Construction Of Molecular-Logic Gates Based On Gold Nanoparticles And Their Applications In Analysis

With the remarkable advantages of molecular devices,such as small size, large storage, facile synthesis and fast response, etc., the study of molecular devices has become one of the most important research areas arising from multi-discipline subjects (chemistry, biology, and materials) in the 21st century. Gold nanoparticles (AuNPs) have found widespread applications in nanodevices, biosensors and other fields due to their unique optoelectronic properties, small size, surface effects and excellent biocompatibility. DNA molecules are considered to be a kind of ideal materials for bio-nanodevices construction with programmable sequence-specific, abundant conformational changes and the specific biological activity. In this thesis, nanodevices have been developed for logic gate operations based on fluorescence enhancement/quenching effect of AuNPs and specific recognition of molecular probes. The content of this thesis is summarized as follows:1. Study of distance-dependent fluorescence enhancement/quenching effect between AuNPs and fluorophores by"molecular ruler"Double-stranded DNA was used as the "molecular ruler" for precise regulation of distances between AuNPs and fluorophores TMR/FAM resulting in fluorescence signal change. Distance-dependent fluorescence enhancement/quenching effect of AuNPs was systemically investigated. The results showed that the fluorescence signal was totally quenched when no DNA base between AuNPs and fluorophores. While in 30 base pairs apart, fluorescence enhancement effect is maximal. When 50 base pairs apart, there was almost no effect on the fluorescence signal. Furthermore, it was found that the fluorescence enhancement/quenching of AuNPs was associated with fluorophores type and the size of AuNPs. The quenching efficiency of AuNPs with different size of 5 nm, 13 nm, and 25 nm on TMR/FAM increased progressively as the size increased, and fluorescene of FAM was greater quenched than that of TMR. TMR/FAM fluorescence enhancement reached 3.08 times and 3.76 times respectively for 13 nm AuNPs. The different fluorescence enhancement/quenching effects by different size of AuNPs were probably contributed to local magnetic enhancement and surface nonradiactive energy transfer. This study will help for further understanding of the mechanism of fluorescence enhancement/quenching effects, and provide an opportunity for the construction of AuNPs-DNA nanodevices. 2. Multi-target detection based on fluorescence enhancement and quenching by AuNPs and their use for logic gate operationsTaking advantage of distance-dependent interactions between AuNPs and fluorophores, FAM-tagged adenosine aptamer and molecular beacon were attached to the surface of AuNPs, and by employing the conformational change of DNA probes caused by the target, the detection of adenosine and cDNA was achieved using the fluorescence signal "ON-OFF" and "OFF-ON" modes. The detection limit was 6.4μM and 0.5 nM for adenosine and cDNA, respectiely. On this basis, adenosine aptamer and molecular beacon were modified on the same AuNPs, multi-target detection was realized via the new XOR logic gate operations. In this project, distance-dependent optical properties of AuNPs were employed in the construction of logic gates, which broadened the application of AuNPs in bioanlaysis.3. The construction of XOR logic gate nanodevices at single particle levelBased on the previous project, XOR logic gate nanodevices were built via distance-dependent optical properties of AuNPs and DNA probe conformational change. FAM fluorophore was replaced with Cy5. Furthermore, single particle imaging was implemented by total internal reflection fluorescence microscopy. Statistical analysis of single particle fluorescence signal change was carried out in the present of target. As in the homgeneous solution, single particle imaging results showed the same response for XOR logic gate, indicating successful construction of single particle nanodevices. This logic gate provided great promising for the construction of multifunctional optoelectronic devices, which had broad prospects in biological sensing and DNA computer.