It is urgent that a convenient and sensitive technique of detecting Hg²⁺ be developed because of its toxicity. Conventional fluorescence analysis works with a single fluorescence probe, and it often suffers from signal fluctuations which are influenced by external factors. In this research, a novel dual-emission probe assembled through utilizing CdTe quantum dots (QDs) and rhodamine B was designed to detect Hg²⁺ visually. Only the emission of CdTe QDs was quenched after adding Hg²⁺ in the dual-emission probe, which caused an intensity ratio change of the two different emission wavelengths and hence facilitated the visual detection of Hg²⁺. Compared to single emission QDs-based probe, a better linear relationship was shown between the variation of fluorescence intensity and the concentration of Hg²⁺, and the limit of detection (LOD) was found to be11.4 nM in the range of 0–2.6 μM. Interestingly, the intensity of the probe containing Hg²⁺ could be recovered in presence of glutathione (GSH) due to the stronger binding affinity of Hg²⁺ towards GSH than that towards CdTe QDs. Based on this phenomenon, an IMPLICATION logic gate using Hg²⁺/GSH as inputs and the fluorescence signal of QDs as an output was constructed.