The paper reported an ultrasensitive electrochemical biosensor for glucose which was based on CdTe-CdS core-shell quantum dot as ultrafast electron transfer relay between graphene-gold nanocomposite and gold nanoparticle. Since efficient electron transfer between glucose oxidase and the electrode was achieved, the biosensor showed high sensitivity (5762.8 nA nM(-1) cm(-2)), low detection limit (S/N = 3) (3 x 10(-12) M), fast response time (0.045 s), wide calibration range (from 1 x 10(-11) M to 1 x 10(-8) M) and good long-term stability (26 weeks). The apparent Michaelis-Menten constant of the glucose oxidase on the medium, 5.24 x 10(-8) mM, indicates excellent bioelectrocatalytic activity of the immobilized enzyme towards glucose oxidation. Moreover, the effects of omitting graphene-gold nanocomposite. CdTe-CdS core-shell quantum dot and gold nanoparticle were also investigated. The result showed sensitivity of the biosensor is 7.67-fold better if graphene-gold nanocomposite. CdTe-CdS core-shell quantum dot and gold nanoparticle are used. This could be ascribed to improvement of the conductivity between graphene nanosheets due to introduction of gold nanoparticles, ultrafast charge transfer from CdTe-CdS core-shell quantum dot to graphene nanosheets and gold nanoparticle due to unique electrochemical properties of the CdTe-CdS core-shell quantum dot and good biocompatibility of gold nanoparticle for glucose oxidase. The biosensor is of best sensitivity in all glucose biosensors based on graphene nanomaterials up to now and has been satisfactorily applied to determination of the glucose in human saliva samples. (C) 2011 Published by Elsevier Ltd.