A new label-free resonance light scattering method for the highly selective and sensitive detection of mercury ion was designed .This strategy makes use of the target-induced DNA conformational change to enhance the resonance light scattering in-tensity leading to an amplified optical signal .The Hg2+ ion ,which possesses a unique property to bind specifically to two DNA thymine (T ) bases ,in the presence of Hg2+ ,the specific oligonucleotide probes form a conformational reorganization of the oli-gonucleotide probes from single-chain structure to duplex-like complexes ,which can greatly enhance the resonance light scatter-ing intensity .Under the optimum experimental conditions ,the enhanced resonance light scattering intensity at 566 nm was in proportion of mercury ion concentration in the range 7.2 × 10-9 ~9 × 10-8 mol・L -1 with the linear regression equation was ΔI=5.12c+3.55(r=0.999 5) .This method was successfully applied to detection of Hg2+ in enviro nmental water samples ,the RSD were less than 1 .9% and recoveries were 99 .4% ~104 .3% .This label-free strategy uses the mercury specific oligonucle-otide probes as recognition elements and control the strength of resonance light scattering by changing the concentration of Hg2+ .It translating the small molecule detection into the DNA hybridization behavior leading to an amplified resonance light scattering signal can well enhance the sensitive detection of Hg 2+ .With amplification by DNA hybridization behavior ,the sensi-tivity for the detection of Hg2+ can achieve 2.16 × 10-9 mol・L -1 .In this study ,the stacked T-Hg2+-Tfunctioned not only as amplification property but also as an selective recognition .The highly specific detection of Hg2+ is attributed to the formation of a stable T-Hg2+-T complex .%根据目标物诱导核酸分子构象发生变化，导致体系共振光散射强度增大的原理建立了检测Hg2＋的新方法。当溶液中有Hg2＋存在时，基于“T-Hg2＋-T”特异性结合作用，促使Hg2＋特异核酸探针的构象发生变化，由单链状态变为刚性双链结构，使体系共振光散射强度增大。在波长566 nm处，当汞离子浓度在7.2×10-9～9×10-8 mol・L -1范围内时，体系的共振光散射增强程度ΔI与汞离子的浓度（c）具有良好的线性关系。其线性方程为ΔI＝5.12c＋3.55（r＝0.9995）。将该方法用于环境水样中汞离子的测定，相对标准偏差（RSD）小于1.9％；样品加标回收率为99.4％～104.3％。该方法以Hg2＋的高度特异性核酸探针作为识别元件，通过控制Hg2＋浓度的变化调节共振光散射强度的变化，将Hg2＋的检测转化为对DNA分子构象变化的检测，该转化有利于增强体系共振光散射强度，提高方法灵敏度，该共振光散射检测方法能检测到浓度为2.16×10-9 mol・L -1的Hg2＋。同时，由于“T-T”错配碱基对对 Hg2＋的特异结合能力，显著提高了该分析方法对Hg2＋的选择性。另外，该方法操作简便、不需标记。
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