An economic, direct synthetic method for producing water soluble QDs that are ready for bioconjugation is provided. The method can produce aqueous QDs with emission wavelengths varying from 400 nm to 700 nm. Highly luminescent metal sulfide (MS) QDs are produced via an aqueous synthesis route. MS QDs are capped with thiol-containing charged molecules in a single step. The resultant MS QDs exhibit the distinctive excitonic photoluminescence desired of QDs and can be fabricated to avoid undesirable broadband emissions at higher wavelengths. This provides a significant improvement over the present complex and expensive commercial processes for the production of QDs. The aqueous QDs are stable in biological fluids over a long period of time. In addition, nontoxic ZnS QDs have been produced with good photoluminescence properties by refluxing the ZnS QD suspensions over a period of time.