## 3 Results and Discussion
Upon addition of TEOS (Figure 2A step 1 and 2), surfactant molecules and TEOS remove the native organic ligands at the NP surface and such hydrophilized NPs can be entrapped within the water pool of the reverse micelle (Figure 2A step 3), the confined space where the formation of the siloxane network takes place (Figure 2A step 4). As demonstrated for CdSe [33; 41; 42; 48], PbS [34] and metal NPs [32], the relatively mild conditions used for the functionalization and the transparency of the silica matrix in the regions of the electromagnetic spectrum where most of the NPs are photoactive, generally do not alter the NPs optical properties once the silica shell is grown. However, the geometry of the final nanostructures has been reported to critically affect the spectroscopic properties and/or the colloidal stability [32; 33],  
Figure 2: **(A)** Scheme of the water-in-oil microemulsion approach for silica shell growth: addition of the organic-capped giant quantum dots (QDs) to the water-in-oil microemulsion (step 1), displacement of the native ligands at the QD surface by surfactant molecules and hydrolyzed TEOS (step 2), inclusion of the surface modified QDs inside the water pool of the inverse micelle (step 3) and formation of the siloxane network around the QDs (step 4). TEM micrographs (Scale bar 50 nm) of the silica nanostructures prepared using native “giant” quantum dots (GQDs) (**B**) and oely amine-treated GQDs at increasing volume of GQDs: 30 \(\mu\)L (**C**) and 80 \(\mu\)L (**D**). The reaction mixture consists of 350 \(\mu\)L Igepal CO-520, 200 \(\mu\)L NH\({}_{4}\)OH, 50 \(\mu\)L TEOS and 30 \(\mu\)L APTS. The reaction is let to proceed overnight at 28 \({}^{\circ}\)C temperature. Arrow used in panel D to highlight the elongated multicore structures (32% yield). making the careful control on the structure of the final product a challenging requirement. While single silica coated NPs have been found to preserve absorption and/or luminescence properties of the as prepared NPs, an increase in the NP core multiplicity in the final silica nanostructure has been reported to induce collective phenomena [32; 49], such as absorption broadening, peak position shift or additional non radiative de-excitation pathways, resulting in partial luminescence quenching and reduced lifetimes [48; 50; 51]. According to the mechanism that underpins the microemulsion synthetic method, the displacement of the native ligands at the QDs surface, which depends on the composition of the ligand passivating layer, ligand density, reactivity and kinetics of the ligand exchange reaction [52; 53; 54], regulates the NP encapsulation within the water droplet. Furthermore, at a fix Igepal-C0520 concentration, thus reverse micelle concentration, the relative NPs/TEOS ratio may affect the silica occupancy and core multiplicity within each silica NP. Here, we performed a systematic control of the synthetic conditions, such as control of the ligand composition at the GQD surface by post synthesis ligand exchange reaction and of GQDs/TEOS molar ratio, to prevent the formation of multicore GQD silica shell structures, and, at the same time, to limit the formation of empty silica NPs that would reduce the yield of photoactive structures, tightly aggregated NPs and inhomogeneous silica shells [47; 55]. Figure 2B-D displays the TEM micrographs of the silica nanostructures prepared from pristine (Figure 2B) and OLA-treated (Figure 2C,D) GQDs, at increasing GQD concentration and fixed surfactant (350 \(\mu\)L) and TEOS volume (50 \(\mu\)L). OLA has been selected for the post synthesis treatment due to its ability to passivate CdS of the GQD outer shell, but not too tightly coordinating the surface, thus enabling an easier subsequent ligand replacement. Asymmetric (Janus type) and off-centered GQDs (Figure 2B) silica based nanostructures were synthesized starting from pristine GQDs (30 \(\mu\)L), while isotropic core-shell NPs have been obtained when the GQDs have been pretreated with OLA (Figure 2C,D).