A biosensor based on CdSe/ZnS quantum dots and fluorescent dye Cy3(C

31

H

37

KN

2

O

8

S

2

)according to the principle of F?rster resonance energy transfer（FRET）is designed.The experiments of fluorescence transfer intensity in different concentration and different p H solution are carried out.The experimental results show that the fluorescence enhancement effect of CdSe/ZnS fluorescence semiconductor quantum dots as donor on Cy3(C

31

H

37

KN

2

O

8

S

2

)dye is obvious.By controlling the ratio of CdSe/ZnS quantum dots to the Cy3 dye molecules

the optimal effi

ciency of fluorescence transfer（CdSe/ZnS∶Cy3=1∶1.2）is up to 83.68%.The FRET is also sensitive to p H value of environment liquid（pH=5.93～8.36）.Moreover

the FRET can clearly recognize prostate cancer cell.These results provide a new method to diagnose early stage of prostate cancer cell formation and design the biosensor of prostate.