Fluorescent Poly(p-phenylene Vinylene) Nanoparticles For Fingerprint Development

Fingerprint has played an important role in forensic fields,identity certification,access control in border entry,and some other special regions,since the pattern of fingerprint is one of direct evidence for personal information storage,individual recognition and identification.All of these characteristics make the fingerprint development,recognition and identification of great significance.The development of fingerprint is especially important since it is the prerequisite for recognition and certification.There are already several conventional methods to develop fingerprints on different substrates;and employing fluorescent reagents with good luminescence property has shown superiority when developing fingerprints on colored backgrounds with interference.In recent years,fluorescent conjugated polymer has been used in fingerprint development as a new fluorescent material.This thesis focuses on conjugated polymer poly(p-phenylene vinylene)(PPV).PPV has been prepared as an aqueous colloidal solution,and its development effects on fingerprint against various backgrounds have been investigated by two different methods.System 1: After the precursor of PPV(pre-PPV)solution was prepared through modified Wessling method,the PPV nanoparticles in aqueous colloidal solution were obtained by adding the surfactant into the pre-PPV solution,followed by thermal elimination.The PPV nanoparticles in aqueous colloidal solution were used to develop visible and latent fingerprint on sticky side of an adhesive tape through simple immersion-rinse process,resulting in excellent fingerprint pattern.The aged fingerprint after at least 50 days' storage was well developed.The developing effect was negligibly affected by treating the fingerprints with water or other organic solvents,whether before or after development.The service life of the developing solution and the shelf life of the stocking solution were also studied;each developing solution(5.0 mL)could develop at least 30 fingerprints without sacrificing the legibility of the pattern,and the colloidal solution after 6 months of storage of still could be used to develop fingerprints effectively.The developing mechanism was explored;and several interference factors,such as surfactant and electrostatic adsorption,were excluded after a series of contro l experiments;and the hydrophobic interaction between PPV nanoparticles and the oily components was proposed to be the main reason for the selective adsorption of PPV on the fingerprint during the development.System 2: Selected substitution of the above pre-PPV solution by methanol was carried out to result in a series of precursor solutions(pre-PPV-N).After the thermal elimination with the presence of surfactant,a series of fluorescent conjugated polymer nanoparticles(PPV NP-N,N=0,1,2,3,4)with different emission color(from green to blue)in aqueous colloidal solution were prepared.These nanoparticles were used to develop fingerprints on various backgrounds(the fingerprints were fumed by 502 superglue in advance)by staining method.The developed fingerprints had stronger emission fluorescence and clearer fingerprint pattern,compared with the one developed by Rhodamine 6G under 365 nm UV light,and had different fluorescence colors under UV light due to the tuned emission of PPV NP-N.The scanning electron microscope(SEM)and laser scanning confocal microscope(LSCM)studies on the staining method of fumed fingerprints suggested that the loose and porous structure formed during the fuming maybe account for the fluorescence development.