APPLICATION OF ELISA IN FORENSIC SCIENCE
Immuno-assays are one of the mass screening methods of choice for the detection of drugs in biological fluids because of their pretreatment simplicity and high ability to treat many samples in a short time.
Enzyme immune-assay (EIA) provides an alternative to radioimmuno- assay (RIA). Enzyme multiplied immunoassay technique (EMIT) has been in use for many years and has been specifically applied to blood specimens. More recently, cloned enzyme donor immuno-assay (CEDIA) and ELISA have become other commercially available EIA technologies.
Enzyme Linked Immuno-sorbent Assay (ELISA)
ELISA is a quick and convenient method for the analysis of drugs in blood and even tissue homogenates. It’s a biochemical technique used mainly in immunology to detect the presence of an antibody or an antigen like drug or poison in a sample.
ELISA uses the micro-titer plate technology used to detect drugs of abuse and is a competitive, solid-phase, heterogeneous, enzyme immuno-assay.
The micro plate technology uses antibodies immobilized on to the surface of a micro-titer plate. Free drug and drugs conjugated to an enzyme (Horseradish Peroxidase) compete for the binding to the antibody. After a short incubation, the plate is washed to remove all unbound enzyme conjugate and sample debris. A substrate solution is added which produces a coloured product in the presence of bound enzyme conjugate. The amount of color produced is measured in absorbance (450nm) and measurements taken are inversely proportional to the amount of free drug that was present in original sample.
- An unknown amount of antigen is affixed to a surface
- A specific antibody is washed over the surface so that it can bind to the antigen.
- This antibody is linked to an enzyme and finally
- A substance is added that the enzyme can convert to some detectable signal. Thus in the case of fluorescence ELISA, when light is shone upon the sample, any antigen/antibody complex will fluoresce so that the amount of antigen in the sample can be measured.
Advantage of ELISA over other immuno-assay techniques is that it’s easily automated.
Applications of ELISA
- As diagnostic tool in medicine and plant pathology
- In quality control check in various industries.
- Detection of statherin for forensic identification of saliva. It is easy to use for screening forensic casework samples.
Because of adaptability of the micro-titer plate technology to the EIA methodology, ELISA has proved adequate for analysing micro-liter quantities of samples.
ELISA for detection of statherin could be an effective tool for the forensic identification of saliva because of its specificity for saliva among other body fluids.