Set comprises a specific coating antibody and a specific antibody - enzyme conjugate. A TAS ELISA Reagent Set comprises a specific coating antibody, a specific detector antibody and an anti-species antibody - enzyme conjugate. A PTA ELISA Reagent Set comprises a specific detector antibody and an anti - species antibody - enzyme conjugate.

Please note that with all our Reagent Sets the working dilutions have been pre-determined by Neogen so there is no need to waste antibodies and time running titration experiments.


Q.  Why do you sell a mixture of das, tas and pta ELISAs?

A.  The assay format depends on the pathogen that we are detecting, the antibodies that are available and the sensitivity required.


Q.  Why do some das ELISAs use monoclonals and some polyclonals?

A.  We use MAbs where they are available and they can be conjugated as this helps to remove potential cross-reactivity problems.  However, our PAbs are extensively screened against a wide range of potentially cross-reacting antigens to ensure that there are no false positives with our reagents.


Q.  If MAbs are more specific why do you use PAbs in some of your assays?

A.  In many cases MAbs are not available.  Although the technology is advanced there is still a high element of chance in the production of a specific monoclonal antibody.
Where we have good specific polyclonals there is no need for monoclonal production.  In some of our assays we use purification methods for our polyclonals which ensures a higher degree of specificity in the assay for difficult to detect fungal pathogens.


Q. What is a false positive?

A. This is when a sample gives a positive reaction by generating an O.D value greater than the negative control when there is no relevant antigen in the sample.  Since the Neogen antibodies are screened against panels of potentially cross-reacting antigens this is not a problem with our antibodies.


Q. How do you determine a positive control?

A. The limits for deciding what is positive and what is negative is the responsibility of the customer.  There are various methods such as determining a positive to be twice the average O.D value generated by the negative control or three times the standard deviation of the mean of the negative control samples.  The method chosen is the full responsibility of the customer and Neogen and the Neogen distributors cannot give advice on this.


Q. What is Neogen Yellow liquid pNPP?

A. This is an extremely stable liquid substrate for the detection of alkaline phosphatase.  When using this the customer has no need to prepare Diethanolamine substrate buffer and grind pNPP tablets immediately before use.
Since our liquid substrate is based on the same substrate (para-Nitrophenylphhosphate) as is traditionally used the customer is using the same detection system without the inconvenience of substrate preparation. This substrate produces a yellow coloured product that is detected at a wavelength of 405nm.


Q. What is Neogen Blue liquid substrate?

A. This is a two component liquid substrate system for the detection of alkaline phosphatase which offers enhanced detection in ELISA This substrate produces a blue coloured product that is detected at wavelengths between 595 – 650nm.


Q. Can I use my existing plate reader if I use the liquid substrates?

A. If you have previously used pNPP substrate tablets in ELISA and detected the product at 405nm then your plate reader is suitable for use with Neogen Yellow substrate.
If your plate reader has a filter in the range of 595 – 650nm then it is suitable for use with Neogen Blue substrate.


Q.  What is a SPOT√CHECK-LF™?

A.  The SPOT√CHECK-LF™ is novel technology for the plant disease diagnostics industry, which has been extensively tested and used, in medical diagnostics for several years. This is an extremely rapid assay and results can be obtained in under 2 minutes.


Q.  What is an ALERT-LF™?

A.  Based on the same technology as the successful SPOT√CHECK-LF™ these simple to use kits incorporate specially purified antibodies to provide sensitive and specific detection of the specified genus.


Q.  What is an IDENTIKIT™?

A.  This is a kit containing all of the reagents, antibodies etc. that are required to test 46 samples in duplicate.
Coated microtitre strips are provided in the das and tas ELISAs for added customer convenience.  Reaction controls are also provided. The customer only requires some basic equipment to run the tests i.e. pipette, mortar and pestle, plastic box.


Q.  What is an IDENTIKIT-Q™?

A.  Like the IDENTIKIT™ this provides all of the reagents for testing a number of samples in duplicate. However, these kits are quantitative and contain specific standards to allow the user to consistently determine the level of infection in their test material.


Q. What is an AGRISCREEN®?

A.  A range of qualitative and semi-qualitative 96 well kits for the detection of  Phytophthora spp., Pythium spp. and Rhizoctonia spp.  Includes all the reagents needed to conduct tests with results in 90mins.  Also available as a quantitative kit on request.


Q.  Why use immunofluorescence for detection?

A.  For many quarantine bacterial pathogens this is the method required by governments for testing.  For example, EU legislation for R. solanacearum demands testing using this method.


Q.  What is an EXPRESS?

A.  A rapid and sensitive verification of bacterial cultures and symptomatic plant material, with results in 60 seconds.


Q.  Why are different extraction buffers used for some pathogens?

A.  The buffers used in our assays have been developed to ensure the optimal performance in ELISA.  Some viruses are very unstable and they require different buffers to ensure that we are able to detect them.


Q.  Should the reaction be stopped before reading?

A.  For the Neogen products that use alkaline phosphatase for detection there is no need to stop the reaction before reading.  However, if the customer requires to stop the reaction then they can use sodium hydroxide to do this.  For the few Neogen products that use HRP for detection we would advise stopping the reaction before reading.  The rate of reaction of HRP is considerably greater than that of alkaline phosphatase and this could result in variation of results if the HRP reaction is not stopped.  We recommend using sulphuric acid to stop the HRP reaction when using a TMB substrate.


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