Synthesis of Carboxyl Functionalized Photoluminescent Nano-SiO2 Fingermark Reagent
CHEN Yu-tai1, HUANG Wei2, JIANG Hong1*, WANG Yuan-feng3, 4*
1. School of Forensic Science, People’s Public Security University of China, Beijing 102623, China
2. Institute of Forensic Science, Ministry of Public Security, Beijing 100038, China
3. China Cooperative Innovation Center of Judicial Civilization, Beijing 100025, China
4. Key Laboratory of Evidence Science, University of Political Science and Law, Beijing 100192, China
Abstract：Fingermark detecting is very important for individual identification over the past decades. However, the health of forensic technicians and our environment had been damaged seriously by these methods. The new method of Nano Particles Reagent for fingermark detection can effectively reduce the nano-dust suspending in the air, andrecover the technicians’ health and environment as well. It also resolved the problem of the disposal of dispersant and organic dye. The research focuses on the synthesis of fluorescent nanosilica functionalized by carboxyl and the migrating of latent fingermarks. In this study, nanoscale silicon dioxide doped with fluorescent dyes was prepared by reverse microemulsion method, and the Tris(2,2’-bipyridine)ruthenium(Ⅱ) chloride hexahydrate was used to make the nano silica luminescent. Amino modification was accomplished by aminosyl-silane coupling agent. Carboxyl modified fluorescent fingermark developing reagent based on silica nanoparticles was prepared by ammonolysis of butyl two anhydride. The surface chemical groups, fluorescence properties, dispersibility in aqueous phase, surface electrical properties and particle size of the target objectives were characterized by infrared spectroscopy, ultraviolet-visible absorption spectroscopy, Zeta potential-DLS tester and micro-spectrophotometer, respectively. The influence of dye concentration on the fluorescence intensity of products was studied. It was found that the electrical ionization efficiency, the concentration of nano-particles and the migrating time can directly impact the development. As a result, the three-factor orthogonal experiment was designed to explore the effects of pH value, dilution multiple and display time on the display effect in this study. The developing conditions of the fingermarks deposited on aluminum foil surface were preliminarily explored. Some conclusion was presented that the molecular structure of fluorescent dye remained comparing to the maximum absorption before reacting with silica, and 15 mmol·L-1 was the best concentration. The surface modifications of amino and carboxyl were accomplished, and the 375 nm was the exciting wavelength. The nanostructure of the objective in suspension was confirmed. According to the charge characteristic in the suspension, it was proved that the modified silica was positively and negatively charged by amino and carboxyl groups respectively. The product could migrate the fresh and aged fingermarks on non-porous surface in the condition: pH 2.8, double dilution, and 5 minutes. The carboxylic nano-SiO2 suspension is an effective method of fingermarks detecting, and according to the smoothness degree, the more detailed features could be obtained.
Key words：Fingermark detecting; Nano silica; Fluorescence; Small particle reagent
