Research On Optical Biosensors Based On Nucleic Acid Probe And Graphene Oxide

In recent years,with the development of social economy and improvement of the level of life,problems about human life safety and health attracted much attention.The detection of biomarkers in clinical samples and imaging in living cells for diagnosis of cancers have become a research hotspot.Biomolecules such as hemoglobin and Lcysteine are related to some diseases.At present,Methods used for the detection of biological molecules includes fluorometric and colorimetric method,electrochemical sensing,surface plasma resonance,and surface enhanced Raman scattering,but these methods suffer from complicated operation and high cost,or need expensive equipment and instruments.So it urgently needs to develop simple,rapid,sensitive and low-cost sensing strategies for biological molecules detection.Nucleic acid can be used as an excellent probe to identify target molecules and has been widely used in the field of biosensing.Graphene oxide(GO)is a novel carbon nanomaterial with good biocompatibility,which can be used as an efficient fluorescence quenching agent and biomolecular carrier material.The specific binding process between nucleic acid probe,GO,and the target can be transformed into easily detectable optical,electrical,thermal and other signals to achieve effective detection of target biomolecules.In this study,highly sensitive optical biosensors were developed based on nucleic acid probe,specific aptamer towards target,and GO with excellent performance.The main work are as follows:1)A multifunctional optical biosensor based on a new hairpin probe for simultaneous detection of hemin/hemoglobin and L-cysteine.Firstly,based on a new G-riched hairpin probe,a platform for the detection of hemin/hemoglobin works in a“turn-on” mode was developed.Fluorescein(FAM)and quenching agent BHQ1 were labeled at the 3’and 5’ ends of the hairpin probe,respectively.The fluorescence of FAM was quenched during the fluorescence resonance energy transfer process.When hemin/hemoglobin binds to hairpin probe,G-quadruplex structure forms and the distance between FAM and BHQ1 becomes larger and restores the fluorescence emission,realizes the effective detection of hemin(the detection limit is 282 p M)and hemoglobin(the detection limit is 108 p M).Furthermore,the G-quadruplex/hemin complex has peroxidase activity and could catalyze the reaction between substrate3,3’,5,5’-tetramethylbenzidine(TMB)and hydrogen peroxide to produce a blue product with an absorption peak at 652 nm.However,in the presence of L-cysteine,the blue product becomes colorless due to the inhibition of L-cysteine to the peroxidase activity of G-quadruplex/hemin DNAzyme.The biosensor is simple,rapid,sensitive,and specific as well as practicability since it can be used to detect targets in serum.2)A biosensor for the detection of microRNA-21 based on nucleic acid probe and graphene oxide.Micro RNA is a new kind of tumor marker and overexpressed in many tumor cells compared with normal cells.In this strategy,a complementary ss DNA of microRNA-21 was used as recognition probe,dye SYBR Green I was used as signal probe,and GO was used as carrier for the detection and imaging of microRNA-21.In the absence of the target,ss DNA adsorbes on the surface of GO through π-π stacking and the free SYBR Green I emits weak fluorescence.Under the mediation of GO,the ss DNA probe enters the tumor cells and specifically binds with microRNA-21 to form a double-stranded structure.SYBR Green I embeds in the groove region of ds DNA and emits strong green fluorescence.By monitoring the fluorescence of SYBR Green I,the target microRNA-21 in buffer or in living cells can be detected.This biosensor has high sensitivity and specificity,and is also suitable for the detection of target in serum samples.It provides a valuable reference for the early diagnosis of cancer based on the detection of microRNA-21.