Using of Quantum dots as optical sensing is becoming more favorable for researchers and scientists in new generation of sensors, because of more advantages and useful development. Likewise future improvements in the nano material and development of optical sensors can be expected, and surely has a bright future. In this thesis, we have reviewed the different steps and different analytical approaches in quantum dot-based sensors. The introduction, several methods for productions, optical properties and optical sensing, ion-selectivity strategies in quantum dot-based sensors, the classification of the quantum dot-based systems according to the active or passive setting up of the quantum dots, and different uses of quantum dots for detection of heavy metal in different applications. And also should be mentioned that there are some other strategies which is not figured out yet, such as the possibility of joining and combinations of natural molecules with synthetic macromolecules which can open up new strategies and applications.