| Biosensing technology is a novel technology developed by integrating with many disciplines including biology, chemistry, physics, optics, electronics, etc. In specific, the optical and electrochemical biosensors are widely used in various fields, because they are of good selectivity, high sensitivity, short analysis time, low cost, ability of on-site monitoring in complex system and so on. Recently, these biosensors have already introduced into many areas for application such as medical diagnosis and food safety analysis. This article is to combine nucleic acid, mainly adopting Ochratoxin A(OTA) and micro RNA as the analyte, with relative nanotechnology to build some novel optical and electrochemical DNA biosensors, which might demonstrate a promising path towards to the detection for OTA in agricultural product or Chinese medicine, or the early diagnostic of cancers.This article includes four chapters. The first, second and third chapters are about three optical or electrochemical DNA biosensors for the detection of OTA. The fourth chapter is about an electrochemical DNA biosensor for the detection of micro RNA-21.Chapter One: In this chapter, a DNA electrochemical biosensor was developed based on the restriction endonuclease and the hairpin aptamer probe signal amplification technology for the detection of ochratoxin A. Under optimal conditions, the sensor linear range is 1.0 to 20 pg/m L and the detection limit is down to 0.4 pg/m L. Under certain conditions, the sensor can better identify the system of OTA, and it is expected for the actual samples OTA detection.Chapter Two: On the basis of Tb3+, structure-switching aptamer and magnetic beads, a signal-on fluorescent aptasensor was developed for the label-free determination of OTA in wheat. By employing the above strategy, this aptasensor can detect as low as 20 pg/m L OTA with high specificity. In comparison with former methods, the method we herein reported has obvious advantages such as label-free, enzyme-free, operation convenience, short detection time, low cost, without sophisticated equipment and so on. The proposed aptasensor use the fluorescent characteristics of Tb3+ for OTA detection, which may represent a promising path toward routine quality control of food safety.Chapter Three: A fluorescent aptasensor based on DNA-scaffolded silver nanoclusters was developed for the sensitive and selective detection of ochratoxin A in field crops. Under optimal conditions, the linear relationship between the fluorescence intensity and the concentration of OTA was plotted in the range of 0.01 to 0.3 ng/m L with a detection limit of 2 pg/m L. Conclusion: Thus, the developed aptasensor by target releasing and silver nanoclusters presented simple, fast, high selectivity and selectivity, which was sufficient for the detection of ochratoxin A in agricultural products.Chapter Four: A novel label-free electrochemical biosensor for micro RNA-21(mi R-21) detection is developed here based on a highly efficient 2’-O-methyl modified G-quadruplex-Hemin Deoxyribozymes(DNAzyme) and duplex-specific nuclease assisted target recycling. By using the strategy, this DNA biosensor can detect as low as 8 a M mi R-21 and exhibits high discrimination ability even against a single-base mismatch. Meanwhile, other advantages, such as easiness of fabrication, operational convenience and low cost, make this sensor a promising candidate for early diagnosis of cancer. |
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