Question

How can the Hematrace ABAcard blood detection test be improved? Why would a sandwich ELISA be a more effective method?

Answer 1

How can the Hematrace ABAcard blood detection test be improved?

The ABAcard HemaTrace test exploits antigen/antibody reactions and protein chromatography methods, targeting human hemoglobin (hHb) that is specific to red blood cells. The cards are compact, disposable, self-contained units that are individually packaged with disposable pipettes. The test has an optimum pH range of pH1 to pH9. It is simple to perform and requiring a minimum of equipment, the HemaTrace can easily be implemented by the crime scene examiner at the crime scene, as a reliable confirmatory test for the detection of human blood.

There is a strong indication from the serial dilution study that the buffer decreases the concentration of the hemoglobin in the sample and therefore decreases the HemaTrace test sensitivity. In the instance of forensic casework, care must be taken in the consideration of buffer volume when extracting weak stains (eg: small or washed). False negatives from these types of samples that produce weak sample solutions, will be the main concern in the use of HemaTrace test, therefore careful attention must be given to the sample type and the optimum testing procedure, to minimise the possibility of false negative results.

The HemaTrace cards can exclude a sample from consideration but cannot shed light on blood sample origins if they prove to be negative for human hemoglobin. In these cases, where necessary, the Ouchterlony test will still be required to determine the non-human species of origin.

This test should reduce the non-human stains sent to biology for DNA profiling reducing costs and time. As the HemaTrace test is up to ten times more sensitive than the current Ouchterlony test it will be a valuable addition to the Evidence Recovery apparatus.

Why would a sandwich ELISA be a more effective method?

The enzyme-linked immunosorbent assay (ELISA) is a common laboratory technique which is used to measure the concentration of an analyte (usually antibodies or antigens) in solution.

The Sandwich Enzyme-Linked Immunosorbent Assay is one of the most efficient laboratory procedures used in detecting the presence and measuring the concentration of a target antigen in a completely unknown sample. Its superior sensitivity and extremely robust nature makes it a great diagnostic tool for medical purposes and is especially useful in identifying potential food allergens and/or testing for certain drugs.

Principle :

Antibody-sandwich ELISAs may be the most useful of the immunosorbent assays for detecting antigen because they are frequently between 2 and 5 times more sensitive than those in which antigen is directly bound to the solid phase. To detect antigen, the wells of microtiter plates are coated with specific (capture) antibody followed by incubation with test solutions containing antigen. Unbound antigen is washed out and an antigen-specific antibody conjugated to enzyme (i.e., developing reagent) is added, followed by another incubation. Enzyme labeled antibody can be produced in the same animal that produced passively adsorbed antibody, or from a different species immunized with the same antigen that is captured. Unbound conjugate is washed out and substrate is added. After another incubation, the degree of substrate hydrolysis is measured. The amount of substrate hydrolyzed is proportional to the amount of antigen in the test solution.

The key advantage of a sandwich ELISA is its high sensitivity; it is 2-5 times more sensitive than direct or indirect ELISAs. Sandwich ELISA also delivers high specificity as two antibodies are used to detect the antigen. It offers flexibility since both direct and indirect methods can be used. These three advantages makes Sandwich ELISA a more effective method.