Biomedical Engineering Reference
In-Depth Information
compounds (i.e., aminopropyl trimethoxysilane or trimethoxysilyl propyl urea)
converts the particles in the water-soluble form. Compared with the mercap-
toacetic acid process, polymerized siloxane-coated QDs are more highly sta-
ble against aggregation. However, only milligram quantities can be prepared
per batch using this process. Furthermore, this process leaves residual silanol
groups on the nanocrystal surface, which can lead to precipitation and gel for-
mation at neutral pH when not properly removed.
3.2.3.1 Protocol for NM Silica Encapsulation
One process for the synthesis of silica-coated NPs is described below.
59
The
process can be scaled for making CdSe/ZnS nanocrystals with any size between
2 and 8 nm.
(1)
Using anhydrous methanol, precipitate 1 mL of nanocrystals in butanol/
TOPO (optical density (OD) of nanocrystals ~2).
(2)
Add 50 µL of mercaptopropyltris(methyloxy)silane (MPS) and vortex to
mix thoroughly.
(3)
Add 5 µL of tetramethylammonium hydroxide (TMAH) and mix thor-
oughly into an optically clear solution.
(4)
Add 120 mL of anhydrous methanol.
(5)
Add 750 µL of TMAH to make it basic with a pH of 10.
(6)
Place in a 500 mL three-neck-flask with a stream of N
2
with mild stirring
for 1 h.
(7)
Gently heat the solution to ~60 °C for 30 min.
(8)
Cool down to RT.
(9)
Add 90 mL of methanol, 10 mL of 18 MΩ Millipore water, 600 µL of
(trihydroxysilyl)propyl methylphosphonate and 20 µL of MPS.
(10)
Stir for ~2 h, heat to ~60 °C for less than 5 min, and cool down to
~30 °C.
(11)
Quench the remaining silanol groups with a mixture of 20 mL of metha-
nol and 2 mL of chlorotrimethylsilane to which ~3 g of solid TMAH
pentahydrate is added to make it basic.
(12)
Stir for ~2 h and then heat back to ~60 °C for ~30 min.
(13)
Store at RT for 2-4 days with constant stirring in an N
2
atmosphere.
(14)
Evaporate with a rotary evaporator down to 2-5× less than the original
volume.
(15)
Leave at RT for 24 h.
(16)
Dialyze in a 10,000 molecular-weight cutoff (MWCO) dialysis tubing
against methanol for 1 day.
(17)
Filter through a 0.45 µm pore size nylon syringe filter.
(18)
Remove the excess of free silane with centrifugal filter devices (YM-
100 centriplus/centricon 100, MWCO 100,000) that leaves about 2 mL
solution.
(19)
Store the 2 mL solution at RT for 12 h.
