Advances in Chemical Development of Latent Fingerprints

Expert Profile

Dr. G.S. Sodhi earned his Ph.D. degree from Delhi University and at present is an Associate Professor in Chemistry and Forensic Science at the S.G.T.B. Khalsa College, Delhi University. He has published 100 research papers and filed 10 Indian patents. He was Visiting Fellow, National Crime Records Bureau, Ministry of Home Affairs, New Delhi during 1996-97. He has successfully completed 10 research projects, sanctioned by the University Grants Commission, Department of Science and Technology, Indian National Science Academy, and the University of Delhi. He received Union Home Minister Award; National Technology Day Award; National Search for Innovation Award; Lockheed Martin India Innovation Award; and India Innovation Initiative Award for innovative work in forensic science. His book entitled Indian Civilization and the Science of Fingerprinting was published by the Publication Division, Ministry of Information and Broadcasting, Government of India in 2013. He is a Member of the International Fingerprint Research Group, Jerusalem. He has organized several symposia on and training courses in forensic science for students, teachers, army officers, and Indian and overseas police personnel.

Overview of Fingerprint:

Fingerprints have been used for about the past 100 years and are called as the oldest sign for identification of an individual or the evidence categories in forensic science. In the early 20th century, fingerprints were formally accepted and then used as an authentic and valid sign of identity by law enforcement justice. The fingerprint comprises of composite dark segments which include light and dark areas are known as hills or ridges and valleys or furrows respectively.  The fingerprint is considered as one of the most important and significant tools in numerous cases.  The world’s first Fingerprint Bureau was established in 1897 in Kolkata. This bureau had worked on the classification of fingerprint system for establishing the authenticity and reliability of the fingerprint as the strong evidential value. In the more lookout of fingerprint as historical development the numerous rural in our country who would sign the regular documents but also put their palm marks or fingerprint as the more significant one. Some noticed rural like Shah Jahan, Maharaja Ranjit Singh, and Aurangzeb, etc.

Classification of Fingerprints:

As we are all very well aware of the fact that fingerprints are systematically classified and alphabetically enumerated as Arch, Loop, and Whorl. According to Samudra Rishi in 3000 BC that fingerprints have their pattern i.e. analogous to Arch its Seep, analogous to Loop its Shankh, and analogous to whorl its Chakra which means the science of fingerprint was known around 5000 years ago.  Apart from pattern analysis, there is the next level of identification which is on the basis of ridge characteristics or minutiae present on the pattern as considered as detailing of the pattern.

Development of Latent Fingerprints:

The development of latent fingerprint is entirely dependent on the fact of the morphology and physiology of fingerprint. The sweat pores on finger ridges mean if the finger comes in contact with any surface they leave the impression as the same present in our fingers but we cannot see the pattern because of the fact that the sweats is colorless and so as the impression i.e. the print is latent which is not visible to our eyes. Hence for a matter of fact, the visibility of the impression is possible by the process of development of fingerprint with the means of different physical and chemical methodology. The composition of sweat plays an important role as it reacts with this methodology and hence the sweat contains 99% water, 0.5% inorganic ions like sodium, potassium, iron, calcium etc, and 0.5% organic ions like amino acids, fatty acids, proteins, carbohydrates etc.

The chemical and physical nature of the prints is not known, so a systematic and sequential approach is adopted for the examination of the prints in order to get their complete picture or friction ridge details. This includes, firstly the application of the least invasive method followed by the most invasive one. The detection of the print through a visual examination using inherent light followed by illumination with oblique light represents the examination of print through the least invasive or destructive method and its treatment with a dye stain or chemical involves the use of the most invasive method.

There are a wide variety of fingerprint powders available for the detection and development of these latent print impressions present at the scene of the crime on different surfaces. The choice of the powder color depends on the surface contrast so that prints developed are clear and visible.  These powders are applied onto the surfaces with the help of a brush having soft bristles. There are certain powders that are commonly used for development namely traditional granular fingerprint powder, magnetic powder, fluorescent powder, and metallic flake powder that exists in different colors. For example- for light-colored surfaces black colored fingerprint powder is used and for dark-colored surfaces white or gray or silver fingerprint powder is used.

There are numerous chemical methods used for the purpose of development of print by the main problem is that numerous police officials are not aware of the fact that use of the appropriate amount of chemicals for the development of latent impression. The most commonly used methods are discussed:

• Ninhydrin Technique: Ninhydrin (triketohydrindene hydrate) is a crystalline solid substance that is colorless to pale yellow in color and is highly soluble in polar solvents such as water and methanol. This method is discovered by Siegfried Rheumann who mistakenly prepared the compound which reacts with the skin and amino acids and produces a purple color product (adduct) namely Rheumann’s Purple (diketohydrindylidene–diketohydrindamine). This reaction occurs in the presence of reagents water and acid. Certain factors like humidity and a rise in temperature increase the reaction. Ninhydrin solution is prepared by mixing the ninhydrin powder with a suitable solvent, such as acetone or ethyl alcohol (0.6% solution). This solution is applied directly onto the surface containing the prints either by spraying or dipping. The reaction between the ninhydrin and the amino acid results in the formation of a purple color adduct (Rheumann’s Purple) and thereby makes the print visible.

• SPR Method: Small Particle Reagent (SPR) is the method that is used for the development of latent impressions on wet surfaces, outdoors, or on waxy or polystyrene surfaces. SPR reagent is sensitive to the sebaceous (water-insoluble) components of the latent fingermark. Suspension of Molybdenum disulfide particles which develops gray-colored prints is said to be the conventional formulation of Small Particle Reagent. The certain shortcomings of this as lack of contrast on dark surfaces, it is beneficial only for submerged items and it is highly toxic of base materials. There is hence a modification in this method i.e. a suspension of boron nitride in concert with a fluorescent dye in water containing reagent and it became advantageous as it has appropriate contrast on both light and dark surfaces and also has broad-spectrum usage.

The fluorescence of Small Particle Reagent detects the fingerprint on items such as the one who is accidental of intentionally wetted, the items buried under ice or soil, items that were removed from mock arson or conventional crime scenes. For the testing, the trial was done on items like metals, plastics, tiles, glass, or crockery. The prepared working solution was composed of water in presence of little detergent, the two representative was taken such as basic yellow 40 dye (due to its yellow color it will be helpful in surfaces that are black or blue) or brilliant blue G (if the surface is white or yellowish), both of them are non-toxic dyes and by mixing and leaving it for 20 minutes the solution is ready. Now this method is used as if the item is large the spraying method has opted and the item is small dipping method was applied for 1 minute and after that wash it with a gentle stream of water and hereby for fluorescence result, this can impinge light of wavelength 505-550 nm. Hence the results were remarkably shown as with different respective duration on different trail items discussed above.

• Phase Transfer Catalysis Method: This innovative method comprised another remarkable result as once our fingerprint comes in contact with any surface they leave numerous chemical like sodium remains sodium, potassium, amino acids remains same but in our, we got both magnesium and calcium ions and hence they immediately react with air and converted into insoluble oxides and carbonates and they become insoluble they will not react with anything. The reason to stick for magnesium and calcium despite of too many chemicals is that insoluble inorganic salts are more stable as compared to soluble salts. This innovative method includes rose Bengal as an analytical reagent and t-tetrabutylammonium iodide as a phase transfer catalyst. This gives a very clear and sharp print development when used it on absorbent items (paper, furniture, etc.), non-absorbent items (glass, metal, etc.), and semi-absorbent items (adhesive tape, polythene, etc.) The pink color print results were observed on different discussed surfaces.

• Iodine Fuming Method: This technique can be applied on both types of surfaces i.e. porous as well as non-porous. It is successful in developing prints on paper, cardboard, metal, and wooden surfaces and also on greasy surfaces. The development method involves the heating of iodine crystals results directly in the formation of iodine vapors because of the process of sublimation. The substrate upon which the latent impression is present is exposed to the iodine vapors, a reaction occurred between the fumes of iodine and the sweat components of the print i.e. fatty acids and oily matter. This reaction results in the formation of the yellowish-brown colored print. The prints developed by this technique are not permanent or fixed and therefore diminish soon.

Conclusion:

The advancement of numerous chemical methodology plays a very significant to make the investigation more reliable and useful for the experts and hence can be utilized in different cases and no more cases were unsolved due to lack of techniques. The entire dialogue with the discussion of numerous famous cases and historical development signified the development of latent fingerprint with more peculiar and detailed methodology with the advancement of properly researched techniques.