Abstract: A method for preparing a composition of matter, the method including: 1) mixing a Zn(NO3)2 solution, a Hg(NO3)2 solution, and a mercaptopropionic acid solution, thereby yielding a precursor solution of Zn2+—Hg2+-mercaptopropionic acid; dissolving a selenium powder and a NaBH4 solid in water thereby yielding a NaHSe slurry; mixing the precursor solution and the NaHSe slurry thereby yielding zinc-mercury-selenium (ZnHgSe) quantum dot; 2) preparing a drug delivery system including dextran-magnetic layered double hydroxide-fluorouracil (DMF); binding the drug delivery system and the ZnHgSe quantum dot in a mass ratio of 1:1-3; and grinding the drug delivery system including the ZnHgSe quantum dot (QD) thereby yielding powders; and 3) dissolving the powders in absolute ethyl alcohol thereby yielding a first suspension; ultrasonically dispersing the first suspension thereby yielding a second suspension, magnetically separating the second suspension thereby yielding a solid product, centrifuging and washing the soli