title: Highly Sensitive Fluorescence Quantitative Detection of Mercury in Soil Based on Non-labeled Molecular Beacon and Fluorescent Dye Hoechst 33258.
abstract: A highly sensitive and selective fluorescence method of quantitative detection for mercury in soil was developed using non-labeled molecular beacon (MB), single-stranded nucleic acid (ssDNA) and fluorescent dye Hoechst 33258. In this analytical method, the loop of MB was designed to be a sequence that was complementary to the ssDNA with multiple T-T mismatches, the stem of MB was completely designed as C-G base pairs, and both ends of the MB are not modified by any fluorophore and quencher. In the absence of Hg2+, the interaction between Hoechst 33258 and the MB was very weak, and the fluorescence signal of Hoechst 33258 was very low. In the presence of Hg2+, the MB and ssDNA with multiple T-T mismatches formed a double-stranded nucleic acid (dsDNA) via the T-Hg2+-T coordination structure which provided binding sites for Hoechst 33258. Then Hoechst 33258 binded to A-T base pairs of dsDNA, and the fluorescence intensity of Hoechst 33258 was significantly enhanced. Thus, a highly sensitive fluorescence quantitative detection method for Hg2+can be realized. In this strategy, the optimal determination conditions for Hg2+were a buffer solution pH of 8.2, an incubated temperature of 50°C, an incubated time of 5 min and NaCl of 60 mmol L-1. Under the optimum conditions, the fluorescence intensity of Hoechst 33258 exhibited a good linear dependence on the concentration of Hg2+in the range of 5 × 10-9- 400 × 10-9mol L-1. The fitted regression equation was ΔI = 2.1084C - 8.9587 with a correlation coefficient of 0.9943 (R2), and the detection limit of this method was 3 × 10-9mol L-1(3σ). The proposed method had a high selection; the common substances in soil such as Ca2+, Mg2+, Mn2+, Fe3+, Cu2+, Pb2+, Al3+, K+, Na+, Ni2+, Cd2+, Cr3+, SiO32-, Cl-, PO43-, NH4+and S2-had no interference to the detection of mercury. The proposed method had a high accuracy, and it was applied to detect mercury of ten different types of soil; the recoveries were 97.65 - 103.22%. In addition, the proposed method had a low background emission, fast detection speed and low detection cost.
authors.affiliation: Key Laboratory of Biologic Resources Protection and Utilization of Hubei Province, Hubei University for Nationalities.
authors.forename: Dongshan
authors.initials: D
authors.lastname: Xiang
authors.forename: Kun
authors.initials: K
authors.lastname: Zhai
authors.forename: Qiuzhang
authors.initials: Q
authors.lastname: Sang
authors.forename: Boan
authors.initials: B
authors.lastname: Shi
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Yang
mesh_terms: D006690:Bisbenzimidazole / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D005453:Fluorescence; D005456:Fluorescent Dyes / Q000737:chemistry*; D008628:Mercury / Q000032:analysis*; D045663:Quantum Dots; D012987:Soil / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
chemical_list: D005456:Fluorescent Dyes; D012987:Soil; D002244:Carbon; D008628:Mercury; D006690:Bisbenzimidazole