CN106974659A - A kind of latent fingerprint detection method based on red fluorescence carbon point material - Google Patents

Abstract

The invention belongs to the technical field of fingerprint detection, in particular to a latent fingerprint detection method based on red fluorescent carbon dot materials. The red fluorescent carbon dot proposed by the invention is prepared by a hydrothermal method, and then filtered, neutralized, washed and freeze-dried to obtain a solid with uniform particle size. This kind of carbon dots is positively charged under acidic conditions, and can be combined with negatively charged sebum in fingerprint residues through electrostatic interaction, and is wrapped by sebum to avoid the fluorescence quenching of carbon dots during the drying process. And those carbon dots that are not combined with sebum, due to dry agglomeration lead to fluorescence quenching. Finally, under ultraviolet light or blue light, the morphology of latent fingerprints can be quickly and accurately displayed. This method can easily and quickly reveal fingerprints by emitting fluorescence, and can be applied to surfaces of various materials such as glass, metal, leather, plastic, and ceramics. The carbon dot itself is safe, non-toxic, inexpensive, easy to manufacture, and suitable for popularization and application.

Description

A Latent Fingerprint Detection Method Based on Red Fluorescent Carbon Dot Material

technical field

The invention belongs to the technical field of fingerprint detection, in particular to a method for detecting latent fingerprints.

Background technique

Everyone has different fingerprints. In accident or criminal scene investigations, fingerprint analysis provides reliable evidence of identification. When a person's fingers touch a solid surface, substances such as sweat and sebum on the hand will leave a unique imprint on the surface. Usually, these imprints cannot be seen by the naked eye and are called latent fingerprints. The goal of fingerprint detection is to enhance the visibility of latent fingerprints. So far, many nano-luminescent materials have been applied to the display of latent fingerprints. Including zinc sulfide quantum dots, zinc oxide quantum dots, cadmium sulfide quantum dots, lanthanide metal complexes, gold nanoclusters, etc.

In the past ten years, carbon dots, as an excellent fluorescent material, have received extensive attention. Its advantages include stable fluorescence performance, low cost, green synthesis method, good biosafety, and environmental friendliness. Applications of carbon dots include bioimaging, drug delivery, fluorescent sensing, and analysis. However, so far, there are very few studies on the application of carbon dots to fingerprint detection. In fact, the application of traditional carbon dots in latent fingerprint display faces many obstacles. First, the fluorescence of most carbon dots is blue-green, which will be interfered by the blue fluorescence of paper and plastic. Secondly, during the process of evaporating and concentrating the solution of carbon dots, its fluorescence is quenched due to the agglomeration of carbon dots. Generally, solid carbon dots have no obvious fluorescence. Finally, water as the most commonly used dispersion medium for carbon dots is difficult to evenly adhere to many smooth surfaces, and organic solvents generally damage fingerprints.

Contents of the invention

The purpose of the present invention is to provide a simple, fast, efficient and safe latent fingerprint detection method.

The latent fingerprint detection method provided by the present invention is based on a red fluorescent carbon dot that emits light efficiently. Since the carbon dots emit red fluorescence, interference from blue background fluorescence of various materials can be minimized. Although traditional carbon dots will cause fluorescence quenching due to particle agglomeration during the solution evaporation process, this feature is cleverly used by the present invention to display fingerprints. Specifically, the present invention firstly synthesizes carbon dots containing a large number of amine groups on the surface. The carbon dots are positively charged when combined with hydrogen ions in acidic aqueous solution, and can interact with negatively charged sebum in fingerprint residues through electrostatic interaction. Effective attraction, the coating of these residues inhibits the evaporation of water, while the carbon dots that are not in contact with fingerprint residues dry naturally and lose fluorescence, and finally show the morphology and details of latent fingerprints clearly and completely under ultraviolet light.

The invention dissolves the red light carbon dots in an acidic solution and puts them into a spray bottle. It only needs to cooperate with an ultraviolet lamp with a power of several watts to detect latent fingerprints on the surface of various materials. It is a simple, fast, portable and efficient method. , Safe way. Specific steps are as follows:

(1) Preparation of red fluorescent carbon dots

Ultrasonically dissolve 0.05~0.2g of organic amine in water, add 0.5~2ml of phosphoric acid, mix well, seal it in a polytetrafluoroethylene-lined stainless steel reactor, at 150~220℃, hydrothermal reaction 4~48 hours; after the hydrothermal reaction was finished, the system was cooled to room temperature, and the solution was filtered with a microporous membrane to obtain a clear solution; the clear solution was neutralized with sodium hydroxide to obtain a suspension, and the bottom precipitate was collected with ethanol and Washed several times; the washed sample was dissolved in an acidic solution, and then freeze-dried to obtain red fluorescent carbon dots;

The prepared carbon dots are mainly composed of carbon elements, and contain a small amount of nitrogen, hydrogen, and oxygen elements at the same time. The particle diameter is 1-5 nanometers and has a graphitized structure;

(2) Latent fingerprint detection

Dissolve red fluorescent carbon dots in acidic solution to obtain red fluorescent carbon dot solution, take 5~15ml of carbon dot solution in a spray bottle; spray the solution on the fingerprint attached to the carrier, and then put it in 50~70℃ Put it in an oven for 1-2 minutes or place it at room temperature for 8-12 minutes. After the moisture on the surface evaporates, under the irradiation of an ultraviolet lamp with a wavelength of 365 nanometers, you can observe the fingerprint lines that appear and take pictures with a camera.

Wherein, the carrier may be glass, metal, leather, plastic, ceramics and the like.

The present invention has the following advantages:

(1) The synthesis method of carbon dots is simple, low in cost, high in yield, safe and non-toxic, and environmentally friendly;

(2) The display method has low requirements on equipment, is easy to operate and portable, and is suitable for popularization and application;

(3) Many substrates emit blue fluorescence under ultraviolet light, while the carbon dots emit red fluorescence, which can greatly reduce background interference and improve the accuracy of analysis;

(4) After carbon dot spray, fingerprints appear stable and long-lasting, and can also appear for fingerprints that have been placed for a long time.

Description of drawings

Figure 1: Transmission electron microscope image of carbon dots.

Figure 2: Fluorescence spectra of carbon dot solutions excited by light of different wavelengths.

Figure 3: Confocal laser microscope image of the carbon dot solution sprayed onto the fingerprint. The image on the right is a dark field photo, and the image on the left is a bright field photo.

Figure 4: Photos of carbon dots solution sprayed on fingerprints on glass (A), aluminum foil (B), leather (C), and plastic (D) surfaces, taken under ultraviolet light.

Fig. 5: a schematic diagram of the process of latent fingerprint detection in the present invention.

detailed description

Example 1

(1) Preparation of red carbon dots:

Weigh 0.1 g of p-phenylenediamine and ultrasonically dissolve it in 40 ml of water, add 1 ml of concentrated phosphoric acid (85%), mix well, seal it in a polytetrafluoroethylene reactor, and heat the system to 180°C for 24 hours. After the system was cooled to room temperature, a clear solution was obtained by filtration. The clear solution was neutralized with sodium hydroxide to obtain a suspension, centrifuged to collect the bottom precipitate, and washed with ethanol and water several times. The washed sample was dissolved in 10 ml of dilute hydrochloric acid (0.1 mol/L), and then freeze-dried to obtain red light carbon dots;

(2) The red light carbon dot solution is applied to the display of latent fingerprints:

Dissolve 0.1 g of red light carbon dots in 100 ml of dilute hydrochloric acid (0.1 mol/L) to obtain a red light carbon dot solution. Pour 10ml of this red light carbon dot solution into a spray bottle. Select glass, metal, leather, plastic, ceramics and other items as the fingerprint carrier, spray the solution on the fingerprint, and then put it in an oven at 60°C for one minute or at room temperature for ten minutes, and wait for the surface moisture to evaporate. Under the irradiation of a special ultraviolet lamp, the fingerprint lines can be observed and recorded with a camera.

Example 2

The preparation method is the same as that in Example 1, but the heating at 180°C for 24 hours in step (1) is changed to heating at 200°C for 20 hours, and other conditions remain unchanged. Dissolve 0.1 g of synthesized red carbon dots in 100 ml of dilute hydrochloric acid (0.1 mol/L), use the spray method to detect latent fingerprints on the surface of glass, metal, leather, plastic, ceramics, etc., and take pictures with a camera.

Example 3

The preparation method is the same as in Example 1, but the amount of p-phenylenediamine used in step (1) is changed to 0.2 g, and other conditions remain unchanged. Dissolve 0.1 g of synthesized red carbon dots in 100 ml of dilute hydrochloric acid (0.1 mol/L), use the spray method to detect latent fingerprints on the surface of glass, metal, leather, plastic, ceramics, etc., and take pictures with a camera.

Example 4

The preparation method was the same as in Example 1, but the amount of p-phenylenediamine used in step (1) was changed to 0.2 g, the heating at 180°C for 24 hours was changed to 200°C for 20 hours, and other conditions remained unchanged. Dissolve 0.1 g of synthesized carbon dots in 100 ml of dilute hydrochloric acid (0.1 mol/L), use the spray method to detect latent fingerprints on the surface of glass, metal, leather, plastic, ceramics, etc., and take pictures with a camera.

Example 5

(1) Preparation of red carbon dots:

Ultrasonically dissolve 0.1 g of o-phenylenediamine in 40 ml of water, add 1 ml of concentrated phosphoric acid (85%), mix well, seal it in a polytetrafluoroethylene reactor, and heat the system at 180°C for 24 hours. After the system was cooled to room temperature, a clear solution was obtained by filtration. The clear solution was neutralized with sodium hydroxide to obtain a suspension, centrifuged to collect the bottom precipitate, and washed with ethanol and water several times. The washed sample was dissolved in 10 ml of dilute hydrochloric acid (0.1 mol/L), and then freeze-dried to obtain red light carbon dots;

(2) The red light carbon dot solution is applied to the display of latent fingerprints:

Dissolve 0.1 g of red carbon dots in 100 ml of dilute hydrochloric acid (0.1 mol/L) to obtain a red light carbon dot solution. Pour 10ml of this red light carbon dot solution into a spray bottle. Select glass, metal, leather, plastic, ceramics and other items as the fingerprint carrier, spray the solution on the fingerprint, and then put it in an oven at 60°C for one minute or at room temperature for ten minutes, and wait for the surface moisture to evaporate. Under the irradiation of a special ultraviolet lamp, the fingerprint lines can be observed, and recorded with a camera.

Example 6

The preparation method is the same as in Example 5, but the heating at 180°C for 24 hours in step (1) is changed to heating at 200°C for 20 hours, and other conditions remain unchanged. Dissolve 0.1 g of synthesized red carbon dots in 100 ml of dilute hydrochloric acid (0.1 mol/L), use the spray method to detect latent fingerprints on the surface of glass, metal, leather, plastic, ceramics, etc., and take pictures with a camera.

Example 7

The preparation method is the same as in Example 5, but the amount of o-phenylenediamine used in step (1) is changed to 0.2 g, and other conditions remain unchanged. Dissolve 0.1 g of synthesized red carbon dots in 100 ml of dilute hydrochloric acid (0.1 mol/L), use the spray method to detect latent fingerprints on the surface of glass, metal, leather, plastic, ceramics, etc., and take pictures with a camera.

Example 8

The preparation method was the same as in Example 5, but the amount of o-phenylenediamine used in step (1) was changed to 0.2 g, the heating at 180°C for 24 hours was changed to 200°C for 20 hours, and other conditions remained unchanged. Dissolve 0.1 g of synthesized red carbon dots in 100 ml of dilute hydrochloric acid (0.1 mol/L), use the spray method to detect latent fingerprints on the surface of glass, metal, leather, plastic, ceramics, etc., and take pictures with a camera.

Example 9

(1) Preparation of red carbon dots:

Ultrasonically dissolve 0.1 g of m-phenylenediamine in 40 ml of water, add 1 ml of concentrated phosphoric acid (85%), mix well, seal it in a polytetrafluoroethylene reactor, and heat the system at 180°C for 24 hours. After the system was cooled to room temperature, a clear solution was obtained by filtration. The clear solution was neutralized with sodium hydroxide to obtain a suspension, centrifuged to collect the bottom precipitate, and washed with ethanol and water several times. The washed sample was dissolved in 10 ml of dilute hydrochloric acid (0.1 mol/L), and then freeze-dried to obtain red light carbon dots;

(2) The red light carbon dot solution is applied to the display of latent fingerprints:

Dissolve 0.1 g of red light carbon dots in 100 ml of dilute hydrochloric acid (0.1 mol/L) to obtain a red light carbon dot solution. Pour 10ml of this red light carbon dot solution into a spray bottle. Select glass, metal, leather, plastic, ceramics and other items as the fingerprint carrier, spray the solution on the fingerprint, and then put it in an oven at 60°C for one minute or at room temperature for ten minutes, and wait for the surface moisture to evaporate. Under the irradiation of a special ultraviolet lamp, the fingerprint lines can be observed and recorded with a camera.

Example 10

The preparation method is the same as in Example 9, but the amount of m-phenylenediamine used in step (1) is changed to 0.2 g, and other conditions remain unchanged. Dissolve 0.1 g of synthesized red carbon dots in 100 ml of dilute hydrochloric acid (0.1 mol/L), use the spray method to detect latent fingerprints on the surface of glass, metal, leather, plastic, ceramics, etc., and take pictures with a camera.

Example 11

The preparation method is the same as that in Example 9, but the heating at 180°C for 24 hours in step (1) is changed to heating at 200°C for 20 hours, and other conditions remain unchanged. Dissolve 0.1 g of synthesized red carbon dots in 100 ml of dilute hydrochloric acid (0.1 mol/L), use the spray method to detect latent fingerprints on the surface of glass, metal, leather, plastic, ceramics, etc., and take pictures with a camera.

Example 12

The preparation method was the same as in Example 9, but the amount of m-phenylenediamine used in step (1) was changed to 0.2 g, the heating at 180°C for 24 hours was changed to 200°C for 20 hours, and other conditions remained unchanged. Dissolve 0.1 g of synthesized red carbon dots in 100 ml of dilute hydrochloric acid (0.1 mol/L), use the spray method to detect latent fingerprints on the surface of glass, metal, leather, plastic, ceramics, etc., and take pictures with a camera.

Attachment: Example result list

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Claims (4)

1. a kind of latent fingerprint detection method based on red fluorescent carbon dot material, it is characterized in that, concrete steps are as follows: (1) Preparation of red fluorescent carbon dots Ultrasonically dissolve 0.05~0.2g of organic amine in water, add 0.5~2ml of phosphoric acid, mix well, seal it in a polytetrafluoroethylene-lined stainless steel reactor, at 150~220℃, hydrothermal reaction 4~48 hours; after the hydrothermal reaction was finished, the system was cooled to room temperature, and the solution was filtered with a microporous membrane to obtain a clear solution; the clear solution was neutralized with sodium hydroxide to obtain a suspension, and the bottom precipitate was collected with ethanol and Washed several times; the washed sample was dissolved in an acidic solution, and then freeze-dried to obtain red fluorescent carbon dots; The prepared carbon dots are mainly composed of carbon elements, and contain a small amount of nitrogen, hydrogen, and oxygen elements at the same time. The particle diameter is 1-5 nanometers and has a graphitized structure; (2) Latent fingerprint detection Dissolve red fluorescent carbon dots in an acidic solution to obtain a red fluorescent carbon dot solution, take 5-15 ml of carbon dot solution in a spray bottle; spray the solution on the fingerprint attached to the carrier, and then put it in 50-70 ℃ oven for 1 to 2 minutes or at room temperature for 8 to 12 minutes. After the moisture on the surface evaporates, the fingerprint pattern can be observed under the irradiation of a 365-nanometer ultraviolet lamp and can be photographed with a camera. 2. the latent fingerprint detection method based on red fluorescent carbon dot material according to claim 1, is characterized in that, described carrier is glass, metal, leather, plastics or pottery. 3. a preparation method of red fluorescent carbon dot, is characterized in that, concrete steps are as follows: Ultrasonically dissolve 0.05~0.2g of organic amine in water, add 0.5~2ml of phosphoric acid, mix well, seal it in a polytetrafluoroethylene-lined stainless steel reactor, at 150~220℃, hydrothermal reaction 4~48 hours; after the hydrothermal reaction was finished, the system was cooled to room temperature, and the solution was filtered with a microporous membrane to obtain a clear solution; the clear solution was neutralized with sodium hydroxide to obtain a suspension, and the bottom precipitate was collected with ethanol and Washing with water for several times; the washed sample is dissolved in an acidic solution, and then freeze-dried to obtain red fluorescent carbon dots. 4. A red fluorescent carbon dot obtained by the preparation method according to claim 1, its main component is carbon, and contains a small amount of nitrogen, hydrogen, and oxygen elements, and the particle diameter is 1 to 5 nanometers, with a graphitized structure.