General and versatile procedure for coating of hydrophobic nanocrystals with thin silica layer enabling facile biofunctionalization and dyes incorporation

Here we report a method for coating of hydrophobic nanocrystals (NCs) with a thin silica layer. By using this approach 11 nm NaGdF4 NCs were coated with a mesoporous silica shell thinner than 20 nm resulting in highly monodisperse core-shell nanocomposite particles smaller than 50 nm. The synthetic protocol used here is based on the two-phase system that ensures high repeatability of the nanoparticle morphology and can be conveniently adapted for large-scale production. The use of an organic solvent as a diluent for tetraethoxysilane allows us to control not only the thickness, but also the porosity of the uniform silica shell. This procedure can be applied for coating NCs of various sizes and can be generalized to encapsulate other nanocrystals, e.g. semi-conductor quantum dots, into silica spheres. Furthermore, it allows facile surface modification with -NH2 groups that can be then used to conjugate biomolecules to the nanoparticle surface, as well as straightforward incorporation of various organic molecules (e.g. dyes or drugs) into the silica shell during its growth. To demonstrate potential applications up-converting NaGd0.80Yb0.18Er0.02F4 NCs were used as cores and zinc phthalocyanine was incorporated into the silica shell as a photosensitizer. Under irradiation with a 980 nm laser diode efficient generation of singlet oxygen was observed indicating that such nanocomposite particles have the capability to be used for photodynamic therapy.

S 2

Singlet oxygen generation.
In the standard procedure 0.81 mg of NGF@OA NCs is used to obtain 10 mg of silica coated NGF@mSiO 2 (Pc) hybrid material.Moreover, the TGA data reveal that NGF cores make about one third of the total mass of NGF@OA nanocrystals.Hence, the concentration of NGF cores in 10 mg/cm 3 solution of NGF@mSiO 2 (Pc) can be evaluated as about 0.001 M. Qian et al. 1 obtained NaGdF 4 :Yb 3+ ,Er 3+ up-converting NPs coated with porous silica using microemulsion method and then incorporated ZnPc into silica layer by soaking.Similarly, as in our case, ABDA fluorescence was used as a probe of 1 O 2 generation.The ABDA fluorescence intensity after 10 minutes exposure time to NIR laser radiation decreased to about 75 % of its initial value in Ref.
[ 1 ], and to about 80 % in our experiment.It is, however, difficult to compare directly results reported here and in Ref.
[ 1 ].In both cases the ABDA concentration in nanoparticles dispersion was kept at the same level (20 M), but the output power of the laser used in our experiment was lower (400 mW) than in Ref. [ Error! Bookmark not defined.] (500 mW) and the concentration of upconverting nanoparticles was10 times lower (10 mg mL -1 here and 100 mg mL -1 in Ref.The kinetic of singlet oxygen generation detected through ABDA fluorescence quenching is presented in Figure S7.The ABDA fluorescence spectra under excitation at 382 nm were collected every one minute during over an hour under continues irradiation of NGF@mSiO 2 (Pc) dispersion with 980 nm laser diode.Since the laser beam spot size was reduced in this experiment the fluorescence intensity decays slower than in Figure 7.It has been observed that emission of ADPA, employed as a probe of single oxygen generated when merocyanine 540 (M-540) incorporated into silica shell of NaYF 4 :Er 3+ ,Yb 3+ NPs was used as a photosensitizing molecule, followed an exponential decay over time 2 .In Figure S7 the dependence of ABDA emission intensity as a function of exposure time is closer to linear than exponential function.

Figure S2 .
Figure S2.FTIR spectra recorded for NGF@mSiO 2 nanoparticles: a) washed with water and ethanol (5 times each); b) washed additionally with HCl solution at pH = 1-2 (2 times) and methanol (1 time); c) washed as in a) and heated at 130 o C in air for 12 hrs.
[ 1 ]).Moreover, the sizes of upconverting cores and silica shells were different.Electronic Supplementary Material (ESI) for Journal of Materials Chemistry B This journal is © The Royal Society of Chemistry 2013S 5The kinetic of singlet oxygen generation.

Figure S7 .
Figure S7.Kinetics of singlet oxygen generation.ABDA fluorescence intensity ( ex = 382 nm) was monitored as a function of exposure time of the sample to NIR laser irradiation (980 nm); all samples were prepared by dispersing of 10 mg of appropriate nanoparticles in 1 ml of 20 M ABDA solution in DI.