Fluorescent DNA And Silver Nanoclusters Sensors For Sensing Metal Ions And Small Organic Moleculars

With the rapid development of some subjects and the introduction of new techniques, the sensitivity, accuracy and selectivity of fluorescence analysis increasingly improve and its applications range many fields. To date, fluorescence analysis has become an important and effective spectral chemical method. This work constructed sensors based on fluorescence analysis for sensing metal ions and small moleculars closely related to human health and safety. In2004, Ono A. and Togashi H. authenticated that Hg2+can specifically recognize thymine (T), and since then, Hg2+was measured based on T-Hg2+-T complex in lots of reports. In this paper, this research focus was followed and developed simple, rapid, sensitive sensors based on T-Hg2+-T based Hg2+were developed. Metal clusters are fluorescent owing to its quantum confinement effect and it has been used as a new type of ultra small size of the fluorescent probe in environmental and biological analysis. On the base of the new type of silver nanoclusters synthesized in our laboratory, fluorescent silver nanoclusters sensors were constructed for sensing Cr (VI), folic acid, and picric acid explosive, which contributed to researchers’ understand the characteristics of silver nanoclusters and expands the application field of silver nanoclusters.The main contents and conclusions of this paper are listed as follows:1. Constructing fluorescent DNA sensor for identification of Hg2+(1) Construction of fluorescent DNA sensor based on duplexes of poly(dT) and graphene oxide (GO)T15hybridize to FAM-A15, forming double stranded DNA, and FAM fluoresces strongly due to the weak interaction between double stranded DNA and GO. In the presence of Hg2+, the stable T15-(Hg2+)n-T15complexes are formed and the single stranded FAM-A15interacts strongly with GO via π-π stacking, so the fluorescence of FAM is quenched by GO. Under the optimum experimental conditions, the fluorescence quenching efficiencies are proportional to the concentrations of Hg2+and a detection limit of0.5nM was obtained. Other potential coexisting metal ions had no significant effects on the determination of Hg2+. The proposed method was applied for the determination of Hg2+in river water samples and recovery experiment, the satisfactory results were achieved.(2) Construction of fluorescent DNA sensor based on fluorescence quenching effect of T-Hg2+-T complexes and ethynyl enhanced fluorescence quenchingHg2+can quench the fluorescence of FAM labeled polyd (T) sequences (denoted as: FAM-Tn, n for the number of T). The fluorescence quenching efficiencies were low for FAM-T1, while higher for FAM-Tn (n>1) and with the increasing number of T in sequence, the fluorescence quenching efficiencies decreased. If FAM and ethynyl were labeled on the two termini of T3, respectively, the fluorescence quenching efficiencies of FAM can be improved. In this study, HC=C-(5’)TTT(3’)-FAM was used as probe and highly sensitive, highly selective, and rapid Hg2+sensor was constructed by aid of signal amplification from ethynyl. In this paper, the principle of signal amplification was discussed in detail and on the basis of the fluorescence-quenching system by Hg2+, the cysteine sensor was further constructed. The experimental results indicate that the proposed method also shows high sensitivity and selectivity for cysteine.2. Constructing fluorescent silver nanoclusters sensors for recognition of metal ions and small molecules(1) Construction of fluorescent silver nanoclusters sensor for Cr(Ⅵ) and the investi-gation of mechanism for silver nanoclusters interacting with different metal ionsPolyethyleneimine-capped silver nanoclusters, which were easy to be synthesized and have excellent performance, were used as the probe for rapid, sensitive detection of Cr (Ⅵ). Under the optimized experimental conditions, the linear response range of0.1nM-1.5μM (R2=0.9991) and the detection limit of0.04nM were obtained. On the basis of the different response of silver nanoclusters to several metal ions, the mechanism for silver nanoclusters interacting with different metal ions were studied in detail based on UV-Vis spectroscopy, the characteristic electron configuration of ion, the solubility of corresponding hydroxide, and the electrode potential. Possible modes of action were concluded that targets were brought into close proximity with silver nanoclusters by hydrogen bonding or target complexing with template, or by metallophilic interaction or direct complexation between target and silver nanoclusters. And fluorescence quenching mechanism based on charge transfer was proposed.(2) Construction of fluorescent silver nanoclusters sensor for folic acid and the investigation of mechanism for silver nanoclusters interacting with folic acidFolic acid can efficiently quench the fluorescence of silver nanoclusters, based on which, the experimental conditions were optimized and the fluorescent silver nanoclusters sensor for folic acid recognition with high sensitivity was constructed. Those potential coexisting species were measured and the results show that the sensing system has high selectivity for detection of folic acid. The proposed method was well used for sensing folic acid in various real samples, such as milk powder, liquid milk, flour, ferment dough, urine, tablets, and so on. Sevral characterizations such as UV-Vis absorption spectroscopy, infrared spectra, high resolution transmission electron microscopy, fluorescence decay profiles, fluorescence spectra, and so on, were adopted to study the fluorescence quenching mechanism in detail. A two-step electron-transfer process, in which the electron is transferred from FA to AgNCs through PEI molecule functioned as a bridge, was proposed.(3) Construction of fluorescent silver nanoclusters sensor for picric acid explosive and the investigation of mechanism for silver nanoclusters interacting with picric acidThe fluorescent silver nanoclusters sensor with high sensitivity for identification of picric acid was founded based on fluorescence quenching reaction between silver nanoclusters and picric acid. Under the optimized experimental conditions, the proposed sening syetem shows excellent linear response characteristics, of which, the linear response range was1nM-2.25μM, and the detection limit was0.7nM. The performance was better than that of other TNP detection methods reported in last few years. The as-developed TNP analysis technology can discriminate between TNT and TNP. Picric acid and silver nanoclusters were brought into close proximity through the electrostatic interaction between picric acid and PEI and the charge transfer from silver nanoclusters to TNP would result in the fluorescence quenching.