Finite-Difference Time Domain Simulation Of Surface-enhanced Raman Spectroscopy By Nobel-Metal Nanoparticles

Conventional approaches of detecting food contaminants are very much limited.Chromatography for instance,is a technique for separation of mixtures which may be a gas or a liquid.Although,chromatography-based techniques have been widely used as standard methods by the Food and Drug Administration?FDA?and other federal agencies,industrial sectors,and academia as well,generally,the limit of detection?LOD?for melamine using chromatography-based methods could reach the parts per billion?ppb?level.Therefore,better technology is needed to achieve food detection.The features of high throughput,reproducibility,selectivity,simplicity,and sensitivity,have made surface enhanced Raman spectroscopy?SERS?relevant in the field of biological sciences.NPs of noble metals,especially gold?Au?,exhibit surface plasmon resonance?SPP?in the visible and Near-infrared?NIR?spectrum ranges,whose plasmon modes arise from the collective oscillations of free electrons driven by the electromagnetic field of the incident light.This work aimed at designing NPs-substrate structure which is high SERS enhancement factor and low cost using finite-difference time-domain?FDTD?method.The result shows that for the selected three types of substrates of SiO₂,Ge and Al₂O₃the SERS effects of Ag followed this trend,SiO₂>Ge>Al₂O₃ which agrees with the order of the previous experiment.Further simulations reveal that the intensity of Ag on Al substrate is greater than that of SiO₂,Ge and Al₂O₃ semiconductor substrates.This shows the edge of the aforementioned substrate over semiconductor substrate cause its surrounding electromagnetic field could be enhanced more.More importantly,the simulation also gave a greater enhancement with AuNP/Al substrate?the localized electric field enhancement effect of AuNP on Al substrate has more signal than the previous?.The pick of it all was the joint effect of AuNP and AgNP with their combination.When two or more materials were combined with metallic structure,the hybrid SERS substrate provided even higher SERS enhancement due to the synergic effect of electromagnetic and chemical enhancement.The concomitant of different diameters of the sphere and interparticle spacing at some specified range of numbers under consideration has expanded the knowledge of SERS substrates.In order to maintain cost efficiency in the work flow,material reduction was necessary.This was carefully done during the work flow to ensure that not only that miniaturization exist but also to bring about more enhancement.The operation?mechanism?of the excitation wavelength was based on the particle's structure,miniaturization and substrate type for the SERS effect.Finally,the extinction spectra of single-crystal Au nanostructure were considered.The extinction peak of the same particle size also has a red-shift,which is due to the occurrence of plasma coupling effect between the nanostructures.This outcome has a certain guiding significance for the development and application of excellent SERS substrate which in turn would likely be the solution to the world problem of food-borne bacteria.