In this paper, we report microwave-assisted, one-stage synthesis of high-quality functionalized water-soluble cadmium telluride (CdTe) quantum dots (QDs). By selecting sodium tellurite as the Te source, cadmium chloride as the Cd source, mercaptosuccinic acid (MSA) as the capping agent, and a borate-acetic acid buffer solution with a pH range of 5-8, CdTe nanocrystals with four colors (blue to orange) were conveniently prepared at 100 °C under microwave irradiation in less than one hour (reaction time: 10-60 min). The influence of parameters such as the pH, Cd:Te molar ratio, and reaction time on the emission range and quantum yield percentage (QY%) was investigated. The structures and compositions of the prepared CdTe QDs were characterized by transmission electron microscopy, energy-dispersive X-ray spectroscopy, selective area electron diffraction, and X-ray powder diffraction experiments. The formation mechanism of the QDs is discussed in this paper. Furthermore, AS1141-aptamer-conjugated CdTe QDs in the U87MG glioblastoma cell line were assessed with a fluorescence microscope. The obtained results showed that the best conditions for obtaining a high QY of approximately 87% are a pH of 6, a Cd:Te molar ratio of 5:1, and a 30-min reaction time at 100 °C under microwave irradiation. The results showed that AS1141-aptamer-conjugated CdTe QDs could enter tumor cells efficiently. It could be concluded that a facile high-fluorescence-strength QD conjugated with a DNA aptamer, AS1411, which can recognize the extracellular matrix protein nucleolin, can specifically target U87MG human glioblastoma cells. The qualified AS1411-aptamer-conjugated QDs prepared in this study showed excellent capabilities as nanoprobes for cancer targeting and molecular imaging.