BODIPY dye, its preparation method, and its application in latent fingerprint recognition.

Abstract

This invention discloses BODIPY dyes, their preparation methods, and their applications in latent fingerprint recognition. The invention prepares four BODIPY dyes with different structures and emission colors, all exhibiting high fluorescence quantum yields (over 55% absolute fluorescence quantum yield) and excellent lipophilicity. Using a spray method, latent fingerprints on different substrates can be efficiently and conveniently detected within 10 seconds. Furthermore, the detection solution demonstrates excellent stability, can be stored for up to 30 days, and achieves a color change from green to red through modulation. This modulation effectively addresses complex background colors, ensuring optimal latent fingerprint detection results under various color backgrounds.

Description

Technical Field

[0001] This invention belongs to the field of detection technology, specifically relating to BODIPY dyes, their preparation methods, and latent fingerprint recognition applications. Background Technology

[0002] Fingerprints are part of the skin, formed by protrusions from the dermis into the epidermis. Latent fingerprints refer to the tiny traces left by the skin when it comes into contact with a surface. Fingerprints can be used not only for identification but also as important evidence in court. Traditional fingerprint detection methods, such as powder blowing, chemical fumigation, multi-metal deposition, and fluorescent staining, are generally unreliable and environmentally polluting, making them unsuitable for practical applications. In contrast, spraying is widely used in practice because it is not limited by the shape of the substrate material and does not directly contact the fingerprint. It has advantages such as simplicity, speed, high sensitivity, economy, and large-area operation, and is considered one of the most promising methods for latent fingerprint detection.

[0003] The raw materials used in spray fingerprinting are mostly organic fluorescent dyes. Organic fluorescent dyes are widely used in latent fingerprint detection due to their good chemical stability, excellent luminescence properties, and ease of detection. Therefore, developing efficient, rapid, and universally applicable organic fluorescent dyes as latent fingerprint developing agents is particularly necessary. BODIPY dyes, with their high fluorescence quantum yield, narrow absorption and emission spectra, good chemical and photostability, and abundant modification sites, have outstanding advantages among many dyes. In recent years, BODIPY has been widely used in detection, imaging, photodynamic therapy, and photothermal therapy. Due to its excellent lipophilicity, BODIPY dyes have good affinity for fingerprint residues, making them a subject of extensive research in the field of fingerprint detection.

[0004] Traditional latent fingerprint detection molecules have a single color, their structure is difficult to change, and their properties are hard to improve significantly. In contrast, BODIPY dyes have more modification sites, and their photophysical properties can be easily adjusted by modifying organic groups. The Knoevenagel condensation reaction between the BODIPY core and aromatic aldehydes is one of the effective methods to extend the conjugated structure of BODIPY, which can then enable gradient changes in emission color to better cope with complex background colors. Summary of the Invention

[0005] This invention provides BODIPY dye, its preparation method, and its application in latent fingerprint recognition. The prepared BODIPY dye has a high fluorescence quantum yield and excellent lipophilicity. It can achieve efficient and convenient detection of latent fingerprints on different substrates within 10 seconds using a spray method. Moreover, the color is adjustable, and it can achieve the best latent fingerprint detection effect under different colored backgrounds.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] Four BODIPY dyes, exhibiting high fluorescence yields with different luminescent colors, were named BDP-G, BDP-Y, BDP-O, and BDP-R, with the following chemical structures:

[0008]

[0009] The preparation methods for the above four types of BODIPY dyes include the following steps:

[0010] (1) Dissolve 2,4-dimethylpyrrole and 4-hydroxybenzaldehyde in tetrahydrofuran in a reaction flask, keep the reaction system oxygen-free, then add a few drops of TFA (trifluoroacetic acid) and stir overnight, then add DDQ (2,3-dichloro-5,6-dicyanobenzoquinone), and stir at room temperature for 5 hours. Add triethylamine dropwise to the solution, then stir at room temperature for 30 minutes, then cool the reaction mixture in an ice bath, add boron trifluoride-diethyl ether solution dropwise, and stir the reaction mixture at room temperature for 12 hours to obtain BDP-G;

[0011] (2) Dissolve BDP-G, benzaldehyde, glacial acetic acid and piperidine in toluene and reflux for 12 h. Use a Dean-Stark apparatus to remove water formed during the reaction by azeotropic reaction. Concentrate the mixture under reduced pressure to obtain BDP-Y.

[0012] (3) Dissolve BDP-G, 4-methoxybenzaldehyde, glacial acetic acid and piperidine in toluene and reflux for 12 h. Use a Dean-Stark apparatus to remove water formed during the reaction by azeotropic reaction. Concentrate the mixture under reduced pressure to obtain BDP-O.

[0013] (4) Dissolve BDP-G, 4-(N,N-diphenylamino)benzaldehyde, glacial acetic acid and piperidine in toluene and reflux for 12 h. Use a Dean-Stark apparatus to remove water formed during the reaction by azeotropic reaction. Concentrate the mixture under reduced pressure to obtain BDP-R.

[0014] In the steps described above, the oxygen-free reaction system is specifically carried out under a nitrogen atmosphere;

[0015] In step (1), the molar ratio of 2,4-dimethylpyrrole to 4-hydroxybenzaldehyde is 2.5:1; the molar ratio of DDQ to 4-hydroxybenzaldehyde is 1.1:1; the molar ratio of triethylamine to 4-hydroxybenzaldehyde is 5-10:1; the molar ratio of boron trifluoride-ethyl ether solution to 4-hydroxybenzaldehyde is 10-20:1; and the TFA is added slowly under dark and light-protected conditions, with an added volume of 0.1 ml.

[0016] The mixing method of 2,4-dimethylpyrrole and 4-hydroxybenzaldehyde is as follows: first, 4-hydroxybenzaldehyde is dissolved in THF in a round-bottom flask, and the reaction flask is kept in an argon atmosphere. Then, 2,4-dimethylpyrrole is added to the reaction flask while continuously stirring.

[0017] The DDQ solution in THF should be added slowly dropwise and completed within one hour; the boron trifluoride-ethyl ether solution should be added dropwise in an ice-water bath.

[0018] In steps (2), (3), and (4), the molar ratio of BDP-G to benzaldehyde, 4-methoxybenzaldehyde, and 4-(N,N-diphenylamino)benzaldehyde is 1:1.

[0019] The volume ratio of glacial acetic acid and piperidine in steps (2), (3), and (4) is 1:1.

[0020] All four of the above-mentioned BODIPY dyes can be used in latent fingerprint detection.

[0021] Beneficial effects: This invention provides BODIPY dye, its preparation method, and its application in latent fingerprint recognition, which has the following advantages compared with existing technologies:

[0022] 1. The method for synthesizing the BODIPY dye prepared by this invention is simple, the raw materials are readily available, and the purification process is convenient and easy to operate;

[0023] 2. The four BODIPY dyes prepared in this invention have high quantum yields, with all four dyes exceeding 55% absolute fluorescence quantum yield.

[0024] 3. The BODIPY dye prepared by this invention can efficiently and conveniently detect latent fingerprints on different substrates (tin foil, coins, glass, cardboard, desktop, steel) within 10 seconds by spraying in a low-concentration (10 μM) detection solution. The detection solution has excellent stability and can be stored for up to 30 days.

[0025] 4. The four BODIPY dyes prepared in this invention achieve color regulation from green to red. This regulation can effectively cope with complex background colors and ensure that the best latent fingerprint detection effect can be achieved under different colored backgrounds. This will greatly improve the work efficiency of investigators and significantly increase the success rate of case resolution. Attached Figure Description

[0026] Figure 1 The following are structural diagrams of four BODIPY dyes in embodiments of the present invention;

[0027] Figure 2 This is a flowchart illustrating the preparation process of BODIPY dye in an embodiment of the present invention;

[0028] Figure 3 This is a diagram showing the latent fingerprint detection effect of four BODIPY dyes on tin foil and the grayscale value variation within yellow or blue in this embodiment of the invention.

[0029] Figure 4 These are latent fingerprint detection results of four BODIPY dyes on different substrate materials in embodiments of the present invention;

[0030] Figure 5 The following are examples of the embodiments of the present invention: (a) the state and detection effect of the BDP-G detection solution after 30 days of storage and fluorescence change graph; (b) the state and detection effect of the BDP-G detection solution after 30 minutes of irradiation with an 80W 365nm ultraviolet lamp and fluorescence change graph.

[0031] Figure 6 In this embodiment of the invention, (a) BDP-G was used to detect latent fingerprints on tin foil and the fingerprints were placed in a natural space for 1 day, 15 days and 30 days, and the gray value changes within the yellow line were shown. (b) Three fresh fingerprints were made on tin foil and placed in a drawer to obtain latent fingerprints aged for 1 day, 4 days and 7 days. The latent fingerprint effect and gray value changes within the yellow line were detected using BDP-G detection solution.

[0032] Figure 7 The following are examples of the fingerprint detection results in this invention: (a) using BDP-O to detect latent fingerprints on glass and placing it on aluminum foil of different colors (green, blue, red, orange); (b) comparing the results of BDP-G and BDP-R on detecting latent fingerprints on a 50-yuan note; and (c) comparing the results of BDP-G and BDP-R on detecting latent fingerprints on a 100-yuan note. Detailed Implementation

[0033] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments: Example 1

[0034] The preparation method of BDP-G includes the following steps:

[0035] In a 500 mL round-bottom flask, 1.94 g (20.47 mmol) of 2,4-dimethylpyrrole and 150 mL of THF were added, and the mixture was degassed with argon for 30 minutes. Then, 1.00 g (8.19 mmol) of 4-hydroxybenzaldehyde was added, and the mixture was purged with argon again for 30 minutes. 0.1 mL of TFA was then added and stirred overnight. DDQ (2.08 g, 9.171 mmol) was dissolved in 10 mL of THF and added dropwise over 1 hour, with stirring at room temperature for 5 hours. The color changed from orange to deep red, then to black. Triethylamine (8.5 mL, 61.13 mmol) was added dropwise to this solution over 40 minutes, with stirring at room temperature for 30 minutes. The reaction mixture was then cooled in an ice bath, and a boron trifluoride-diethyl ether solution (17.3 mL, 137.33 mmol) was added dropwise. The reaction mixture was stirred at room temperature for 12 hours, and THF was removed under reduced pressure. The crude product was dissolved in dichloromethane and treated with 0.5 M... The sample was washed with NaHCO3 solution, then washed several times with water. The organic solvent was dried on Na2SO4 and evaporated to dryness. BDP-G was obtained by silica gel column chromatography with ethyl acetate:n-hexane (1:4) as the eluent. Example 2

[0036] The preparation method of BDP-Y includes the following steps:

[0037] A mixture of BDP-G (0.30 g, 0.88 mmol), benzaldehyde (0.09 g, 0.88 mmol), glacial acetic acid (0.6 mL), and piperidine (0.6 mL) in toluene (60 mL) was refluxed for 12 h. Water formed during the reaction was removed by azeotropic extraction using a Dean-Stark apparatus. The mixture was concentrated under reduced pressure, washed three times with distilled water, extracted with ethyl acetate, dried over anhydrous sodium sulfate, filtered, and the solvent was removed by reduced pressure distillation to obtain the crude product. The crude product was purified by column chromatography using ethyl acetate / n-hexane (1:4) as the eluent. The residue was subjected to silica gel column chromatography, and the pink fraction was collected. The solvent was removed under reduced pressure to obtain the pink solid product BDP-Y. Example 3

[0038] The preparation method of BDP-O includes the following steps:

[0039] A mixture of BDP-G (0.30 g, 0.88 mmol), 4-methoxybenzaldehyde (0.12 g, 0.88 mmol), glacial acetic acid (0.6 mL), and piperidine (0.6 mL) in toluene (60 mL) was refluxed for 12 h. Water formed during the reaction was removed by azeotropic extraction using a Dean-Stark apparatus. The mixture was concentrated under reduced pressure, washed three times with distilled water, extracted with ethyl acetate, dried over anhydrous sodium sulfate, filtered, purified by column chromatography, concentrated under reduced pressure, and subjected to silica gel column chromatography with ethyl acetate / n-hexane (1:4) as the eluent. The pink fraction was collected, and the solvent was removed under reduced pressure to obtain the pink solid product BDP-O. Example 4

[0040] The preparation method of BDP-R includes the following steps:

[0041] A toluene solution (60 mL) of BDP-G (0.30 g, 0.88 mmol), 4-(N,N-diphenylamino)benzaldehyde (0.24 g, 0.88 mmol), glacial acetic acid (0.6 mL), and piperidine (0.6 mL) was refluxed for 12 h. Water formed during the reaction was removed by azeotropic extraction using a Dean-Stark apparatus. The mixture was concentrated under reduced pressure, washed three times with distilled water, extracted with ethyl acetate, dried over anhydrous sodium sulfate, filtered, purified by column chromatography, concentrated under reduced pressure, and subjected to silica gel column chromatography with ethyl acetate / n-hexane (1:7) as the eluent. The red fraction was collected, and the solvent was removed under reduced pressure to obtain the black solid product BDP-R.

[0042] The NMR data are as follows:

[0043] BDP-G: 1 H NMR (400 MHz, DMSO- d 6) δ 9.90 (s, 1H), 7.08 (d, J = 8.5 Hz, 2H), 6.93 (d, J = 8.5 Hz, 2H), 6.14 (s, 2H), 2.44 (s, 6H), 1.42 (s, 6H). 13 C NMR (101 MHz, DMSO) δ158.63,154.90,143.23,143.20,131.68,29.40,124.70,121.61,116.52,14.63, 14.59.

[0044] BDP-Y: 1 H NMR (400 MHz, DMSO- d6) δ 9.89 (s, 1H), 7.59 (d, J = 8.6 Hz,2H), 7.51 (s, 2H), 7.45 (t, J = 8.0 Hz, 2H), 7.40 – 7.34 (m, 1H), 7.14 (d, J =8.5 Hz, 2H), 6.94 (d, J = 8.5 Hz, 2H), 6.92 (s, 1H), 6.20 (s, 1H), 2.49 (s,3H), 1.49 (s, 3H), 1.45 (s, 3H). 13 C NMR (101 MHz, DMSO) δ 158.66,155.38,151.95,143.37,142.59,142.08, 136.65,136.57,133.01,132.30,129.64,129.58,127.47,124.73,122.01,118.68,118.33, 116.52,14.83,14.68.

[0045] BDP-O: 1 H NMR (400 MHz, DMSO-d6) δ 9.85 (s, 1H), 7.58 – 7.51 (m, 2H),7.48 (s, 1H), 7.35 (d, J = 16.4 Hz, 1H), 7.14 (d, J = 8.5 Hz, 2H), 7.03 (d, J= 8.8 Hz, 2H), 6.94 (d, J = 8.5 Hz, 2H), 6.89 (s, 1H), 6.17 (s, 1H), 3.81 (s,3H), 2.48 (s, 3H), 1.49 (s, 3H), 1.44 (s, 3H). 13 C NMR (101 MHz, DMSO) δ160.82, 158.61, 154.12, 153.04, 142.87, 142.39, 141.43, 137.06, 133.08,131.93, 129.70, 129.21, 124.85, 121.55, 118.30, 116.48, 116.33, 115.14,56.50, 55.79, 19.02, 14.88, 14.76, 14.61.

[0046] BDP-R:1 H NMR (400 MHz, DMSO- d 6) δ 9.86 (s, 1H), 7.47 (d, J = 8.8 Hz,3H), 7.38 – 7.31 (m, 6H), 7.14 – 7.07 (m, 9H), 6.99 – 6.88 (m, 7H), 6.16 (s,1H), 2.46 (s, 3H), 1.48 (s, 4H), 1.43 (s, 3H). 13 C NMR (101 MHz, DMSO) δ158.60, 153.99, 153.03, 148.80, 146.98, 142.83, 142.24, 141.22, 136.93,133.19, 131.94, 130.19, 130.05, 129.70, 128.94, 125.39, 125.31, 124.87,124.44, 122.40, 121.50, 118.45, 116.48, 14.87, 14.76, 14.61.

[0047] Test Example 1

[0048] The four BODIPY dyes prepared above were used to detect latent fingerprints on tin foil. The specific experimental steps are as follows:

[0049] Different volunteers were invited to wash their hands, gently touch their foreheads with their fingers, and then lightly press their fingers onto aluminum foil to leave fingerprints. A 1x10 solution containing 60% water was then prepared. -5 M ethanol solution is used as the detection solution; 0.5 ml of the four detection reagents are placed into the spray tank of the purchased (KF-WHQ-601B) device, the start button is pressed, and the latent fingerprint is sprayed for detection. Then, a 365nm ultraviolet lamp is used for irradiation. A clear latent fingerprint development effect can be observed within 10 seconds, and the secondary structure (forks, encirclement, endpoint) and tertiary structure (pores, scratches, edges) of the latent fingerprint can be clearly seen. Figure 3As shown, the gray values ​​within the yellow or blue lines were measured. These latent fingerprints exhibited good fluorescence contrast. The minimum gray value was denoted as G0. G / G0 serves as an important parameter for analyzing image resolution. A significant difference between the maximum and minimum gray values ​​indicates that the captured latent fingerprint image has excellent resolution. Notably, BDP-O and BDP-R were used to detect latent fingerprints from female volunteers on tin foil. Due to the slenderness of women's fingers and their greater susceptibility to various cosmetics, it is difficult to detect tertiary structures in practical applications. However, the four BODIPY dyes prepared above successfully detected tertiary structures, indicating that the four BODIPY dyes prepared above have strong practicality.

[0050] Test Example 2

[0051] Latent fingerprints on different substrates were detected using four types of BODIPY dyes. The specific experimental steps are as follows:

[0052] Different volunteers washed their hands, gently touched their foreheads with their fingers, and then pressed their fingers lightly on different surfaces to leave fingerprints. Latent fingerprint detection was performed on aluminum foil, coins, glass, cardboard, tabletops, and steel surfaces. Figure 4 As shown, these test reagents can clearly reveal latent fingerprints on different substrates.

[0053] Test Example 3

[0054] The stability of the BDP-G detection solution was tested by placing it under light and then exposing it to light. The specific test steps are as follows:

[0055] The prepared BDP-G detection solution was stored for one month and then used for latent fingerprint detection to determine the stability of the detection solution. Figure 5 As shown in (a), the test reagent stored for one month did not show obvious precipitation, and there was no significant difference in fluorescence intensity. Furthermore, the solution clearly detected the tertiary structure of the fingerprint, indicating that the test solution can maintain stability over a long period. The photostability of the BDP-G test solution was also tested; after continuous irradiation with an 80 W UV lamp for 30 minutes, as shown... Figure 5 As shown in (b), no obvious fluorescence decay was observed, and the fluorescence intensity remained almost constant. The tertiary structure of the latent fingerprint could still be effectively detected by continuing to use the solvent, indicating that the detection solution has good photostability.

[0056] Test Example 4

[0057] The stability of BDP-G detection molecules and the detection effect of aged fingerprints were determined by aging fingerprint analysis. The specific test steps are as follows:

[0058] BDP-G detection solution was used to detect latent fingerprints on aluminum foil, and the detected latent fingerprints were placed in a natural environment for 1 day, 15 days, and 30 days. Figure 6 As shown in (a), a clear fingerprint image can still be obtained, and it is almost identical. By measuring the gray value within the yellow line, it was found that the gray value still showed obvious fluorescence signal changes after 30 days. This also indicates that the detection molecule has excellent stability.

[0059] Volunteers created three fresh fingerprints on tin foil and placed them in a drawer to obtain latent fingerprints after aging for 1 day, 4 days, and 7 days, respectively. These latent fingerprints were then tested using BDP-G. Figure 6 As shown in (b), clear fingerprint images were obtained in both cases, and the gray values ​​within the yellow lines were measured. Significant changes in fluorescence signals were also observed, which means that the detection molecules still have a good detection effect on aged fingerprints.

[0060] Test Example 5

[0061] The detection effect was measured by examining fingerprints on glass against different colored backgrounds. The specific testing steps are as follows:

[0062] After immersing the glass in an ethanol solution and allowing it to air dry, volunteers washed their hands and gently touched their foreheads with their fingers. They then pressed their fingers lightly onto the glass surface. Using BDP-O as an example, the latent fingerprints on the glass surface were detected, easily obtaining the characteristics of its tertiary structure. Subsequently, different colored tin foils were placed behind the glass substrate to simulate different background colors. Figure 7 As shown in (a), the tertiary structure of orange latent fingerprints is more clearly visible against green and blue backgrounds, while against red and orange backgrounds, although the tertiary structure is still visible, it is not as clear as against green and blue backgrounds.

[0063] Volunteers left their fingerprints against a red background of a 100-yuan note. Using red and green testing reagents for latent fingerprint detection, a significant difference in detection results was observed. Similarly, fingerprints were detected against a green background of a 50-yuan note. Figure 7 As shown in (b), the green detection reagent is far less effective than the red detection reagent. Detection reagents with high-contrast colors can more effectively cope with the challenges of different background colors, and also verify that the four detection molecules synthesized above have high practicality.

[0064] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A BODIPY dye, characterized in that, There are three types of BODIPY dyes, named BDP-Y, BDP-O, and BDP-R, with the following chemical structures: 。 2. The method for preparing the BODIPY dye according to claim 1, characterized in that, Includes the following steps: 2,4-Dimethylpyrrole and 4-hydroxybenzaldehyde were dissolved in tetrahydrofuran. The reaction system was kept anaerobic. 0.1 ml of trifluoroacetic acid was added and the mixture was stirred overnight. Then, 2,3-dichloro-5,6-dicyanobenzoquinone was added and stirred at room temperature for 5 hours. Triethylamine was added dropwise to the solution, and the mixture was stirred at room temperature for 30 minutes. The reaction mixture was cooled in an ice bath, and a boron trifluoride-diethyl ether solution was added dropwise. The reaction mixture was stirred at room temperature for 12 hours to obtain BDP-G. The structural formula of BDP-G is: ； BDP-G, benzaldehyde, glacial acetic acid, and piperidine were dissolved in toluene and refluxed for 12 h. Water formed during the reaction was removed using an azeotropic apparatus in a Dean-Stark system. The mixture was then concentrated under reduced pressure to obtain BDP-Y. BDP-G, 4-methoxybenzaldehyde, glacial acetic acid, and piperidine were dissolved in toluene and refluxed for 12 h. Water formed during the reaction was removed using an azeotropic apparatus in a Dean-Stark system. The mixture was then concentrated under reduced pressure to obtain BDP-O. BDP-G, 4-(N,N-diphenylamino)benzaldehyde, glacial acetic acid, and piperidine were dissolved in toluene and refluxed for 12 h. Water formed during the reaction was removed using an azeotropic apparatus in a Dean-Stark system. The mixture was then concentrated under reduced pressure to obtain BDP-R.

3. The method for preparing BODIPY dye according to claim 2, characterized in that, The reaction system is oxygen-free and is carried out under a nitrogen atmosphere.

4. The method for preparing BODIPY dye according to claim 2, characterized in that, The molar ratio of 2,4-dimethylpyrrole to 4-hydroxybenzaldehyde is 2.5:1; the molar ratio of 2,3-dichloro-5,6-dicyanobenzoquinone to 4-hydroxybenzaldehyde is 1.1:1; the molar ratio of triethylamine to 4-hydroxybenzaldehyde is 5-10:1; and the molar ratio of boron trifluoride-diethyl ether solution to 4-hydroxybenzaldehyde is 10-20:

1.

5. The method for preparing BODIPY dye according to claim 2 or 3, characterized in that, The trifluoroacetic acid was added in the dark, protected from light, at a volume of 0.1 ml.

6. The method for preparing BODIPY dye according to claim 2 or 4, characterized in that, The mixing method of 2,4-dimethylpyrrole and 4-hydroxybenzaldehyde is as follows: first, 4-hydroxybenzaldehyde is dissolved in tetrahydrofuran in a round-bottom flask, and the reaction flask is kept in an argon atmosphere. Then, 2,4-dimethylpyrrole is added to the reaction flask while continuously stirring.

7. The method for preparing BODIPY dye according to claim 2 or 4, characterized in that, The 2,3-dichloro-5,6-dicyanobenzoquinone was dissolved in tetrahydrofuran and added dropwise over one hour.

8. The method for preparing BODIPY dye according to claim 2, characterized in that, The molar ratio of BDP-G to benzaldehyde, 4-methoxybenzaldehyde, and 4-(N,N-diphenylamino)benzaldehyde is 1:1; the volume ratio of glacial acetic acid to piperidine is 1:

1.

9. The application of the BODIPY dye according to claim 1 in latent fingerprint detection.

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