Non - Labeled Fluorescence Detection Of Heavy Metal Ions And Bio - Mercaptans Based On Functional Transformation Of Functional Nucleic Acids

With the rapid development of industrialization process and the improvement of people’s living standard, environmental problems and people’s health have attracted more and more attentions. It is very important significance to analyze and detect toxic metal ions and biological small molecules in the field of environmental monitoring, prevention of disease diagnosis.The discovery of functional nucleic acids(aptamer and DNAzymes) and the corroboration of non-canonical nucleic acid structures broke through the concept of nucleic acid only as understanding the genetic material and transport carrier. Many manmade functional nucleic acids have been generated via in vitro selection or SELEX(systematic evolution of ligands by the exponential enrichment) techniques and they have excellent catalytic properties and high affinity towards their targets. In addition, it proved some advantages in easier synthesis and modification, good stability in practical application. Under certain conditions, it can interact with target molecules by specific recognition, which induced conformational changes. These advantages show great promise in the development of novel sensors for the area of biochemical analysis.In this paper, functional nucleic acids and its fluorescence sensor applications in environmental and biochemical analysis has been reviewed. On that basis, we developed several new label-free fluorescence methods for the detection of metal ions and biological small molecules by combining functional nucleic acids and commercially available water soluble fluorescent dyes, Thioflavin T and riboflavin. These sensing approaches are based on conformational switch of functional nucleic acids controlled by target analyte. The main contents are summarized as follows:1. A label-free fluorescence assay for Pb2+ is developed using functional nucleic acids AGRO100 sequence and riboflavin. In the presence of Pb2+, AGRO100 mainly adopts quadruplex structure which could stack with riboflavin, resulting in fluorescence intensity decrease. Under the optimal conditions, the fluorescence intensity change was linearly related to Pb2+ concentration in the range of 50 nM to 400 nM and the detection limit for Pb2+ is 15 nM. With the help of NaSCN, this sensing approach has good selectivity for Pb2+. The potential of this method in practical applications have been demonstrated by detecting environmental water samples. Compared with some reported fluorescence sensors, the present method has several significant advantages including the use of non-toxic and low-cost dye, simple operation and rapid detection, high sensitivity and selectivity.2. A new, label-free and sensitive off-on fluorescence sensor for Hg2+ and biothiols detection based on Thioflavin T direct inducing conformation-specific G-quadruplex is developed. The sensing approach is based on a conformational switch of functional nucleic acids AGRO100 controlled by Hg2+ and a commercially available water soluble fluorescent dye, Thioflavin T(ThT). A noticeable fluorescence light-up in ThT on binding to the G-quadruplex grants the sensor excellent sensitivity. The specific quadruplex conformation induced directly by ThT and pronounced structural selectivity of ThT for G-quadruplex could generate more stable luminescence and make sure high specificity in complex samples. Under the optimal conditions,AGRO100-ThT complex have fluorescence change towards 50 nM Hg2+; AGRO100-ThT-Hg2+ allows for the selective determination of cysteine and glutathione in the range of 20.0 nM–2.5 μM and 30.0 nM–2.0 μM with a detection limit of 8.4 nM and 13.9 nM respectively. The diagnostic capability and potential in practical applications of this method have been demonstrated by detecting biothiols in human blood serum.