A comprehensive investigation of amino grafted mesoporous silica nanoparticles supramolecular assemblies to host photoactive chlorophyll a in aqueous solution

Highly ordered Mesoporous Silica Nanoparticles (MSNs), belonging to MCM-41 family (100 nm wide), with a mean pore size of about 4 nm, are used as carrier for the hydrophobic photosensitizer (PS) Chlorophyll a (Chl) in water medium. In future perspective to study the proposed system in Photodynamic Therapy (PDT) and/or in antimicrobial-PDT (aPDT), advances in Chl studies in aqueous solution, mimicking the biological environment, were presented during this work with the main aim to obtain a supramolecular assembly able to host photoactive Chl in water medium. As synthetized MSNs and amino grafted MSNs (MSNs-NH 2 ) were studied and carefully characterized, with and without Chl, using TGA, SEM, TEM, SAXS, Nitrogen physisorption isotherms, Z-potential investigation, FTIR-ATR and UV–vis absorption/fluorescence analyses, including also the Chl fluorescence lifetime evaluation. To drive Chl inside the pores, the drug loading method by using the adsorption process, was adopted. The NH 2 moieties exerted a key role to host Chl inside the MSNs-NH 2 pores, allowing to obtain Chl as monomer. Electrostatic interactions through positively charged amino groups were evidenced, along with the hydrogen bond presence involving the pigment hydrated form and the MSNs-NH 2 . Two Chl populations, i.e. ascribed to the monomeric and dimeric one, were revealed by 1 Chl* lifetime measurements and steady state fluorescence emission. The presence of photoactive Chl molecules was demonstrated with the qualitative evaluation of 1 O 2 by means of chemical probes.