Novel Mn2+-doped quantum dots are provided. These Mn2+-doped quantum dots exhibit excellent temperature sensitivity in both organic solvents and water-based solutions. Methods of preparing the Mn2+-doped quantum dots are provided. The Mn2+-doped quantum dots may be prepared via a stepwise procedure using air-stable and inexpensive chemicals. The use of air-stable chemicals can significantly reduce the cost of synthesis, chemical storage, and the risk associated with handling flammable chemicals. Methods of temperature sensing using Mn2+-doped quantum dots are provided. The stepwise procedure provides the ability to tune the temperature-sensing properties to satisfy specific needs for temperature sensing applications. Water solubility may be achieved by passivating the Mn2+-doped quantum dots, allowing the Mn2+-doped quantum dots to probe the fluctuations of local temperature in biological environments.