Aqueous based ultra-small magnetic Cr-doped CdSe quantum dots as a potential dual imaging probe in biomedicine.

The substitution of semiconductor quantum dots (QDs) by a small number of transition-metal ions with magnetic properties gives rise to magnetic-doped semiconductors. With a balance of optical and magnetic properties, these magnetic semiconductors are widely used in spintronics, bioimaging and magnetic resonance imaging (MRI) applications. To facilitate their usage in bio-applications, it is critical to synthesize water-soluble magnetic QDs with a stabilized structure while maintaining their optical and magnetic properties. Here in our work, we have developed a facile substituted synthetic route to achieve Cr-doped CdSe (Cr-CdSe) via hydrothermal method. The effects of doping on the structural, optical, and magnetic properties of Cr-CdSe were studied using X-ray diffraction, UV-visible spectroscopy, and photoluminescence lifetime. We then explored their chemical nature and change in morphology with an increase in doping concentration via X-ray photoelectron spectroscopy and transmission electron microscopy. Water-soluble QDs have been used as bioimaging probes for the past few decades due to their strong fluorescence, photostability and improved tissue or cellular penetration. However, incorporating magnetic material into a fluorescent entity harnesses the ability to control the strengths of both modalities, which enhances diagnostic accuracy and facilitates its application in bio-systems, especially in early accurate diagnosis. Finally, we demonstrate the competency of Cr-CdSe as a dual-imaging probe with fluorescent cellular imaging and MRI applications.