PNA是一种合成的DNA类似物，在PNA中，核酸的带负电的脱氧核糖磷酸骨架被不带电且相对柔性的类缩氨酸骨架所代替。它显示很高的生物和化学稳定性，不易被蛋白酶和核酸酶降解，且与互补的RNA或DNA作用显示很高的亲和性和专一性。金属离子可以与DNA作用，影响DNA膜的导电性，对于金属离子来说，DNA有四个不同作用位置：带负电的磷酸骨架，核糖羟基，碱基环中的N原子以及碱基的环外酮羰基。为了阐述金属离子对PNA膜导电性的影响，本论文以[Fe(CN)6]3-/4-为氧化还原探针，采用电化学阻抗法研究了不同金属离子与无标记的PNA的作用并检测了铅离子。1. 以[Fe(CN)6]3-/4-为氧化还原探针，采用电化学阻抗法研究ds-PNA膜与不同金属离子的作用。在pH=8.8时，比较加入不同金属离子(二价的Ni2+、Co2+、Zn2+、Mg2+、Pb2+、Hg2+，一价的Ag+、K+，三价的Fe3+、Al3+)前后ds-PNA膜的电荷转移电阻差ΔRCT，结果发现，加入Mg2+、Al3+后，ds-PNA膜的RCT几乎不变，而加入其它的金属离子后，ds-PNA膜的RCT都减小；在pH=7.0和pH=5.0时，比较了加入不同金属离子Ni2+、Co2+、Zn2+、Mg2+前后ds-PNA膜的电荷转移电阻差ΔRCT，结果发现加入这四种金属离子后，ds-PNA膜的RCT都减小。此外，以[Ru(NH3)6]2+/3+为氧化还原探针，研究了在pH=8.8时，ds-PNA膜在加入金属离子Mg2+和Ni2+前后的膜电阻的变化，结果发现，加入Mg2+后，膜电阻基本不变，而加入Ni2+后，膜电阻变大。综上所述，在pH=8.8时，Mg2+、Al3+几乎不与PNA作用，而Ag+、K+、Ni2+、Co2+、Zn2+、Pb2+、Hg2+、Fe3+均与PNA作用；在pH=7.0和pH=5.0时，Ni2+、Co2+、Zn2+、Mg2+均与PNA作用，具体的作用机理还有待于进一步研究。2. 将PNA与特异性识别Pb2+的DNAzyme结合，以[Fe(CN)6]3-/4-为氧化还原探针，采用电化学阻抗法检测铅离子。以PNA为探针链，将已杂化的匹配的PNA/DNAzyme/Substrate组装到金电极上，当有Pb2+存在时，底物链被切割，PNA/DNAzyme/Substrate膜的电阻减小。PNA/DNAzyme/Substrate膜与Pb2+作用前后的电荷转移电阻差ΔRCT与Pb2+浓度之间呈线性关系，Pb2+的检出限为10 pM，这种方法检测Pb2+有很高的灵敏度和选择性。然后将与Pb2+作用后的膜浸入S1核酸酶中，发现突出的单链部分被降解，得到的是PNA/DNA膜，但是当PNA与DNAzyme含有一个碱基错配时，DNAzyme链也被降解，只剩下PNA膜，因此，PNA与S1核酸酶结合可以有效地区分匹配和单个碱基错配。

Peptide nucleic acids (PNA) is a synthetic DNA analog. In PNA, negatively charged ribose-phosphate backbone of nucleic acids is replaced by uncharged and relatively flexible peptide backbone. PNA exhibits high biological and chemical stability, resistant to protease and nuclease degradation, and high binding affinity and specificity to complementary DNA or RNA. The DNA has four different principal binding sites for metal ions: the negatively charged phosphate backbone, the ribose hydroxyls, the base ring nitrogens, and the exocyclic base keto groups. The interactions of metal ions with DNA are known to alter the electrochemical properties of ds-DNA films. The purpose of this work was to investigate if metal ions will affect the electrochemical properties of ds-PNA films. Here, we investigated the interaction of different metal ions with unlabeled PNA and detected lead ion by Electrochemical impedance spectroscopy (EIS) with [Fe(CN)6]3-/4- as the redox probe.1. Electrochemical impedance spectroscopy (EIS) has been used to investigate the interaction of metal ions with unlabeled ds-PNA films on gold electrodes exploiting [Fe(CN)6]3-/4- as a solution-based redox probe. We compared the difference in RCT (ΔRCT)for ds-PNA film in the absence and presence of divalent Ni2+, Co2+, Zn2+, Mg2+, Pb2+, Hg2+, univalent Ag+, K+, and trivalent Fe3+, Al3+ at pH=8.8. The results show that RCT for ds-PNA film decreases significantly in the presence of Ni2+, Co2+, Zn2+, Pb2+, Hg2+, Ag+, K+, Fe3+, while RCT remains unaffected upon the addition of Mg2+ and Al3+. Then, we compared ΔRCT for ds-PNA film in the absence and presence of divalent Ni2+, Co2+, Zn2+, Mg2+ at pH=7.0 and pH=5.0. The results show that RCT for ds-PNA film decreases by addition of Ni2+, Co2+, Zn2+, Mg2+. Interaction of Mg2+, Ni2+ with unlabeled ds-PNA film on gold electrodes was further investigated with [Ru(NH3)6]2+/3+ as the redox probe at pH=8.8, the results show that RCT for ds-PNA film increases significantly in the presence of Ni2+, while RCT remain virtually unchanged upon addition of Mg2+. To sum up, Mg2+ and Al3+ hardly interact with PNA，while Ag+、K+、Ni2+、Co2+、Zn2+、Pb2+、Hg2+ and Fe3+ can interact with PNA at pH=8.8. Ni2+、Co2+、Zn2+、Mg2+ can interact with PNA at pH=7.0 and pH=5.0. The interaction mechanism of metal ions with PNA will be further studied in detail.2. The combination of PNA and Pb2+-specific DNAzyme was used for detection of lead ion by Electrochemical impedance spectroscopy (EIS) with [Fe(CN)6]3-/4- as redox probe. We use PNA as probe, and hybridized with DNAzyme/Substrate and assembled on the Au electrode. Upon binding of Pb2+ to the DNAzyme, the DNAzyme catalyzes the hydrolytic cleavage of the substrate, resulting in the removal of the substrate strand, so charge-transfer resistance of film modified on the Au electrode decreased. The difference in RCT (ΔRCT)for PNA/DNAzyme/Substrate film in the absence and presence of Pb2+ may be correlated with Pb2+ concentration, and a linear relation was obtained ranging from 1×10-6 M~1×10-12 M, with a detection limit of 10 pM. Then, Exposing the modified electrode to a single-strand DNA specific nuclease, S1 nuclease, was found the protruding DNA sequence to be cleaved, leaving PNA/DNA film on the electrode. In the presence of a single-base mismatch between PNA and DNAzyme, however, the DNAzyme is completely digested by S1 nuclease, leaving PNA film modified electrode. The discrimination of perfectly complementary DNA from a single-base mismatched sequence is accomplished by the combination of peptide nucleic acid (PNA) with S1 nucleases.