Method and solution for rapidly developing ninhydrin of potential fingerprint

Abstract

The invention provides a ninhydrin rapid development method and a ninhydrin rapid development solution for potential fingerprints. The ninhydrin rapid development method of the potential fingerprint comprises the following steps: heating a ninhydrin development solution to be not lower than 100 DEG C; immersing a potential fingerprint sample into the ninhydrin appearing solution; taking out and volatilizing the displayed fingerprint sample, and photographing to fix a display result; the ninhydrin developing solution for the potential fingerprints is applied to the ninhydrin rapid developing method for the potential fingerprints and comprises a color developing agent and a solvent, the color developing agent is selected from ninhydrin; the solvent is selected from ethyl benzoate. According to the method, the time for potential fingerprint showing is shortened to only several seconds, the instant showing effect of object immersion and fingerprint showing is achieved, accordingly, two-step showing of first immersion and second heating in the prior art is simplified into one-step showing of immersion and heating, whether the fingerprint is left on the object or not can be directly judged without aftertreatment, the showing efficiency is remarkably improved, and the method is suitable for popularization and application. And the workload of identification personnel is reduced.

Description

Technical Field

[0001] This invention belongs to the field of forensic fingerprint identification technology, and specifically relates to a rapid method and solution for the development of potential fingerprints using ninhydrin. Background Technology

[0002] Fingerprints are hailed as the "king of evidence" and are crucial for identifying individuals. According to Edmund Locard's principle of exchange of substances, after a perpetrator touches items at a crime scene, substances such as free amino acids and α-amino proteins secreted from their hands will inevitably remain on the surface of the object, forming fingerprint residue. Because these residues are colorless, they form latent fingerprints invisible to the naked eye. Therefore, they must be revealed and transformed into visible fingerprints before they can be used for morphological identification to identify an individual.

[0003] Ninhydrin reacts sensitively with amino acids in fingerprint residues and has long been a commonly used developing agent for latent fingerprints. However, the reaction between ninhydrin and amino acids is relatively slow, typically requiring several hours or even days to complete, resulting in low developing efficiency. To address this, the standards "Technical Specification for Ninhydrin Fingerprint Development in Forensic Science (GA / T 1239-2015)" and "Research on Influencing Factors of Ninhydrin Development of Sweaty Latent Fingerprints on Thermal Paper" disclose methods for first immersing latent fingerprints in a ninhydrin developing solution, then removing and drying them, followed by additional heating in a heating device. This increases the reaction rate between the amino acid-sensitive reagent and amino acids, thereby shortening the fingerprint development time.

[0004] However, the existing two-step development method, which involves immersion followed by heating, is cumbersome and takes several minutes to tens of minutes, resulting in low development efficiency. Moreover, since visible fingerprints cannot be immediately reflected after immersion, objects without latent fingerprints still require subsequent heating treatment, increasing the workload of the examiners and further reducing development efficiency. Summary of the Invention

[0005] The purpose of this invention is to overcome the technical problems of cumbersome operation and low development efficiency in existing technologies. To solve the above-mentioned technical problems, this invention provides a rapid development method and solution for latent fingerprints using ninhydrin.

[0006] In a first aspect, the present invention provides a method for rapid development of potential fingerprints using ninhydrin, the method comprising the following steps:

[0007] 1) Heat the ninhydrin development solution to at least 100°C;

[0008] 2) Immerse the potential fingerprint sample in the ninhydrin development solution;

[0009] 3) Remove and dry the fingerprint sample, then take a photo to fix the display result;

[0010] Furthermore, as described above, the potential fingerprint sample is immersed in the ninhydrin development solution for 0.1-10 s.

[0011] In a second aspect, the present invention provides a ninhydrin development solution for latent fingerprints, wherein the ninhydrin development solution for latent fingerprints is applied to any of the ninhydrin rapid development methods for latent fingerprints in the first aspect; the ninhydrin development solution for latent fingerprints comprises a color developer and a solvent; the color developer is selected from ninhydrin; and the solvent is selected from ethyl benzoate.

[0012] Furthermore, the ninhydrin mass concentration in the ninhydrin development solution of the potential fingerprint as described above is 0.1-5.0%.

[0013] Compared with the prior art, the present invention has at least the following beneficial effects:

[0014] 1) This invention provides a rapid ninhydrin development method for latent fingerprints, which reduces the development time of latent fingerprints to only a few seconds, achieving an instant development effect of "subject immersion and fingerprint appearance". This simplifies the existing "two-step" development method of soaking and heating into a "one-step" development that integrates soaking and heating. No post-processing is required to directly determine whether a fingerprint is left on the object, reducing the workload of the identification personnel and significantly improving the development efficiency.

[0015] 2) This invention provides a ninhydrin development solution for the rapid development of latent fingerprints. It utilizes ethyl benzoate, a high-boiling-point solvent, to replace lower-boiling-point solvents such as ethyl acetate, ethanol, and hydrofluoroether in existing technologies. This ensures the development solution remains stable at temperatures above 100°C, thereby increasing the reaction temperature of the ninhydrin-amino acid reaction system, thus enhancing the reaction rate and shortening the reaction time. This enables a rapid ninhydrin development method for latent fingerprints. Simultaneously, ethyl benzoate has low polarity and does not readily dissolve fingerprint residues or the developed fingerprint lines, improving development efficiency while helping to ensure the quality of fingerprint development. Attached Figure Description

[0016] Figure 1 This is a diagram showing the development effect of a potential handprint being immersed in a 100°C developing solution for 10 seconds in Example 1 of the present invention.

[0017] Figure 2 This is a diagram showing the development effect of a potential handprint immersed in a 180°C development solution for 1 second in Example 2 of the present invention.

[0018] Figure 3 This is a rendering of the potential fingerprint immersed in a 0.1% mass concentration rendering solution in Example 3 of the present invention.

[0019] Figure 4This is a comparison diagram showing the potential handprint effect between existing technology and the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] Existing technologies all employ a two-step development method of immersion followed by heating, which is cumbersome and takes several minutes to tens of minutes, resulting in low development efficiency. Moreover, visible fingerprints do not immediately appear after immersion, requiring subsequent heating treatment for objects without latent fingerprints, increasing the workload of the examiners and further reducing development efficiency.

[0022] To address the above problems, this invention proposes a rapid method for developing latent fingerprints using ninhydrin, comprising the following steps:

[0023] S1: Heat the ninhydrin development solution to at least 100°C;

[0024] S2: Immerse the potential fingerprint sample in the ninhydrin development solution;

[0025] S3: Remove and dry the fingerprint sample, take a photo to fix the display result.

[0026] This invention heats the ninhydrin development solution to at least 100°C, thereby increasing the temperature of the ninhydrin-amino acid reaction system, which in turn increases the reaction rate, shortens the development time, and improves the development efficiency of latent fingerprints. This invention integrates the soaking and heating processes, simplifying the existing "two-step" development process into a "one-step" process, significantly improving development efficiency.

[0027] In one specific embodiment, the latent fingerprint sample is immersed in a heated ninhydrin development solution for 0.1-10 seconds. This ensures sufficient contact between the amino acids in the fingerprint residue and the development solution, maintaining a continuous environment at a temperature not lower than 100°C. This improves the reaction rate, shortens the reaction time, and eliminates the need for the heating step following immersion in existing technologies, thus enhancing the latent fingerprint development efficiency. Similarly, in other embodiments, the heated ninhydrin development solution can be transferred to the latent fingerprint sample using conventional methods such as smearing, spraying, or dripping, thereby increasing the temperature of the reaction system through the transferred development solution.

[0028] In the prior art, ninhydrin development solutions are typically prepared by dissolving ninhydrin in solvents such as methanol, ethyl acetate, or hydrofluoroether (e.g., HFE7100). However, since these solvents have relatively low boiling points at normal pressure, they evaporate or decompose in large quantities when the solution temperature rises above 100°C, failing to provide a stable solution environment. Therefore, the existing technology cannot be used to achieve the rapid development method for latent fingerprints described in this invention.

[0029] Therefore, this invention provides a ninhydrin developing solution for latent fingerprints, enabling a rapid ninhydrin developing method for latent fingerprints. The developing solution comprises a color developer and a solvent. The color developer is selected from ninhydrin, used to react with amino acids in the fingerprint residue to generate Luhrmann violet, reflecting the fingerprint lines. The solvent is preferably ethyl benzoate, with a boiling point above 200°C at normal pressure. Its high boiling point ensures the developing solution remains stable at temperatures not lower than 100°C, thereby increasing the temperature of the ninhydrin-amino acid reaction system, increasing the reaction rate, and shortening the developing time. Simultaneously, ethyl benzoate has weak polarity and does not readily dissolve the latent fingerprint itself or the developed fingerprint lines, avoiding damage to the integrity of the fingerprint. In other words, the above developing solution not only shortens the developing time of latent fingerprints but also helps to ensure the developing effect.

[0030] In one specific embodiment, the mass concentration of ninhydrin in the development solution used in this invention is preferably 0.1-5.0%. The specific preparation method is as follows: dissolve 0.1-5.0 g of ninhydrin in 100 mL of ethyl benzoate to obtain the ninhydrin development solution.

[0031] The following detailed description of the latent fingerprint rapid development method and solution of the present invention, with reference to specific embodiments, is provided. Unless otherwise specified, the methods used in the following embodiments are conventional methods, performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available.

[0032] Example 1: Potential fingerprints were immersed in a 100°C developing solution for 10 seconds. The specific steps are as follows:

[0033] 1) Volunteers pressed their fingers on the printed paper for 1 second to create potential fingerprint samples;

[0034] 2) Heat a 0.5% (w / w) ethyl ninhydrin benzoate solution to 100°C;

[0035] 3) The potential fingerprint sample was immersed in the ethyl ninhydrin benzoate solution for 10 seconds;

[0036] 4) Remove and dry the fingerprint sample, then take a photo to fix the display result.

[0037] Figure 1 This is a diagram showing the development effect of a potential fingerprint in Example 1 after immersion in a 100°C ethyl ninhydrin benzoate solution for 10 seconds.

[0038] Example 2: Potential fingerprints were immersed in a 180°C ethyl ninhydrin benzoate solution for 1 second. The specific steps are as follows:

[0039] 1) Volunteers pressed their fingers on the printed paper for 1 second to create potential fingerprint samples;

[0040] 2) Heat a 0.5% (w / w) ethyl ninhydrin benzoate solution to 180°C;

[0041] 3) The potential fingerprint sample was immersed in the ethyl ninhydrin benzoate solution for 1 second;

[0042] 4) Remove and dry the fingerprint sample, then take a photo to fix the display result.

[0043] Figure 2 This is a diagram showing the development effect of a potential fingerprint in Example 2 after immersion in a 180°C ethyl ninhydrin benzoate solution for 1 second.

[0044] Example 3: Potential fingerprints were immersed in a 0.1% ninhydrin ethyl benzoate solution. The specific steps are as follows:

[0045] 1) Volunteers pressed their fingers onto printed paper to create potential fingerprint samples;

[0046] 2) Heat a 0.1% (w / w) ethyl ninhydrin benzoate solution to 140°C;

[0047] 3) The potential fingerprint sample was immersed in the ethyl ninhydrin benzoate solution for 1 second;

[0048] 4) Remove and dry the fingerprint sample, then take a photo to fix the display result.

[0049] Figure 3 This is a diagram showing the effect of immersing a potential fingerprint in a 0.1% ninhydrin ethyl benzoate solution in Example 3.

[0050] Example 4: Comparison of the prior art and the present invention in revealing latent fingerprints, the specific steps are as follows:

[0051] 1) Accurately transfer 35g of ninhydrin and dissolve it in 425mL of ethanol, then add 35mL of ethyl acetate and 40mL of glacial acetic acid in sequence to prepare ninhydrin stock solution; accurately transfer 65mL of ninhydrin stock solution and dilute it with 935mL of HFE-7100 to prepare ninhydrin working solution.

[0052] 2) Dissolve 0.5 g of ninhydrin in 100 mL of ethyl benzoate to obtain a 0.5% ninhydrin ethyl benzoate solution;

[0053] 3) Volunteers pressed their fingers on the printed paper for 1 second to create a potential handprint sample, and divided it into two equal parts along the midline of the handprint;

[0054] 4) Immerse the left half in ninhydrin working solution for 10 seconds, remove and dry it, then place it on a heating plate and treat it at 140°C for 10 seconds.

[0055] 5) Heat a 0.5% ninhydrin ethyl benzoate solution to 140°C, immerse the right half of the part in the ninhydrin ethyl benzoate solution for 1 second, remove and dry.

[0056] 6) Re-merge the left and right parts and take a picture under the same field of view to fix the display result.

[0057] Figure 4 This is a comparison diagram showing the potential handprint effect between existing technology and the present invention.

[0058] As can be seen from the above results, the ninhydrin rapid development method and solution for latent fingerprints provided by this invention simplifies the existing "two-step" development process of soaking followed by heating into a "one-step" process that integrates soaking and heating. This eliminates the need for post-processing, allowing direct determination of whether a fingerprint remains, thus improving the efficiency of latent fingerprint development and reducing the workload of forensic personnel. The method and solution of this invention shorten the latent fingerprint development time, achieving an immediate development effect of "object immersion, fingerprint appearance," with excellent development results. This further improves development efficiency and helps to quickly provide investigative clues and court evidence for personal identification.

[0059] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A rapid method for developing latent fingerprints using ninhydrin, characterized in that, Includes the following steps: 1) Heat the ninhydrin development solution to at least 100°C; 2) Immerse the potential fingerprint sample in the ninhydrin development solution; 3) Remove and dry the fingerprint sample, and take a photo to fix the display result.

2. The method for rapid development of latent fingerprints using ninhydrin according to claim 1, characterized in that, The potential fingerprint sample was immersed in the ninhydrin development solution for 0.1-10 s.

3. A ninhydrin development solution for latent fingerprints, characterized in that, The ninhydrin development solution for latent fingerprints is applied to the rapid ninhydrin development method for latent fingerprints according to any one of claims 1-2; the ninhydrin development solution for latent fingerprints comprises a developer and a solvent; the developer is selected from ninhydrin; the solvent is selected from ethyl benzoate.

4. The ninhydrin development solution for latent fingerprints according to claim 3, characterized in that, The ninhydrin mass concentration in the ninhydrin development solution of the latent fingerprint is 0.1-5.0%.

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