Organic-coating of 1-2 nm size silicon nanoparticles: effect on the particle properties

Abstract

Photoluminescent silicon nanoparticles of 1-2 nm size were synthesized by a wet chemical procedure and derivatized with propyl amine (NH2SiNP). Surface NH2 groups were used as linkers for further PEG and folic acidattachment (PEG-NHSiNP and Fo-NHSiNP, respectively) in order to provide the particles with efficient targeting to tumors and inflammatory sites.The particles were characterized by TEM, FTIR, XPS,  potential, DLS, and time-resolved anisotropy. Thephotophysical properties, photosensitizing capacity, and interaction with proteins were observed to depend on the nature of the attached molecules.WhilePEG attachment to NH2SiNPdid not change the particles photophysical behavior, attached folic acid diminishestheparticlesphotoluminescence. Despite all the particles retained the capacity for 1O2 generation, the efficient 1O2quenching by the attached surface groups might be a drawback when using these particles as photosensitizers of 1O2.In addition, attached folic acid provided the particles with the capacity of superoxide radical anion,O2.-, generation. The particles are capable of binding to bovine serum albumin (BSA) within quenching distancestotryptophanresidues.NH2SiNPand PEG-NHSiNP ground state complexes with BSA showed binding constantsof (3.1 ± 0.3)104 and (1.3  0.4)103 M-1, respectively. The lower value observed for PEG-NHSiNPcomplexesindicates that surface PEGylation effectively leads to a reduction in protein absorption, as required for opsonization prevention. An increase in the particles luminescence upon binding to BSA was observed and attributed to the hydrophobic environment provided by the protein. Moreover, NH2SiNP-BSAcomplexesalsoshowedcapacity for resonance energy transfer.