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The DNA modified gold nanoparticles (DNA-AuNPs) have been broadly used in the analytic chemistry.However,people found that the assembly efficiency of the DNA molecules on the AuNPs were very important for the sensitivity of the DNA-AuNPs based sensors.Here,by extending a short duplex (12 bp) proximal to the AuNPs,we built a new kind of DNA-AuNP sensor (Figure 1).This sensor showed twice the sensitivity of similar sensors published previously.Meanwhile,when 30 nm AuNPs were applied in this sensor,the sensor could detect as low as 20 pM target DNA,this concentration was much lower than the limit of detection of the 50 nm sensor previously reported.It is foreseen that this strategy can be applied in many other sensors based on DNA-AuNPs.And more importantly,other signal amplification method could be further adopted on this sensor,which makes it possible to get better sensor system based on this kind of DNA-AuNps sensor.