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College of Chemistry and Molecular Sciences,Wuhan University,Wuhan 430072,China Aptamers are nucleic acid molecules that were selected in vitro which can bind to the corresponding targets with high affinity and specificity.Aptamers offer many advantageous features compared with the protein-based affinity reagents,such as well-established chemical synthesis,thermostability,low production cost and so on.Typically,the systematic evolution of ligands by exponential enrichment(SELEX)process is used for the conventional screening high-specific and affinity aptamers [l] However,the conventional SELEX is an iterative process which requires multiple rounds of selection and amplification.The process is time-assuming and labor-intensity [2] To address this problem,we describe a selecting system for aptamer selection and real time monitoring on a valve-integrated microfluidic chip based on micromagnetic separation and the fluorescence labels for DNA,named fluorescence assisted micromagnetic microfluidic SELEX(FMM-SELEX).This method is rapid,automatable,high efficient and could be used for the aptamer screening in a wide range of targets.The FMM-SELEX was carried on to manipulate small amount of magnetic beads at the microscale precisely,separate bound and unbound molecules rapidly and real-time monitor the enrichment.Meanwhile,the magnetic nanospheres(MNs)were fabricated by a convenient and highly controllable layer-by-layer assembly method.The MNs were nanosized with fast magnetic response and very stable without aggregation or precipitation.As a model to demonstrate the efficiency of the FMM-SELEX process,we showed the isolation of aptamers of an attractive cancer marker-MUCI protein.