The problem of cancer therapy is acute for scientists and doctors around the world. The frequency of cases of cancer diagnosis increases every year. On average, ten million people worldwide fall ill each year. This is associated both with the improvement of diagnostic methods and with the influence of factors that provoke such diseases. One of the most interesting objects from the point of view of application in biomedicine are hybrid structures based on magnetic nanoparticles (NPs) and noble metal NPs, which make it possible to simultaneously introduce two types of ligands onto the surface of NPs for their further use. This type of dumbbell-shaped NP opens up the possibility of their functionalization for further use in cancer photodynamic therapy (PDT) and fluorescence diagnostics (FD) [a combination of a photosensitizer (PS) for therapy and a fluorophore (FP) for platform detection]. Due to the conjugation of PS and FP at an optimal distance, obviously greater than the typical values of the Förster radius, which will avoid the FRET effect. However, the question also arises about the need to create a more complex Fe₃O₄–Au/PS/FP system or a mixture of Fe₃O₄–Au/PS + Fe₃O₄–Au/FP. The goal of this work was to synthesize and compare the properties of Fe₃O₄-Au/PS/FP systems with a mixture of Fe₃O₄-Au/PS + Fe₃O₄-Au/FP conjugates. The previously synthesized hybrid magnetite and gold NPs had sizes of Fe₃O₄ 10.8 ± 1.5 nm and Au 4.4 ± 0.8 nm (according to TEM data). The NPs were doubly modified with 3,4-dihydroxyphenylacetic acid (DOPAC) for subsequent coating with stabilizing polyethylene glycol (PEG) using the carbodiimide method. Since it is necessary to combine two different substances (PS and FP) in one system, Fe₃O₄-Au NPs (stabilized) were used as a ‘link’. Modification of DOPAC and PEG NPs with subsequent activation of EDC/NHS allows effective attachment of PS to the magnetic surface of NPs in a two-phase system (water–DMSO). The hydrodynamic size of the Fe₃O₄-Au/PS/FP system was 35.9 nm, the Fe₃O₄-Au/PS + Fe₃O₄-Au/FP mixture was 36.4 nm, respectively (dynamic light scattering method). For the Fe₃O₄–Au/PS/FP systems under study, as well as the Fe₃O₄–Au/PS + Fe₃O₄–Au/FP mixture, absorption maxima corresponding to solutions of pure PS and FP were recorded by spectroscopy, which confirms the efficiency of their conjugation. For the mixture Fe₃O₄–Au/PS + Fe₃O₄–Au/FP, a resonant transfer of fluorescence energy was discovered: upon excitation of the FP with a wavelength of 660 nm, additional emission of the PS in the region of 770 nm. It was shown that Fe₃O₄–Au/PS/FP systems and a mixture of Fe₃O₄–Au/PS and Fe₃O₄–Au/FP could be internalized by CT26 colon cancer cells with preservation of optical properties. Studies of the cytotoxicity of the systems on CT26 cell lines showed that the systems do not have dark toxicity in the studied concentration range. Studies of the light toxicity of the systems showed photo induced activity of the systems. Phototoxicity studies showed that after 4 h of incubation, the IC50 value for the Fe₃O₄–Au/PS + Fe₃O₄–Au/FP mixture was 1763 ± 15 ng/mL, and for Fe₃O₄–Au/PS/FP it was 483 ± 7 ng/mL. Based on the obtained comparative results, we can talk about higher efficiency of Fe₃O₄–Au/FS/FP for all parameters studied. However, in vivo studies are planned in the near future to finalize the findings.

Acknowledgements:
This work was supported in part by the State Registration Theme AAAA-A21-121011290089-4 and 121041500039-8. The equipment was purchased within the framework of the Development Program of the Lomonosov Moscow State University.

Conflicts of interest:
The authors declare that they have no conflict of interest in the publication of this article. The authors have no conflicts of interest to report in this work. Abstract was not submitted elsewhere and was first published here.

Funding:
This study was supported in part by Russian Science Foundation (grant: 22-13-00261), MSU State Topic (121041500039-8 and 123032300028-0) and MSU Program of Development. Also, this work was supported partly by the State Registration Theme AAAA-A21-121011290089-4 and 121041500039-8. The equipment was purchased within the framework of the Development Program of the Lomonosov Moscow State University.