Synthesis Of Carbon Dots And Their Application On Latent Fingerprint Detection

Because of semiconductor quantum dots’ excellent optical,electrical,and catalytic properties,they have generated considerable interest of researchers and are gradually applied in solar cells,bio-labeling and other fields.In 2000,semiconductor quantum dots was firstly introduced in fingerprint detection by Menzel.Gradually,researchers found that the heavy metal element contained in quantum dots could do harm to the health of users.In 2015,a nontoxic nano-material called carbon dots was proposed to solve the above problem by Fernandes.On this basis,the application of carbon dots in fingerprint detection will be investigated further in this paper.C-dots solution was prepared by gelatin and distilled water through one-synthesis hydrothermal method and then was characterized by TEM、FTIR、XRD and fluorescence spectrum.C-dots solution and colloidal silica were respectively mixed thoroughly by volume ratio 3:1、2:1、1:1、1:2、1:3.Then five kinds of fluorescent C-dots powders were prepared by freezing-dry.The study showed that volume ratio 2:1 was the optimum formula by comparing the appearance and fingerprint detection results of these five kinds of fluorescent Cdots powders.Then the fingerprints developed by the optimum fluorescent powder were excited respectively at 365 nm UV 、 405 nm violet laser 、 447 nm blue laser.Through comparing fingerprint detection results on many kinds of objects under different light sources,447 nm blue laser was finally determined as the optimum light source.The stability of powder determines its value in practical working.Study showed that good fingerprint effects were also obtained by the fluorescent powder reserved six months with high fluorescence intensity.Besides,compared with magnetic powder and commercial green fluorescent powder,the fluorescent C-dots powder showed good fingerprint detection effects when applied to 7-day and 15-day old fingerprints.Although fluorescence intensity of fluorescent C-dots powder was less than commercial green fluorescent powder,fluorescent C-dots powder was not easy to float and could not pollute the background.The in vitro cytotoxicity of fluorescent C-dots powder was also evaluated by MTT test.The test showed that the C-dots fluorescent powder solution was non-toxic to L929 cells when the concentration was less than 1000μg/mL.The C-dots fluorescent powder was respectively mixed with 200 mesh 、 400 mesh 、600mesh、800mesh and 1000 mesh iron powders by mass ratio 1:1、1:2、1:4、1:6、1:8.Then twenty-five kinds of fluorescent magnetic powders were obtained.The C-dots fluorescent powder mixed with 800 mesh iron powder by mass ratio 1:4 was determined as the optimum formula by comparing the appearance,structure,stability of powders and fingerprint detection effects.The study showed that the fluorescent magnetic powder made by the optimum formulahad high sensitivity and good detection effects.Therefore,it had referential meaning in practical working.