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We have developed a fluorescence quantitative analysis method for the simultaneous detection of Hg2+ and Pb2+ based on nucleic acid aptamer molecular beacon (MB) probes. In this analytical method, two MB probes for Hg2+ (PHg) and Pb2+ (PPb) were designed. The carboxyl fluorescein (FAM) and tetramethyl-6-carboxyrhodamine (TAMRA) were selected as fluorophores of PHg and PPb, Black Hole Quencher 1 (BHQ-1) and Black Hole Quencher 2 (BHQ-2) were selected as organic quenchers, and several continuous nucleotides with guanine (G base) were connected to organic quenchers. The aptamers are put in as a part of stem and loop. In general, the fluorescence of fluorophores was dually quenched by BHQ and G bases, so the fluorescence signals were weak. In the presence of Hg2+ and Pb2+, PHg and PPb bonded with them, and the stem-loop structure of MB was destroyed and the fluorescence recovered. Under the optimal conditions, the fluorescence intensity of FAM had a good linear relationship with the concentration of Hg2+ in the range from 0.7 nmol/L to 84 nmol/L, and that of TAMRA and Pb2+ in the range from 0.2 nmol/L to 24 nmol/L. The detection limit of Hg2+ is 0.36 nmol/L and that of Pb2+ is 0.16 nmol/L (3σ, n = 11). The relative standard deviations (RSD) for determination of Hg2+ and Pb2+ were both lower than 5%, the average recoveries of this method in real samples were 96.55–102.78%, which indicated that the method had a high accuracy. [ABSTRACT FROM AUTHOR]

The bifunctionality of graphene oxide (GO) which can highly adsorb single-stranded DNA (ssDNA) and effectively quench the emission of organic dyes is reasonably utilized in a multiplexed DNA detection system, achieving sensitive and selective detection of HIV, VV and EV, respectively. [ABSTRACT FROM AUTHOR]

We have developed a fluorescence quantitative analysis method for the simultaneous detection of Hg 2+ , Pb 2+ and Ag + based on fluorescently labelled nucleic acid aptamer probes and graphene oxide (GO). By this method, three nucleic acid aptamer probes (P Hg , P Pb , P Ag ) were designed. The carboxyl fluorescein (FAM), tetramethyl-6-carboxyrhodamine (TAMRA) and cyanine-5 (Cy-5) were respectively selected as fluorophore of aptamer probes, and GO was chosen as quencher. In general, these probes were on free single-stranded state and adsorbed on the surface of GO via π-π interactions, which brought fluorophores of probes and GO into close proximity. Due to the fluorescence resonance energy transfer occurred between fluorophores and GO, the fluorescence was quenched and fluorescence signals were all weak. Under the optimal condition, fluorescence intensities of three fluorophores exhibited a good linear dependence on corresponding ions concentration. The detection limit for Hg 2+ , Pb 2+ and Ag + were 0.2, 0.5 and 2 nmol/L (3σ, n  = 11). Average recoveries of this method were 97.56-104.92%, which indicated the method had a high accuracy and low detection limit. In addition, this proposed method has good selectivity, and there was no crosstalk effect among these probes.