development of bloody fingerprints-Katherine

Question 1

two types

Answer 1

those that use heme group

those that react with proteins of their breakdown products

• no specific for blood
• high content in blood of protein and protein breakdown products, these techniques are the most sensitive

Question 2

techniques using heme group

Answer 2

catalyses production of coloured compound

1863=hydrogen peroxide

1906=KM

subject to false negatives and positives

chemical oxidants, e.g bleach, false positives

rely on peroxidase activity of the heme group

coupled to the oxidation of colourless reduced dyes

Question 3

when was luminol first synthesised?

Answer 3

1853

Question 4

luminol

Answer 4

uses sodium perborate

faint blue glow, 30 secs only

Question 5

disadvantages of luminol

Answer 5

can damage fine detail of blood-contaminated fingerprints

produces false positives

time-consuming to prepare

Question 6

positives of luminol

Answer 6

sensitive

long lasting

applied numerous times and still receive DNA typing results

Question 7

benzidine

Answer 7

enzyme in blood oxidises benzidine to give a blue coloured derivative

banned in 1974 as carcinogenic

replaced by phenolphthalein

Question 8

phenolphtalein

Answer 8

alcohol used to dissolve the phenolphthalein as insoluble in water

nondestructive to sample

sample reaction with blood from any animal

H2O2 dripped onto sample previously treated with phenolphthalein, if sample contains haemoglobin it will turn pink

Question 9

fluorescein

Answer 9

reduced to colourless fluorescein by alkaline solution of zinc

fluorescin and H2O2 added to bloody print

heme catalyses reaction of H2O2 oxidation of fluorescin to fluorescein

fine bloodstains and blood smears will fluoresce when treated with fluorescein

Question 10

tests for proteins and breakdown products

Answer 10

ninhydrin and DFO target amino acids in blood

sensitive technique does not require lysing cell to release haemoglobin

proteins water soluble have to be denatured and fixed before staining, this is incorporated in the dye staining technique

Question 11

methodology for staining proteins in blood

Answer 11

fixing solution - sulphosalicylic acid in water (precipitates proteins)

staining solution - acid dye in distilled water, ethanol and acetic acid (helps to prevent blood diffusing away)

washing solution - distilled water, ethanol and acetic acid

Question 12

what are the most effective protein dues for visualisation?

Answer 12

acid dyes

contain sulphonate

• provide solubility in water or alcohol
• assist reaction because of negative charge

in acidic medium, the blood protein molecules become protonates and this attracts the acid dye anions

hydrogen bonding and van der waals forces exist between acid dyes and protein

Question 13

amido black

Answer 13

can be absorbed by porous surfaces

suited as protein indicator

Question 14

acid yellow 7

Answer 14

stains proteins to give pale yellow colour

fluoresces bright yellow under blue-green light

not recommended for porous surfaces - difficult to wash dye out

Question 15

critical issues

Answer 15

correct sequence of processing must be used - asprotein stains may ruin other evidence

other tests should be done to confirm whether mark really is in blood

fixing stage is crucial otherwise ridge detail may diffuse out

current solutions are inflammable and have a low flash point of 30 degrees

Question 16

development using fatty acids in sweat

Answer 16

crystal violet or gentian violet is a triarylmethane dye

basic dye

formerly important as a topical antiseptic