Rationally Designed SERS Substrates And Their Application On The Detection

With the development of modern nanometer technology and laser technology, surface enhanced Raman spectroscopy (surface-enhanced Raman spectroscopy, SERS) has been developed rapidly like bamboo shoots after a spring rain. SERS can detect molecules that on or near the surface of plasmonic nanostructures (noble metals such as gold and silver), and it greatly extends the role of standard Raman spectroscopy. SERS has high sensitivity, rapid detection, spectral narrow that can achieve multicomponent determination and fingerprint spectrum characteristics and so on, is widely used in explosives detection, environmental monitoring and biological imaging and other fields. With the development of material science, substrate materials from noble metal nanoparticles sol gradually developed to composite structures, for example, SERS and fluorescent, magnetic, and optical catalytic. In order to improve the universal detection of SERS technique, the substrates need to have good stability, reproducibility, the affinity between molecules and the surface of substrate through rational modification. To make a long story short, the rational design of SERS substrates according to the different needs and the substrates are rationally modified are the soul of SERS detection technology. In this paper, several kinds of noble metal materials were used as SERS substrates and rationally modified them, at last they were applied to detect explosives, the diagnosis of cancer cells and so on. The main research contents are as follows:1. The inkjet printing of AgNPs colloid as ink on cellulose paper is highly simple for the fabrication of large-area SERS substrates. The increment of layer-by-layer printing achieves the highly uniform coverage of AgNPs on the paper. The differences on the various districts of paper for analyte collection and SERS effect are completely eliminated. On the other hand, the change of layer numbers can adjust the surface plasmon properties of aggregating nanoparticles to maximize the SERS response.The layer-by-layer printed AgNPs paper was modified with p-aminobenzenethiol (PABT) for efficiently collecting airborne trinitrotoluene (TNT) via a charge-transfer reaction and for greatly enhancing the Raman scattering of PABT by multiple spectral resonances. Thus, a Raman switch concept by the Raman readout of PABT for the detection of TNT was proposed:The Raman spectrum intensity of PABT can indirectly reflect the content of TNT. Using a beam of near-infrared low-energy laser, inkjet-printed silver nanoparticle paper sensor can be used to detect of explosive particulate residues in various matrices using an approach similar to the olfactory system.2. The ultrathin g-C3N4/ Au@Ag nanoparticle hybrids were fabricated according to a self-assembly procedure. The surface of g-C3N4 modified with cationic polymer polyethyleneimine (PEI) to anchor the Au@AgNPs through electrostatic adsorption. Self-assembly is an ordinary method to fabricate hybrids in which the loading ratio and the morphology of the nanoparticles are tunable. In contrast to Au@AgNPs, the hybrids show stronger SERS activity owing to the large specific surface area and π-π* interaction. Finally, the folic acid molecules physically adsorbed on the hybrids as targeting ligand with folic acid receptor on cancer cells to for cancer cell diagnosis.3. Using the seed growth method to fabricate Fe3O4/Au nanohybrids, and then continue to generate a layer of silver on the gold nanoparticle to form Fe3O4-Au@Ag dumbbell-shaped nanohybrids. The Fe3O4/Au nanohybrids could be finely tuned from heterodimer nanoparticles to core-shell nanoparticles, by controlling the ratio of gold nanoparticles "seed" and iron oleate. The dumbbell nanohybrids are both superparamagnetic and SERS activity, and then could be modified with different molecules to be a promising substrate material.