Covalent bonding of grafted polymer brushes of poly(poly(ethylene glycol) monomethacrylate) on surface of silicon quantum dots and the activation of the end hydroxyls

Abstract A technique of covalent bonding of grafted polymer brushes of poly(poly(ethylene glycol) monomethacrylate) (P(PEGMA)) on the surface of silicon quantum dots (SiQDs) and activation of the end hydroxyls with N-hydroxysuccinimide (NHS) esters were described in this work in detail. Firstly, a Si/SiQDs slice was disposed with hydrofluoric acid solution to produce surface Si-H x ( x  = 1, 2 or 3) species, which combined with vinyl group of 1-undecenol covalently gives terminal hydroxyls. Such hydroxyls were initialized and were involved in atom transfer radical polymerization to construct grafted polymer brushes of P(PEGMA). Hence the density of the surface hydroxyls was enhanced extremely on account of the end hydroxyls of the side chains of the polymer brushes. Then carboxyl groups were introduced via terminal esterification with succinic anhydride, which were activated subsequently with NHS giving NHS esters under rather mild conditions. The reactivity of the terminal NHS esters was demonstrated by SDS-PAGE gel electrophoresis and fluorescence imaging. The SiQDs were demonstrated by transmission electron microscopy. The stepwise modifications on SiQDs were characterized by infrared and X-ray photoelectron spectra. The photoluminescence of the SiQDs was remained during the chemical modifications, proved by the measurements of fluorescence spectra.