Aptamer-based Methods For Detection Of AFP And MiRNA-21

Tumor,a complex group of diseases characterized by the uncontrolled growth and spread of abnormal cells,has been the leading cause of death in many countries.The early and accurate detection of cancer is highly important for clinical diagnosis,effective toxicity monitoring,and ultimately for the successful treatment of cancers.Tumor markers are present in tumour tissues or serum and encompass a wide variety of molecules,including prodeins,enzymes,nucleic acids,hormone,cell surface receptors and transcription factors.In the past few decades,various promising detection methods based on tumor markers have been developed,including electrochemical assay,fluorescence methods,chemiluminiscence,radioimmunoassay(RIA),enzyme-linked immunosorbent assay(ELISA),polymerase chain reaction(PCR),surface plasmon resonance(SPR),surface enhanced Raman spectroscopy(SERS)and so on.Although robust and highly efficient,most of these methods still have limitations,such as relatively complex sample preparation,expensive equipment,low specificity and sensitivity,time consuming and so on.Therefore,simple,fast and economic methods for the detection of tumor markers in clinical is needed.Aptamers are single-stranded DNA or RNA molecules which are screened via an in vitro selective method known as systematic evolution of ligands by exponential enrichment(SELEX).Compared with antibodies,aptamers offer a great deal of attractive characteristics,including small size,good chemical stability,synthesis convenience,reusability,easy modification,nontoxicity and lack of immunogenicity.Based on these properties,aptamers have been widely used to detect metal ions,small molecules,proteins,living cells,viruses and bacteria with high affinity,specificity and sensitivity by folding into distinct secondary or tertiary structures.This paper established three sensitive and selective strategies based on aptamers for the detection of AFP and mi RNA-21.The details are as summarized as follows.Chapter 1: This chapter gives an overview of tumor markers,alpha-fetoprotein(AFP)and mi RNAs);describes the definition,characteristic,screening process and application of aptamers;introduce fluorescence methods and electrochemical assay for the dection of tumor markers.The details are summarized as follows.Chapter 2: A turn–on fluorescence biosensor for AFP detection was developed.Fluorescence of FAM-labeled single-stranded DNA(FAM-ss DNA)could be quenched by GO,and upon the addition of AFP,fluorescence was recovered.Compared with the previous AFP assay methods,the proposed strategy is simple,cost effective and rapid,which might become a new method for highly sensitive and selective AFP detection.Chapter 3: An electronic aptamer-based(E-AB)sensor for AFP detection was established.In the absence of AFP,the aptamer remains relatively unfolded.Upon addition of AFP,the aptamer undergoes binding induced folding which makes the redox tag(Fc)be away from the electrode,thus reducing faradaic current.Chapter 4: A signal–off electrochemical biosensor for mi RNA-21 detection was developed.This sensor employs an electrode-attached,molecular beacon-like DNA stem–loop labeled with an electroactive reporter as the hybridization sensing element.On hybridization,the distance between the label and the electrode is significantly altered,leading to a large,readily measurable signal change.The aptasensor thus provides a ready means for mi RNA-21 detection.