99mTc-conjugated manganese-based mesoporous silica nanoparticles for SPECT, pH-responsive MRI and anti-cancer drug delivery.

In recent decades, hybrid imaging techniques that exploit the advantages of multiple imaging technologies have aroused extensive attention due to the deficiencies of single imaging modes. Along with the development of single photon emission computed tomography-magnetic resonance imaging (SPECT-MRI), it is currently necessary to develop a series of dual probes that can combine the outstanding sensitivity of SPECT with the high spatial resolution of MRI. Herein, the commonly used technetium-99 (99mTc) was labelled on the surface of manganese oxide-based mesoporous silica nanoparticles (MnOx-MSNs) for use in SPECT-MRI dual-modal imaging. The radiolabelling yield was as high as 99.1 ± 0.6%, and the r1 value of the nanoprobes was able to reach 6.60 mM-1 s-1 due to the pH-responsive properties of the MnOx-MSNs. The high-performance SPECT-MRI dual-modal imaging was confirmed in vivo in tumour-bearing mice, which could also provide semi-quantitative information for tumour detection. Importantly, these nanoprobes can deliver anti-cancer drugs in cancer therapy due to their unique mesoporous structures. Thus, nanotheranostics combining dual-modal imaging with anti-cancer therapeutic properties were achieved.