The structural disorder of a silica network probed by site selective luminescence of the nonbridging oxygen hole centre

Progress in Nanotheranostics Based on Mesoporous Silica Nanomaterial Platforms

Theranostics based on nanoparticles (NPs) is a promising paradigm in nanomedicine. Mesoporous silica nanoparticle (MSN)-based systems offer unique characteristics to enable multimodal imaging or simultaneous diagnosis and therapy. They include large surface area and volume, tunable pore size, functionalizable surface, and acceptable biological safety. Hybridization with other NPs and chemical modification can further potentiate the multifunctionality of MSN-based systems toward translation. Here, we update the recent progress on MSN-based systems for theranostic purposes. We discuss various synthetic approaches used to construct the theranostic platforms either via intrinsic chemistry or extrinsic combination. These include defect generation in the silica structure, encapsulation of diagnostic NPs within silica, their assembly on the silica surface, and direct conjugation of dye chemicals. Collectively, in vitro and in vivo results demonstrate that multimodal imaging capacities can be integrated with the therapeutic functions of these MSN systems for therapy. With further improvement in bioimaging sensitivity and targeting specificity, the multifunctional MSN-based theranostic systems will find many clinical applications in the near future.

Luminescence from nearly isolated surface defects in silica nanoparticles

A structured emission/excitation pattern, proper of isolated defects, arises in a vacuum from silica nanoparticles. The luminescence, centered around 3.0-3.5 eV, is characterised by a vibronic progression due to the phonon coupling with two localised modes of frequency  ∼1370 cm(-1) and  ∼360 cm(-1), and decays in about 300 ns at 10 K. On increasing the temperature, the intensity and the lifetime decrease due to the activation of a non-radiative rate from the excited state. Concurrently, the temperature dependence of the lineshape evidences the low coupling with non-localised modes of the matrix (Huang-Rhys factor S ~ 0.2) and the poor influence of the inhomogeneous broadening. These findings outline an uncommon behaviour in the field of the optical properties of defects in amorphous solids, evidencing that the silica surface can allocate luminescent defects almost disentangled from the basal network.