Surface Modified Inorganic Materials for Nano Forensic Applications

Abstract

Surface modified Inorganic Materials have attracted considerable research interest due to their advantages of bi or multi-functionality and various applications. In this thesis, I demonstrate Metal-ion-modified silica powder for colorimetric forensic sensor, Photoluminescent europium(III) complex intercalated in natural and synthetic clay minerals for enhanced latent fingerprint detection and Semiconductor Quantum Dots as a Fluorescent Inorganic Nanomaterial for Forensic Application. In Chapter 1, we briefly explain evidence in forensic science and summarized On-site Colorimetric Sensor using Metal-ion-modified silica powder, latent fingerprint detection using Nanocomposite materials and fingerprint development using Fluorescent Inorganic Nanomaterials for Forensic Application. In Chapter 2, we demonstrated Quantitative Detection of Toxic H2S and NH3 Gases using Metal-Ion-Modified Silica Powders. A highly sensitive on-site colorimetric forensic sensor has been developed for the quantitative detection of hydrogen sulfide and ammonia gases. The sensor consists of metal-ion-modified silica-gel powders placed in a glass tube. The powder color changes upon reaction with toxic hydrogen sulfide and ammonia gases. It is capable of easily detecting toxic gases in the concentration range between 100 ppm, which is considered as immediately dangerous to life and health, and 3000 ppm, which may cause death, by using a glass tube with an inner diameter of 3 mm. Since the sensor reported here is insensitive to environmental conditions such as temperature or humidity, and is featured by simplicity, fast response, high sensitivity, and easily understandable results based on absolute affirmative/negative response, it is expected to be effectively used for on-site applications such as testing the existence of toxic gases in confined working and industrial spaces. In Chapter 3, we examined Quantitative Detection of Toxic S2- Ion in Blood Plasma using Metal-Ion-Modified Silica Powders. Immensely sensitive, accurate and simple on-site colorimetric sensor has been developed for the quantitative detection of the sulfide ion in human blood plasma. The colorimetric sensor consists of lead-ion-modified silica-gel powders placed in a glass tube. The powder color changes upon reaction with sulfide ions in blood plasma. It is capable of easily detecting toxic sulfide ion by using a glass tube with an inner diameter of 3 mm. By employing the type of colorimetric sensor to a blood sample, it is possible to detect the sulfide ion with a concentration limit of 0.1 ppm and excellent reproducibility, thus making it superior to conventional analysis methods that need multiple preparation processes and various sophisticated instruments. Since the sensor reported here is insensitive to environmental conditions such as temperature or humidity, and is featured by simplicity, fast response, high sensitivity, and easily understandable results based on absolute affirmative/negative response, it is expected to be effectively used for on-site applications such as detecting poisonous ions in blood samples. In Chapter 4, we demonstrated Photoluminescent europium(III) complex intercalated in natural and synthetic clay minerals for enhanced latent fingerprint detection. Fluorescent nanohybrid materials, europium(III) complex intercalated Na+-smectite clay minerals (synthetic hectorite and natural montmorillonite), have been developed to visualize latent fingerprints. The guest europium(III) complex ([EuCl2(Phen)2(H2O)2]Cl·H2O) was obtained by simple complex reaction between europium chloride hexahydrate (EuCl3·6H2O) and 1,10-phenanthroline (Phen) as a 1:2 molar ratio of Eu3+ ion to ligand molecules. The intercalated nanohybrids ([Eu(Phen)2]3+-clay minerals) were obtained through ion exchange reaction of interlayer sodium cation with europium complex ion. Guest europium(III) complex and [Eu(Phen)2]3+-clay mineral hybrids were characterized by powder X-ray diffraction, Fourier transform infrared, thermal analysis (TG-DTA), elemental analysis, UV-visible and fluorescence spectroscopy. The intercalated complex maintains a characteristic red 5D0-7F2 emission at wavelength 617 nm, which is comparable to the free complex. The 5D0-7F2 emission intensity of [Eu(Phen)2]3+-hectorite was ca. 3.5 times higher than that of [Eu(Phen)2]3+-montmorillonite, due to the presence of quenching impurities in natural montmorillonite itself. Fingerprint residues on glass slides were harvested by using [Eu(Phen)2]3+-clay mineral powders, resulting in good definition for enhanced latent fingerprint detection. Particularly, [Eu(Phen)2]3+-hectorite hybrid powder was more clearly separated from the background compared to the montmorillonite hybrid powder. In Chapter 5, we described Nano Forensic Application: Latent Fingerprint Detection on Diverse Surfaces by means of the Multifunctional Properties of Nanocomposite powder. We used photoluminescent [Eu(Phen)2]3+-clay nanocomposite powder to enhance the visualization of latent fingerprints on diverse porous and non-porous surfaces. We obtained nanocomposites powder through the ion exchange reaction of interlayer sodium cation in two different types of clay (synthetic hectorite type and natural montmorillonite-type) with europium (III) complex ion. Moreover, in order to improve interaction between latent fingerprint residue and nanocomposites powder, we successfully modified the surface property of [Eu(Phen)2]3+-hectorite nanocomposite to be more hydrophobic by means of simple sillylation reaction with hydroxyl group at the edge of clay and hexadecyltrimethoxysilane molecules. The nanocomposites powder showed a characteristic red emission at wavelength 617 nm. We detected and visualized latent fingerprints on the non-porous surfaces of glass, polymer film, plastic, metal, and adhesive tape. Also, we detected latent fingerprints on the porous surfaces of adhesive tape made of paper, credit card receipts, and paper money. In Chapter 6, we explored Latent Fingerprint Detection using Semiconductor Quantum Dots as a Fluorescent Inorganic Nanomaterial for Forensic Application. We synthesized QD@SiO2 by a modified Stober method to enhance the visualization of latent fingerprints on diverse surfaces with maintaining PL efficiency. In order to synthesize green-emitting QD (GQD) gradient alloy QDs (λem = 530 nm) emitting green light, CdO and Zn(OAc)2 were put into a 100-mL two-neck-RBF, and a condenser and a thermocouple were connected to the RBF. Then OA and ODE were put into the RBF, which was heated at 180 °C until the color of the solution went transparent. Amphiphilic polymers such as polyvinylpyrrolidione (PVP) were directly adsorbed onto the surface of semiconductor QDs. Also, silica shells were introduced to the QDs to synthesize QD@SiO2 which maintains PL efficiency. QD@SiO2 synthesized by a modified Stober method was appropriate for the detection and visualization of latent fingerprint as it maintained very strong emission efficiency as well as biocompatibility due to the silica shells on the surface. The strong fluorescence of QD could effectively visualize latent fingerprint deposited on various substrates found at the crime scenes such as aluminum foil, paper money, transparent polymer film and glass using Olympus camera. Most of the obtained fluorescent GQD@SiO2 nano-powders based latent fingerprint developers proved successful in developing latent fingerprints on porous and nonporous substrates. Moreover, Photographs of latent fingerprints developed with GQD@SiO2 nano-powders on porous surfaces of paper money and on non-porous surfaces of plastic materials using Video spectral comparator 6000. The results show superior fingerprint ridge images with photoluminescent property for the latent fingerprint detection in forensic application.