| Exosome is a nano-vesicle with membrane structure,which consists of lipids and proteins,while proteins and nucleic acids,such as DNA,messenger RNAs,microRNAs and other non-coding RNAs are exist in their lumen.Exosomes originate from the exocytosis of cells and are absorbed by target cells and circulated in body fluids.In this way,they can convey functional information to neighboring or distant cells,thus promoting intercellular communication without the need for cell-to-cell contact.Exosome secretion is a constitutive phenomenon that is involved in both physiological and pathological processes and determines both the exosomal surface molecules and the contents.Tumor-derived exosomes can transfer oncogenetic cargo and modulate the genetic expression of recipient cells,thereby playing a crucial role in the progression,survival and metastasis of tumor,and drug resistance.Over the past years,several studies have demonstrated the diagnostic and therapeutic potential of exosomes and exosomal content(i.e.,nucleic acids and proteins)in many diseases including cancer as well as cardiovascular,neurodegenerative and infectious diseases.The surfaces of exosomes contain a variety of membrane proteins,such as cell-type-specific protein(A33),heat-shock proteins,and tetraspanins(CD63,CD81 and CD9),which has associated with cancer development.To date,several methods have been used to detect tumor-derived exosomes via recognition and binding of an antibody or aptamer with proteins on the exosome surface.Compared to antibodies,aptamers have many advantages,including low cost,ease of synthesis,long-term stability and ease of chemical modification.We constructed two kinds of aptamer biosensors to detect the cancer cell-derived exosomes,respectively.1.Herein,a novel electrochemiluminescence(ECL)aptasensor was constructed for the detection of exosomes from breast tumor cells(MCF-7 cells)using G-quadruplex/hemin DNAzyme as a catalytic amplifier.We used mercaptopropionic acid(MPA)-modified Eu3+-doped CdS nanocrystals(MPA-CdS:Eu NCs)as ECL emitters and H2O2 as coreactant.The MPA modified Eu3+-doped CdS nanocrystals(MPA-CdS:Eu NCs)modified GCE linked with CD63 aptamer.Subsequently,DNA S1 is connected to the exosome surface via an aptamer-sequence domain,and G-quadruplex/hemin DNAzymes are formed when hemin and K+are introduced,resulting an amplified decrease in ECL.Therefore,the ECL signal is related to concentration of exosomes and establishes the basis for an exosome detection assay.Under optimum conditions,a good linear relationship was found for exosome detection in the range of 3.4×105 to 1.7×108 particles/mL with a detection limit of 7.41×104 particles/mL.More importantly,the proposed ECL aptasensor can be applied for the detection of exosomes in clinical plasma,indicating that this method has potential application in clinical diagnosis.2.Here,taking advantages of proximity hybridization and split aptamer,we also developed a electrochemical biosensor for exosomes detection.As shown in scheme 1,the thiolated probe was immobilized on the surface of gold electrode,Ru(NH3)63+as an electroactive.With the adding of target exosomes and the DNA,the target-induced proximity hybridization occurred to capture exosome on the surface of gold.The self-assembed DNA can absorb a plenty of Ru(NH3)63+,resulting in a higher peak current.Under optimum conditions,a good linear relationship was found for exosome detection in the range of particle/mL with a 2.375×106～9.5×108 particles/mL detection limit of 6.607×105 particles/mL. |
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