Synthesis and characterization of quantum dot modified mercaptopropionic acid (CdS@MPA) and its application in laser soft desorption/ionization for labile metal–drug interactions is reported. CdS@MPA was synthesised via a hydrothermal method and characterized using TEM, UV-vis absorption, fluorescence, and FTIR spectroscopy. These tiny nanocrystals (<5 nm) provide a large surface area and a UV-vis absorption that is a good match with the N2 laser (337 nm) of matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS). Thus, they softly desorb/ionize labile metallodrugs without destroying the weak noncovalent bonds between the drug and the heavy transition metals (HTMs). Because of the UV absorption at 337 nm and large surface area, the present technique is coined as quantum enhanced laser desorption/ionization mass spectrometry (QELDI-MS). Detection of the interactions of …