Size‐Tunable Highly Luminescent SiO₂ Particles Impregnated with Number‐Adjusted CdTe Nanocrystals

Abstract

Highly luminescent SiO(2) particles impregnated with CdTe nanocrystals (NCs) are prepared by a sol-gel procedure. Partial ligand exchange from thioglycolic acid to 3-mercaptopropyltrimethoxysilane (MPS) on the NCs enables retention of the initial photoluminescence (PL) efficiency of the NCs in water, while the simultaneous addition of a poor solvent (ethanol) results in regulated assembly of the NCs through condensation of hydrolyzed MPS. The SiO(2) particles thus prepared have, for example, a diameter of 16 nm and contain three NCs each. The PL efficiency of these particles is 40 %, while the initial efficiency is 46 % in a colloidal solution. The redshift and narrowed spectral width in PL observed after impregnation indicate that the concentration of NCs in these nearly reaches the ultimate value (on the order of 10(21) particles per liter). The porosity of these particles is investigated by means of N(2) adsorption-desorption isotherms. Due to the SiO(2) shell, these particles have higher stability in phosphate-buffered saline buffer solution than the initial NCs. Their potential use for labeling in bio-applications is investigated by conjugating biotinylated immunoglobulin G to them by using streptavidin maleimide as linker. Successful conjugation is confirmed by electrophoresis in agarose gel. This preparation method is an important step towards fabricating intensely emitting biocompatible SiO(2) particles impregnated with semiconductor NCs.

Controlled self-assembly of hydrophobic quantum dots through silanization

“…This is first example for QD assembly by silanization. The result is drastically different from our previous report [22][23][24][25]. In that case, highly luminescent QDs were encapsulated into SiO 2 beads via several sol-gel approaches.…”

“…The selfassembly of the QDs can be created in this two-phase system by adjusting the QD surface ligand. In previous papers, we successfully encapsulated hydrophobic and hydrophilic QDs in SiO 2 beads by using such emulsions [22][23][24][25]. With controlling the surface chemistry of the QDs, these SiO 2 beads revealed high photoluminescence (PL) efficiencies.…”

Surface modification of SiO2 beads with multiple hydrophobic quantum dots for bioapplications

“…The preparation procedure of the hydrophobic QDs encapsulated into SiO 2 beads is by a three-step synthesis: silanization of the QDs (Step 1), phase transfer and assembly of the silanized QDs to form seeds (Step 2), and the growth of a SiO 2 shell to form beads (Step 3). This is similar to our previous reports [9,16]. During Step 1, the silanization of the QDs was carried out by adding TEOS to the toluene solution of CdSe/ZnS and CdSe/Cd x Zn 1 − x S QDs, which was then stirred for 3-5 h to obtain precursor solution A. Precursor solution B was obtained by adding MPS in the solution of ethanol, H 2 O, and ammonia.…”

“…PEG, CES, and mercapto decoration of the SiO 2 beads were carried out using our previous methods [9,16]. Amino-activated SiO 2 beads were prepared by using 3-aminopropyltrimethoxysilane (APS).…”

“…Because PL brightness plays an important role for super sensitive bioprobes, multiple QDs were encapsulated into SiO 2 beads [15]. We have developed a method for impregnating multiple CdTe QDs into small SiO 2 beads (10-50 nm in diameter) by using a controlled sol-gel process [16]. The SiO 2 beads thus prepared had, for example, a diameter of 16 nm and contained 3 QDs each.…”