Green synthesis of multimodal 'OFF-ON' activatable MRI/optical probesElectronic supplementary information (ESI) available. See DOI: 10.1039/c6dt02840c

Diagnosis by MRI is frequently non-trivial due to the low sensitivity of the technique. Signal enhancing contrast agents (CAs) are used to aid in the analysis of MR images. We present here a simple protocol for the preparation of responsive CAs based on Mn nanosheets. Mn nanostructures presented here undergo a chemical and structural change in the presence of altered physiological conditions that activate their signal. This strategy allows for a reduction of background, increasing the sensitivity of the technique. The simple synthetic protocol followed allows for the combination of the nanosheets with reporter molecules for other imaging techniques, like carbon quantum dots for optical imaging. We report a simple and green protocol for the preparation of redox responsive multimodal MRI/optical contrast agents based on Mn nanosheets and carbon dots.