br Results and discussion br To
3. Results and discussion
To fabricate the nanoprobe [email protected], two lumines-cent dye-conjugated precursors, APTES-CTMR and APTES-BHHBCB-Eu3+, were first prepared (Scheme S1). Specifically, APTES-CTMR was prepared through the EDC/NHS-triggered reaction of carboxyl group (eCOOH) of CTMR with amino group of APTES, and APTES-BHHBCB-Eu3+ was prepared by reacting the chlorosulfonyl group (eSO2Cl) of BHHBCB with amino group of APTES, followed by the coordination with Eu3+ ions. The core–shell nanoparticles, [email protected], were then fabricated in a water-in-oil (W/O) reverse microemulsion through a two-step Methylpiperidino pyrazole growth procedure initiated by ammonia, i.e.,
(i) preparation of CTMR-doped silica core by the copolymerization re-action between APTES-CTMR and TEOS, (ii) the shell growth onto the CTMR-doped silica core by the copolymerization reaction among APTES-BHHBCB-Eu3+, TEOS and APTES. The addition of free APTES in second step is for allowing primary amino groups to be introduced on the surface of nanoparticles for further FA conjugation.
The optimized condition for preparing the core–shell nanoparticles was obtained by evaluating the changes of nanoparticles’ morphology and luminescence properties over additions of increased amounts of APTES-CTMR and APTES-BHHBCB-Eu3+ precursors. At first, the na-noparticles of CTMR-doped silica core coated with pure silica shell (without BHHBCB-Eu3+-doping) were prepared. As shown in Fig. 1A, increasing in the amount of APTES-CTMR from 1.5 to 6 μmol, the na-noparticles were monodisperse, spherical and uniform in size (Fig. 1A, a-c), while further increasing the amount of APTES-CTMR to 9 μmol, the nanoparticles became irregular and less smooth (Fig. 1A, d). The increased luminescence intensity of nanoparticles in increasing the amount of APTES-CTMR suggested that more CTMR molecules could be encapsulated into the nanoparticles (Fig. 1B). Meanwhile, the ratio of luminescence intensity to the amount of APTES-CTMR (intensity/ APTES-CTMR amount) was decreased. Considering the eﬀects of the APTES-CTMR amount on morphology and fluorescence intensity of the nanoparticles, the optimized concentration of APTES-CTMR for the preparation of core–shell nanoparticles was selected to be 6 μmol.
The amount of APTES-BHHBCB-Eu3+ was then optimized by coating BHHBCB-Eu3+-doped silica shell onto the pure silica core (without CTMR-doping). As shown in Fig. 1C, accompanied by the in-crease of the APTES-BHHBCB-Eu3+ amount from 1 to 5 μmol, mono-disperse nanoparticles were obtained in all groups. However, the na-noparticles became less smooth when 3.75 and 5 μmol APTES-BHHBCB-Eu3+ were used (Fig. 1C, c,d). Similarly, upon increasing the amount of APTES-BHHBCB-Eu3+, the luminescence intensity of nanoparticles was increased, and the ratio of luminescence intensity to the amount of APTES-BHHBCB-Eu3+ (intensity/APTES-BHHBCB-Eu3+ amount) was decreased. Thus the optimized concentration of APTES-BHHBCB-Eu3+ for the preparation of core–shell nanoparticles was selected to be 2.5 μmol.
On the basis of above results, the core–shell nanoparticles, [email protected] BHHBCB-Eu, were prepared by using 6 μmol APTES-CTMR and 2.5 μmol APTES-BHHBCB-Eu3+ for preparing the silica core and shell, respectively. As shown in Fig. 2, the as-prepared nanoparticles are monodisperse and spherical (Fig. 2A), with average size of ~52 nm in diameter (Fig. 2B). The hydrated particle diameter measured on a Nano Zeta-Sizer is 240.5 nm (Fig. S1A). By covalently conjugating FA-PEG2000-COOH to the surface amino groups of [email protected] via the EDC/NHS-triggered procedure, the FA-functionalized nanoprobe, [email protected], was then prepared. The TEM image of [email protected] showed that the nanoparticles remained still