Fluorescence resonance energy transfer (FRET) between a quantum dot as donor and an organic fluorophore as acceptor has been widely used for detection of nucleic acids and proteins. In this paper, we developed a new method, characterized by 605-nm quantum dot (605QD) fluorescence intensity increase and corresponding Cy5 fluorescence intensity decrease, to detect adenosine triphosphate (ATP). The new method involved the use of three different oligonucleotides: 3'-biotin-modified DNA that binds to streptavidin-conjugated 605QD; 3'-Cy5-labelled DNA; and a capture DNA consisting of an ATP aptamer and a sequence which could hybridize with both 3'-biotin-modified DNA and 3'-Cy5-labelled DNA. In the absence of the target ATP, the capture DNA binds to 3'-biotin-modified DNA and 3'-Cy5-labelled DNA, bringing quantum dot and Cy5 into close proximity for greater FRET efficiency. When ATP is introduced, the release of the 3'-Cy5-labelled DNA from the hybridization complex took place, triggering 605QD fluorescence intensity increase and corresponding Cy5 fluorescence intensity decrease. Taken together, the virtue of FRET pair 605QD/Cy5 and the property of aptamer-specific conformation change caused by aptamer-ATP interaction, combined with the fluorescence intensity change of both 605QD and Cy5, provide prerequisites for simple and convenient ATP detection.