SERS Detection Of Melamine With Surface-bound Gold Nanoparticles On Polymer Monolith: A Comparative Study Of Spheres,Rods And Prisms With Monolith

Porous polymer monoliths represent a new class of polymer materials emerged in the early 1990s that revolutionized separation techniques.These separation media are bulk porous materials in which microporous channels along the whole column allow clear flow-through of solvents.Material transfer is dominated by mass convection and the separation occur in micro and meso-pores.The physiochemical properties of porous polymer monolith make it an ideal base material for food analysis,drugs extraction and separation from biological samples.Several techniques are developed to investigate separation and detection of biological and chemical compounds.Most important detection technique is Surface Enhanced Raman Spectroscopy（SERS）to identify molecules through Raman spectra.This surface sensitive technique enhances Raman scattering by molecules adsorbed on rough surfaces.Monolith,in this case,provide large specific surface area,crystalline alignment and clean surface for the target molecules to be detected accurately.To enhance the SERS detection limit,Metallic nanostructures（e.g.,nanoparticles,nanowires,nanotubes,and Nanorods）interact with analyte molecules and result in amplified Raman scattering signals,thus allowing for sensitive detection down to the single molecule level without the requirement of labeling target molecules.The accurate binding of metal nanoparticles inside the porous network provide great SERS adsorption of analyte molecules.This thesis investigates the impact of gold nanomaterials surface chemistry and morphology to monolith scaffold through SERS.Monolith is synthesized by the polymerization of EDMA-co-GMA（cross linker and functional monomer）,Cyclohexanol（Porogen formation）and 2,2-Dimethoxy-2-phenyl-acetophenone（photo-initiator）on gold coated silicon wafer.Three types of gold nanomaterials（Gold nanoparticles（GNPs）,Gold Nanorods（GNRs）and Triangular Gold Nanoprisms（GNPrs））are immobilized on monolithic surface to evaluate the comparative sensitivity of SERS signals with monolith.TEM,SEM and Raman Enhancement assess the morphology,surface chemistry,optical properties,size,shape and stability respectively.Using well-characterized SERS scaffold on planar surface,nanomaterials inside the pores are studied.Monolith functionalized with GNPs provide large SERS enhancement（upto to 10⁸-fold）in comparison with Gold NRs and GNPrs composition.Raman signal molecule Rhodamine（R6G）is applied to validate the SERS signal amplification effect of these nanomaterials embedded on monolith.From these data,a novel monolith sensor with a perfect binding of GNPs（GNP@GMA-EDMA）is developed.To understand the detection ability of selected GNP@GMA-EDMA SERS-active monolith sensor,melamine is analyzed in commercial milk.Melamine is a toxic nitrogen rich compound which has been extensively added to food and milk to increase the protein content of products.Therefore,the monolith sensor has significant advantage for its ability to detect lowest limit of melamine in milk.The method shows a good linear relationship（R²=0.99）between the height area of melamine SERS band(at 710cm^-1)and melamine concentration ranging from6.5<mgl^-l<0.125.The limit of detection（LOD）for melamine is 0.11mgl^-1 which is a practical concentration to determine milk toxicity with melamine,and acceptable recoveries ranging from 94.99-102%.The analysis time to determine melamine in whole milk is 10 minutes and can be reliably used for melamine detection in milk in accordance with the FDA’s tolerance limit of 1mgl^-1 in USA and China.