Amplified fluorescence turn-on assay for mercury(II) based on conjugated polyfluorene derivatives and nanospheres

Abstract

Detection of mercury with high sensitivity and selectivity constitutes a significant research concern. Here, we report an amplified fluorescence turn-on assay for mercury(II) with an improved performance. This sensing system takes advantage of optically amplifying fluorescent conjugated polyfluorene derivatives and DNA immobilized silica nanospheres (NSs) in addition to the specific thymine- mercury(II)-thymine(T- Hg2+-T) interaction. The employment of ion-specific T- Hg2+-T coordination increases the melting temperature (Tm) of the double-stranded DNA (dsDNA) on the hybridized NS surface. After thermal washing at 45°C, the Hg2+ treated sample (dsDNA-NS) was effectively differentiated from that treated with nonspecific ions through monitoring fluorescence emission of fluorescein (Fl) labeled target DNA remained on the NS surface. Finally, a cationic conjugated polyfluorene derivative (CCP) was introduced to electrostatically associate with the DNA molecules on the NS surface, resulting in an amplified Fl signal via fluorescence resonance energy transfer (FRET) from the CCP to the dye molecule. In comparison with the use of Fl alone as a signal reporter, the presence of CCP significantly enhances the detection fluorescence intensity, reduces false-positive signal, and improves the detection selectivity for mercury(II). Further improvement in the probe design could yield more efficient metal ion sensors, which have the potential to be operated at room temperature and for the detection of other metal ions besides mercury(II). © 2009 Materials Research Society.