Liangqia Guo

Visual detection of melamine in milk products by label-free gold nanoparticles

A simple, rapid, field-portable colorimetric method for the detection of melamine based on melamine-induced color change of label-free gold nanoparticles (Au NPs) was developed in this study. Melamine can induced the aggregation of Au NPs and results in the color change from wine-red to purple, which provided a platform for rapid and field-portable colorimetric detection of melamine. The proposed method can be used to detect melamine in liquid milk and infant formula with a detection limit of 1.0 and 4.2ppm, respectively, within 30min by naked eyes observation without the aid of any advanced instrument and the need of any complex pretreatment, and detect as low as 0.15ppm of melamine in liquid milk and 2.5ppm of melamine in infant formula with UV-vis-spectroscopy. The proposed method is promising for on-site screening of melamine adulterant in milk products.

Preparation of a new core-shell Ag@SiO2 nanocomposite and its application for fluorescence enhancement.

Ag@SiO(2) nanoparticles with different shell thicknesses were synthesized via modified Stöber method. Rhodamine B isothiocyanate was covalently bound onto the surface of Ag@SiO(2) nanoparticles to form fluorescent core-shell Ag@SiO(2) nanocomposites. Effects of shell thickness on the fluorescence enhancement were examined using the corresponding nanobubbles prepared by cyanide etching as a control. The result showed that the fluorescence enhanced as the shell thickness increased till the distance between fluorophore and metal core reached about 75nm with the optimal enhancement factor of ∼5-folds. Further increasing of fluorophore-metal distance caused a decrease in the enhancement factor.

A novel sensor based on the porous plastic probe for determination of dissolved oxygen in seawater

A new sensor based on the porous plastic probe has been developed for the detection of dissolved oxygen. This probe was prepared by co-polymerization of monomer, cross-linking reagent, porogent and luminescent ruthenium(II)diimine complex. The porous plastic probe exhibits good response to dissolved oxygen and resistance to indicator leaching out due to its high hydrophobicity. The preparation and characteristics of the probe were investigated in detail. This porous plastic probe serves as analyte-sensitive function as well as optical wave-guide, which make it easy to assemble the fiber-optical chemical sensor (FOCS). The developed sensor has been applied to the determination of dissolved oxygen in seawater with satisfactory results compared with the standard method.