Study On Novel Fluorescent Powders And Their Application Of Latent Fingerprints Development

Fingerprints,considered as“king of physical evidences”,are important clues in targeting the criminal suspects and crucial evidences for individual recognition in criminal investigation and forensic sciences.Therefore,the development and identification of fingerprints are especially important.The traditional developing methods,such as ordinary fingerprint powders,cyanoacrylate fuming,silver nitrate,ninhydrin methods and etc,which have the disadvantages of low sensitivity,selectivity,contrast and high detection limit,result in the difficulty of recovery of latent sfingerprints at the scenes;Some fluorescent nanomaterials such as noble metal nanoclusters,semiconductor quantum dots and rare earth up-conversion nanoparticles emerging in forensic science in recent years,which have the shortcomings of high cost,complicated process,high toxicity,will limit their further applications in the development of latent fingerprints.In this paper,carbon dots and rare earth complexes were studied to deeply exploit the value of fluorescent nanomaterials in the field of latent fingerprint development and polymer composites.Three novel types of nanopowders,SiO₂@C-dots,Eu_xTb_1-x?AA?₃Phen and Ce_xLa_1-x?SSA?₃Phen complexs,were synthesized for the luminescence detection of latent fingerprints and fluorescent films.Main works are listed as follows:?1?Preparation of SiO₂@C-dots composite microspheres and its application in the development of latent fingerprints.SiO₂@C-dots composite microspheres with strong fluorescence-emission were synthesized using monodispersed silicon dioxide microspheres as carriers and dispersants,citric acid as carbon source and aminosilane as nitrogen source by hydrothermal method;The preparation conditions were optimized,such as the types and concentrations of amino silane,reaction time and temperature.The results showed,when molar ratio?CA:AS?reached 1:3,hydrothermal temperature is 200?and reaction time is 3 hours,the product had the strongest fluorescence intensity.At the same time,we studied the influence of particle size of silica and aminosilane to luminescent properties,and probed into the mechanism of solid-state luminescence.This method had the advantages of low cost,simple operation.The SiO₂@C-dots prepared through this method have controllable particle size and strong fluorescence intensity,and they realized a fast detection for latent fingerprints on different substrates and for different aging time when applied in the field of latent fingerprint development.According to the results from automatic fingerprint identification system?AFIS?,the recognition rate of detail feature of aged fingerprint from this method was higher than commercial fluorescent powders of 22.2%,super cyanoacrylate fuming method of 29.2%,magnetic powders of 47.2%.This novel method featured nontoxicity,high contrast,high sensitivity,high selectivity,low background interference and widespread application,which showed the potential applications of carbon dots as a new fluorescent probe in latent fingerprint development.?2?Preparation of Eu_xTb_1-x?AA?₃Phen nanopowder and its application in fingerprint development.Solid powder Eu_xTb_1-x?AA?₃Phen of nanoscale was synthesized by solvothermal method using rare earth europium?Eu?and terbium?Tb?as raw materials,acyclic acid as the first ligand,Phen as the second ligand.The preparation condition was optimized,such as the relative content of rare earth ions,reaction temperature and time.The results showed when reaction temperature was 140?,reaction time was 4h,binuclear Eu_0.5Tb_0.5?AA?₃Phen powders had the strongest emission intensity of red light,and the emission wavelength fixed at 619nm;While mononuclear Tb?AA?₃Phen powders had the strongest emission intensity of green light at about 546nm.In the design of Eu and Tb system,an energy transfer process of Phen?AA?Tb³⁺?Eu³⁺was demonstrated by spectral analysis,in which Tb³⁺was suggested as sensitizer to Eu³⁺and Eu³⁺as quencher to Tb³⁺.Our Eu_xTb_1-x?AA?₃Phen nanopowder prepared through this method can effectively recognized the latent fingerprints on different substrates with a lower limit of detection.Fingerprint ridges details were obviously observed and the second and third-level features of the ridges were clearly distinguishable mainly due to the specific interaction between rare earth complexes and DNA in the fingerprint residues.The results from AFIS showed that the recognition rate of detail feature of aged fingerprint ridges from this method was higher than commercial fluorescent powders of23.2%,cyanoacrylate fuming method of 30.1%,magnetic powders of 47.9%,provding a new alternative for luminescence measurement of latent fingerprint.?3?Preparation of TCA/Eu_xTb_1-x?AA?₃Phen thin-film and its fluorescent properties.To widen the application of Eu_xTb_1-x?AA?₃Phen complexes,a series of tri-cellulose acetate TCA/Eu_xTb_1-x?AA?₃Phen composites were prepared by solution blending method and their luminescent properties were studied.The excitation spectra of all composites indicated that the TCA matrix probably affected the energy absorption and transfer of organic ligands,especially in TCA/Eu?AA?₃Phen system.With the increasing doping contents of complexes,the impact became weaker gradually.In TCA/Eu_0.5Tb_0.5?AA?₃Phen composites,the introduced Tb³⁺ions had some influence on the energy absorption and transfer of organic ligands.The luminescence intensity of TCA/Eu_0.5Tb_0.5?AA?₃Phen composites was obviously higher than that of TCA/Eu?AA?₃Phen composites,which indicated that Tb³⁺benefited the characteristic emission of Eu³⁺.The dilution effect of TCA to terbium ion and europium ion was helpful to overcome concentration quenching.In summary,TCA/Eu_0.5Tb_0.5?AA?₃Phen composite?doping ratio of 88:12?thin-film,with the CIE coordinates of?0.67,0.35?,showed the red intensest influorescence and thermostability and was expected to be used in the field of fluorescent marking and flexible display material.?4?Preparation of Ce_xLa_1-x?SSA?₃Phen powder and its development of latent fingerprints.Ce_xLa_1-x?SSA?₃Phen solid powder of nanoscale with blue light was synthesized using rare earth cerium and lanthanum as raw materials,sulfosalicylic acid as the first ligand and Phenanthroline as the second ligand.The preparation condition was optimized,such as the relative content of rare earth ions,reaction temperature and time.The results showed fluorescence intensity and concentration were nonlinearly related in Ce_xLa_1-x?SSA?₃Phen system.When the molar ratio of Ce³⁺and La³⁺were 1:4 and 1:7,La³⁺could obviously strengthen luminescent intensity of Ce³⁺and the Ce_0.125La_0.875?SSA?₃Phen complex had the strongest luminescent emission at about437nm.This indicated that the introduction of La³⁺had influence on the energy absorption and transfer of the organic ligands.Ce_xLa_1-x?SSA?₃Phen powders prepared by this method were spherical with an average particle size of 150 nm,which can efficiently develop latent fingerprints on different substrates.The result from AFIS showed the recognition rate of of detail feature of aged fingerprint ridges from this method was higher than commercial fluorescent powders of 24.6%,cyanoacrylate fuming method of 31.5%,magnetic powders of49.3%,which provided a new way for the application of rare earth complex to the detection of latent fingerprints at crime scenes.?5?Preparation of TCA/Ce_xLa_1-x?SSA?₃Phen composite film and its fluorescent property.A series of cellulose triacetate TCA/Ce_xLa_1-x?SSA?₃Phen?x=0.8,0.875?composites were synthesized by solution blend method.The characterization results showed that TCA matrix in such ternary compound may influenced the energy absorption and transfer of the organic ligands because of the formation of hydrogen bond between SSA and TCA.When the doping content of complexes reached highly,this influence was almost disappeared.The luminescent intensity of TCA/Ce_0.2La_0.8?SSA?₃Phen composites were obviously stronger than that of TCA/Ce?SSA?₃Phen composites,indicating La³⁺was success in sensitizing the characteristic emission of Ce³⁺.In brief,TCA/Ce_0.2La_0.8?SSA?₃Phen composite?doping ratio of 85:10?thin-film,with the CIE coordinates of?0.67,0.35?,showed the red intensest influorescence and thermostability and was expected to be used in the field of fluorescent marking and flexible display material.