Forensic Science International 242 (2014) 123–126
Contents lists available at ScienceDirect
Forensic Science International journal homepage: www.elsevier.com/locate/forsciint
Studies on the development of latent fingerprints by the method of solid–medium ninhydrin Ruiqin Yang *, Jie Lian College of Forensic Science, People’s Public Security University of China, 1 No. Muxidi Nanli, Xicheng District, Beijing 100038, China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 24 April 2014 Received in revised form 23 June 2014 Accepted 27 June 2014 Available online 6 July 2014
A new series of fingerprint developing membrane were prepared using ninhydrin as the developing agent, and pressure-sensitive emulsifiers as the encapsulated chemicals. The type of emulsifier, plastic film, concentration of the developing agent, modifying ions and thickness of the membrane were studied in order to get the optimized fingerprint developing effect. The membrane can be successfully applied to both latent sweat fingerprints and blood fingerprint on many different surfaces. The sensitivity of the method toward the latent sweat fingerprint is 0.1 mg/L amino acid. The membrane can be applied to both porous and non-porous surfaces. Fingerprints that are difficult to develop on surfaces such as leather, glass and heat-sensitive paper using traditional chemical methods can be successfully developed with this membrane. ß 2014 Elsevier Ireland Ltd. All rights reserved.
Keywords: Fingerprint developing membrane Latent fingerprint Preparation Application
1. Introduction The fingerprint is one of the most important evidences of crime scene. In most cases, the fingerprints on many types of surface are invisible. The study of fingerprint developing methods is always one of the hot topics in the forensic science area. The traditional used fingerprint development methods are chemical processes. Commonly used chemicals for fingerprint development on porous surfaces are ninhydrin [1,2] and 1,8-diaza-9-fluorenone (DFO) [2– 4]. There have been a number of improvements to the ninhydrin development method such as treatment with divalent metal ions [5,6], freeze-treatment with liquid nitrogen and treatment with laser or visible light [7]. In 1997, a new fingerprint developing agent, 1,2-indanediones was reported by Ramotowski et al. [8]. Most of the previous studies focus either on the synthesis of the ninhydrin-similar chemicals or the post-treatment after fingerprint development. With the improvements of these processes, the sensitivity has increased. Ninhydrin is a successful reagent for developing latent fingerprints on porous surfaces and has sufficient sensitivity for real-life application. However, there are several limitations to using ninhydrin, such as background coloration, dissolution of the printing ink and its flammable characteristics. In 1974, a most remarkable breakthrough in
optimizing the formulation of the ninhydrin reagent was reported by Morris. They described an improved ninhydrin reagent based on another nonpolar solvent, Freon 113, or CFC113. This formulation is nonflammable, nontoxic, and doesn’t dissolve ink on documents [9]. In 1997, a formulation that appeared to satisfy all the requirements for fingerprint work was based on the work of Hewlett and Suzuki, which uses the solvent HEE7100 as the carrier [10,11]. This provides a safe and effective replacement to Feron 113 in the ninhydrin process. However, solid–medium ninhydrin method can overcome these disadvantages, by avoiding the need for the ninhydrin development cabinet, developing fingerprints more quickly detecting fingerprints on both porous and nonporous surfaces. In this work, a new fingerprint development method was studied which involves the stabilization of ninhydrin in a membrane, together with the encapsulated chemicals. A new series of fingerprint developing membrane (FDM) were prepared and applied to many different surfaces. The membrane’s preparation and application are reported in this article. It is a nondestructive fingerprint development method. 2. Experimental 2.1. Materials and chemicals
* Corresponding author. Tel.: +86 10 83903298. E-mail address: [email protected] (R. Yang). http://dx.doi.org/10.1016/j.forsciint.2014.06.036 0379-0738/ß 2014 Elsevier Ireland Ltd. All rights reserved.
The pressure-sensitive emulsifiers were used as the encapsulated chemicals. Three kinds of water-soluble pressure-sensitive
124
R. Yang, J. Lian / Forensic Science International 242 (2014) 123–126
were screened as the encapsulated chemical to get the optimized water-soluble FDM. All the FDMs performed well at developing the latent fingerprints but each effect the background differently. Then the water-soluble FDM with the reacting emulsifier, and liposoluble FDM were chosen for the following studies.
emulsifier: general emulsifier, combined emulsifier and reacting emulsifier were used and were self-prepared in our laboratory. Liposoluble pressure-sensitive emulsifier was from Changchun Chemical Institute of Chinese Academy of Science. Dichlorodibutyltin was used as the organic tin compound and was supplied by Chinese Northeastern Normal University. Ninhydrin and other chemical pure reagents were purchased from Tianjin Chemical Institute. The separating papers were obtained from The Seventh Paper Plant in Beijing.
3.1.2. Selection of the plastic film There is no other need for the plastic film other than the softness, transparency, extending strength. In this study, polypropylene film was used. The surface of the plastic film must be treated with the electric corona to get satisfactory adsorpstion.
2.2. Preparation of the FDMs The water-soluble FDMs were prepared by spreading the parent mixture solution of the developing agent (ninhydrin) and watersoluble pressure-sensitive emulsifier (polyvinyl alcohol) on polypropylene film. Similarly, the liposoluble FDM was prepared by using the mixture of ninhydrin and liposoluble pressure-sensitive emulsifier (polyacrylic). The liquid membrane obtained was then dried at 70 8C for 5 min and covered with the separating paper ready for use. The membrane was spread out in a controlled manner to a thickness of 10–20 mm. In order to color the enhanced fingerprint, 1% dichlorodibutyltin was added as the organic Sn compound to the parent mixture solution of the ninhydrin and emulsifier, to get the modified FDM. 2.3. Fingerprint developing Prior to laying down the fingermarks a grooming procedure developed for this study was carried out. This was intended to mimic natural behavior and minimize variability due to exogenous sources. The grooming procedure was as follows: (1) hands were washed three times thoroughly with soap; (2) fingers were then gently wiped across the forehead; (3) latent fingermarks were deposited onto the substrates with good quality. 100 sebaceous fingermarks from ten healthy donors aged from 20 to 40 were collected on different paper types, such as print papers, heatsensitive papers, news papers and leather. The images were taken with a Nikon D 80 digital camera and a Nikon 60 mm60F/2.8D Macro Lens. The latent fingerprint samples were left for 30 min before being covered with the FDM and tightly pressed for a few minutes after which development had occurred. The time needed to the develop the fingerprint is dependent on the aging of the fingerprint. Older fingerprints need more time to develop. The developing time could be shortened by using UV or sun light irradiation, or heating with a flatiron (70–110 8C) or hot water bottle. The heating time with a flatiron should not be longer than 30 s. In this article, the 100– 110 8C flatiron was used to accelerate fingerprint development. The development should be checked every 3–5 s to avoid darkening the background due to the excessive heating. The sensitivity of this process was tested using the following procedures. For the sweat fingerprint, aqueous glycine solutions of different concentrations (0.005, 0.01, 0.05, 0.5, 1.0 mg/L) were added dropwise to thin layer chromatographic plates, which were then kept in room conditions for 1 h before development with the FDM. For the latent blood fingerprint, human blood was diluted with distilled water before being inked on the print-paper. The FDM was then used to develop this.
3.1.3. The concentration of the developing agent (ninhydrin) The optimization of the concentration of the fingerprint developing agent has been well studied by many other researchers [12–15]. It was found in this study that the concentration of the developing agent ninhydrin in the parent mixture solution needs to be controlled at 0.5–2.0% (w/v). Concentrations lower than 0.5% would decrease the sensitivity and concentration higher than 2.0% would destroy the stability of the liquid membrane. Concentrations higher than 10% cause background to darken during development. 3.1.4. Effect of the modifying ion The divalent Zn2+ and Cd2+ ions are traditionally used to enhance the effects of fingerprint development. In this study, introducing modifying ions into the water-soluble membrane would accelerate the inner and external transportation of the developing agent in the liquid membrane. The homogeneous dispersion of the ions in the liposoluble membrane could not be obtained due to their low solubility. The organic Sn compound (dichlorodibutyltin) was used as a modifying agent. Users should wear suitable protective clothing, gloves and eye protection, and avoid release into the environment. A good result was obtained as shown in Fig. 1. A similar color could be obtained using either the organic Sn compound or Zn2+ ion. The combination of the Sn organic compound with the fingerprint developing agent gives the better effects. And furthermore, the fingerprint development process is much simpler. 3.1.5. Controlling of the thickness of the liquid membrane on FDMs The thickness of the liquid membrane has an important influence on the fingerprint development. The agents in the thick membrane are difficult to transport to the samples and would get no developing effects on the latent fingerprints. A thinner membrane has less agents resulting in poorer development. In this study, it was found that the optimized thickness of the liquid membrane is 10–15 mm. The dissolved solid content in the parent
[(Fig._1)TD$IG]
3. Results and discussion 3.1. Study on the FDM preparation 3.1.1. Screening on the encapsulated chemical Three kinds of water-soluble pressure-sensitive emulsifier: general emulsifier, combined emulsifier and reacting emulsifier
Fig. 1. Fingerprint on print-paper enhanced using Sn modified FDM. (Natural Fingerprint left on paper for 10 days).
R. Yang, J. Lian / Forensic Science International 242 (2014) 123–126 Table 1 Examining sensitivity of FDMs at developing fingerprints by varying amino acid concentration present. FDM type
Water-soluble FDM Liposolubility FDM
stick to the samples. Wet rinse of the sample surface is necessary when the liposolubility FDM is used. It can be seen from Fig. 2 that the FDM has a good effect on these aged fingerprints aged after different time.
Amino acid concentration 1%
0.1%
0.05%
0.01%
0.005%
+++ +++
+++ +++
+++ +++
++ ++
– –
3.3.2. Application for the latent fingerprint on the heat sensitive papers The latent fingerprint samples on the print-papers and on heatsensitive paper could not be successfully developed using traditional methods as the color of the surface may vary due to the property of the paper. This problem could be resolved with selfprepared FDM. The results are shown in Fig. 3. The FDM was applied to the fingerprint samples on heat-sensitive papers. Fingerprint development was observable after 2 h without any additional treatment. The development was best after 4–6 h. The time could be shortened to 5 min if the membrane is irradiated under solar light or hand pressed. The color was a little redder than that with the traditional ninhydrin method. This is due to the reactions between metal ions in the heat-sensitive paper and the ninhydrin or amino acid in the membrane, and has little adverse effect on the development or the sensitivity.
+++ strong development; ++weak development; – not observed by naked eyes.
mixture solution of the membrane should be controlled at 30–35% to get the optimized thickness of the membrane. 3.2. The developing sensitivity of the FDMs Table 1 shows the sensitivity of the FDMs toward the latent sweat fingerprint by using different amino acid concentrations. For the latent blood fingerprint, the fingerprint can be observed under natural sun light for a sample that has been diluted 4 times. These results mean the sensitivity of the FDMs toward the latent sweat fingerprint is 0.01% amino acid, and that toward the latent blood fingerprint is 25% (v/v).
3.3.3. Application for the latent fingerprints on the leather and glass Fingerprints on the leather surface were not well developed using traditional chemical or physical methods because there are amino acids within the leather itself. The FDM prepared in this study makes contact with the object’s surface only. Therefore, the development of fingerprints on the surface should not be influenced by reactive species within the leather itself. Fig. 4 shows a well-developed latent fingerprint on leather.
3.3. Application of the FDM 3.3.1. Application for the aged fingerprint The latent fingerprint samples on the print-papers were kept in a room for 5, 15 and 30 days to observe the effects of the FDM on the aging of the fingerprints. The water-soluble FDM can directly
[(Fig._2)TD$IG]
125
Fig. 2. Effect of ageing fingerprints on print paper before developing with FDM.
[(Fig._4)TD$IG] [(Fig._3)TD$IG]
Fig. 3. Application of FDM to fingerprints on the heat-sensitive paper. (Fingerprints left on the heat-sensitive papers for 5 days).
Fig. 4. Application of FDM to a fingerprint on leather (Fingerprints left on leather for 1 day).
[(Fig._5)TD$IG]
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R. Yang, J. Lian / Forensic Science International 242 (2014) 123–126
fingerprint developing procedures. Furthermore, the method can widen the application scope from the porous to the non-porous surfaces. The study also supplies a new membrane method for other fingerprint developing chemicals. At the same time, development of this membrane is in progress in our study. Acknowledgements This work was supported by Beijing Municipal Commission of Education (JD100410669) and Program for New Century Excellent Talents in University (NCET-10-0082). We also are appreciated to Miss Laura Daly who is a Ph.D. student in University of Strathclyde. She helps us correct our English for our paper.
Fig. 5. Comparison of FDM with other fingerprint development processes FDM (left) and ninhydrin (right) on print-paper.
The fingerprint on glass could not be easily obtained using traditional Ninhydrin methods. The developing agent was stabilized on the FDM and therefore could be applied to the glass surface. This also enlarges the application of ninhydrin. 3.4. Comparison between FDM and other methods The fingerprints on the print-paper were divided into two parts, and FDM and the traditional ninhydrin method was used to develop them. The results are shown in Fig. 5. It can be seen from the results that the FDM gives a better result than the traditional ninhydrin method, especially the FDM process did not stain the surface background. 4. Conclusion A new series of fingerprint developing membrane were prepared by stabilizing the developing agents, together with the encapsulated chemicals and modifying ions, on the plastic film. It can be successfully applied to different surfaces with results that are better or comparable to traditional methods. The problem of agent mobility in the traditional chemical developing methods was avoided. The application of this method will simplify the on-site
References [1] S. Oden, B. Von Hofsten, Detection of fingerprints by ninhydrin reaction, Nature 173 (1954) 449. [2] H.C. Lee, R.E. Gaensslen, Methods of Latent Fingerprint Development, Advances in Fingerprint Technology, second ed., CRC Press, New York, NY, 2001, pp. 105–177. [3] R. Grigg, S.T. Mongkolaussavaratana, C.A. Pounds, S. Sivagnanam, 1, 8-diazafluorenone and related compounds. A new reagent for the alpha-amino acids and fingerprints, Tetrahedron Lett. 31 (1990) 7215. [4] C.A. Pounds, R. Grigg, S.T. Mongkolaussavaratana, The use of DFO for the fluorescent detection of latent fingerprints on paper, a preliminary evaluation, J. Forensic Sci. 35 (1990) 169. [5] H.J. Kobus, M. Stoilovic, R.N. Warrener, Simple luminescence post-ninhydrin treatment for the improved visualization of fingerprints on documents in cases where ninhydrin alone gives poor results, Forensic Sci. Int. 22 (1983) 161. [6] M. Stoilovic, H.J. Kobus, P. Margot, R.N. Warrener, Improved enhancement of ninhydrin developed fingerprints by cadmium complexion using low temperature photoluminescence techniques, J. Forensic Sci. 31 (1986) 432. [7] D.W. Herod, E.R. Menzel, Laser detection of latent fingerprints: ninhydrin, J. Forensic Sci. 27 (1982) 200. [8] R. Ramotowski, M.M. Jouille, O. Petrovskaia, 1,2-Indanediones; a preliminary evaluation of a new class of amino acid visualizing compounds, Fingerprint World 23 (1997) 131. [9] J.R. Morris, G.C. Goode, NFN—an improved ninhydrin reagent for detection of latent fingerprints, Police Res. Bul. 24 (1974) 45–53. [10] D.F. Hewlett, V.G. Sears, Replacements for CFC113 in the ninhydrin process: Part 1, J. Forensic Ident. 47 (3) (1997) 287–299. [11] D.F. Hewlett, V.G. Sears, S. Suzuki, Replacements for CFC113 in the ninhydrin process: Part 2, J. Forensic Ident. 47 (3) (1997) 300–306. [12] A.V. Petruncio, A comparative study for the evaluation of two solvents for use in ninhydrin processing of latent print evidence, J. Forensic. Ident. 50 (5) (2000) 462–469. [13] H.A. Speaks, The use of ninhydrin in the development of latent fingerprints, Fingerprint Ident. Mag. 45 (1964) 41. [14] W.A. Shulenberger, Present status of the ninhydrin process for developing latent fingerprints, Ident. News 13 (1963) 9. [15] D.G. Mooney, Development of latent fingerprints and palmprints by ninhydrin, Ident. News 16 (1966) 4.
Contents lists available at ScienceDirect
Forensic Science International journal homepage: www.elsevier.com/locate/forsciint
Studies on the development of latent fingerprints by the method of solid–medium ninhydrin Ruiqin Yang *, Jie Lian College of Forensic Science, People’s Public Security University of China, 1 No. Muxidi Nanli, Xicheng District, Beijing 100038, China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 24 April 2014 Received in revised form 23 June 2014 Accepted 27 June 2014 Available online 6 July 2014
A new series of fingerprint developing membrane were prepared using ninhydrin as the developing agent, and pressure-sensitive emulsifiers as the encapsulated chemicals. The type of emulsifier, plastic film, concentration of the developing agent, modifying ions and thickness of the membrane were studied in order to get the optimized fingerprint developing effect. The membrane can be successfully applied to both latent sweat fingerprints and blood fingerprint on many different surfaces. The sensitivity of the method toward the latent sweat fingerprint is 0.1 mg/L amino acid. The membrane can be applied to both porous and non-porous surfaces. Fingerprints that are difficult to develop on surfaces such as leather, glass and heat-sensitive paper using traditional chemical methods can be successfully developed with this membrane. ß 2014 Elsevier Ireland Ltd. All rights reserved.
Keywords: Fingerprint developing membrane Latent fingerprint Preparation Application
1. Introduction The fingerprint is one of the most important evidences of crime scene. In most cases, the fingerprints on many types of surface are invisible. The study of fingerprint developing methods is always one of the hot topics in the forensic science area. The traditional used fingerprint development methods are chemical processes. Commonly used chemicals for fingerprint development on porous surfaces are ninhydrin [1,2] and 1,8-diaza-9-fluorenone (DFO) [2– 4]. There have been a number of improvements to the ninhydrin development method such as treatment with divalent metal ions [5,6], freeze-treatment with liquid nitrogen and treatment with laser or visible light [7]. In 1997, a new fingerprint developing agent, 1,2-indanediones was reported by Ramotowski et al. [8]. Most of the previous studies focus either on the synthesis of the ninhydrin-similar chemicals or the post-treatment after fingerprint development. With the improvements of these processes, the sensitivity has increased. Ninhydrin is a successful reagent for developing latent fingerprints on porous surfaces and has sufficient sensitivity for real-life application. However, there are several limitations to using ninhydrin, such as background coloration, dissolution of the printing ink and its flammable characteristics. In 1974, a most remarkable breakthrough in
optimizing the formulation of the ninhydrin reagent was reported by Morris. They described an improved ninhydrin reagent based on another nonpolar solvent, Freon 113, or CFC113. This formulation is nonflammable, nontoxic, and doesn’t dissolve ink on documents [9]. In 1997, a formulation that appeared to satisfy all the requirements for fingerprint work was based on the work of Hewlett and Suzuki, which uses the solvent HEE7100 as the carrier [10,11]. This provides a safe and effective replacement to Feron 113 in the ninhydrin process. However, solid–medium ninhydrin method can overcome these disadvantages, by avoiding the need for the ninhydrin development cabinet, developing fingerprints more quickly detecting fingerprints on both porous and nonporous surfaces. In this work, a new fingerprint development method was studied which involves the stabilization of ninhydrin in a membrane, together with the encapsulated chemicals. A new series of fingerprint developing membrane (FDM) were prepared and applied to many different surfaces. The membrane’s preparation and application are reported in this article. It is a nondestructive fingerprint development method. 2. Experimental 2.1. Materials and chemicals
* Corresponding author. Tel.: +86 10 83903298. E-mail address: [email protected] (R. Yang). http://dx.doi.org/10.1016/j.forsciint.2014.06.036 0379-0738/ß 2014 Elsevier Ireland Ltd. All rights reserved.
The pressure-sensitive emulsifiers were used as the encapsulated chemicals. Three kinds of water-soluble pressure-sensitive
124
R. Yang, J. Lian / Forensic Science International 242 (2014) 123–126
were screened as the encapsulated chemical to get the optimized water-soluble FDM. All the FDMs performed well at developing the latent fingerprints but each effect the background differently. Then the water-soluble FDM with the reacting emulsifier, and liposoluble FDM were chosen for the following studies.
emulsifier: general emulsifier, combined emulsifier and reacting emulsifier were used and were self-prepared in our laboratory. Liposoluble pressure-sensitive emulsifier was from Changchun Chemical Institute of Chinese Academy of Science. Dichlorodibutyltin was used as the organic tin compound and was supplied by Chinese Northeastern Normal University. Ninhydrin and other chemical pure reagents were purchased from Tianjin Chemical Institute. The separating papers were obtained from The Seventh Paper Plant in Beijing.
3.1.2. Selection of the plastic film There is no other need for the plastic film other than the softness, transparency, extending strength. In this study, polypropylene film was used. The surface of the plastic film must be treated with the electric corona to get satisfactory adsorpstion.
2.2. Preparation of the FDMs The water-soluble FDMs were prepared by spreading the parent mixture solution of the developing agent (ninhydrin) and watersoluble pressure-sensitive emulsifier (polyvinyl alcohol) on polypropylene film. Similarly, the liposoluble FDM was prepared by using the mixture of ninhydrin and liposoluble pressure-sensitive emulsifier (polyacrylic). The liquid membrane obtained was then dried at 70 8C for 5 min and covered with the separating paper ready for use. The membrane was spread out in a controlled manner to a thickness of 10–20 mm. In order to color the enhanced fingerprint, 1% dichlorodibutyltin was added as the organic Sn compound to the parent mixture solution of the ninhydrin and emulsifier, to get the modified FDM. 2.3. Fingerprint developing Prior to laying down the fingermarks a grooming procedure developed for this study was carried out. This was intended to mimic natural behavior and minimize variability due to exogenous sources. The grooming procedure was as follows: (1) hands were washed three times thoroughly with soap; (2) fingers were then gently wiped across the forehead; (3) latent fingermarks were deposited onto the substrates with good quality. 100 sebaceous fingermarks from ten healthy donors aged from 20 to 40 were collected on different paper types, such as print papers, heatsensitive papers, news papers and leather. The images were taken with a Nikon D 80 digital camera and a Nikon 60 mm60F/2.8D Macro Lens. The latent fingerprint samples were left for 30 min before being covered with the FDM and tightly pressed for a few minutes after which development had occurred. The time needed to the develop the fingerprint is dependent on the aging of the fingerprint. Older fingerprints need more time to develop. The developing time could be shortened by using UV or sun light irradiation, or heating with a flatiron (70–110 8C) or hot water bottle. The heating time with a flatiron should not be longer than 30 s. In this article, the 100– 110 8C flatiron was used to accelerate fingerprint development. The development should be checked every 3–5 s to avoid darkening the background due to the excessive heating. The sensitivity of this process was tested using the following procedures. For the sweat fingerprint, aqueous glycine solutions of different concentrations (0.005, 0.01, 0.05, 0.5, 1.0 mg/L) were added dropwise to thin layer chromatographic plates, which were then kept in room conditions for 1 h before development with the FDM. For the latent blood fingerprint, human blood was diluted with distilled water before being inked on the print-paper. The FDM was then used to develop this.
3.1.3. The concentration of the developing agent (ninhydrin) The optimization of the concentration of the fingerprint developing agent has been well studied by many other researchers [12–15]. It was found in this study that the concentration of the developing agent ninhydrin in the parent mixture solution needs to be controlled at 0.5–2.0% (w/v). Concentrations lower than 0.5% would decrease the sensitivity and concentration higher than 2.0% would destroy the stability of the liquid membrane. Concentrations higher than 10% cause background to darken during development. 3.1.4. Effect of the modifying ion The divalent Zn2+ and Cd2+ ions are traditionally used to enhance the effects of fingerprint development. In this study, introducing modifying ions into the water-soluble membrane would accelerate the inner and external transportation of the developing agent in the liquid membrane. The homogeneous dispersion of the ions in the liposoluble membrane could not be obtained due to their low solubility. The organic Sn compound (dichlorodibutyltin) was used as a modifying agent. Users should wear suitable protective clothing, gloves and eye protection, and avoid release into the environment. A good result was obtained as shown in Fig. 1. A similar color could be obtained using either the organic Sn compound or Zn2+ ion. The combination of the Sn organic compound with the fingerprint developing agent gives the better effects. And furthermore, the fingerprint development process is much simpler. 3.1.5. Controlling of the thickness of the liquid membrane on FDMs The thickness of the liquid membrane has an important influence on the fingerprint development. The agents in the thick membrane are difficult to transport to the samples and would get no developing effects on the latent fingerprints. A thinner membrane has less agents resulting in poorer development. In this study, it was found that the optimized thickness of the liquid membrane is 10–15 mm. The dissolved solid content in the parent
[(Fig._1)TD$IG]
3. Results and discussion 3.1. Study on the FDM preparation 3.1.1. Screening on the encapsulated chemical Three kinds of water-soluble pressure-sensitive emulsifier: general emulsifier, combined emulsifier and reacting emulsifier
Fig. 1. Fingerprint on print-paper enhanced using Sn modified FDM. (Natural Fingerprint left on paper for 10 days).
R. Yang, J. Lian / Forensic Science International 242 (2014) 123–126 Table 1 Examining sensitivity of FDMs at developing fingerprints by varying amino acid concentration present. FDM type
Water-soluble FDM Liposolubility FDM
stick to the samples. Wet rinse of the sample surface is necessary when the liposolubility FDM is used. It can be seen from Fig. 2 that the FDM has a good effect on these aged fingerprints aged after different time.
Amino acid concentration 1%
0.1%
0.05%
0.01%
0.005%
+++ +++
+++ +++
+++ +++
++ ++
– –
3.3.2. Application for the latent fingerprint on the heat sensitive papers The latent fingerprint samples on the print-papers and on heatsensitive paper could not be successfully developed using traditional methods as the color of the surface may vary due to the property of the paper. This problem could be resolved with selfprepared FDM. The results are shown in Fig. 3. The FDM was applied to the fingerprint samples on heat-sensitive papers. Fingerprint development was observable after 2 h without any additional treatment. The development was best after 4–6 h. The time could be shortened to 5 min if the membrane is irradiated under solar light or hand pressed. The color was a little redder than that with the traditional ninhydrin method. This is due to the reactions between metal ions in the heat-sensitive paper and the ninhydrin or amino acid in the membrane, and has little adverse effect on the development or the sensitivity.
+++ strong development; ++weak development; – not observed by naked eyes.
mixture solution of the membrane should be controlled at 30–35% to get the optimized thickness of the membrane. 3.2. The developing sensitivity of the FDMs Table 1 shows the sensitivity of the FDMs toward the latent sweat fingerprint by using different amino acid concentrations. For the latent blood fingerprint, the fingerprint can be observed under natural sun light for a sample that has been diluted 4 times. These results mean the sensitivity of the FDMs toward the latent sweat fingerprint is 0.01% amino acid, and that toward the latent blood fingerprint is 25% (v/v).
3.3.3. Application for the latent fingerprints on the leather and glass Fingerprints on the leather surface were not well developed using traditional chemical or physical methods because there are amino acids within the leather itself. The FDM prepared in this study makes contact with the object’s surface only. Therefore, the development of fingerprints on the surface should not be influenced by reactive species within the leather itself. Fig. 4 shows a well-developed latent fingerprint on leather.
3.3. Application of the FDM 3.3.1. Application for the aged fingerprint The latent fingerprint samples on the print-papers were kept in a room for 5, 15 and 30 days to observe the effects of the FDM on the aging of the fingerprints. The water-soluble FDM can directly
[(Fig._2)TD$IG]
125
Fig. 2. Effect of ageing fingerprints on print paper before developing with FDM.
[(Fig._4)TD$IG] [(Fig._3)TD$IG]
Fig. 3. Application of FDM to fingerprints on the heat-sensitive paper. (Fingerprints left on the heat-sensitive papers for 5 days).
Fig. 4. Application of FDM to a fingerprint on leather (Fingerprints left on leather for 1 day).
[(Fig._5)TD$IG]
126
R. Yang, J. Lian / Forensic Science International 242 (2014) 123–126
fingerprint developing procedures. Furthermore, the method can widen the application scope from the porous to the non-porous surfaces. The study also supplies a new membrane method for other fingerprint developing chemicals. At the same time, development of this membrane is in progress in our study. Acknowledgements This work was supported by Beijing Municipal Commission of Education (JD100410669) and Program for New Century Excellent Talents in University (NCET-10-0082). We also are appreciated to Miss Laura Daly who is a Ph.D. student in University of Strathclyde. She helps us correct our English for our paper.
Fig. 5. Comparison of FDM with other fingerprint development processes FDM (left) and ninhydrin (right) on print-paper.
The fingerprint on glass could not be easily obtained using traditional Ninhydrin methods. The developing agent was stabilized on the FDM and therefore could be applied to the glass surface. This also enlarges the application of ninhydrin. 3.4. Comparison between FDM and other methods The fingerprints on the print-paper were divided into two parts, and FDM and the traditional ninhydrin method was used to develop them. The results are shown in Fig. 5. It can be seen from the results that the FDM gives a better result than the traditional ninhydrin method, especially the FDM process did not stain the surface background. 4. Conclusion A new series of fingerprint developing membrane were prepared by stabilizing the developing agents, together with the encapsulated chemicals and modifying ions, on the plastic film. It can be successfully applied to different surfaces with results that are better or comparable to traditional methods. The problem of agent mobility in the traditional chemical developing methods was avoided. The application of this method will simplify the on-site
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