Two-Photon CQDs-Based Dual-Mode Nanoprobe for Fluorescence Imaging and Magnetic Resonance Imaging of Intracellular Wide pH

Biological fluorescence imaging technologies have attracted a lot of attention and have been widely used in biomedical fields. Compared with other technologies, fluorescence imaging has a lower cost, higher sensitivity, and easier operation. However, due to the disadvantages of one-photon (OP) fluorescence imaging, such as low spatial and poor temporal resolution and poor tissue permeability depth, the application of OP fluorescence imaging has some limitations. Though two-photon (TP) fluorescence imaging can well overcome these shortcomings of OP, the single-mode imaging remains deficient. Therefore, dual-mode imaging combined with TP imaging and magnetic resonance imaging (MRI) can make up for the deficiency well, which make dual-mode imaging for the early diagnosis of diseases more accurate. Hence, a dual-mode nanoprobe TP-CQDs@MnO₂ was designed for probing the fluorescence/MR dual-mode imaging strategy of intracellular H⁺ by using TP-CQDs (two photon-carbon quantum dots) and MnO₂ nanosheets. The MnO₂ nanosheets treated as fluorescence quenching agents of TP-CQDs exhibited a supersensitive response to H⁺, which made the fluorescence signals turn “off” to “on” for TP fluorescence imaging, in the meantime, large amounts of Mn²⁺ were generated for MRI. A dual-mode nanoprobe TP-CQDs@MnO₂ can monitor intracellular wide pH (4.0–8.0), and the fluorescence intensity of TP-CQDs@MnO₂ has recovered up to more than six times and the corresponding results of MRI were satisfactory. TP fluorescence imaging of cells and tissues showed higher detection sensitivity and deeper tissue penetration (240.0 μm) than OP. The dual-mode imaging platform hold great promise for pH-related early diagnosis and treatment, which has great potential to improve clinical efficacy.