PURPOSE:Early cancer diagnosis using MRI imaging is of high global interest as a non-invasive and powerful modality. In this study, methionine was conjugated on gadolinium-based mesoporous silica nanospheres to evaluate intra-cellular uptake and its accumulation in human breast cancer cells. PROCEDURES:The contrast agent was synthesized and characterized using different techniques including N2 physisorption, thermal gravimetric analysis, dynamic light scattering, and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The intra-cellular uptake of Gd(3+) was measured by ICP-AES, fluorescent microscopy, and flow cytometry. Finally, cellular and tumor MR imaging were performed to determine in vitro and in vivo relaxometry. RESULTS:According to the results, the contrast agents accumulated in tumor cells both in vitro and in vivo. There was no significant cellular toxicity on either normal or cancer cells along with strong intense signal on T 1 compared to the unlabeled cells. CONCLUSIONS:The results showed that the novel contrast agent could become a useful tool in early detection of cancer.