Development of Latent Fingerprints Using Ninhydrin Reagent - Essay Example

Published: 2023-09-28
Development of Latent Fingerprints Using Ninhydrin Reagent - Essay Example
Type of paper:  Essay
Categories:  Knowledge Chemistry
Pages: 7
Wordcount: 1674 words
14 min read

For a long time now, Ninhydrin has been known as the best solution for the detection of LFPs on absorbent surfaces. The reagent, as soon as it interacts with amino acids, emits a strong purple color. This essay discusses the background of Ninhydrin and its chemical reaction when the chemical reacts with amino acids. Moreover, the various enhancement methods that can be used with ninhydrin reagents to identify hidden fingerprints on latent surfaces will be elaborated.

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Background of Ninhydrin

The German chemist Siegfried Ruhemanna proposed Ninhydrin (2,2-dihydroxyindane-1,3-dione) in 1910. Ruhemanna illustrated the reagent synthesis and demonstrated that the colorless ninhydrin prisms transform into a red prism at 125 ° C (Crown, 1969). In addition, Abderhalden noted in 1913 that ninhydrin reagents could be a valuable reagent for identifying amino acids, including different tissues of the ninhydrin reaction plasma, urine, and sweat. Until Oden and von Hofsten identified ninhydrate for the uncovering of hidden fingerprints on paper in 1955. Since then, the technique has been commonly used in biochemical and medical research methods (Friedman, 2004). It was then proposed that Ninhydrin dissolved in Acetone was the ideal solvent for latent fingerprint visualization on paper. In numerous labs, the hidden fingerprints on permeable surfaces are based on the existing ninhydrin techniques (Bleay et al., 2017)

1.2- Formulation of Ninhydrin Reagent

For several years, Ninhydrin was used as a chemical for the picturing of hidden fingerprints on absorbent surfaces, including paper. Due to Acetone's high solubility with Ninhydrin, Acetone was the most convenient chemical for the production of hidden fingerprints in permeable surfaces that made it a useful working solution (Lee, and Gaensslen, 2001). Ninhydrin is also dissolved with other additives in non-flammable solvents to help the chemical dissolve in one-polar solvents. This solvent does not allow paper ink to run on the material because of a nonpolar solvent. Many research suggested alternative formulations for Ninhydrin, such as petroleum ether with a minimal methanol addition rather than acetone solvent. Diethyl ether may be used as a solvent. However, because of a flammable environment, Diethyl ether found that the volatile solvent could be used to spray documents. Many studies have indicated alternative formulation of Ninhydrin to increase contrast and reduce background discoloration (Bleay et al., 2017). HFE7100, based on Hewlett, Sears, and Suzuki 's 1997 work, is the recently satisfactory formulation of Ninhydrin for imaging of hidden finger impressions. Two hydrofluoroethers contain HFE 7100 solvent, 50% to 70% of methylnonafluoroisobutyl, and some 30% to 50% of methylnonafluorobutyl ether. 0.5 percent Ninhydrin and ethanol, acetate acid ethyl acetate are found in the working solvent. HFE7100 is a volatile, non-toxical, nonpolar, and non-flammable liquid that, in the formulation of Ninhydrin is regarded as safe and effective (Lee & Gaensslen, 2001).

1.3- Application of Ninhydrin

Ninhydrin has three most common uses that could be adopted to imagine the latent fingerprints that spray, dip, or swab (Odén & Hofsten,1954). In many laboratories, the dipping process is commonly used (Lee & Gaensslen, 2001). A 30 to 50-gram ninhydrin mixture is presented in the filter paper, which dissolved in one-and-a-half liters of Acetone. The mixture then permits the solvent to be dried. The substratum with a latent fingerprint or synthesis is put among two treated papers with Ninhydrin, screened for one week in a plastic bag. Therefore, the dipping process is used with nonpolar solvent HFE 7100. The show is immersed in a solution that can grow at room temperature in a dark and moist atmosphere for two to three days. The dipping technique improves the fingerprint contrast and is suitable for any paper type (Bleay et al., 2017). For extremely fragile paper, the spraying method is highly recommended. Swabbing is the least desirable technology because the tinkling of documents tends to be inked (Lee & Gaensslen, 2001).

1. 4- Post-treatment

Throughout the production of latent pore fingerprints, ninhydrin reactions with alpha-amino acids are commonly used. The chemical interaction between amino acids and ninhydrin in the fingerprint residue at room temperature is relatively slow and could be processed in a few days (Friedman & Williams, 1973). Applications for accelerating the reaction such as heating and steaming have been implemented, which considerably speed up the latent fingerprint development process. Different temperatures and equipment for use for speeds like fireplace, microwave, hairdryer, and iron. When the processed document with Ninhydrin, under 80 percent of humidity, was heated to 80 degrees Fahrenheit. This was so that the optimum temperature for developing latent fingerprints could be achieved (Lee & Gaensslen, 2001). However, the heating process has been unwanted, which reduces contrast and causes damage to paper (Bleay et al., 2017). The best result in the production of latent fingerprints without thermally applying the latent fingerprint was obtained in an environmental situation of 50 to 80% of humidity for a minimum of 48 hours at room temperature. The best result in the production of latent fingerprints without thermally applying the latent fingerprint was obtained in an environmental situation of 50 to 80% of humidity for a minimum of 48 hours at room temperature (Lee, and Gaensslen, 2001).

2-Ninhydrin Reaction with Alpha-amino Acids

Ninhydrin as a widely used chemical for paper latent fingerprint development (Stoilovic, Kobus, Margot, & Warrener, 1986). Ninhydrin chemically combines with alpha-amino acid to form a purple mixture; today referred to as Ruhemanna's purple color. This primary identification and quantitative storage of amino acids are used for the manufacture of Ruhemanna violet color. The chromophore that is formed depends upon the concentrations of alpha-amino acids in all primary amino acids. The strength of the Ruhemanna purple color is also dependent on concentrations of alpha-amino acids in all primary amino acids (Perrett & Nayuni, 2014). A carbon dioxide, aldehyde that is less carbonous than alpha-amino and ammonia acids, is the product of alpha-amino acids reaction with Ninhydrin (Yamashita and French, 2014). Figure 1 shows the color that has been formed with the diketohydrindylidenediketohydrindamine anion (DYDA) (Friedman, & Williams, 1973).

2. Mechanism of ninhydrin reaction with alpha-amino acids

The mechanism of Ninhydrin with alpha-amino acid reaction has been suggested in several studies. The process recently recognized is illustrated in sheme1 (Wilkinson, 2002). The current mechanism, where Ninhydrin undergoes an alpha-amino acid condensation reaction that forms a base for Schiff. Then a hydrolysis cycle follows the reaction, forming an intermediate that reacts with another ninhydrin to create Ruhemann’s purple (Bottom, Hanna, Siehr,1986).

3- Development of Latent Fingerprints Using Ninhydrin Analogs

Although the Ninhydrin most common fingerprinted reagent on many permeable surfaces is used to detect latent fingerprints, some limitations are present (Hansen and Joullie, 2005). The ninhydrin methods are insufficient for the uncovering of latent fingerprints (Lennard, Margot, Stoilovic & Warrener, 1998). Nevertheless, substantial work has sought to do more to improve the use of Ninhydrin. The aim is to increase the background to this issue by treating ninhydrin prints with a solution of metal salts. In addition, multiple chemical modifications were made to ninhydrin reagent to create better products for latent fingerprint production (Hansen & Joullie, 2005).

3.1-Pre-treatment by metal salts

Secondary treatment with metal salt solution may change the purple coloring produced by the production of fingerprints in Ninhydrin (Lennard, 2005). Herod and Menzel found that zinc chloride compounds alter the colors and cause light fluorescences when exposed to fingerprints of a laser argon ninhydrin (Hansen & Joullie,2005). The use of zinc (II) or cadmium salts, for instance, for the treatment of growing ninhydrin fingerprints results in a change of color (Bleay at el., 2017). The variations in color are due to the high-level development of ninhydrin-reaction-metal ion in Ruhemann's purple (Lennard, 2005). Creating a highly fluorescent print allows the contrast between different backgrounds and sensitivity to be better than the traditional method. A more general procedure in various laboratories is a metal salt treatment based on fluorescence detection methods (Hansen & Joullie, 2005).

3.2- 1,8-Diazafluorene-9-one (DFO)

In 1990, Grigg and Pounds applied for1,8-Diazafluorene-9-one (DFO) a chemical that helps to identify hidden fingerprints (Hansen & Joullie,2005). A strong DFO compound has been reported for hidden fingerprints on permeable surfaces as the best intense fluorescent reaction. Today, the DFO reagent is broadly used to identify latent fingerprints on absorbent surfaces using Ninhydrin (Yamashita & Frenc, 2014). As indicated in Figure 3 below, the latent fingerprints treated with 1,8-Diazafluorene-9-one produce a slight red color. Still, the color is a brightly luminescent one under green light that requires pre-treatments with metal springs to cause fluorescence. The color is a brightly luminescent color with green light, and comprehensive treatment with a metal salt is required. The best neurological ninhydrin reagent sequence for the production of latent fingerprints is 1,8-Diazafluorene-9-one (DFO) (Lee & Gaensslen, 2001).

3.3- 1,2-Indanedione

In the first instance, 1,2-indanedione was studied as a possible ninhydrin analog by Joullié and colleagues to image latent fingerprints in1997 (Levin-Elada, Liptzb, Bar-Ora, & Almogc, 2016). With amino acids, the new reactive produces a bright pink color, named pink figure 4 by Joullié (Almog and Glasner, 2010). The fluorescent rose color is lighted brighter with green color. For the fluorescence to expand, 1,2-indanedione required a second treatment with zinc nitrate. 1,2-indanedione, also a much stronger fluorescent light, is quicker with amino acids than with DFO. Several countries have thoroughly studied 1,2-indanedione in a criminal investigation for operational use (Lee & Gaensslen, 2001).


Ninhydrin has been and is still the best compound for detecting hidden fingerprints on adsorbent surfaces for more than thirty years. The nature of ninhydrin interaction with amino acids has been examined, to provide an appropriate mechanism of Ruhemanna's reaction. The studies have been carried out to improve the limitation of the technique of Ninhydrin by the treatment of prints developed with metallic salts like zinc chloride or by developing new analogs of Ninhydrin.


Almog, J., & Glasner, H. (2010). Ninhydrin thiohemiketals: basic research towards improved fingermark detection techniques employing nano-technology, J. Forensic Sci. 55(2010) 215–220.

Bleay, S. Sears, V. Downham, R. Bandey, H. Gibson, A. Bowman, V. Fitzgerald, L. Ciuksza, T. Ramadani, J. & Selway, C. (2017). Chemical and Physical Processes: Fingerprint Source. Ch-3, P 1-30

Bottom C. B., Hanna S.S., & Siehr, D. J. (1978) Mechanism of the ninhydrin reaction. Biochem Educ 6:4–5

CB, B. S.S., & H. DJ, S. (1978) Mechanism of the ninhydrin reaction. Biochem Educ 6:4–5

Crown, D. A. (1969). The development of latent fingerprints with Ninhydrin. The Journal of Crimi...

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