We show that hybrid organic-inorganic particles are efficient for accurate sensing of mercury ions and following up trace amounts of the mercury pollutions spread in the environment. The process of synthesis of a working substance starts from preparation of rhodamine 6G derivative. Then the dye molecules are bound on the surface of Au-Pd core-shell nanorods. Mercury ions with different concentrations are finally attached onto this fluorescence sensor. Fluorescence emission of the sensor is detected with a luminescence spectrophotometer. The experimental results demonstrate that the fluorescence intensity of one of our sensors, a sensor B, is remarkably enhanced when the mercury-ion concentration increases from 0 to 15.5 µM. The limit of detection of the ions is as low as 20.6 nM. The working mechanism of our fluorescence sensor can be explained through the fluorescence-energy transfer and the plasmonic effect associated with spirolactam forms of rhodamine and conducting bimetallic nanoparticles.

Abstract. We have applied a response surface approach to study the fluorescence quantum yield (FQY) of rhodamine 6G (Rh6G) mixed with Au-Pd core-shell nanorods (Au-Pd NRs). The FQYs have been measured for the Rh6G concentrations varying from 3.53×10 -7 to 1.70×10 -6 mol/L and the concentrations of Au-Pd NRs from 7.06×10 -6 to 1.36×10 -4 mol/L. Our experimental results testify that the FQY depends notably on the proportions of Rh6G and Au-Pd NRs. A specific relationship between the FQY and the concentrations has also been confirmed by a response surface plot. It is found that the discrepancy between the experiment and the calculations is less than 2%.

Fluorescence polarization and emission spectra of Rhodamine 6G solution with gold nanoparticles have been studied. It is found that the emission intensities tend to be low when the gold nanoparticles are added into the solution partly due to the energy transfer from the Rhodamine 6G to gold nanoparticles. The fluorescence polarization increases as the concentration ratio of the gold and Rhodamine 6G is more than 124 and decreases as the ratio is about 1115. The enhancement and reduction of fluorescence polarization values are understood as the shortening of the fluorescence lifetime and a temperature effect from the heating of gold nanoparticles, respectively.