Amplified Fluorescence Turn-on Assay for Mercury(II) Based on Conjugated Polyfluorene Derivatives and Nanospheres
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Amplified Fluorescence Turn-on Assay for Mercury(II) Based on Conjugated Polyfluorene Derivatives and Nanospheres Yusong Wang and Bin Liu* Department of Chemical and Biomolecular Engineering, 4 Engineering Drive 4, National University of Singapore, Singapore 117576 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 falsepositive 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). INTRODUCTION Recognition and detection of mercury(II) (Hg2+) and its derivatives is of vital importance due to their deleterious effect on the environment and human health [1]. Different strategies for the analysis of Hg2+ have been developed, and the majority is based on fluorescence and colorimetric methods. Recently, the complexation of metal ions with nucleotide purine and pyrimidine bases has attracted considerable interests [2], and the specific interaction between thymine-mercury(II)-thymine (T- Hg2+-T) has been widely used for Hg2+ detection [3-6]. Water-soluble conjugated polymers (CPs) as optically sensitive materials have been widely used in chemical and biological sensors [7]. In comparison with small molecular counterparts, the large absorption cross section and delocalized electronic backbone structure of polymers allow efficient light-harvesting and rapid intrachain and interchain energy transfer [710]. Particularly, cationic conjugated polyfluorene derivatives (CCPs), have been proven useful for signal amplification of dye labeled biomolecules through fluorescence resonance energy transfer (FRET) from the CCPs to dye molecules attached to the biomolecules [11-12]. By taking advantage of the signal
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