A one-step synthesis of glutathione-capped Zn(x)Hg(1-x)Se quantum dots (QDs) has been accomplished by reacting a mixture of Zn(ClO(4))(2) and Hg(ClO(4))(2) with NaHSe and using glutathione as surface-stabilizing agent. The fluorescent color of the alloyed QDs could be tuned by varying the Zn(2+):Hg(2+) molar ratio, reaction pH, intrinsic Zn(2+) and Hg(2+) reactivity toward NaHSe, and the concentration of NaHSe. The size, composition, and inner structures of these QDs are characterized using dynamic light scattering, inductively coupled plasma-mass spectrometry, and X-ray powder diffraction. By varying the molar ratio of Zn(2+) to Hg(2+) in the precursor solution, the Zn(x)Hg(1-x)Se QDs exhibited a tunable PL wavelength in the range of 548-621 nm. These QDs offered advantages of short reaction time (1 h), low reaction temperature (95 degrees C), high quantum yield, water solubility and biocompatibility. Additionally, glutathione-capped Zn(0.96)Hg(0.04)Se QDs (quantum yield=78%) have been applied for sensing Cu(2+).