CdTe quantum dots (QDs) are attractive candidates for fluorescent functional materials. The construction of multi-emitting CdTe QDs for better application performance is significant. Herein, a dual-emitting material was designed by modifying a fluorescence metal indicator (8-hydroxyquinoline-5-sulfonic acid, HQS) on CdTe QDs via the coordination with Cd2+. CdTe QDs possessed an emission at 655 nm. The coordination of HQS with Cd2+ in CdTe QDs inhibited the excited state intramolecular proton transfer of HQS, triggering the emission of HQS at 525 nm. With combining the emissions of CdTe QDs and HQS, HQS-CdTe QDs achieved dual emissions. HQS-CdTe QDs were applied to the ratiometric fluorescence detection of 2,6-dipicolinic acid (DPA), a biomarker for anthrax. The competitive coordination between Cd2+ and DPA caused the release of HQS from CdTe QDs, reducing the emission of HQS at 525 nm but retaining the emission of CdTe QDs at 655 nm. HQS-CdTe QDs measured DPA in the concentration range of 0.5–20 μM with a low detection limit of 0.25 μM and a short response time of 1 min. It was confirmed that HQS-CdTe QDs could be used in actual samples.