Triplex signal amplification for electrochemical DNA biosensing by coupling probe-gold nanoparticles-graphene modified electrode with enzyme functionalized carbon sphere as tracer

► This work constructs an ultrasensitive electrochemical DNA biosensor. ► We propose a triplex signal amplification strategy to enhance the sensitivity. ► Probe labeled gold nanoparticles are assembled on graphene modified electrode. ► Horseradish peroxidase tagged carbon sphere is used for electrochemical detection. ► This biosensor can detect target DNA down to attomolar level with high selectivity.