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A theranostic nanosystem based on indocyanine green (ICG) covalently conjugated to mesoporous silica nanoparticles (MSNs) loaded with the anticancer drug mitoxantrone (MTX) is proposed as an innovative photoacoustic probe. Taking advantage of the characteristic PA signal displayed by both ICG and MTX, a PA-ratiometric approach was applied to assess the drug release profile from the MSNs. After complete in vitro characterization of the nanoprobe, a proof-of-concept study has been carried out in tumour-bearing mice to evaluate in vivo its effectiveness for cancer imaging and chemotherapeutic agent delivery.

Indocyanine green was encapsulated inside the pores of pegylated amino-functionalized MCM-41 Mesoporous Silica Nanoparticles (ICG-MSNs). In addition to a greater stability and a decrease of toxicity, the photoacoustic effect of ICG-MSNs increases by nearly 400% compared to free ICG due to fluorescence quenching and high photothermal conversion of the encapsulated dyes. Upon i.v. administration in tumor-bearing mice, an overall photoacoustic enhancement of ca. 25% was measured in the tumor region.

The formation of ternary complexes between neutral Ln(III)-DO3A chelates anchored on MCM-41 mesoporous silica nanoparticles (MSNs) and silanol groups on the surface allows obtaining highly efficient chemical exchange saturation transfer (CEST) MRI nanoprobes. These new probes achieve excellent sensitivity in the μM range (per Ln(III) ion), significantly greater than that of other paramagnetic CEST nanosystems such as dendrimers or micelles and three orders of magnitude higher than that of the corresponding molecular agents.