A highly efficient photocathode, based on graphite-like carbon nitride nanosheets (CNNS) sensitized CdTe quantum dots (QDs), was constructed for photoelectrochemical (PEC) biosensing. Using dissolved oxygen as an electron acceptor, the hybrid photocathode showed a sensitive photocuffent response at -0.2 V bias potential under 405 nm illumination. The CdTe/CNNS hybrid photocathode demonstrates about 100% increase of photocurrent compared to CdTe QDs modified electrode owing to the formation of heterojunction through contact of two semiconductor materials. The improved charge separation efficiency was identified by the extension of electron transit time (tau(d)) and electron lifetime (tau(n)) in this PEC system. The introduction of Cu2+ on the surface of hybrid photocathode could decrease photocurrent via the exciton trapping quenching effect. A sensitive PEC sensor for Cu2+ was thus developed with a good linear range from 20 nM to 100 mu M and a detection limit of 33 nM, and was successfully applied in the detection of Cu2+ in human hair samples. The CNNS-sensitized photocathode provides a good alternative for enhancement of the PEC signal transduction and could be widely used in biosensing and clinical diagnosis. (C) 2015 Elsevier B.V. All rights reserved.