Fingerprint developing agent as well as developing method and application thereof

Abstract

The invention relates to the field of developing agents, in particular to a fingerprint developing agent and a developing method and application thereof. Wherein the fingerprint developing agent comprises a compound I and an organic solvent; the molecular structural formula of the compound I is I; wherein X is selected from CH3O <->,-CH3,-CH2CH3 or NO2; y is selected from CH3O <->,-CH3,-CH2CH3, NO2 or halogen; x and Y are the same or different. Compared with a traditional fingerprint display method, the compound can realize higher sensitivity and clearer imaging effect; and only protein and amino acid in fingerprints are combined to form a fluorescent product, and other substances (such as paper and the like) do not have a showing effect, so that highly selective fingerprint showing can be realized. And the method has a good application value in the actual development of the developing reagent.

Description

Technical Field

[0001] This invention relates to the field of developing agents, specifically to a fingerprint developing agent and its developing method and application. Background Technology

[0002] Fingerprints, due to their uniqueness and lifelong immutability, have become recognized in the legal field as the "king of evidence." Fingerprints present at crime scenes are usually latent; these latent fingerprints are called latent fingerprints. The discovery, development, and identification of latent fingerprints play a crucial role in solving cases and identifying criminals. Therefore, the development of latent fingerprints has become a key research focus for researchers.

[0003] Currently, latent fingerprint development technologies include ninhydrin (reacting with amino acids), silver nitrate (reacting with chlorides), DFO (fluorescence reaction), and high-vacuum metal coating (suitable for porous surfaces). Among these, ninhydrin development is the most commonly used method for developing latent sweat fingerprints on porous objects, and it is also one of the most widely used methods by grassroots public security departments. Practice has also proven that this method can effectively develop latent sweat fingerprints on paper surfaces, with high sensitivity and good development results, making it a widely adopted method by criminal technical personnel. However, it still encounters many problems in practical applications. Although the ninhydrin development method is simple to operate and easy to learn, its development effect is easily affected by external conditions such as temperature, requiring high-temperature treatment in certain weather conditions, as well as the fingerprint-bearing object, pH, and concentration of the developing solution. Achieving ideal fingerprint development results is a considerable challenge.

[0004] Currently, researchers are able to synthesize ninhydrin derivatives with different properties and application backgrounds. However, for the development of potential fingerprints, there is still a high background that is difficult to distinguish, and the synthesis cost is relatively high and the yield is relatively low, which limits the practical application and application of ninhydrin derivative-related development reagents. Summary of the Invention

[0005] To address the above problems, the present invention provides a fingerprint developer, a fingerprint development method thereon, and its application.

[0006] To achieve the above technical objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a fingerprint developer comprising compound I and an organic solvent; the molecular structural formula of said compound I is: Ⅰ: ; Wherein, X is selected from CH3O-, -CH3, -CH2CH3 or -NO2; Y is selected from CH3O-, -CH3, -CH2CH3, -NO2 or halogen; X and Y may be the same or different.

[0007] Furthermore, X is selected from CH3O-, and Y is selected from CH3O-.

[0008] Furthermore, the synthetic steps of compound I include: compound A is reacted with a Friedel-Crafts reaction to obtain compound B, and compound B is oxidized to obtain compound I. The synthetic route is as follows: ; Wherein, X is selected from CH3O-, -CH3, -CH2CH3 or -NO2; Y is selected from CH3O-, -CH3, -CH2CH3, -NO2 or halogen.

[0009] Furthermore, compound A is reacted with Friedel-Crafts to obtain compound B, wherein the solvent is dichloromethane, the catalyst is trifluoromethanesulfonic acid, and the reaction conditions are 3-5 h at room temperature.

[0010] Furthermore, the organic solvent is one or a combination of anhydrous ethanol, acetone, ethyl acetate, and Freon.

[0011] Furthermore, the organic solvent is acetone.

[0012] Furthermore, the mass-to-volume ratio of compound I to the organic solvent is (20~215):10, mg:mL.

[0013] The mass-volume ratio of compound I to the organic solvent can be 20:10, 30:10, 70:10, 100:10, 150:10, 200:10 or 215:10, etc., but is not limited to the values ​​listed above. Other unlisted values ​​within the above range are also applicable.

[0014] In one embodiment of the present invention, the mass-to-volume ratio of compound I to organic solvent is 23.8:10.

[0015] In one embodiment of the present invention, the mass-to-volume ratio of compound I to organic solvent is 71.4:10.

[0016] In one embodiment of the present invention, the mass-to-volume ratio of compound I to organic solvent is 142.8:10.

[0017] In one embodiment of the present invention, the mass-to-volume ratio of compound I to organic solvent is 214.2:10.

[0018] A second aspect of the present invention provides a method for developing a latent fingerprint, wherein the fingerprint developer described above is used for the reaction.

[0019] Furthermore, the method includes: applying developer to the sample using a cotton ball, allowing it to air dry naturally until the fingerprint is fully developed, and then taking a photograph for record-keeping; Alternatively, use a cotton ball soaked in developer to apply to the sample, set the program to 80% humidity and 80°C, and take a photo for record-keeping after the fingerprint has fully developed.

[0020] Further, the concentration of the developing agent is 0.01~1 mol / L, preferably, the concentration of the developing agent is 0.01~0.03 mol / L.

[0021] A third aspect of the present invention provides the application of the aforementioned potential fingerprint developer in fingerprint development.

[0022] The beneficial effects of this invention are as follows: The 5,6-dimethoxyninhydrin prepared in this invention can be used as a fingerprint developing agent. It is a compound with an aromatic ring structure that can chemically react with amino acids and proteins in fingerprints to form specific colors, thus making the fingerprint pattern clearly visible. Compared with traditional fingerprint developing methods, this compound achieves higher sensitivity and clearer imaging. While ninhydrin develops fingerprints in purple, the compound prepared in this invention develops fingerprints in red, making them more prominent. Furthermore, it only binds to proteins and amino acids in fingerprints to form fluorescent products, and has no effect on other substances (such as paper), achieving highly selective fingerprint development. Compared with conventional fingerprint developing agents, 5,6-dimethoxyninhydrin has lower toxicity and pollution, meeting environmental protection requirements. Attached Figure Description

[0023] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0024] Figure 1 The 5,6-dimethoxyninhydrin prepared in Example 1 of this invention 1 HNMR spectrum; Figure 2 The 5,6-dimethoxyninhydrin prepared in Example 1 of this invention 13 CNMR spectrum; Figure 3 The images show the development effects of 5,6-dimethoxyninhydrin formulations in different solvents on copy paper. A compares the development effects of formulation A (left) and formulation C (right) on copy paper; B compares the development effects of formulation A (left) and formulation B (right) on copy paper; and C compares the development effects of formulation B (left) and formulation C (right) on copy paper. Figure 4The images show the development effects of 5,6-dimethoxyninhydrin formulations in different solvents on kraft paper. A compares the development effects of formulation A (left) and formulation B (right) on kraft paper; B compares the development effects of formulation C (left) and formulation B (right) on kraft paper; C compares the development effects of formulation A (left) and formulation C (right) on kraft paper. Figure 5 The images show the display effects of 5,6-dimethoxyninhydrin formulations in different solvents on newspaper. A compares the display effects of formulation A (left) and formulation B (right) on newspaper; B compares the display effects of formulation A (left) and formulation C (right) on newspaper; C compares the display effects of formulation B (left) and formulation C (right) on newspaper. Figure 6 The images show the development effects of different concentrations of developer formulations on copy paper; where A represents the development effects of formulation a and formulation b on copy paper; B represents the development effects of formulation b and formulation d on copy paper; and C represents the development effects of formulation a and formulation b on copy paper. Figure 7 The images show the development effects of different concentrations of developer formulations on kraft paper; where A represents the development effects of formulations a and c on kraft paper; B represents the development effects of formulations b and d on kraft paper; and C represents the development effects of formulations b and a on kraft paper. Figure 8 The images show the display effects of different concentrations of developer formulations on newspapers; where A represents the display effects of formulations a and c on newspapers; B represents the display effects of formulations b and d on newspapers; and C represents the display effects of formulations a and b on newspapers. Figure 9 The development results of developer formulation b prepared in Example 2 on copy paper at different retention times; Figure 10 The development results of developer formulation a prepared in Example 2 on kraft paper at different retention times; Figure 11 The development results of developer formulation a prepared in Example 2 on newspaper at different retention times; Figure 12 The comparison of the development effects of the developer formulation prepared in Example 2 and the ninhydrin solution is shown in Figure A, which compares the development results of formulation b (left) and ninhydrin (right) on kraft paper; Figure B compares the development results of formulation b (right) and ninhydrin (left) on copy paper; and Figure C compares the development results of formulation a (right) and ninhydrin (left) on copy paper. Detailed Implementation

[0025] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0026] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0027] The main reagents used in the examples are as follows: Anhydrous ethanol was purchased from Chengdu Kelong Chemical Co., Ltd.; acetone was purchased from Chengdu Kelong Chemical Reagent Factory; ethyl acetate was purchased from Chengdu Kelong Chemical Reagent Factory; and ninhydrin was purchased from Beijing Xinghua Ruian Technology Co., Ltd.

[0028] Example 1 The synthetic route for 5,6-dimethoxyninhydrin is as follows:

[0029] S1: Add 106.11 g (0.5 mol) of 4,5-dimethoxyphenylpropionic acid to a 1 L three-necked round-bottom flask, dissolve it in 500 mL of dichloromethane, and install a reflux condenser (with a liquid seal) and a 100 mL dropping funnel. Place the flask in an ice-water bath under nitrogen purging and stir to cool. After the system stabilizes, add 66 mL (1.5 eq.) of trifluorobenzenesulfonic acid to the dropping funnel, adding slowly over approximately 20 min while maintaining nitrogen purging. React in the ice-water bath for 0.5 h, then remove the ice-water bath and allow the reaction to continue for 4 h at room temperature. After the reaction is complete, cool the system in an ice-water bath, add 100 mL of saturated sodium carbonate solution to the dropping funnel, and add slowly over approximately 20 min at low temperature. Separate the reaction mixture in the flask, wash the remaining organic phase with saturated sodium bicarbonate until no gas is produced, dry with anhydrous sodium sulfate, and concentrate to obtain a yellow oily liquid. After separation and purification by column chromatography, 61.21 g of pale yellow 4,5-dimethoxy-1-indanone was obtained, with a yield of 63.03%.

[0030] S2: In a 500°C round-bottom flask, add 19.42 g (0.1 mol) of 4,5-dimethoxy-1-indanone, 79 g (5 eq.) of N-bromosuccinimide, and 300 mL of dioxane sequentially. Attach a reflux condenser and stir the mixture at 100°C for 5 hours. After cooling to room temperature, filter the reaction mixture to remove the solvent, yielding a yellow oily liquid. Column chromatography purification yields 10.52 g of the pale yellow product 5,6-dimethoxyninhydrin, with a yield of 47.34%. The product is highly hygroscopic and must be stored in a sealed, dry container.

[0031] The reaction products exhibit high symmetry, with only three types of hydrogen atoms, none of which are adjacent or coupled. Theoretically, the proton NMR spectrum should only show three singlets. However, in the presence of water, the products combine with a water molecule to form a carboxyketone structure, complicating the proton NMR spectrum. Deuterated chloroform interferes with the hydrogen atoms in the aromatic region, while deuterated methanol further complicates the carboxyketone structure (due to its water content and participation in ketone formation). Ultimately, deuterated DMSO dried from molecular sieves was used as the solvent. After multiple analyses, a high-quality proton NMR spectrum was obtained, as shown below. Figure 1 As shown, the peak at 2.55 is the solvent peak, the peak at 3.34 is the two hydrogens on the carboxyl ketone, the peak at 3.98 is the six hydrogens on the methoxy group, and the peak at 7.40 is the two hydrogens on the benzene ring. Other impurity peaks are due to hemiketals and configurational changes, and do not indicate low sample purity. δ 3.34 (s, 2H), 3.98 (s, 6H), 7.40 (s, 2H).

[0032] Similar to 1H NMR, 1C NMR is also affected by the structure of carboxyl ketones, but to a lesser extent. Using deuterated DMSO dried from molecular sieves as the solvent, the resulting 1C NMR spectrum is as follows: Figure 2 As shown, position 56.86 represents the carbon atom of the methoxy group, position 87.90 represents the carbon atom of the carboxyl-ketone structure, position 104.30 represents the unsubstituted carbon atom on the benzene ring, position 133.88 represents the carbon atom of the benzene ring attached to the indene ring, position 156.66 represents the carbon atom of the benzene ring attached to the methoxy group, and position 196.13 represents the carbonyl group. Δ196.13, 156.66, 133.88, 104.30, 87.90, 56.86.

[0033] Example 2 Weigh out the 5,6-dimethoxyninhydrin prepared in Example 1 and prepare a development solution according to the formulation in Table 1 below.

[0034] Table 1

[0035] Note: "-" in the table indicates none.

[0036] Comparative Example 1 Dissolve 8.9 mg of ninhydrin in 5 mL of acetone to prepare a 0.01 mol / L reagent solution.

[0037] Comparative Example 2 Dissolve 26.7 mg of ninhydrin in 5 mL of acetone to prepare a 0.03 mol / L developer solution.

[0038] Experimental Example 1: Exploring the Effects of Different Solvents on Development Results Fingerprint sample preparation: (1) Three types of paper were selected as experimental samples for the development of latent handprints: photocopy paper, newspaper, and kraft paper.

[0039] (2) Cut the three types of paper into A4 paper size. Draw a line in the middle of each type of paper with a pencil to divide the paper into two parts, left and right. Draw four vertical lines in the middle of each part, at the first, second, third, and fourth quarters of the paper, to divide the paper into ten fingerprinting areas. Perform fingerprinting according to the two-part sample.

[0040] (3) Before making the sweat fingerprint samples, the maker should wash their hands with soap to remove oils and other substances that may affect the development effect. After washing, dry the hands and allow them to sweat naturally to ensure that the hands are clean and dry. Press the fingerprint 5 times from top to bottom in the standard area of ​​each sheet of paper. Pay attention to the pressure and the time the fingerprint stays on the paper to ensure that the amount of sweat in each fingerprint is roughly the same. Press 10 fingerprints on each sheet of paper. Mark the sample making time and number on the edge of the paper.

[0041] Methods for revealing latent fingerprints: The traditional development method, the wiping method, is used. A cotton swab is dipped in the prepared developer solution, and 1-2 drops are applied to the front of the latent fingerprint area of ​​the sample. Then, the swab is used to gently smear the back of the fingerprint area, ensuring the solution fully wets the paper. After allowing the sample to dry naturally, it is placed in a constant temperature incubator for 50 minutes at 80°C and 80% humidity. The fingerprint lines will then appear purple (Ruhrmann purple). The sample is then photographed and fixed under natural light.

[0042] Fingerprint evaluation methods and standards The dichotomy method was used to evaluate the fingerprint development effect. The dichotomy method is mainly suitable for comparing two development effects. The procedure involves cutting the imprinted sample into two parts along the middle, making the latent fingerprint area in both regions as similar as possible. Two different development methods are used on each part. After successful development, the two parts are joined together for easy comparison of the development effects.

[0043] The evaluation criteria for handprint quality mainly include the following aspects: Clarity: The handprint pattern is clear, and the lines are quite sharp.

[0044] Completeness: The completeness of the handprint pattern, whether there are any omissions or blurry parts.

[0045] Accuracy: The accuracy of the fingerprint pattern is based on the accuracy of fingerprint recognition.

[0046] Comparability: Comparability of handprint patterns, whether there are overlapping parts or errors.

[0047] Standardization: Does the handprint pattern conform to international standards, such as ISO / IEC 19794?

[0048] Based on the above standards, the quality of handprints can be divided into five levels as shown in Table 2.

[0049] Table 2 Fingerprint Quality Levels

[0050] The developer solutions A, B, and C prepared in Example 2 were used to develop fingerprints on three different objects: newspaper, kraft paper, and copy paper. The development effect was observed after the samples were pressed using a dichotomy method. Figures 3 to 5 The results were compared on photocopy paper, kraft paper, and newspaper.

[0051] from Figure 3 As can be seen, when formula A is used as the developing solvent, the clarity, completeness, and accuracy of the fingerprint pattern displayed on the copy paper are greater than those of formulas B and C, resulting in better development and higher comparability.

[0052] from Figure 4 It can be seen that when Formula A and Formula C are used as developing reagents, the clarity, completeness, and accuracy of the fingerprint patterns displayed on kraft paper are greater than those of Formula B; when Formula A and Formula C are used as developing reagents, the development effect is more complete and the fingerprint lines are clearer.

[0053] from Figure 5 As can be seen, when fingerprints are displayed on newspaper, the effects of formulations A, B, and C are consistent, with the fingerprint lines being basically clear and continuous, and the patterns being clear.

[0054] Based on the experimental results, acetone showed the best development effect as a solvent for developing latent fingerprints on photocopy paper; the development effects of the three solvents were roughly the same when developing fingerprints on newspaper; and acetone and ethyl acetate showed the best development effect when developing latent fingerprints on kraft paper. Therefore, anhydrous ethanol was ruled out as a solvent for the solution formulation. Acetone is less dangerous than ethyl acetate, has a higher flash point, meaning it is less flammable, less toxic, and its volatilization at room temperature is less likely to cause a fire. Considering all factors, acetone was chosen as the solvent for the 5,6-dimethoxyninhydrin formulation.

[0055] Experimental Example 2: Investigation of the Effects of Different Concentrations of Developing Solution on Developing Results The methods for preparing fingerprint samples, revealing latent fingerprints, and evaluating fingerprints, as well as the evaluation criteria, are the same as in Experiment 1.

[0056] The developer solutions a, b, c, and d prepared in Example 2 were used to develop fingerprints on three different objects: newspaper, kraft paper, and copy paper. The development effect was observed after the samples were pressed using a dichotomy method.

[0057] like Figure 6As shown, formulation a develops more clearly on copy paper than formulation c, with more detailed features. The central pattern of formulation c is somewhat blurry and may be unrecognizable. Formulation b, when used as a developing agent, exhibits complete ridge detail features, and the pattern is clearer than that of formulation d. Both formulations a and b possess complete ridge detail features, with generally clear and continuous ridges and a distinct pattern. Their development effects are consistent. However, formulation b develops fingerprints in a shorter time than formulation a. Considering the time factor, the optimal concentration for developing latent fingerprints on copy paper is 0.03 mol / L.

[0058] like Figure 7 As shown, when kraft paper is used as the developing agent, the fingerprint ridges are clearer and more continuous than those in formula a, resulting in a more complete fingerprint. When formula b is used as the developing agent, the fingerprints are clearer and more complete than those in formula d, making them easier to observe and showing more detailed features. Furthermore, the fingerprint ridges are clearer and more complete than those in formula a, making them easier to identify. Therefore, the optimal concentration for developing latent fingerprints on kraft paper is 0.03 mol / L.

[0059] like Figure 8 As shown, when newspaper is used as the developing agent, formulation a displays more detailed fingerprint features than formulation c, resulting in a more complete development effect and clearer, more continuous fingerprint ridges. Formulation b, as the developing agent, produces fingerprint patterns with higher clarity, and the central pattern is more pronounced than that of formulation d. Formulation a, as the developing agent, produces clearer, more easily identifiable fingerprint patterns with clear and continuous ridges, demonstrating a superior development effect compared to formulation b. Therefore, the optimal concentration for developing latent fingerprints on newspaper is 0.01 mol / L.

[0060] In summary, the experimental results show that when acetone is used as a solvent to develop fresh sweat latent fingerprints on copy paper and kraft paper, the optimal concentration is 0.03 mol / L, achieving a comparable and verifiable result. When developing fresh sweat latent fingerprints on newspaper, the optimal concentration is 0.01 mol / L, also achieving a comparable and verifiable result.

[0061] Experiment 3: An Investigation into the Development Results of Handprints at Different Durations The methods for preparing fingerprint samples, revealing latent fingerprints, and evaluating fingerprints, as well as the evaluation criteria, are the same as in Experiment 1.

[0062] Formula b was selected as the developing agent for copy paper and kraft paper, and formula a was selected as the developing agent for newspaper. The fingerprints of different retention times and different objects were developed, and the quality of the developing effect was analyzed.

[0063] The results are as follows Figures 9 to 11As shown, with increasing time, the amount of sweat in latent fingerprints on the object gradually decreases. Over time, the development effect on any material—copier paper, kraft paper, or newspaper—gradually deteriorates, resulting in blurred fingerprint lines, incomplete fingerprints, and unclear details. The 5,6-dimethoxyninhydrin development method shows significant results when developing latent fingerprints on copier paper left more than 10 days prior, and the developed fingerprints are valuable for analysis. Similarly, the 5,6-dimethoxyninhydrin development method shows significant results when developing latent fingerprints on newspapers and kraft paper left more than 3 days prior, and the developed fingerprints are also valuable for analysis.

[0064] Test Example 4 The methods for preparing fingerprint samples, revealing latent fingerprints, and evaluating fingerprints, as well as the evaluation criteria, are the same as in Experiment 1.

[0065] The developing agent prepared in Comparative Example 1 and the developing agent solution prepared in Formula a in Example 1 were compared on newspaper to develop fresh sweat, and the difference in the developing effect between the two was observed.

[0066] The developer prepared in Comparative Example 2 and the developer solution prepared in Formula b in Example 1 were compared on copy paper and kraft paper to develop fresh sweat. The difference in the development effect between the two was observed, and the results are shown in Table 3.

[0067] Table 3

[0068] Combination Figure 12 It can be seen that for fresh fingerprints on kraft paper, both 5,6-dimethoxyninhydrin and ninhydrin produce clear fingerprint lines, prominent details, and good fingerprint integrity, making them identifiable. However, 5,6-dimethoxyninhydrin exhibits better integrity, with more and clearer details. For fresh fingerprints on copy paper, both 5,6-dimethoxyninhydrin and ninhydrin produce fingerprint patterns with high clarity and integrity, making them highly comparable; the fingerprint rendering effects of both are roughly the same, with similar rendering quality. For fresh fingerprints on newspaper, both 5,6-dimethoxyninhydrin and ninhydrin produce relatively high clarity, good integrity, and high accuracy; however, the fingerprint lines of ninhydrin are clearer, more complete, and easier to observe than those of 5,6-dimethoxyninhydrin. In conclusion, 5,6-dimethoxyninhydrin and ninhydrin have their own advantages and disadvantages in rendering effects on different objects.

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A fingerprint developing agent characterized by comprising: The compound I and an organic solvent are included; the molecular structural formula of the compound I is: ； X is selected from CH3O-, -CH3, -CH2CH3 or -NO2; Y is selected from CH3O-, -CH3, -CH2CH3, -NO2 or halogen; X is the same as or different from Y.

2. The fingerprint developer according to claim 1, wherein X is selected from CH3O-, and Y is selected from CH3O-.

3. The fingerprint developer according to claim 1, wherein The synthesis steps of the compound I include: compound A is obtained through a Friedel-Crafts reaction to obtain compound B, and compound B is obtained through oxidation to obtain compound I, and the synthesis route is as follows: ； X and Y are as defined in claim 1.

4. The fingerprint developer according to claim 3, wherein Compound A is obtained through a Friedel-Crafts reaction to obtain compound B, wherein the solvent is dichloromethane, the catalyst is trifluoromethanesulfonic acid, and the reaction condition is normal temperature for 3-5 hours.

5. The fingerprint developer according to claim 1, wherein The organic solvent is one or a combination of anhydrous ethanol, acetone, ethyl acetate and freon.

6. The fingerprint developer according to claim 5, wherein The organic solvent is acetone.

7. The fingerprint developer according to claim 1, wherein The mass-volume ratio of the compound I to the organic solvent is (20-215):10, mg:mL.

8. A method of developing latent fingerprints, characterized by, The reaction is carried out by using the fingerprint developing agent in any one of claims 1-7.

9. The rendering method of claim 8, wherein, The developing agent is dipped on the sample by using absorbent cotton, and is naturally air-dried until the fingerprint is completely developed and then is photographed and filed; Or, the developing agent is dipped on the sample by using absorbent cotton, and is set to be 80% humidity and 80℃ temperature until the fingerprint is completely developed and then is photographed and filed.

10. The fingerprint developing agent in any one of claims 1-7 is applied in fingerprint development.

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