Shulei Li

The fabrication of nanochain structure of gold nanoparticles and its application in ractopamine sensing

The illegal food additives including ractopamine and melamine throw a serious threat to human health. In this paper, the ractopamine and melamine were first used to form the nanochain structure of citrate-stabilized gold nanoparticles (AuNPs) with a convenient and inexpensive method. The fabricated nanochain structure consisting of several AuNPs was characterized by Scanning Electron Microscopy. A new longitudinal surface plasma resonance, which could be adjusted from visible to near infrared range, was observed in absorption spectra due to the aggregation of AuNPs. This could be well explained by Finite Different Time Domain algorithm theoretically. As confirmed by Fourier Transform Infrared Spectroscopy, the complex formed by hydrogen-bonding interaction between melamine and ractopamine could effectively promote the aggregation of AuNPs that was useful to develop the sensitivity and selectivity for the detection of ractopamine. Hence, the plasmonic coupling phenomenon of gold nanochain could be applied in bio-assay for ractopamine through the change of solutions color and optical absorption band with naked eye or absorption spectra. The linear range was broadened to (1.23 × 10(-7)M, 1.11 × 10(-6)M) and the limit of detection was extended to 4.10 × 10(-8)M (S/N=3). More importantly, this time-saving method will be promising in rapid and selective detection of β-agonist for clinical applications.

Photorefractive photonic crystals fabricated with PMMA and 5CB based materials using three-dimensional colloidal crystals

The variation of the refractive index is the key property of photorefractive materials and an important factor that affects photonic crystals. Therefore, photorefractive photonic crystals are interesting optical materials in physics. One of the typical groups of photorefractive materials, polymer dispersed liquid crystals (PMMA, 5CB, and C60), are filled into three dimensional silica colloidal crystals by solvent-induced phase separation to fabricate photonic crystals. The stop band shifts to shorter wavelength when a low voltage is applied. By using the z-scan and two-beam coupling technique, several band gap dependent optical properties of photorefractive photonic crystals are studied whilst continuously adjusting the wavelength of the stop band. The third-order nonlinear refractive coefficient is enhanced at the edge of the photonic stop band. The photorefractive diffraction efficiency achieves a maximum value when the stop band wavelength overlaps with the laser beam wavelength.