Fabrication And Application Of Hybrid SERS Probes With Tunable Resonance Wavelength

With specific geometrical features,the hybrid structures composed of noble metal nanomaterials and dielectric components undergo intensive electric field(E-field)enhancement as well as extended effective electric enhancement volume,which are efficient and reliable probes for surface enhanced Raman spectroscopy(SERS).At present,due to the insufficient research on morphology and mechanisms,the enhancement performance of hybrid probe is still vague.Therefore,the design and fabrication of more efficient metal-dielectric composites that meet the needs of practical applications become an important field in SERS research field.In this work,the electrostatic assisted self-assembly method was used to fabricate a core-satellite hybrid particle composed of a silica microsphere surrounded by a layer of gold nanorods(AuNRs)with various aspect ratio.The physical properties of hybrid particles were explored using finite-difference time-domain(FDTD)numerical simulation.With the help of portable Raman spectrometer,on-site detection of prohibited drugs,such as 3,4-Methylenedioxymethamphetamine(MDMA),was performed for crime scenario simulation.The specific studies are listed as follows.1.AuNRs with aspect ratios ranging from 2.4 to 7.0 were synthesized using the seed growth method.The surface modified AuNRs and silica microspheres with opposite charge were self-assembled into core-satellite structures.The SERS signals of the hybrid particles with different aspect ratios of AuNRs were investigated at different excitation wavelengths.Raman spectroscopy was performed at 633 nm and 785 nm excitation lasers.The results show that AuNRs with aspect ratios of 2.4 and 3.2 were found to produce relatively stronger SERS signals.As the aspect ratio of AuNRs was fixed,the strongest SERS signal was obtained from a hybrid particle with a diameter of 4 ?m.2.AuNRs and hybrid structures with aspect ratios ranging from 2.4 to 7.0 were simulated by FDTD to investigate the modulation of the resonance wavelength by changing the aspect ratio of the AuNRs.The results show that the resonance wavelengths of both AuNRs and hybrid structures change from 650 nm to 1100 nm in the range of corresponding aspect ratios.The E-field enhancement of the hybrid particles was simulated.The simulation results show that the trend of E-field enhancement as a function of particle size diminishes as the particle diameter larger is than 4 ?m.The above experimental results can be verified by FDTD simulations.3.The optimal monolayer detection plane and stability of the hybrid particles were investigated.The results confirm that the hybrid particles had great stability in highly salty conditions.The SERS signals of MDMA solution and its precursors(safrole and piperonal)were detected at different concentrations and the limits of detection(LODs)were achieved down to the scale of 5 n M,8 n M and 8 n M,respectively.On-site detection of the three substances and a simulation of mixed MDMA drug detection were performed with portable Raman spectrometer.The hybrid particles provide a new option for on-site detection as a SERS probe with augmented enhancement,high stability and low LODs.