The Application Of Fluorescent Probes In Detecting Latent Fingerprint

Fingerprints are widely used in criminal investigation due to their inherent uniqueness and long lasting property.Latent fingerprints(LFPs)refer to the invisible print left on the surface of objects after the contact of fingers or palms.Fluorescent probes are seemed to be ideal material for LFPs identifications due to their intrinsic high sensitivity,low background signal,satisfactory resolution and simple operational process.Increasing efforts have been made by researchers to develop new kind fluorescent reagents visualizing LFPs.In this thesis,we utilized three fluorescent compound: fluorescent dye,fluorescent nano material,targeted fluorescent reagent(NO fluorescent probe)detecting LFPs.First,a type of perylene derivative fluorescent dye with four positive charges visualizing LFPs.This probe has a large conjugate ring and a rigid plane,which has excellent luminous property under UV excitation.The four positive charges can be specifically adsorbed with the material on the fingerprint ridge.In the developing process,the effects of concentration and pH were investigated and the fluorescence sensitization of the surfactant was studied.And the optimum condition was: c = 1 mM,p H = 7.3.The dipping method and the ultrasonic spraying method were used to develop LFPs.It was found that the fluorescent fingerprint obtained by dipping method was better in the resolution aspect but was limited in the laboratory study,and can not be applied to the crime scene for dipping big objects in the solution.Ultrasonic spraying method can solve this restriction,and receive good quality fingerprint images in the meantime.In addition,ultrasonic spraying method can be extended to other fluorescent reagents developing LFPs,providing a new idea.Taking into account that the cumbersome steps in the synthesis of fluorescent dyes and the using some of organic solvents,which do not meet the purpose of green synthesis.And fluorescent dyes to the human body is potentially dangerous.Nano-materials used in fingerprint detection prospects are very broad,has become a research hotspot in the criminal investigation field.A series of fluorescent carbon dots(CDs)were prepared by different materials and synthesis methods.It was found that most of the CDs had the solid state fluorescence quenching property,which limited their application in fingerprint development.Among them,CDs synthesized by regulating the microwave radiation method were still fluorescent in solid state,through controlling the power of microwave to avoid the CDs of complete carbonation,and thus they can maintain the characteristics of solid-state fluorescent.In addition,the CDs synthesized by the hydrothermal method and use high polymer as raw material taking the chain of the polymer compound as a matrix,and the solid-state fluorescence can be maintained,either.Two types of CDs were selected for developing LFPs.The results showed that the CDs using citric acid and glutathione as raw material and synthesized by regulating the microwave radiation method whose average particle size of CDs was 5.3 nm and the FQY was 48.1%.Which achieved the best developing effect,the best,can detect up to 30 days of aging fingerprints and LFPs deposited on a variety of objects,and can be applied to both spraying and powder method developing LFPs.The powder method compensated for the applicability of the spraying method to the non-porous material,while the spraying method compensated for the consumable property of the powder method.Therefore,the two methods complemented each other,and can be applied to the actual crime scene information collection,can be used as a kind of ideal fingerprint development material.At last,an novel method detecting LFPs was set up,which was based on the specific absorption of nitric oxide(NO)on the hydrophobic ridges of fingerprints and a fluorescence probe 1,2-diaminoanthraquinone(DAQ).The method was proved to be universally applicable to many different substrate materials and effective to the aged LFPs for as long as 30 days.It was effective in detecting LFPs on the non-porous materials but less effective in porous materials.The decomposition of grease and dust in the air can affect the quality of fluorescent fingerprints.This method is also proven to be very reproducible and highly sensitive.In addition,this method can be extended to other sensitive NO fluorescence probes.When this method is replaced by a more sensitive NO probe,the LFPs can be developed with greater sensitivity.This method can be applied at the crime scene by using miniaturized instruments such as vial NO gas cylinders,portable UV lamps and digital cameras.