Latent fingerprint fluorescence visualization identification probe and method on substrate

Abstract

The present invention belongs to the field of fingerprint identification technology, specifically a fluorescent visualization identification probe and method for latent fingerprints on a substrate. The fluorescent probe of the present invention is a clamp-type Zn (II) metal organic complex, with 2,2':6',2''-terpyridine or 2,6-diimidazolylpyridine as the framework, and different substituents are introduced at the 4' position; the fluorescent probe can perform fluorescent visualization identification on latent fingerprints on different substrate surfaces, specifically immersing the substrate with fingerprints in the probe solution or spraying the probe aqueous solution uniformly on the substrate surface, and under 365nm ultraviolet light excitation, clear and bright fingerprint lines and detailed features can be observed, which is suitable for fingerprint color development identification. The fluorescent probe of the present invention can emit fluorescence of different colors by changing the substituent group in the pure water phase, adjusting the fluorescence emission wavelength to be located in different visible light regions, and overcoming the interference of the color development substrate's own fluorescence; the probe is simple to synthesize, low in cost, low in toxicity, and environmentally friendly.

Description

Technical Field

[0001] The invention belongs to the technical field of fingerprint identification, and in particular relates to a latent fingerprint fluorescence visualization identification probe and method. Background Art

[0002] Fingerprints are unique characteristics of individuals and will not change throughout a person's life. The information characteristics contained in fingerprints can be used as a personal "identity card" and "information library", and are very important evidence in criminal cases. Fingerprints are formed by the material left after the finger touches an object. They are mainly divided into three categories: visible fingerprints, plastic fingerprints, and latent fingerprints. Among them, latent fingerprints are the most common type at the crime scene, but they are difficult to observe directly with the naked eye, so the development of technology to reveal such fingerprints has become a research hotspot. At present, the conventional color development methods for latent fingerprints include powder spraying, fumigation, and chemical methods. The powder spraying method is currently the simplest and most commonly used method, but it is easy to damage fingerprint details during the powder spraying process; the color development reagents used in the fumigation method and chemical method, such as iodine, silver nitrate, ninhydrin and other chemical reagents, may cause damage to the skin, eyes, mucous membranes or DNA. At the same time, the fluorescent color of many latent fingerprint color development reagents is similar to the fluorescent color of the substrate itself, which reduces the contrast and resolution. These traditional methods all have the disadvantages of low contrast, low sensitivity, poor selectivity, strong background interference, and high toxicity.

[0003] In recent years, molecular fluorescence sensors have made a lot of progress in the rapid, real-time and highly sensitive identification of guest molecules and fluorescence imaging. Fluorescence visualization identification can be performed through strategies such as fluorescence enhancement / quenching and ratio change to improve the sensitivity of identification. At the same time, the instruments and equipment involved in the fluorescence method are easy to operate and take a short time, which further improves the efficiency of molecular identification. Therefore, the field of latent fingerprint visualization identification using molecular fluorescence sensors has developed rapidly. However, traditional fluorescent molecules have an aggregation-induced quenching effect (ACQ effect). When combined with latent fingerprints, the degree of molecular aggregation increases, which may lead to fluorescence quenching, greatly limiting the application of such molecular fluorescent probes in latent fingerprint color development.

[0004] At present, many types of compounds are used in the field of latent fingerprint recognition, such as tetraphenylethylene molecules, quantum dots and gold nanoparticles with aggregation-induced emission (AIE effect). Among the above methods, the following problems still exist: 1. The fluorescence color of the fingerprint outline is close to the substrate's own fluorescence color, which reduces the contrast of the fingerprint color development and causes large background interference; 2. The color development process mostly requires organic solvents, which are environmentally unfriendly and easily damage the latent fingerprint; 3. The synthesis process of the probe is relatively complicated and the stability of the nanoparticles is poor. Therefore, it is a research hotspot to develop a latent fingerprint fluorescent visualization recognition probe that is easy to synthesize, low in price, has a clear fluorescence color from the substrate background's own fluorescence color, and uses pure water solvent.

[0005] Tweezer metal organic complexes have excellent fluorescence properties and modifiability, and are widely used in the fields of bioimaging, chemistry, and materials science. For example, terpyridine Zn(II) metal organic complexes are used in the field of fluorescent visualization of biological molecules such as ATP and ADP (see ACS Appl. Mater. Interfaces 2016, 8, 20583-20590), while there are few reports on the fluorescent visualization of latent fingerprints by such molecules.

[0006] The present invention uses 2,2':6',2"-terpyridine or 2,6-diimidazolylpyridine as a framework, introduces different functional substituent groups at the para position of the intermediate pyridine nitrogen, and endows it with the ability to recognize special units. A series of clamp-type Zn(II) metal organic complexes are designed and synthesized, and latent fingerprints on different substrate surfaces are developed. Summary of the invention

[0007] The purpose of the present invention is to provide a probe and method for fluorescent visualization identification of latent fingerprints on different substrates, wherein the fingerprint lines and detailed features obtained by the visualization are clear, bright and stable.

[0008] The latent fingerprint fluorescent visualization identification probe on the substrate provided by the present invention is a clamp-type Zn (II) metal organic complex, and its structural formula is shown in the following (I) or (II):

[0009]

[0010] Here, the compound represented by the structural formula (I) is 2,2':6',2"-terpyridine, and the compound represented by the structural formula (II) is 2,6-diimidazolylpyridine. Different substituents R are added to the para position of the pyridine nitrogen in the middle of them to obtain the corresponding pincer-type Zn(II) metal organic complex; wherein X, Y, Z, and E are alkoxy chains containing 1 to 16 carbon atoms; and L is different anions, including OAc. - , Cl - 、NO3 - 、SO4 2- 、BF4 - PF6 - ,OTf - . n is the number of benzene rings, which is 0-3, and preferably n is 1-3.

[0011] In the present invention, a substituent R with different characteristics is introduced at the para position of the intermediate pyridine nitrogen, such as a substituent R with AIE characteristics and an electron induction effect, so that the fluorescence properties of the entire molecule can be comprehensively adjusted. For example, as the electron donating ability of the substituent R increases, the fingerprint profile fluorescence color displayed by the probe provided by the present invention gradually shifts to the red; the solubility of the molecule can be further adjusted by adjusting the type of the metal ligand ion L. For example, when the types of L are different, the probe provided by the present invention has different water solubilities; when L=OAc - It is best soluble in water.

[0012] The fluorescent probe provided by the present invention can emit fluorescence of different colors by changing the substituent group R in a pure water phase, and the fluorescence emission wavelength can be adjusted to be located in different visible light regions, thereby overcoming the fluorescence interference of the color development substrate itself.

[0013] The present invention also provides a method for preparing the above-mentioned probe for fluorescent visualization identification of latent fingerprints on the substrate, namely, a clamp-type Zn (II) metal organic complex, comprising:

[0014] (I) The composition of the probe based on 2,2':6',2"-terpyridine framework;

[0015] (ii) Synthesis of probes based on 2,6-diimidazolylpyridine;

[0016] The specific steps are as follows:

[0017] (I) Synthesis of a probe based on 2,2':6',2"-terpyridine, the specific steps are as follows:

[0018] Step 1a: Synthesis of starting disubstituted amine

[0019]

[0020] Wherein, X=F, Cl, Br; Y and Z are alkoxy chains containing 1-16 carbon atoms.

[0021] In a 10 mL Schlenk tube, a halogenated benzene derivative (4 mmol), substituted aniline (6 mmol), potassium tert-butoxide (6 mmol), 10 mg [Pd] catalyst, and 5 mL toluene were added and reacted at 80° C. for 12 h. After the reaction, the disubstituted amine raw material was separated by column chromatography.

[0022] Step 1b: Synthesis of starting 2,2':6',2"-terpyridine derivatives

[0023]

[0024] Wherein, X=F, Cl, Br;

[0025] In a 500 mL round-bottom flask, para-substituted benzaldehyde (10 mmol), 2-acetylpyridine (20 mmol), potassium hydroxide (27.5 mmol), 35 mL of ammonia water, and 75 mL of ethanol were added and reacted at room temperature for 12 h. After the reaction, the crude product was filtered and recrystallized from ethanol to obtain a 2,2':6',2"-terpyridine derivative.

[0026] Step 1c: Synthesis of probe ligand

[0027]

[0028] Wherein, X=F, Cl, Br; Y and Z are alkoxy chains containing 1-16 carbon atoms.

[0029] In a 10 mL Schlenk tube, the substituted diamine (2.2 mmol) obtained in step 1a, the terpyridine derivative (2 mmol) obtained in step 1b, potassium tert-butoxide (3 mmol, 0.336 g), 10 mg [Pd] catalyst, and 5 mL toluene were added and reacted at 100° C. for 12 h. After the reaction, the probe ligand was separated by column chromatography.

[0030] Step 1d: Synthesis of probe

[0031]

[0032] Where L = OAc - , Cl - 、NO3 - 、SO4 2- 、BF4 - PF6 - ,OTf - , n=1 or 2.

[0033] The probe ligand (1 mmol) and zinc salt (1.2 mmol) prepared in step 1c were added to a 10 mL round-bottom flask and reacted at room temperature for 6 h. After the reaction, the solvent was removed under reduced pressure to obtain a probe powder.

[0034] (ii) Synthesis of a probe based on 2,6-diimidazolylpyridine, the specific steps are as follows:

[0035] Step 2a: Synthesis of starting material 1-(1H-benzimidazol-2-yl)ethanone derivative

[0036]

[0037] Wherein, E is a long chain containing 1-16 carbon atoms; X=Cl, Br.

[0038] Add lactic acid (26mmol), o-phenylenediamine (30mmol), 15mL of 3M HCl solution into a 50mL round-bottom flask and reflux at 100℃ overnight. After the reaction, adjust the pH value to 10 with saturated sodium carbonate solution, extract with ethyl acetate, dry, and remove the solvent under reduced pressure to obtain a brown crude product; dissolve the above crude product in 35mL of a mixed solution of dichloromethane: methanol (volume ratio of 6:1), add manganese dioxide, stir at room temperature overnight, filter the insoluble matter after the reaction, and obtain 1-(1H-benzimidazol-2-yl)ethanone; react with halogenated hydrocarbons of different chain lengths to obtain its derivatives.

[0039] Step 2b: Synthesis of 2,6-diimidazolylpyridine framework

[0040]

[0041] Wherein, E is a long chain containing 1-16 carbon atoms, and Y is an alkoxy chain containing 1-16 carbon atoms.

[0042] The product obtained in step 2a (8 mmol), benzaldehyde derivative (4 mmol), potassium hydroxide (10 mmol), 50 mL of ammonia water, and 100 mL of ethanol were added to a 500 mL round-bottom flask and reacted at room temperature for 12 h. After the reaction, the solvent was removed under reduced pressure, and dichloromethane was added for extraction, and the solvent was removed under reduced pressure to obtain a ligand with 2,6-diimidazolylpyridine as the framework.

[0043] Step 2c: Synthesis of probes based on 2,6-diimidazolylpyridine

[0044]

[0045] Where L = OAc - , Cl - 、NO3 - 、SO4 2- 、BF4 - PF6 - ,OTf - , n=1 or 2.

[0046] The ligand (1 mmol) and zinc salt (1.2 mmol) prepared in step 2b were added to a 10 mL round-bottom flask and reacted at room temperature for 6 h. After the reaction, the solvent was removed under reduced pressure to obtain a probe with 2,6-diimidazolylpyridine as the framework.

[0047] The method for fluorescent visualization identification of latent fingerprints on a substrate provided by the present invention uses the above-mentioned probe as a display agent, and the specific steps are as follows:

[0048] Immerse the substrate with fingerprints in the developer solution (in the experiment, press the fingerprint on the substrate surface), or directly spray the developer solution evenly on the substrate surface; then rinse the substrate treated with the developer solution with deionized water to remove residual liquid; then expose it to ultraviolet light with a wavelength of 365nm to observe clear and bright fingerprint patterns and detailed features for fingerprint color identification; and record it.

[0049] In the present invention, the range of the substrate material is very wide, for example: glass, tin foil, plastic, paper, metal, wood, leather and the like.

[0050] In the present invention, the operating temperature is 0-50 degrees Celsius, preferably 10-530 degrees Celsius; the substrate with fingerprints is immersed in the display agent solution for 1s-120s, preferably 40s-100s.

[0051] In the present invention, the concentration range of the display agent solution is 0.01-10 mol / L, preferably 1-8 mol / L.

[0052] In the present invention, the shooting tool can be a common shooting device such as a camera, a mobile phone, etc.

[0053] The principle of the present invention is that 2,2':6',2"-terpyridine and 2,6-diimidazolylpyridine are a class of common tridentate chelating agents, which can effectively chelate metal ions to form stable metal organic complexes. By introducing substituents with different characteristics at the para position of the intermediate pyridine nitrogen, such as introducing a substituent R with AIE characteristics and an electron induction effect, the fluorescence properties of the entire molecule can be comprehensively adjusted; by adjusting the type of the metal ligand L, the solubility of the molecule can be further adjusted.

[0054] The clamp-type Zn(II) metal organic complex prepared by the present invention has good water solubility, avoiding the use of organic solvents. The lipophilic R group in the developer molecule can combine with the oil in the fingerprint component. After the developer acts on the fingerprint, the molecular aggregation degree increases, resulting in an increase in the molecular fluorescence intensity (AIE effect). Therefore, after the developer is selectively adsorbed on the fingerprint, it emits fluorescence under ultraviolet light excitation to achieve the purpose of color development.

[0055] The fluorescent probe provided by the present invention can emit fluorescence of different colors by changing the substituent group in a pure water phase, and the fluorescence emission wavelength can be adjusted to be located in different visible light regions, thereby overcoming the fluorescence interference of the color development substrate itself.

[0056] Compared with the prior art, the advantages of the present invention are:

[0057] 1. By adjusting the electronic properties of the substituent, the fluorescence color of the fingerprint can be adjusted. The developer provided by the present invention can adjust the fluorescence emission wavelength to the visible light region, which can be distinguished from the fluorescence color of the substrate itself, thereby improving the contrast and reducing background signal interference.

[0058] 2. The latent fingerprint coloring method provided by the present invention is carried out in an aqueous solution, thus avoiding the damage of fingerprints by organic solvents, posing no potential threat to the health and safety of users, being simple to operate, and having a significant coloring effect.

[0059] 3. The developer solution provided by the present invention can be used to visualize latent fingerprints on the adhesive surfaces of different tapes (such as transparent tape and yellow tape), and can also be used to visualize latent fingerprints on artificial leather substrates which are more difficult to visualize.

[0060] 4. The latent fingerprint revealed by the developer provided by the present invention can be copied at least 5 times by using transparent tape. Specifically, the substrate with the latent fingerprint is placed in a culture dish containing the probe solution, soaked for 1s-120s and then taken out. Under the excitation of ultraviolet light at 365nm, yellow fingerprint outline fluorescence can be observed. The fingerprint on the substrate is pasted with transparent tape, and the same fluorescent pattern appears on the tape. This process can be repeated at least 5 times. Fig.10 shown. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 The terpyridine Zn (II) metal organic complex solution provided by the present invention has an effect of revealing fingerprints on tin foil, glass, polytetrafluoroethylene, label paper, rough cardboard and filter paper.

[0062] Figure 2 The invention discloses an effect of the terpyridine Zn(II) metal organic complex solution with different substituents on revealing fingerprints on artificial leather.

[0063] Figure 3 The color of fingerprints on tinfoil can be adjusted by changing the substituents of terpyridine Zn(II) metal organic complex.

[0064] Figure 4 The present invention provides a terpyridine Zn (II) metal organic complex solution that has an effect on the appearance of primary, secondary and tertiary features of fingerprints.

[0065] Figure 5 The fingerprint on the tin foil substrate is colored by the terpyridine Zn (II) metal organic complex solution provided by the present invention, and then the fingerprint is copied to the surface of the tape after being pasted with transparent tape.

[0066] Figure 6This is the effect after the fingerprint on the tin foil substrate is developed by the terpyridine Zn (II) metal organic complex solution provided by the present invention, and the substrate is pasted with a transparent tape six times.

[0067] Figure 7 The invention discloses an effect of revealing fingerprints on tinfoil by spraying a solution of a terpyridine Zn(II) metal organic complex with different substituents provided by the invention.

[0068] Figure 8 The invention uses the terpyridine Zn (II) metal organic complex solution provided by the invention, takes tin foil as a substrate, and presses the fingerprint for multiple times to produce the effect of appearance.

[0069] Fig. 9 It is a fingerprint grayscale image displayed by terpyridine Zn(II) metal organic complex solution with tin foil as the substrate.

[0070] Fig.10 The grayscale value image of the fingerprint displayed by the terpyridine Zn(II) metal organic complex solution is based on a plastic plate.

[0071] Fig.11 This is the effect of Zn(II) metal organic complex solutions with different anions on the appearance of fingerprints on tin foil. From left to right, the anions are NO3 - ,OAc - , Cl - .

[0072] Fig.12 This is the effect of different anion 2,6-diimidazolylpyridine structure as the skeleton of the clamp-type Zn (II) metal organic complex solution on the fingerprint on the foil. From left to right in the figure, the anions are NO3 - ,OAc - , Cl - . DETAILED DESCRIPTION

[0073] The present invention is further described below in conjunction with the examples and drawings, but the present invention is not limited thereto. The following methods, unless otherwise specified, are conventional methods. The test materials used in the following examples, unless otherwise specified, are commercially available and do not require special purification.

[0074] Example 1. Preparation of terpyridine Zn(II) metal organic complex

[0075] Step 1a: Synthesis of starting material 4-methoxy-N-phenylaniline

[0076]

[0077] Chlorobenzene (4 mmol, 0.448 g), p-methoxyaniline (6 mmol, 0.751 g), potassium tert-butoxide (6 mmol, 0.673 g), 10 mg [Pd] catalyst, and 5 mL toluene were added to a 10 mL Schlenk tube and reacted at 80° C. for 12 h. After the reaction, 700 mg of a white solid was obtained by column chromatography separation with a yield of 88%.

[0078] Step 1b: Synthesis of starting material 4'-(4-chlorophenyl)-2,2':6',2"-terpyridine

[0079]

[0080] In a 500mL round-bottom flask, add p-chlorobenzaldehyde (10mmol, 1.41g), 2-acetylpyridine (20mmol, 2.42g), potassium hydroxide (27.5mmol, 1.54g), 35mL ammonia water, and 75mL ethanol, and react at room temperature for 12h. After the reaction, filter the obtained white precipitate, and recrystallize it with ethanol to obtain 3.08g of white solid, with a yield of 90%.

[0081] Step 1c: Synthesis of the probe ligand provided by the present invention

[0082]

[0083] In a 10mL Schlenk tube, 4-methoxy-N-phenylaniline (2.2mmol, 0.44g), 4'-(4-chlorophenyl)-2,2':6',2"-terpyridine (2mmol, 0.68g), potassium tert-butoxide (3mmol, 0.336g), 10mg [Pd] catalyst, and 5mL toluene were added and reacted at 100°C for 12h. After the reaction, 710mg of light yellow solid was obtained by column chromatography separation with a yield of 70%.

[0084] Step 1d: Synthesis of the probe provided by the present invention

[0085]

[0086] The probe ligand (1 mmol, 0.68 g) prepared in step 1c and zinc acetate (1.2 mmol, 0.22 g) were added to a 10 mL round-bottom flask and reacted at room temperature for 6 h. After the reaction, the solvent was removed under reduced pressure to obtain 650 mg of a yellow solid with a yield of 95%.

[0087] Example 2: Preparation of a color developing reagent with 2,6-diimidazolylpyridine as a skeleton

[0088] Step 2a: Synthesis of starting materials

[0089]

[0090] Add lactic acid (26mmol, 2.3mL), o-phenylenediamine (30mmol, 3.25g), 15mL of 3M HCl solution into a 50mL round-bottom flask, and reflux at 100℃ overnight. After the reaction, adjust the pH value to 10 with saturated sodium carbonate solution, extract with ethyl acetate, dry, and remove the solvent under reduced pressure to obtain a brown crude product; the above crude product is dissolved in 35mL of a mixed solution of dichloromethane: methanol (volume ratio of 6:1), add 23g of manganese dioxide, stir at room temperature overnight, filter the insoluble matter after the reaction, and obtain 2.8g of a red solid with a yield of 72%.

[0091] Step 2b: Synthesis of 2,6-diimidazolylpyridine skeleton

[0092]

[0093] In a 500mL round-bottom flask, the raw material in step 2a (8mmol, 1.28g), p-methoxybenzaldehyde (4mmol, 0.48mL), potassium hydroxide (10mmol, 0.8g), 50mL ammonia water, and 100mL ethanol were added and reacted at room temperature for 12h. After the reaction, the solvent was removed under reduced pressure, and dichloromethane was added for extraction, and the solvent was removed under reduced pressure to obtain 1.88g of yellow solid with a yield of 90%.

[0094] Step 2c: Synthesis of probes based on 2,6-diimidazolylpyridine

[0095]

[0096] The ligand (1 mmol, 0.417 g) prepared in step 2b and zinc acetate (1.2 mmol, 0.22 g) were added to a 10 mL round-bottom flask and reacted at room temperature for 6 h. After the reaction, the solvent was removed under reduced pressure to obtain 540 mg of a yellow solid with a yield of 90%.

[0097] Embodiment 3: Method for revealing latent fingerprints by immersion

[0098] 1. Preparation of fingerprint color working solution

[0099] 5 mg of the prepared developer was weighed and dissolved in 25 mL of distilled water to prepare a developer aqueous solution with a mass fraction of 20 wt%.

[0100] 2. Latent fingerprints appear

[0101] 1. The tester presses the fingerprint on different substrates (glass slides, plastic sheets, tape surfaces, tin foil, paper, leather, etc.).

[0102] 2. Detect different substrates with fingerprints in step 1, and follow the steps below:

[0103] (1) Soaking the substrate obtained in step 1 in a fingerprint color developing working solution for 1 second to 120 seconds;

[0104] (2) Take out the substrate and rinse it with water;

[0105] (3) Use a mobile phone or camera to take photos without color filtering equipment.

[0106] Some effects such as Figure 1-7 shown.

[0107] The results show that the fingerprint developer provided by the present invention has a high degree of specificity and sensitivity in the display of fingerprints, is suitable for displaying fingerprints on a variety of substrates, and has good stability.

[0108] Example 4: Stability test of fingerprint color development effect

[0109] The latent fingerprint revealed by the developer provided by the present invention can be copied at least 5 times by sticking with transparent tape, specifically: put the tin foil with fingerprints in a culture dish containing the probe solution, soak for 1s-120s and then take it out. Under the excitation of ultraviolet light at 365nm, yellow fluorescence of fingerprint lines can be observed, and the fingerprint on the tin foil is stuck with transparent tape, and the same fluorescence image appears on the tape. This process can be repeated at least 5 times, and the fingerprint image on the substrate still has visible lines.

[0110] Effects such as Figure 5 shown.

[0111] Embodiment 5: Method for revealing latent fingerprints by spraying

[0112] 1. Preparation of fingerprint color working solution

[0113] Weigh 5 mg of the prepared developer and dissolve it in 25 mL of distilled water to prepare a developer aqueous solution with a mass fraction of 20 wt%.

[0114] 2. Latent fingerprints appear

[0115] 1. The tester presses his finger on the substrate surface (tin foil, filter paper) for 1-2 seconds to leave fingerprints.

[0116] 2. Detect different substrates with fingerprints in step 1, and follow the steps below:

[0117] (1) Spray the fingerprint color developing working solution evenly on the substrate and let it stand for 2 minutes.

[0118] (2) Rinse off any excess liquid with water.

[0119] (3) Use a mobile phone or camera to take photos without color filtering equipment.

[0120] Effects such as Figure 7 Shown

[0121] Example 6: Press the fingerprint on the tin foil continuously to develop the color of the fingerprint.

[0122] Take several pieces of tin foil and press the fingerprints one by one. Soak the tin foil in the prepared developer aqueous solution for 1s-120s, then take it out, rinse off the excess developer solution, and place it under ultraviolet light one by one. Use 365nm wavelength light source to excite and observe the fingerprint outline without obvious attenuation of intensity.

[0123] Effects such as Figure 8 shown.

Claims

1. A latent fingerprint fluorescence visualization identification probe on a substrate, characterized in that: It is a pincer-type Zn(II) metal organic complex, and its structural formula is shown below (II): ； The compound represented by the structural formula (II) is a 2,6-diimidazolylpyridine zinc complex, wherein L is a different anion selected from OAc - , Cl - 、NO3 -- ; By adjusting the type of metal ion L, the solubility of the molecule can be adjusted.

2. The method for preparing a latent fingerprint fluorescent visualization identification probe on a substrate as claimed in claim 1, characterized in that: The specific steps are: Step 2a: Synthesis of starting material 1-(1H-benzimidazol-2-yl)ethanone derivative ； 26 mmol lactic acid, 30 mmol o-phenylenediamine, and 15 mL 3M HCl solution were added to a 50 mL round-bottom flask, and refluxed at 100°C overnight; after the reaction, the pH value was adjusted to 10 with a saturated sodium carbonate solution, extracted with ethyl acetate, dried, and the solvent was removed under reduced pressure to obtain a brown crude product; the crude product was dissolved in 35 mL of a mixed solution of dichloromethane:methanol, manganese dioxide was added, and stirred at room temperature overnight. After the reaction was completed, the insoluble matter was filtered to obtain 1-(1H-benzimidazol-2-yl)ethanone; Step 2b: Synthesis of 2,6-diimidazolylpyridine framework ； In a 500 mL round-bottom flask, add 8 mmol of the product obtained in step 2a, 4 mmol of benzaldehyde derivative, 10 mmol of potassium hydroxide, 50 mL of ammonia water, and 100 mL of ethanol, and react at room temperature for 12 h; after the reaction, remove the solvent under reduced pressure, add dichloromethane for extraction, and remove the solvent under reduced pressure to obtain a ligand with 2,6-diimidazolylpyridine as the framework; Step 2c: Synthesis of probes based on 2,6-diimidazolylpyridine ； Where L = OAc - , Cl - or NO3 -- ; In a 10 mL round-bottom flask, 1 mmol of the ligand prepared in step 2b and 1.2 mmol of zinc salt were added and reacted at room temperature for 6 h. After the reaction, the solvent was removed under reduced pressure to obtain a probe with 2,6-diimidazole pyridine as the framework.

3. A method for fluorescent visualization identification of latent fingerprints on a substrate, characterized in that: Using the probe described in claim 1 as a display agent, the specific steps are: Soak the substrate with fingerprints in the developer solution, or directly spray the developer solution evenly on the substrate surface; then rinse the substrate treated with the developer solution with deionized water to remove residual liquid; then expose it to ultraviolet light with a wavelength of 365nm to observe the fingerprint pattern and detailed features for fingerprint color identification; and record it.

4. The method for fluorescent visualization identification of latent fingerprints on a substrate according to claim 3, characterized in that: The operating temperature is 0-50 degrees Celsius, and the substrate with fingerprints is immersed in the display agent solution for 1s-120s.

5. The method for fluorescent visualization identification of latent fingerprints on a substrate according to claim 3, characterized in that: The concentration of the display agent solution is 0.01-10 mol / L.

6. The method for fluorescent visualization identification of latent fingerprints on a substrate according to any one of claims 3 to 5, characterized in that: The solvent used for the display solution is water.

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