Disclosed herein is a micro-reactor for synthesizing a molecule, for example, compound, a nanoparticle, or a quantum dot. According to embodiments of the present disclosure, the apparatus comprises a processor, a storage unit, a reaction unit, a detector, and a collector, in which the storage unit and the reaction unit are independently controlled by the process. Optionally, the present micro-reactor further comprises a diagnostic device for performing a diagnostic test on a biological sample by use of the molecule. Also disclosed wherein are methods of diagnosing and treating a disease in a subject with the aid of the present micro-reactor.