Yanying Zhu

Density-matrix evaluation of the enhancement to resonant Raman scattering and fluorescence of molecules confined in metallic nanoparticle dimers

In the present work we study the surface-enhanced resonant Raman scattering (SERRS) and fluorescence (SEF) spectra of a general model molecule confined in metallic dimers consisting of Ag, Au and hybrid AuAg nanoparticles (NPs). The electromagnetic (EM) enhancement factors were simulated by the generalized Mie scatting method and the scattering cross section of the molecules were obtained by density-matrix calculations. The influence of the size of the NPs and the separation between the dimer on the Raman scattering and fluorescence were systematically studied and analyzed in detail. It was found that the SERRS mainly related to EM enhancement and the SEF depended on the competition between EM enhancement and quantum yield, both of which could be controlled by tuning the radius and separation of the metallic dimers. The optimal radius of the NPs for SERRS were found to be around 30 nm for AgNPs, 40 nm for AuNPs and 50 nm for hybrid AuAgNPs. The strongest Raman enhancement as predicted by the theoretical simulations were 6.2 × 1010, 1.5 × 107 and 5.2 × 108 for the three types of structures, respectively. These results could offer valuable information for the design of metallic substrates for surface enhanced Raman and fluorescence measurements.

Au-Decorated Dragonfly Wing Bioscaffold Arrays as Flexible Surface-Enhanced Raman Scattering (SERS) Substrate for Simultaneous Determination of Pesticide Residues

Rapid sampling and multicomponent analysis are vital in pesticide residue detection. In this work, we proposed a SERS platform to detect three kinds of pesticides on apple peels simultaneously by a straightforward “press and peel off” method. The flexible Au/dragonfly wing (Au/DW) substrate was obtained from sputtering Au nanoislands on DW bioscaffold arrays by a simple direct current (DC) magnetron sputtering system. The high-performance substrate exhibited a low limit of detection (LOD) to 4-aminothiophenol (4-ATP) (10−9 M), outstanding reproducibility (less than 12.15%), good stability and suitability in multifold pesticide residues detection. Considering its excellent sample collection efficiency, the Au/DW substrate was employed to solve critical pesticide residue problems for detection of acephate (APT), cypermethrin (CPT), tsumacide (MTMC) and their multiple components on apple peels. The results show that the LOD was 10−3 ng/cm2 for APT obtained on the apple surface with a calculation equation of y = 0.26x + 6.68 and a determination coefficient (R2) of 0.970. Additionally, the LOD values for CPT and MTMC were 10−3 ng/cm2 and 10−4 ng/cm2, respectively. The finding in this work may provide a promising biomimetic SERS platform for on-spot detection of other organic pollutants in the food industry and inenvironmental protection.

Rotational analysis of birefringent crystal particles based on modified theory in optical tweezers

In order to achieve high-precision, controllable rotation of uniaxial birefringent crystal particles, we study the principle of optical rotation due to the transfer of spin angular momentum from light to birefringent crystal particles. The interaction process between the beam and particles is affected by various factors existed actually, for instance: the reflection of beam on the crystal surface, laser power, the set of angle between the crystal optical axis and surface, radius, phase difference between the ordinary ray and extraordinary ray. According to the analysis of these factors, the theoretical model of optical rotation is reconstructed. The theoretical curves of calcium carbonate and silicon particles chosen as experimental material between the rotational frequency and the radius are simulated and calculated. The result shows that the rotation frequency is inversely proportional to the cube of radius, and compared the performance of modified model with traditional model. The birefringent particles are rotated by optical tweezers in the experiment, and rotation frequency is measured with the same laser power. According to the experimental results of optical rotation, the modified Friese theoretical model is proved to be the reasonably and excellence, in addition, the result shows the maximum frequency of calcium carbonate is 19.1Hz, and the maximum frequency of silicon particles is 11.5Hz. The rationality of our experiment is testified by compared with theoretical analysis. Our study has great directive significance to the design of optical driven micro-mechanical motor and the material selection of rotor.