Simultaneous detection of lead (II) and mercury (II) ions using nucleic acid aptamer molecular beacons

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.