## 3 Applications of Multimodal Fluorescent-Magnetic Nanoparticles
### Cancer Therapy  
Back in 1957, [PERSON] et al. carried out investigations using magnetic nanoparticles in hyperthermia. The experiment involved heating of tissue samples containing \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) nanoparticles in a size range of 20-100 nm and exposed to a 1.2 MHz magnetic field [90]. Magnetic hyperthermia is heating of the nanoparticles previously placed in a targeted tissue by applying an AC magnetic field. Consequently, the heat is applied directly to the diseased tissue surrounding the magnetic material and the cancer is destroyed if the temperature can be held at 42 \({}^{\circ}\)C for 30 min. This technique gives the possibility of treating cancer cells directly by heating while the healthy tissues are kept untouched. The principles of hyperthermia are also based on the fact that cancer cells are more sensitive to the changes in  
Figure 12: MRI tracking of fmSiO\({}_{4}\)@SPION-labeled C17.2 cells infused intracerebrally, contralateral to the ischemic area and histological studies of MCAO mouse brain. (**a**) \(T_{2}\)-weighted magnetic resonance images of MCAO mouse brains after injection with plain cells, fmSiO\({}_{4}\)@SPIONs or fmSiO\({}_{4}\)@SPION-labeled C17.2 cells; (**b**) Scheme of a brain section indicating the sites of migrated cells; (**c-j**) fluorescence images of MCAO mouse brain sections after infusion of fmSiO\({}_{4}\)@SPION-labeled C17.2 cells; (**c-f**) labelled cells confined in the injection site; (**g-j**) labelled cells migrating to the ischemic area; (**c,g**) fluorescence images of fmSiO\({}_{4}\)@SPION-labeled C17.2 cells; (**d,h**) DAPI staining of cell nuclei; (**e,i**) nestinimmunostaining of the labelled cells; (**f**) overlap of (**c-e**); (**j**) overlap of (**g–i**). Scale bar: 50 \(\upmu\)m. Adapted from ref. [87]. temperature than healthy cells. Magnetic nanomaterials are chosen for this technique because they are able to absorb the energy from the AC magnetic field to convert it to heat, and the effect of the resultant heating is higher than for other materials. Another advantage of using magnetic nanoparticles is that they can be targeted to the cancer cells magnetically or using biomarkers to ensure that only the intended target tissue is heated [1]. The main drawbacks of magnetic hyperthermia include the necessity of a high dosage of magnetic nanoparticles in tumor to achieve reasonable hyperthermia effect, the toxicity of nanomaterials used and high costs [91; 92]. By contrast, photodynamic therapy involves the administration of a photosensitizing drug followed by the illumination of the target tissue with light corresponding to the absorbance wavelength of the drug, that results in generation of highly reactive singlet oxygen killing cancer cells [93]. This therapy has some advantages including the precise targeting of drugs, low costs, less invasive (compared to surgery) and it can also be repeated many times. However, photodynamic therapy can only be used to treat tissues that could be exposed to light and it is not suitable in the case of cancer that has spread to many places in the body. In addition, photodynamic therapy requires extra precautions as photosensitizing drugs cause high sensitivity of the patient's body to light for some period of time [94]. Overall, magnetic hyperthermia and photodynamic therapy could be complementary methods in the cancer treatment and used together, if appropriate magnetic-photosensitizing nanocomposites are available. It has been previously demonstrated that hyperthermia and photodynamic therapy can be synergistic and there was a clear enhancement of the effects of 5-aminolevulinic acid-mediated photodynamic therapy by concurrent hyperthermia in glioma spheroids [95]. It was also shown that photodynamic therapy effects can be greatly enhanced by thermal modulation that results in an increase of reactive oxygen species in albumin-photosensitizer nanoassemblies [94]. In addition, these therapies can be combined together with MRI and optical imaging enabling the monitoring of the treatment.