CN109557066B - Preparation method of copper nano-cluster sweat latent fingerprint developing reagent and sweat latent fingerprint developing method - Google Patents
Preparation method of copper nano-cluster sweat latent fingerprint developing reagent and sweat latent fingerprint developing method Download PDFInfo
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Abstract
The invention provides a preparation method of a copper nano-cluster sweat latent fingerprint developing agent and a sweat latent fingerprint developing method. The method for displaying the sweat latent fingerprints is adopted, and the latent fingerprints are observed, photographed and fixed by means of a self-built latent fingerprint display observation system. The prepared nano particles have the advantages of small size, good stability, strong fluorescence and the like. The fingerprint is clear in the average lines and obvious in detail characteristics under the excitation of natural light and a multiband light source. The drop-developed fingerprint can emit different fluorescence under the multiband light source, and can eliminate the interference of background color. Compared with the traditional method, the method overcomes the defects of low sensitivity, weak binding capacity and difficulty in removing background color interference of the traditional reagent for developing the fingerprints, and has the advantages of high sensitivity, strong fluorescence, no toxicity and economy.
Description
Technical Field
The invention relates to the field of public security criminal technical fingerprint identification, in particular to a preparation method of a copper nano-cluster sweat latent fingerprint developing reagent and a sweat latent fingerprint developing method.
Background
Fingerprints are formed by the combined action of heredity and environment and have the characteristics of being different among people and unchanging in life. Due to the influence of various factors such as genetic materials, skin tissue structures, pathology, trauma and the like, the mastoid streaks of the fingerprints have specificity, diversity and stability, and the characteristics provide scientific basis for identifying and identifying the human body through analysis, identification and authentication of the fingerprint streaks. Meanwhile, due to the characteristic of object touching and mark retaining, fingerprints left on the object can truly reflect the fingerprint characteristics of the left-behind person, and play an important role in disclosing crime facts, locking criminal suspects, providing investigation directions for investigation personnel and providing scientific basis for trial and judgment in criminal cases.
In the fingerprint developing technology, the traditional methods include an illumination method, a solution method, a powder method, a fuming method and the like, and by selecting the corresponding method, the potential fingerprint is developed in a colored fingerprint by utilizing the combination reaction of a substance for developing the fingerprint and sweat, grease, blood, dirt and the like in the fingerprint or utilizing light irradiation. With the continuous development of scientific technology, in recent years, nanomaterials are focused on by researchers in various fields by virtue of their specific optical, magnetic, electrical, acoustic and mechanical properties. In the development application of latent fingerprints, researchers find that nano materials are easier to combine with inorganic and organic substances in the latent fingerprints compared with common materials. In addition, some fluorescent nano materials can generate fluorescence when being irradiated and excited by a light source such as ultraviolet light, and fingerprint characteristics can be clearly reflected by detecting fluorescence images emitted by the nano materials combined on fingerprints. Meanwhile, the nano material can be combined with other materials to form a nano composite material, so that the difficult and complex fingerprints left on various objects by criminal marks can be effectively displayed, and the problems that the existing display reagent is toxic and harmful, the display method has potential safety hazards and the like can be overcome.
The fluorescent nano-materials applied to the latent fingerprint display at present comprise cadmium sulfide, cadmium selenide, aluminum oxide, zinc oxide nano-particles and the like coated by molecules. However, the poor selective combination with fingerprint residues leads to unclear and inconspicuous fingerprint lines and contrast, and the expected effect is difficult to achieve; moreover, the reagent contains heavy metal ions, and the reagent is very likely to cause harm to the health of operators in the synthesis and use processes. Therefore, the application of nanomaterials gradually comes into the sight of people.
In nanomaterials, metal nanoclusters, which are aggregates composed of several to several tens of atoms, are in a transition state between a single metal atom and a larger metal nanoparticle, are smaller than 2nm in size, and are between a single atom and a nanocrystal in size. Compared with larger nanoparticles, the metal nanoclusters have more unique physicochemical properties, and have good fluorescence and water solubility. Meanwhile, the nano-silver nanoparticle has the characteristics of quantum size effect, strong light stability, good biocompatibility and the like, and is widely applied to the aspects of biological imaging, biomedicine, biological tracing, environmental detection, novel catalysts and the like, but the research and the application in the technical field of criminal science are only reported in documents and are still in the starting stage.
In the nano material, the metal nanocluster has unique optical properties and good biocompatibility besides the properties shared by the nano materials such as small-size effect, surface effect, quantum size effect, macroscopic quantum tunneling effect and the like, and is easy to perform surface functionalization and modification, such as non-covalent bond adsorption with amino groups, covalent bond with sulfydryl groups and the like. In the prior art, for example, in the preparation method of the gold nanocluster sweat fingerprint revealing reagent and the sweat fingerprint revealing method described in patent application No. 201610384933.4, gold nanoclusters are used as seeds, a layer of bovine serum albumin BSA is coated on the surfaces of the gold nanoclusters, the gold nanoclusters are reduced on the surfaces of the gold nanoclusters in a water phase by using the BSA as a template, and the gold nanocluster powder revealing reagent is obtained after separation, drying and grinding; the gold particles used in the method are heavy metals, the price of the gold particles is expensive, and the gold particles are very likely to cause harm to the health of operators in the synthesis and use processes.
In addition, the existing fingerprint display technology has the following defects: 1. it is difficult to exclude the interference of the background color: in the actual case, shooting of some fingerprints can be interfered by the background patterns of objects left, such as cigarette cases, bank cards, beverage bottles and the like, the materials which are applied to latent fingerprint display at present generally comprise gold powder, silver powder, magnetic powder, ninhydrin and the like, but the displayed color is single and is easily influenced by complex background colors; 2. fingerprint development technique latent fingerprints of rough objects appear difficult: for a rough object, when the depth of the concave part on the surface of the object is relatively greater than the height of the papillary striations on the epidermis of the finger, when a person contacts the part of the object, even if the pressure is larger, the fingerprint form with high value can not be left on the concave part on the surface of the object, and no appearing condition exists; in addition, the uneven characteristics of the rough object surface determine the discontinuity of sweat fingerprint lines, which causes difficulties in fingerprint appearance, extraction and analysis. For the sweat latent fingerprints on the rough object surface, the light irradiation on the surface can only be diffuse reflection, the contrast between the fingerprint substance and the left object is weak, the left condition is not enough to provide direct extraction, the laser method detection has certain limitation on the excitation of the inherent fluorescence of the fingerprints, and the laser method detection can be combined with other physical and chemical methods to exert the display effect to the maximum extent.
In summary, the prior art has the following disadvantages: 1. the used heavy metal is expensive and has high possibility of causing harm to the health of operators in the synthesis and use processes; 2. the interference of background color is difficult to eliminate in the using process; 3. fingerprint development technique latent fingerprints of rough objects appear difficult.
Disclosure of Invention
The invention aims to provide a preparation method of a copper nano-cluster sweat latent fingerprint developing reagent, which has the advantages of high sensitivity, low cost, safety, environmental protection, good developing effect, variable fluorescence and good stability, can eliminate the interference of background color, and has excellent developing effect on objects with rough surfaces and uneven surfaces.
Another objective of the present invention is to provide a method for displaying latent fingerprints, which is simple, safe and environmentally friendly.
The object of the present invention is achieved by the technical means that a developing reagent is prepared by using Branched Polyethyleneimine (BPEI) as a template, Ascorbic Acid (AA) as a reducing agent, and copper sulfate as a raw material under controlled heating conditions during a reaction.
The preparation method of the copper nano-cluster sweat latent fingerprint developing reagent comprises the following steps:
s101, dissolving BPEI in ultrapure water to prepare a solution of 0.01g/ml, and performing ultrasonic treatment for 5-10 min; dissolving AA in ultrapure water to prepare a solution of 0.1M/ml; mixing CuSO4Dissolving in ultrapure water to prepare 0.1g/ml solution;
s102, taking 0.1ml of BPEI solution, dropwise adding the BPEI solution into 10ml of ultrapure water, and slowly dropwise adding CuSO under stirring41ml (0.625 mM) of the solution, and after 3-5 min, dropwise adding 1ml AA (0.1M);
s103, respectively reacting at 30 ℃, 60 ℃, 90 ℃, 120 ℃ and 150 ℃ for 6-8 hours to obtain copper nanocluster solutions at all temperatures;
and S104, mixing and stirring the solution, and carrying out ultrasonic treatment for 10-15 min.
The other purpose of the invention is realized by the technical scheme that the method for developing the sweat latent fingerprints comprises the following steps:
s201, preparing a reagent, namely preparing a copper nano-cluster sweat latent fingerprint developing reagent by adopting the fingerprint developing reagent preparation method of claim or 2;
s202, pressing the finger print, wherein the volunteer presses the finger print on the surface of the object to prepare a finger print sample;
s203, displaying fingerprints in a dripping mode, wherein the latent fingerprints of the sweat on different objects are displayed by the display reagent in the step S201;
s204, drying the dripped latent fingerprints in an oven under the conditions of vacuum and 30-50 ℃;
s205, independently building a display observation system by utilizing a multiband light source, a colored filter and a digital single-lens reflex camera to observe the fluorescent sweat latent fingerprint, and photographing and fixing;
s206, in a darkroom, a multi-band light source is used for irradiating the latent fingerprint of the sweat displayed by the developing reagent prepared by the method, the fluorescence generated by the fingerprint is transmitted through a colored filter lens and recorded by a digital single-lens reflex camera, and the fingerprint papillary lines and the detailed characteristics thereof are fixed.
The invention provides a preparation method of a copper nano-cluster sweat latent fingerprint developing reagent, which takes BPEI as a template and AA as a reducing agent, changes reaction conditions, reduces copper nano-clusters with smaller particle size and changeable fluorescence, and uses the prepared novel nano material for developing latent fingerprints. The diameter of the copper nanocluster is generally less than 2nm and is close to the fermi wavelength of electrons, so the copper nanocluster can show strong fluorescence properties. Compared with other photoluminescent nano composite materials such as micromolecular fluorescent dyes, quantum dots and the like, such as gold, silver, platinum and the like, the copper nano cluster has the advantages of safety, no toxicity, easy surface modification, strong fluorescence stability and the like, and is relatively low in price. Based on the controllability of the size of nano-cluster particles and good biocompatibility, the copper nano-cluster is formed by reducing polyethylene imine as a template, so that the size of the copper nano-cluster is regulated and controlled to obtain fluorescence variability, the novel fluorescence developing reagent is prepared to carry out fluorescence labeling on the latent fingerprint of sweat, and a multiband light source is used for detecting the fingerprint presenting fluorescence. Objects bearing fingerprints (such as various metals, plastics, leather products, paint, the surface of natural-color woodenware and the like) do not emit light under the irradiation of ultraviolet light, blue-green light and the like, and are dark and dark tones. The copper nanoclusters emit fluorescence under multiband irradiation, so that the contrast between a background and fingerprints is improved, and when the background has weak fluorescence, the fluorescence variability of the copper nanoclusters is used for selecting the fluorescence color with the best effect, so that the interference of the background color is eliminated.
In the sweat latent fingerprint developing method, under an acidic condition, organic substances and amino-containing substances in the latent fingerprint are positively charged, while the surface of the metal nano-particles is negatively charged due to the adsorption of hydroxyl groups, so that the negatively charged nano-particles can be combined with latent fingerprint lines through electrostatic adsorption. According to the coordination principle, copper atoms can form stable complexes with molecules, ions or groups containing lone-pair electrons, so that copper nanoclusters and the like can form stable complexes with lone-pair electron-containing groups such as mercapto groups (-SH) and amino groups (-NH)2) Groups such as carboxyl (-COOH) groups are bonded by coordination bonds, and potential streaks are visualized by fluorescence emitted from CuNCs by electrostatic adsorption and coordination bond bonding. The copper nanocluster can be combined with biomacromolecules in the latent fingerprint, and even if fingerprints exist on the surface of a rough object, the copper nanocluster can be combined with sulfydryl (-SH) and amino (-NH) in the fingerprint2 ) The groups such as carboxyl (-COOH) and the like are bonded by coordination bonds, and the fluorescence thereof is utilized to effectively increase the contrast, thereby developing latent fingerprints.
In addition, the preparation method of the copper nano-cluster sweat fingerprint revealing reagent is simpler and more convenient in the whole preparation process compared with the existing preparation processes of gold, silver, platinum and the like, copper is used as an element commonly existing in the nature compared with gold nano-clusters, silver nano-clusters, platinum nano-clusters, copper nano-clusters and the like, and compared with gold, silver, platinum and other nano-clusters, the reagent has the advantages of abundant raw materials, economy, practicability, easiness in obtaining of the raw materials and low preparation cost in the preparation and use processes. The copper nanocluster also has the characteristic of no toxicity, and has stronger safety in use.
The method for showing the sweat latent fingerprints only needs to be dripped and shown when in use, is more simple and convenient compared with powder coating, avoids the phenomenon that dust is sucked into an operator in the process of powder coating, and uses heavy metals which can directly or indirectly influence the environmental safety; compared with the use of nano materials such as gold, silver and platinum, the fingerprint sensor is more sensitive, the effect meets the fingerprint requirement, and the whole manufacturing and using process is more stable and reliable. Except water molecules, the ultrapure water has almost no impurities, no organic matters such as bacteria, viruses and chlorine-containing dioxin, and certainly no mineral trace elements required by a human body, namely the ultrapure water almost without all atoms except oxygen and hydrogen, greatly reduces the influence of impurities and the like in the process compared with common water, and ensures that the result is more accurate.
Due to the adoption of the technical scheme, the invention has the following advantages: the preparation method of the copper nano-cluster sweat latent fingerprint developing reagent has the advantages of high sensitivity, low cost, safety, environmental protection, good developing effect, variable fluorescence and good stability, can eliminate the interference of background color, and has excellent developing effect on objects with rough surfaces and uneven surfaces; the method for displaying the latent fingerprints of sweat is simple and convenient to operate, safe and environment-friendly.
Drawings
FIG. 1 is a schematic diagram of the reaction of copper nanoclusters according to the present invention;
FIG. 2 is a schematic diagram of an autonomous construction visualization observation system and visualization principle in the present invention;
FIG. 3 is a schematic view of natural illumination of copper nanoclusters of the present invention;
FIG. 4 is a UV spectrum of a copper nanocluster of the present invention;
FIG. 5 is a schematic view of the fluorescence illumination of CuNCs synthesized in the present invention under different heating temperature environments;
FIG. 6 is a diagram of the fluorescence spectra of CuNCs synthesized under different heating temperature environments in the present invention;
FIG. 7 is a diagram illustrating the effect of latent fingerprints appearing on the surface of glass in the present invention.
Detailed Description
The invention is further described below with reference to the figures and examples.
Example 1
The preparation method of the copper nano-cluster sweat latent fingerprint developing reagent comprises the following steps:
s1, preparing a developing reagent by using branched polyethyleneimine, ascorbic acid and copper sulfate as raw materials; the method specifically comprises the following steps:
s101, dissolving BPEI in ultrapure water to prepare a solution of 0.01g/ml, and performing ultrasonic treatment for 5-10 min; dissolving AA in ultrapure water to prepare a solution of 0.1M/ml; mixing CuSO4Dissolving in ultrapure water to prepare 0.1g/ml solution;
s102, taking 0.1ml of BPEI solution, dropwise adding the BPEI solution into 10ml of ultrapure water, and slowly dropwise adding CuSO under stirring41ml (0.625 mM) of the solution, and after 3-5 min, dropwise adding 1ml AA (0.1M);
s103, respectively reacting at 30 ℃, 60 ℃, 90 ℃, 120 ℃ and 150 ℃ for 6-8 hours to obtain copper nanocluster solutions at all temperatures;
and S104, mixing and stirring the solution, and carrying out ultrasonic treatment for 10-15 min.
Example 2
The preparation method of the copper nano-cluster sweat latent fingerprint developing reagent comprises the following steps:
s101, dissolving BPEI in ultrapure water to prepare a solution of 0.01g/ml, and performing ultrasonic treatment for 6-8 min; dissolving AA in ultrapure water to prepare a solution of 0.1M/ml; mixing CuSO4Dissolving in ultrapure water to prepare 0.1g/ml solution;
s102, taking 0.1ml of BPEI solution, dropwise adding the BPEI solution into 10ml of ultrapure water, and slowly dropwise adding CuSO under stirring41ml (0.625 mM) of the solution, and after 3-5 min, dropwise adding 1ml AA (0.1M);
s103, respectively reacting at 30 ℃, 60 ℃, 90 ℃, 120 ℃ and 150 ℃ for 6-8 hours to obtain copper nanocluster solutions at all temperatures;
and S104, mixing and stirring the solution, and carrying out ultrasonic treatment for 12-14 min.
Example 3
A method of revealing latent fingerprints of sweat comprising the steps of:
s201, preparing a reagent, namely preparing a copper nano-cluster sweat latent fingerprint developing reagent;
s202, pressing the finger print, wherein the volunteer presses the finger print on the surface of the object to prepare a finger print sample;
s203, displaying fingerprints in a dripping mode, wherein the latent fingerprints of the sweat on different objects are displayed by the display reagent in the step S201;
s204, drying the dripped latent fingerprints in an oven under the conditions of vacuum and 30-50 ℃;
s205, independently building a display observation system by utilizing a multiband light source, a colored filter and a digital single-lens reflex camera to observe the fluorescent sweat latent fingerprint, and photographing and fixing;
s206, in a darkroom, a multi-band light source is used for irradiating the latent fingerprint of the sweat displayed by the developing reagent prepared by the method, the fluorescence generated by the fingerprint is transmitted through a colored filter lens and recorded by a digital single-lens reflex camera, and the fingerprint papillary lines and the detailed characteristics thereof are fixed.
Example 4
S201, preparing a reagent, namely preparing a copper nano-cluster sweat latent fingerprint developing reagent;
s202, pressing down the fingerprints, washing hands of the same volunteer with soap, drying the hands, touching two sides of the forehead and the nasal wings with thumbs, pressing down the sweat latent fingerprints on the objects to obtain clear fingerprint samples, and storing the fingerprint samples in a natural state;
s203, dripping fingerprints, and respectively and uniformly dripping the sweat latent fingerprints on the glass along the fingerprint papilla lines by the developing reagent in the step S201 clockwise;
s204, drying the dripped latent fingerprints in an oven under the conditions of vacuum and 30-50 ℃;
s205, independently building a display observation system by utilizing a multiband light source, a colored filter and a digital single-lens reflex camera to observe the fluorescent sweat latent fingerprint, and photographing and fixing;
s206, in a darkroom, a latent fingerprint of sweat developed by the developing reagent prepared by the method is irradiated by an ST55-12F multiband light source, fluorescence generated by the fingerprint is transmitted through a colored filter lens and recorded by a digital single-lens reflex camera, and fingerprint papillary lines and detailed characteristics thereof are fixed.
In the invention, in order to simulate the latent fingerprints on the actual case site as much as possible, the experimental fingerprint sample is stored in a natural state; when the thumb touches the forehead and the two sides of the nasal wing, more sweat, grease and other substances exist at the parts, and the printed fingerprint is better. The rubber head dropper respectively takes a proper amount of copper nanoclusters to be dripped and displayed clockwise along the fingerprint mastoid line, so that the damage probability of the fingerprint mastoid line can be greatly reduced, and the integrity of the fingerprint mastoid line is ensured as much as possible. The vacuum condition of the oven machine avoids the influence of other substances (such as moisture) in the air, and ensures the fast and efficient drying.
The invention provides a copper nano-cluster sweat latent fingerprint developing reagent, which takes BPEI as a template and AA as a reducing agent, changes reaction conditions, reduces copper nano-clusters with smaller particle size and changeable fluorescence, and uses the prepared novel nano-material for developing latent fingerprints. The diameter of the copper nanocluster is generally less than 2nm and is close to the fermi wavelength of electrons, so the copper nanocluster can show strong fluorescence properties. Compared with other photoluminescent nano composite materials such as micromolecular fluorescent dyes, quantum dots and the like, such as gold, silver, platinum and the like, the copper nano cluster has the advantages of safety, no toxicity, easy surface modification, strong fluorescence stability and the like, and is relatively low in price. Based on the controllability of the size of nano-cluster particles and good biocompatibility, the copper nano-cluster is formed by reducing polyethylene imine as a template, so that the size of the copper nano-cluster is regulated and controlled to obtain fluorescence variability, the novel fluorescence developing reagent is prepared to carry out fluorescence labeling on the latent fingerprint of sweat, and a multiband light source is used for detecting the fingerprint presenting fluorescence. Objects bearing fingerprints (such as various metals, plastics, leather products, paint, the surface of natural-color woodenware and the like) do not emit light under the irradiation of ultraviolet light, blue-green light and the like, and are dark and dark tones. The copper nanoclusters emit fluorescence under multiband irradiation, so that the contrast between a background and fingerprints is improved, and when the background has weak fluorescence, the fluorescence variability of the copper nanoclusters is used for selecting the fluorescence color with the best effect, so that the interference of the background color is eliminated.
In copper nanoclusterWhen the latent fingerprint developing reagent is used, organic substances and amino-containing substances in the latent fingerprint are positively charged under an acidic condition, and the surface of the metal nanoparticle is negatively charged due to the adsorption of hydroxyl groups, so that the negatively charged nanoparticle can be combined with the latent fingerprint line through electrostatic adsorption. According to the coordination principle, copper atoms can form stable complexes with molecules, ions or groups containing lone-pair electrons, so that copper nanoclusters and the like can form stable complexes with lone-pair electron-containing groups such as mercapto groups (-SH) and amino groups (-NH)2) Groups such as carboxyl (-COOH) groups are bonded by coordination bonds, and potential streaks are visualized by fluorescence emitted from CuNCs by electrostatic adsorption and coordination bond bonding. The copper nanocluster can be combined with biomacromolecules in the latent fingerprint, and even if fingerprints exist on the surface of a rough object, the copper nanocluster can be combined with sulfydryl (-SH) and amino (-NH) in the fingerprint2 ) The groups such as carboxyl (-COOH) and the like are bonded by coordination bonds, and the fluorescence thereof is utilized to effectively increase the contrast, thereby developing latent fingerprints.
In addition, the copper nano-cluster sweat fingerprint revealing reagent is simpler and more convenient in the whole manufacturing process compared with the existing manufacturing processes of gold, silver, platinum and the like, copper is used as an element commonly existing in the nature compared with gold nano-clusters, silver nano-clusters, platinum nano-clusters, copper nano-clusters and the like, and compared with gold nano-clusters, silver nano-clusters, platinum nano-clusters, copper nano-clusters and the like, the reagent has the advantages of abundant raw materials, economy, practicability, easiness in obtaining of the raw materials and low manufacturing cost in the manufacturing and using processes. The copper nanocluster also has the characteristic of no toxicity, and has stronger safety in use. The method for displaying the latent fingerprints of the sweat is provided, only dripping display is needed when the method is used, the method is simple and convenient compared with powder coating, the phenomenon that dust is sucked into an operator in the process of powder coating is avoided, and the used heavy metal can directly or indirectly influence the environmental safety; compared with the use of nano materials such as gold, silver and platinum, the fingerprint sensor is more sensitive, the effect meets the fingerprint requirement, and the whole manufacturing and using process is more stable and reliable. Except water molecules, the ultrapure water has almost no impurities, no organic matters such as bacteria, viruses and chlorine-containing dioxin, and certainly no mineral trace elements required by a human body, namely the ultrapure water almost without all atoms except oxygen and hydrogen, greatly reduces the influence of impurities and the like in the process compared with common water, and ensures that the result is more accurate.
FIG. 1 is a schematic diagram of a copper nanocluster reaction in which Branched Polyethyleneimine (BPEI) is dissolved in ultrapure water and slowly added dropwise with CuSO under stirring4The solution was mixed well, and Ascorbic Acid (AA) was added dropwise. BPEI is the template, and AA is the reductant, and metallic copper ion and template interact make the copper ion can reduce into the atom through the reductant, and the gathering forms the nanometer cluster on the template, and the BPEI as template protective agent then makes the atom that reduces can not gather too much because of the interact each other simultaneously, has avoided the formation of large granule metal particle to guaranteed that copper nanometer cluster has good stability.
FIG. 2 is a schematic diagram of an autonomous construction visualization observation system and visualization principle in the present invention; and (3) taking a proper amount of copper nanoclusters by using a rubber head dropper, uniformly dripping latent fingerprints, drying and fixing after the solution is fully combined with the fingerprints. A multi-band light source, a colored filter and a digital single-lens reflex camera are utilized to independently build a display observation system to observe the fluorescent sweat latent fingerprint and take a picture for fixation; in a darkroom, a multi-band light source is used for irradiating sweat latent fingerprints displayed by the developing reagent prepared by the method, fluorescence generated by the fingerprints is transmitted through a colored filter lens and recorded by a digital single-lens reflex camera, and fingerprint papillary lines and detailed characteristics thereof are fixed. At present, the latent fingerprints are actually displayed by brushing with powder, and the powder which is brushed is fine and easy to form floating objects in the using process, so that the human body is greatly damaged. The method shows the latent fingerprints by a solution drop display method, effectively solves the problem of dust, simultaneously, the prepared copper nanocluster has no toxicity, basically does not pollute human bodies and the environment in the using process, and has the characteristics of safety and environmental protection.
FIG. 3 is a schematic view of natural illumination of copper nanoclusters of the present invention, and FIG. 4 is a graph of an ultraviolet spectrum of copper nanoclusters of the present invention; FIGS. 4(a) to (e) are ultraviolet spectrograms of CuNCs produced under conditions of 30 ℃, 60 ℃, 90 ℃, 120 ℃ and 150 ℃, respectively. As can be seen from the graph, the ultraviolet spectrogram of CuNCs changes obviously at 365nm along with the change of the temperature, the CuNCs changes from no peak to a peak at 365nm along with the increase of the temperature, and the intensity of the peak also increases along with the increase of the temperature. We speculate that this is probably because CuNCs has the characteristic of adjustable size, and different heating conditions change the particle size of CuNCs particles, so that the particle size of the CuNCs particles increases due to the increase of temperature, and the properties of the CuNCs change accordingly. As can be seen from the figure, CuNCs underwent a change from blue to yellow, with blue at 30 ℃, blue-green at 60 ℃, yellow-green at 90 ℃, dark-green at 120 ℃ and pale-yellow at 150 ℃. The color change also proves that the particle size of the CuNCs can be changed by temperature, and different sizes of the CuNCs can be obtained by different heating conditions.
FIG. 5 is a schematic view of the fluorescence illumination of CuNCs synthesized in different heating temperature environments of the present invention, and FIG. 6 is a schematic view of the fluorescence spectrum of CuNCs synthesized in different heating temperature environments of the present invention; as can be seen from FIGS. 5 and 6, the fluorescence intensity of CuNCs exhibits a significant red shift (145nm) from 420nm (blue emission) to 565nm (yellow emission) as the temperature is increased from 30 ℃ to 150 ℃. Under the environment of 30 ℃, when the excitation wavelength is 345nm, the emission wavelength of CuNCs is positioned at 420nm, and blue fluorescence is obtained; under the environment of 60 ℃, when the excitation wavelength is 365nm, the emission wavelength of CuNCs is positioned at 460nm, and blue-green fluorescence is obtained; under the environment of 90 ℃, when the excitation wavelength is 400nm, the emission wavelength of CuNCs is positioned at 490nm, and yellow green fluorescence is obtained; under the environment of 120 ℃, when the excitation wavelength is 450nm, the emission wavelength of CuNCs is at 530nm, and light yellow fluorescence is obtained; under the environment of 150 ℃, when the excitation wavelength is 470nm, the emission wavelength of CuNCs is at 550nm, and yellow fluorescence is obtained. In the figure we clearly see the change of CuNCs from blue to yellow, which demonstrates that CuNCs has tunability. We speculate that this is due to the increased size of CuNCs, which results in a red shift of the absorption peak of the fluorescence spectrum of CuNCs, which also further confirms the emission mechanism of nanoclusters under the particle size effect.
FIG. 7 is a graph showing the effect of developing latent fingerprints on the glass surface in example 4 of the present invention; in the figure, a-c are respectively the latent fingerprints of the gold nanocluster, platinum nanocluster and copper nanocluster solution appearing on the glass. As can be seen from FIG. 7, the copper nanocluster solution has the best effect of developing latent fingerprints, clear fingerprint lines, obvious mastoid lines and furrow line levels, and clear and distinct detailed features. The gold nanocluster solution and the platinum nanocluster solution have poorer developing effects on latent fingerprints than the copper nanocluster solution. The basic outline of latent fingerprints displayed by the gold nanocluster solution drops is visible, most of lines are clear, but the detailed features are weaker to appear. The fingerprint shown by the platinum nanocluster solution is visible, but the definition of the lines and the appearance of the detail features are poor. The reason is that after the copper nanoclusters are optimized, BPEI and copper ions are combined more completely, and copper particles are combined with mercapto (-SH), amino (-NH 2), carboxyl (-COOH) and other groups in the latent fingerprint more easily through coordination bonds. Thereby allowing the latent streaks to be visualized by fluorescence from CuNCs. The gold nanocluster solution is prepared by taking BSA as a template, but as the BSA is a biological macromolecule, a shell membrane is easily formed when fingerprints are displayed, so that the specific binding capacity of the nanoparticles to the mastoid lines is weakened, and the contrast with the furrow lines is reduced. The platinum nanoclusters and the copper nanoclusters are prepared by taking the BPEI as a template, and as the combination of platinum ions and the BPEI is not thorough in reaction, platinum atoms formed on the BPEI are sparsely gathered, the identification of biomolecules contained in latent fingerprints is weaker, and the contrast between mastoid lines and furrow lines is reduced.
According to the experiment and the related figures, the preparation method of the copper nano-cluster sweat fingerprint revealing reagent has the advantages of high sensitivity, low cost, safety, environmental protection, good revealing effect, variable fluorescence and good stability, can eliminate the interference of background colors, and has excellent revealing effect on objects with rough surfaces and uneven surfaces; the method for displaying the latent fingerprints of sweat is simple and convenient to operate, safe and environment-friendly.
Claims (6)
1. A method for developing sweat latent fingerprints is characterized in that a copper nanocluster CuNCs sweat latent fingerprint developing reagent is used for developing the sweat latent fingerprints, and the method comprises the following steps:
s201, preparing a copper nano-cluster sweat latent fingerprint developing reagent:
preparing a developing reagent by using Branched Polyethyleneimine (BPEI) as a template, Ascorbic Acid (AA) as a reducing agent and copper sulfate as a raw material under the condition of controlling the heating condition during reaction; the method comprises the following steps:
s101, dissolving BPEI in ultrapure water to prepare a solution of 0.01g/ml, and performing ultrasonic treatment for 5-10 min; dissolving AA in ultrapure water to prepare a solution of 0.1M/ml; mixing CuSO4Dissolving in ultrapure water to prepare 0.1g/ml solution;
s102, taking 0.1ml of BPEI solution, dropwise adding the BPEI solution into 10ml of ultrapure water, and slowly dropwise adding CuSO with the concentration of 0.625mM under stirring41ml of solution is added, and after 3-5 min, 1ml of AA with the concentration of 0.1M is added dropwise;
s103, respectively reacting at 30 ℃, 60 ℃, 90 ℃, 120 ℃ and 150 ℃ for 6-8 hours to obtain copper nanocluster solutions at all temperatures;
s104, mixing and stirring the solution, and carrying out ultrasonic treatment for 10-15 min;
the fluorescence intensity of CuNCs shows obvious red shift from 420nm to 565nm as the temperature is increased from 30 ℃ to 150 ℃, and the emission wavelength of CuNCs is positioned at 420nm when the excitation wavelength is 345nm under the environment of 30 ℃, so that blue fluorescence is obtained; under the environment of 60 ℃, when the excitation wavelength is 365nm, the emission wavelength of CuNCs is positioned at 460nm, and blue-green fluorescence is obtained; under the environment of 90 ℃, when the excitation wavelength is 400nm, the emission wavelength of CuNCs is positioned at 490nm, and yellow green fluorescence is obtained; under the environment of 120 ℃, when the excitation wavelength is 450nm, the emission wavelength of CuNCs is at 530nm, and light yellow fluorescence is obtained; under the environment of 150 ℃, when the excitation wavelength is 470nm, the emission wavelength of CuNCs is at 550nm, and yellow fluorescence is obtained;
s202, pressing the finger print, wherein the volunteer presses the finger print on the surface of the object to prepare a finger print sample;
s203, displaying fingerprints in a dripping mode, wherein the latent fingerprints on different objects are displayed in a dripping mode by the aid of the display reagent in the step S201;
s204, drying the dripping latent sweat fingerprint in an oven machine under vacuum at 30-50 ℃;
s205, independently building a display observation system by utilizing a multiband light source, a colored filter and a digital single-lens reflex camera to observe the fluorescent sweat latent fingerprint, and photographing and fixing;
s206, in a darkroom, a multi-band light source is used for irradiating and displaying sweat latent fingerprints displayed by the reagent drop, fluorescence generated by the fingerprints penetrates through the colored filter lens and is recorded by the digital single-lens reflex camera, and fingerprint papillary lines and detailed characteristics thereof are fixed.
2. The method for manifesting latent fingerprints of sweat as in claim 1, wherein S202 comprises the steps of: the volunteer washed his hands with soap and dried, touched his thumb on the forehead and the sides of his nose, pressed the sweat latent fingerprint on his object to obtain a clear fingerprint sample, and stored the fingerprint sample in a natural state.
3. A method of revealing latent fingerprints according to claim 2, wherein the fingerprint samples are all provided by the same volunteer.
4. The method for manifesting latent fingerprints of sweat as in claim 1, wherein S203 comprises the steps of: and (3) respectively taking a proper amount of copper nanoclusters by using a rubber head dropper, and dripping along fingerprint papilla lines until the solution is fully combined with fingerprint substances.
5. The method for developing latent fingerprints of sweat according to claim 4, wherein an amount of copper nanoclusters are uniformly dripped clockwise along the fingerprint papilla lines.
6. A method of revealing latent fingerprints according to claim 1, wherein: in S203, the fingerprint remaining object is glass, plastic or metal object.
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