Forensic Biology

COLLECTION OF BIOLOGICAL EVIDENCE.

The strength of any forensic evidence presented in a court of law highly depends on how effective its collection was and the sensitivity with which the evidence was handled after that. This previously ignored part of court proceedings seems to be catching up as evidenced with the professionalism witnessed in the police department lately.

Care is being taken during collection of this evidence just as required. Just to remind ourselves, biological evidence tends to deteriorate quite fast and get contaminated hence measures should be taken to prevent that and ensure its integrity.

The success in finding biological material depends upon the search method employed and also the integrity and state of the scene. It is important to adhere to the following guidelines while collecting the evidence:

•      Wear the appropriate gear. These include full overalls, shoe covers, gloves and face masks.
•       Seclude the area by marking it with tape to minimize human traffic.
•       Start collecting evidence from outwards going inwards to capture as much evidence as possible.
•       A range of light sources can be operated at fixed wavelengths and be used to detect stains.
• ·   Take as many photographs as possible at different angles( Thats a whole topic all together)

Methods used for collection will vary depending on the type of sample. For example,

•   Searching a crime scene or items recovered from a crime scene for blood can be aided by use of luminol (3-aminophthalhydrazide)The chemical can be sprayed onto a wide area and will become  oxidized and luminescent in the presence of haemoglobin, which is found in red blood cells. It is necessary to darken the area being searched in order that the luminescent are detected.
•   Dry stains and contact marks on large immovable items are normally collected using a sterile swab that has been moistened with distilled water, in other cases scraping or cutting the material may be appropriate.
•   Lifting from the surface using high quality adhesive tape is an alternative method for collecting epithelial cells.
•   Liquid blood can be collected using a syringe. It can also be applied to FTA paper that is impregnated with chemicals to prevent action of microbial agents and stabilize the DNA.
•   Smaller movable objects such as weapons, which might contain biological material should be packaged at the scene and examined in there controlled environment of a forensic laboratory.

TO BE CONTINUED…

APPLICATION OF ELISA IN FORENSIC SCIENCE

APPLICATION OF ELISA IN FORENSIC SCIENCE

Introduction

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.

In general;

1. An unknown amount of antigen is affixed to a surface
2. A specific antibody is washed over the surface so that it can bind to the antigen.
3. This antibody is linked to an enzyme and finally
4. 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

1. As diagnostic tool in medicine and plant pathology
2. In quality control check in various industries.
3. Detection of statherin for forensic identification of saliva. It is easy to use for screening forensic casework samples.

Conclusion

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.

Thin Layer Chromatography

THIN LAYER CHROMATOGRAPHY AND ITS APPLICATION IN FORENSIC SCIENCE

INTRODUCTION
A central part of many forensic investigations is the analysis of materials that are recovered from the scene of the investigation.
Chromatography is the main technique used to separate and identify individual components in a mixture of compounds. Thin layer chromatography (TLC) is a type of liquid chromatography that can separate chemical compounds of differing structure based on the rate at which they move through a support under defined conditions. Chromatography involves separation using two phases; a mobile phase and a stationary phase. Thin layer chromatography, the stationary phase is a thin layer (alumina or silica) on a plate. The mobile phase depends on the nature of the sample you want to separate.
MECHANISM OF THIN LAYER CHROMATOGRAPHY
In thin layer chromatography, a solution of the sample is added to a layer of support material (i.e. grains of silica or alumina) that has been spread out and dried on a sheet of material such as glass.
The support material is known as the plate. The sample is added as a spot at one end of the plate. The plate is then put into a sealed chamber that contains a shallow pool of chemicals (the solvent) which is enough to wet the bottom of the plate.
As the solvent moves up through the plate support layer by capillary action, the sample is dragged along. The different chemical constituents of the sample do not move at the same speed and will become physically separated from one another. The solvent is allowed to move up the plate but must be removed before the solvent reaches the top.
The point at which the solvent has reached on the plate is then marked and is the solvent front which is important in calculating the retardation factor or the RF value.
The distance each part of the sample has travelled up the plate is also marked and this distance divided by the solvent front gives the RF value. This can be compared with known RF values to try and identify a compound, although a direct comparison with a standard and unknown on the same plate would produce the most accurate results.
The position of the various sample constituents and their chemical identities are determined by physical methods e.g. ultraviolet light or by the addition of other chemical sprays that react with the sample constituents.
While the very similar technique of paper chromatography is only carried out on coloured samples, the use of visualization reagents means that a wider array of samples can be tested with TLC.
USES OF THIN LAYER CHROMATOGRAPHY IN FORENSICS
Advances in thin layer chromatography technology largely driven by the efforts to quell terrorism have benefited forensic science.
Thin layer chromatography is useful in detecting chemicals of forensic concern including a wider aspect in Narcotics, Toxicology and Chemistry i.e.:
1.Chemical weapons
2.Inks
3.Dyes
4.Explosives and
5.Illicit drugs.

DISCUSSION AND CONCLUSION
In identification and comparison of drugs, explosives, inks and dyes the samples need to be soluble for the technique to be accurate. This is a particular issue when investigating pen inks since the development of gel pens, the ink of which is insoluble. Gel inks cannot be analysed via thin layer chromatography.
However liquid dye samples and ink within pens can be applied directly to TLC plate.
Thin layer chromatography of drugs and explosives is used as a presumptive test, a means to provide an indication of the nature of the sample rather than being used for positive identification of a sample.