Water-soluble ZnxCd1−xSe quantum dots (QDs) with different amounts of Cd dopant are synthesized with 3-mercaptopropionic acid as a modifier under ambient conditions. Hydrazine hydrate is used as the surface stabilizer and pH adjuster during preparation. The effect of dopant amount, initial pH values, and heating time on the fluorescence properties are systematically studied. Based on the emission wavelength shift of ZnxCd1−xSe QDs from 430 to 578 nm, the colors of these QDs are adjustable from blue to orange. This adjustment is beneficial for developing sweat fingerprints on scotch tape. Fresh blood fingerprints on foil, ceramic tile, black plastic, scotch tape, and old bloody fingerprints on black ceramic tile are developed by the QDs. The results show that Zn0.77Cd0.23Se QDs (calculated composition; measured composition: Zn0.83Cd0.17Se) are the most effective material for developing blood fingerprints and is even superior to the traditional tetramethylbenzidine reagent.