CN115322775B - Fingerprint developer based on nitrogen-doped carbon quantum dots, preparation method and application thereof - Google Patents

Abstract

The invention relates to a fingerprint revealing agent based on nitrogen doped carbon quantum dots, a preparation method and application thereof. Dissolving perylene tetracarboxylic acid in dimethyl sulfoxide solution, adding ethylenediamine, fully mixing, reacting under microwave conditions to obtain nitrogen-doped carbon quantum dots with carboxyl and amino groups on the surfaces, and preparing a fingerprint developing agent by taking water as a solvent; the non-woven fabric is used as a base material, the latent fingerprint developing agent is loaded, the latent fingerprint developing cotton sheet is prepared, and the grease latent fingerprint and the latent blood fingerprint are developed by adopting a cotton sheet developing method. The latent fingerprint revealing cotton piece provided by the invention can reveal oil latent fingerprints and latent blood fingerprints, so that fingerprint revealing is more efficient; and the luminous color of the fingerprint pattern after appearance can be adjusted by changing the wavelength of the excitation light, so that the interference of the object background fluorescence can be effectively avoided. The visualization technology provided by the invention is simple and convenient to operate and low in cost, and can be suitable for criminal investigation sites to cope with various complex conditions.

Description

Fingerprint developer based on nitrogen-doped carbon quantum dots, preparation method and application thereof

Technical Field

The invention relates to a fingerprint visualization technology, in particular to a fingerprint developer based on a carbon quantum dot solution and a method for visualizing grease latent fingerprints and blood latent fingerprints on different objects, belonging to the application field of carbon nano fluorescent materials.

Background technique

Fingerprints are an important basis for identity recognition because they are different for each person, remain unchanged throughout life, and leave marks on objects. They play a very important role in criminal investigation and inspection and identification. As criminals' anti-detection awareness continues to improve, high-definition visible fingerprints are not common at crime scenes, and latent fingerprints are often ignored by criminals because they are invisible to the naked eye. Therefore, fingerprint visualization technology is the core and key of fingerprint technology.

Fingerprints differ in composition, and common fingerprints at crime scenes include grease fingerprints and blood fingerprints. Traditional methods for revealing grease fingerprints include powder method, physical developer method, chemical fumigation method, etc.; commonly used latent blood fingerprint developers in my country include tetramethylbenzidine, amino black 10B, acid yellow, etc. However, traditional revealing technology cannot meet the needs of front-line criminal investigations due to its certain defects. In particular, most traditional revealing methods can only reveal one type of fingerprint, and the composition of the fingerprint needs to be judged before revealing, which causes inconvenience to criminal investigation work. Therefore, it is of great significance to develop a simple, efficient, and universal latent fingerprint revealing method.

Fluorescent reagents have attracted the attention of fingerprint developers due to their unique luminescence properties that can resist the interference of background fluorescence from the object. In recent years, carbon quantum dots have been widely used in fluorescence sensing, bioimaging, and biomedicine due to their excellent optical properties, low toxicity, good biocompatibility, and simple preparation. And because most carbon quantum dots have excitation light wavelength dependence, carbon quantum dots have great application prospects in multicolor imaging. At present, there have been reports on the use of carbon quantum dots in the field of latent fingerprint visualization, for example: the preparation of carbon quantum dots with a single luminescent color for the visualization of grease latent fingerprints on different objects (see references: ACS Appl. Mater. Interfaces 2020, 12, 29549−29555 and J.Colloid Interface Sci. 2019, 554, 344–352). The literature also reported a carbon quantum dot with excitation light wavelength dependence for the visualization of grease latent fingerprints on different objects (see reference: Anal. Methods 2017, 9,4770-4775), but did not involve the visualization of latent blood fingerprints.

Summary of the invention

In view of the deficiencies in the prior art, the present invention provides a fingerprint developer based on nitrogen-doped carbon quantum dots, which can be used for revealing grease latent fingerprints and blood latent fingerprints, and can obtain fingerprint images of various colors by adjusting the wavelength of the excitation light, and is resistant to the interference of guest background fluorescence, as well as a preparation method and a method for revealing latent fingerprints.

The technical solution to realize the present invention is to provide a method for preparing a fingerprint developer based on nitrogen-doped carbon quantum dots, comprising the following steps:

(1) According to the amount of the substance, 1 part of perylene tetracarboxylic acid is dissolved in a dimethyl sulfoxide solution, and then 2.5 to 25 parts of ethylenediamine are added, and after being fully mixed, the mixture is reacted for 5 to 8 minutes under a microwave power of 700 to 900 W, and a nitrogen-doped carbon quantum dot having a carboxyl group and an amino group on the surface is obtained after purification;

(2) Dissolving the nitrogen-doped carbon quantum dots obtained in step (1) in deionized water at a concentration of 5×10 ^-5 g/L to 1×10 ^-4 g/L to obtain a fingerprint developer based on nitrogen-doped carbon quantum dots.

The technical solution of the present invention includes a fingerprint developer based on nitrogen-doped carbon quantum dots obtained according to the above preparation method.

The fingerprint developer of the present invention selects different excitation wavelengths within the range of 300-520 nm to obtain multicolor fluorescence emission with different wavelengths having a maximum emission wavelength within the range of 436-545 nm.

The technical solution of the present invention also includes an application of a fingerprint developer based on nitrogen-doped carbon quantum dots, wherein the fingerprint developer is prepared into a latent fingerprint developer cotton sheet for developing grease latent fingerprints and latent blood fingerprints.

The latent fingerprint revealing cotton sheet is prepared by using non-woven fabric as substrate, immersing the substrate in a fingerprint developer, and adsorbing the developer in an amount of 5 μL/cm ² to 50 μL/cm ² .

The fingerprint developer based on nitrogen-doped carbon quantum dots described in the present invention is applied to the visualization of latent blood fingerprints and comprises the following steps:

(1) Fixation of fresh latent blood fingerprints: immerse the object loaded with fresh latent blood fingerprints in anhydrous ethanol for 2 to 3 minutes, take it out and dry it naturally; or place the object loaded with fresh latent blood fingerprints in a cool and dry place for more than 12 hours;

(2) Place the latent fingerprint revealing cotton sheet evenly on the object with latent blood fingerprint treated in step (1), press lightly to make the cotton sheet fully contact with the object, and let it stand for 1 to 5 minutes;

(3) Peel the cotton sheet off the object smoothly and after drying, use an excitation wavelength in the range of 300-520 nm, select a filter that matches the emission wavelength, and photograph the revealed latent blood fingerprint image.

The fingerprint developer based on nitrogen-doped carbon quantum dots described in the present invention is applied to the visualization of latent fingerprints of grease, and comprises the following steps:

(1) Place the latent fingerprint revealing cotton sheet evenly on the object with grease latent fingerprints, press lightly to make the cotton sheet fully contact with the object, let it stand for 1 to 5 minutes, and then remove the object;

(3) Peel the cotton sheet off the object smoothly and after drying, use an excitation wavelength in the range of 300-520 nm, select a filter that matches the emission wavelength, and photograph the revealed latent blood fingerprint image.

The present invention provides a carbon quantum dot solution using perylenetetracarboxylic acid as a carbon source and doped with ethylenediamine as a developer. The carbon quantum dots contain amino groups on their surfaces that can react with proteins in the blood, thereby revealing latent blood fingerprints. Also, due to the large conjugated structure of perylenetetracarboxylic acid, the carbon quantum dots have a wide maximum emission wavelength range, thereby effectively resisting interference from guest background fluorescence, and obtaining a fingerprint image with clear textures and a high ridge-groove contrast ratio.

Compared with the prior art, the present invention has the following beneficial effects:

1. The carbon quantum dots prepared by the present invention have a large number of amino and carboxyl groups on their surfaces, which can act as reaction sites with proteins in the blood, thereby revealing latent blood fingerprints while revealing grease fingerprints.

2. After the latent fingerprint is revealed by the latent fingerprint revealing method provided by the present invention, by changing the wavelength of the excitation light and matching the filter of the corresponding emission wavelength, fingerprint images of different luminescent colors (blue to red) can be obtained, effectively avoiding the interference of the object background fluorescence, and the revealing effect is clear and bright.

3. The latent fingerprint developing method provided by the present invention is simple to operate, the developing cotton sheet can be stored for a long time, and the latent fingerprint developing agent contained is low in concentration, small in dosage, and low in use cost.

4. The latent fingerprint developer provided by the present invention uses water as a solvent, has low toxicity, and can be stored for a long time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a nuclear magnetic resonance spectrum of perylene tetracarboxylic acid prepared in an embodiment of the present invention;

FIG2 is an infrared spectrum of carbon quantum dots prepared in an embodiment of the present invention;

FIG3 is a transmission electron microscope photograph of carbon quantum dots prepared in an embodiment of the present invention;

FIG4 is a fluorescence emission spectrum of a carbon quantum dot solution prepared in an embodiment of the present invention at different excitation light wavelengths;

FIG5 is a photograph of a latent blood fingerprint that is not visible on an aluminum foil object provided by an embodiment of the present invention:

FIG6 is a photograph of a latent blood fingerprint revealed on an aluminum foil object under different excitation light conditions provided by an embodiment of the present invention;

FIG. 7 is a photograph of an unrevealed grease latent fingerprint on an aluminum foil object provided by an embodiment of the present invention;

FIG8 is a photograph of a latent fingerprint of oil on an aluminum foil object after being revealed under 365 nm excitation light provided by an embodiment of the present invention.

Detailed ways

The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

Example 1

This embodiment provides a carbon quantum dot solution fingerprint display cotton sheet with perylenetetracarboxylic acid as a carbon source, and the steps of the preparation method are as follows:

1. Preparation of perylene tetracarboxylic acid:

Add 3,4,9,10-perylenetetracarboxylic dianhydride (5.00 g, 12.74 mmol), potassium hydroxide (5.00 g, 89.13 mmol), and 100 mL of deionized water to the flask, and stir under reflux for 12 h. Cool to room temperature, add 100 mL of 10% sulfuric acid, stir thoroughly, filter to obtain a red solid, and dry. Yield 5.12 g (94%). 1H NMR (400MHz, DMSO-d6, δ) 8.01 (s, 4H), 8.61 (t, 4H), 13.04 (s, 4H).

See Figure 1, which is the NMR spectrum of perylenetetracarboxylic acid provided in this example.

2. Preparation of carbon quantum dots using perylenetetracarboxylic acid as carbon source:

Perylene tetracarboxylic acid (0.251 g, 0.59 mmol) and 15 mL of dimethyl sulfoxide were added to a pre-dried 400 mL beaker, stirred until fully dissolved, ultrasonicated for 1 min, and ethylenediamine (900 μL, 12.80 mmol) was added. After stirring at room temperature until fully mixed, the beaker was covered with a layer of plastic wrap and placed in a microwave oven for microwave reaction for 5 min. After the reaction was completed, it was cooled to room temperature, 15 mL of deionized water was added, and the reactants were fully dispersed in the deionized water, centrifuged, and the solid obtained by centrifugation was dispersed in 15 mL of deionized water, filtered with a 0.45 μm filter head, and finally the filtrate was freeze-dried to obtain a dark purple solid, which was the carbon quantum dots.

Referring to FIG. 2 , it is an infrared spectrum of the carbon quantum dots provided in this embodiment. The surface of the carbon quantum dots contains carboxyl groups and amino groups.

Referring to FIG. 3 , it is a transmission electron microscope photograph of the carbon quantum dots in this embodiment, FIG. a is a transmission electron microscope photograph of the carbon quantum dots magnified 3.5K times, and FIG. b is a transmission electron microscope photograph of the carbon quantum dots magnified 150K times. It can be seen from the figure that the particle size is about 50 nm and is a relatively regular spherical shape.

Referring to FIG. 4 , it is a fluorescence emission spectrum of the carbon quantum dot solution in this embodiment under different excitation light wavelengths. It can be seen from the figure that by adjusting the wavelength of the excitation light in the range of 300 to 520 nm, the maximum emission wavelength of the carbon quantum dot solution can be adjusted to a range of 436 to 545 nm.

3. Preparation of latent fingerprint developer:

Take 0.5 g of carbon quantum dot solid in a 10 mL centrifuge tube, add 5 mL of deionized water, and shake the centrifuge tube to evenly disperse the carbon quantum dots to obtain 5 mL of latent fingerprint developer.

4. Preparation of developer-loaded cotton sheets:

Take 400 μL of developer in a weighing bottle; cut two cotton non-woven fabric substrates into a size of 2 cm×3 cm, put them into the weighing bottle and soak for 1 min to obtain a latent fingerprint developing cotton sheet with a loading of about 20 μL/ ^cm2 of developer.

Seal the weighing bottle containing the latent fingerprint revealing cotton pad and store it in a cool and dry place.

Example 2

This embodiment provides a method for developing a fresh latent blood fingerprint on the surface of an aluminum foil object. The latent blood fingerprint is developed using the developing cotton sheet prepared in Example 1. The specific steps are as follows:

1. Place the object loaded with fresh latent blood fingerprints in a cool and dry place for 12 hours;

2. Place the latent fingerprint developing cotton sheet loaded with the latent blood fingerprint developing agent in Example 1 evenly on the object loaded with latent blood fingerprint, press lightly to make the cotton sheet fully contact with the object, and let it stand for 2 minutes;

3. Peel the cotton sheet off the object smoothly and after drying, take photos of the latent blood fingerprint images of different colors under the illumination of 300-520 nm wavelength and select the filter that matches the emission wavelength.

See Figure 5, which is a photo of an unrevealed latent blood fingerprint on an aluminum foil object provided in this embodiment, Figure a is a photo taken under natural light, and Figure b is a photo taken under 365 nm light irradiation; it can be seen from the figure that no fingerprint pattern can be observed for the unrevealed latent fingerprint under 365 nm light excitation, and the fingerprint ridge-groove contrast is low under natural light.

See Figure 6, which is a photo of the latent blood fingerprint on the aluminum foil object provided by this embodiment after being revealed under different excitation light conditions: Figure a is a fingerprint photo under 405 nm excitation and matching 445 nm filter, and the fingerprint ridge image is yellow-green; Figure b is a fingerprint photo under 445 nm excitation and matching 495 nm filter, and the fingerprint ridge image is yellow; Figure c is a fingerprint photo under 470 nm excitation and matching 535 nm filter, and the fingerprint ridge image is orange-yellow; Figure d is a fingerprint photo under 500 nm excitation and matching 570 nm filter, and the fingerprint ridge image is red. It can be seen from the figure that the latent fingerprint revealing method of the present invention has a good effect on latent blood fingerprints, the fingerprint pattern after revealing is clear, and the excitation light wavelength can be changed as needed to change the color of the fingerprint.

Example 3

This embodiment provides a method for revealing grease latent fingerprints on the surface of an aluminum foil object. The revealing cotton sheet prepared in Example 1 is used to reveal grease latent fingerprints. The specific steps are as follows:

1. Cover the latent fingerprint revealing cotton sheet prepared in Example 1 evenly on the aluminum foil object loaded with grease latent fingerprints, press lightly to make the cotton sheet fully contact with the object, let it stand for 2 minutes, and take out the object;

2. Peel the cotton sheet off the object smoothly, dry it, and then take a photo of the oily latent fingerprint under a light wavelength of 365 nm.

See Figure 7, which is a photograph of the unrevealed greasy latent fingerprint on the aluminum foil object provided in Example 3. Figure a is a photograph under natural light, and Figure b is a photograph under 365 nm light irradiation. It can be seen from the figure that under 365 nm excitation light, no unrevealed latent fingerprint pattern is observed, and the fingerprint ridge-groove contrast is low under natural light.

8 is a photograph of the greasy latent fingerprint on the aluminum foil object provided in this embodiment after being revealed under 365 nm excitation light conditions; as can be seen from FIG8 , the latent fingerprint revealing method of the present invention has a good effect on greasy latent fingerprints, and the fingerprint pattern after revealing is clear.

Claims (7)

1. A method for preparing a fingerprint developer based on nitrogen-doped carbon quantum dots, characterized by comprising the following steps: (1) According to the amount of the substance, 1 part of perylene tetracarboxylic acid is dissolved in a dimethyl sulfoxide solution, and then 2.5 to 25 parts of ethylenediamine are added, and after being fully mixed, the mixture is reacted for 5 to 8 minutes under a microwave power of 700 to 900 W, and a nitrogen-doped carbon quantum dot having a carboxyl group and an amino group on the surface is obtained after purification; (2) Dissolving the nitrogen-doped carbon quantum dots obtained in step (1) in deionized water at a concentration of 5×10 ^-5 g/L to 1×10 ^-4 g/L to obtain a fingerprint developer based on nitrogen-doped carbon quantum dots. 2. A fingerprint developer based on nitrogen-doped carbon quantum dots obtained by the preparation method according to claim 1. 3. A fingerprint developer based on nitrogen-doped carbon quantum dots according to claim 2, characterized in that: different excitation wavelengths are selected within the range of 300 to 520 nm to obtain multicolor fluorescence emission with different wavelengths having a maximum emission wavelength within the range of 436 to 545 nm. 4. The use of a fingerprint developer based on nitrogen-doped carbon quantum dots as claimed in claim 2, characterized in that the fingerprint developer is prepared into a latent fingerprint developer cotton sheet for developing grease latent fingerprints and latent blood fingerprints. 5. The use of a fingerprint developer based on nitrogen-doped carbon quantum dots according to claim 4, characterized in that: a non-woven fabric is used as a substrate, the substrate is immersed in the fingerprint developer, the amount of the developer adsorbed is 5 μL/cm ² to 50 μL/cm ² , and a latent fingerprint developer cotton sheet is prepared. 6. The use of a fingerprint developer based on nitrogen-doped carbon quantum dots according to claim 4 or 5, characterized in that the application of the developer to latent blood fingerprints comprises the following steps: (1) Fixation of fresh latent blood fingerprints: immerse the object loaded with fresh latent blood fingerprints in anhydrous ethanol for 2 to 3 minutes, take it out and dry it naturally; or place the object loaded with fresh latent blood fingerprints in a cool and dry place for more than 12 hours; (2) Place the latent fingerprint revealing cotton sheet evenly on the object with latent blood fingerprint treated in step (1), press lightly to make the cotton sheet fully contact with the object, and let it stand for 1 to 5 minutes; (3) Peel the cotton sheet off the object smoothly and after drying, use an excitation wavelength in the range of 300-520 nm, select a filter that matches the emission wavelength, and photograph the revealed latent blood fingerprint image. 7. The use of a fingerprint developer based on nitrogen-doped carbon quantum dots according to claim 4 or 5, characterized in that the application of the developer to the visualization of latent fingerprints of oils and fats comprises the following steps: (1) Place the latent fingerprint revealing cotton sheet evenly on the object with grease latent fingerprints, press lightly to make the cotton sheet fully contact with the object, let it stand for 1 to 5 minutes, and then remove the object; (3) Peel the cotton sheet off the object smoothly and after drying, use an excitation wavelength in the range of 300-520 nm and select a filter that matches the emission wavelength to obtain the revealed oil latent fingerprint image.