We successfully synthesize water-dispersible CTAB-capped CdSe@ZnS quantum dots with the crystal size of the CdSe quantum dots controlled from green to orange colors. The quenching effect of Fe(DTC)3 is very efficient to turn off the emission light of quantum dots at four molar ratios of the CdSe quantum dots, that is, the effective covering the surface of quantum dots with Fe(DTC)3. However, the reaction with Fe(DTC)3 for more than 24 h is required to completely realize the quenching effect. The highly quenched quantum dots efficiently detect nitric oxide at nano-molar concentration of 110nM of NO with 34% of recovery of emission light intensity. We suggest that Fe(DTC)3-hybridized CdSe@ZnS quantum dots are an excellent fluorescence resonance energy transfer probe for the detection of nitric oxide in biological systems.

Abstract
1. Introduction
2. Experimental
    2.1. Materials
    2.2. The synthesis of CdSe quantum dots
    2.3. The synthesis of CdSe@ZnS quantum dot withcore@shell structure
    2.4. Water-dispersible quantum dots by CTAB surfacemodification
    2.5. NO detection of CdSe@ZnS quantum dots byFluorescence Resonance Energy Transfer (FRET)
3. Results
4. Discussion
5. Conclusions
Acknowledgments
References

• Chang-Yeoul Kim(Nano-composite Materials Center, Korea Institute of Ceramic Engineering and Technology) Corresponding author