Recent advances in solution phase synthesis of luminescent QDs have provided access to nanoheterostructures with multiple states [9; 22; 23; 24; 25] capable of efficient light emission of different colors, and with great potential for their use in ratiometric sensors. Ratiometric fluorescent probes are, in general, more robust and reliable than nonratiometric ones, which monitor a change of a single fluorescence signal. In the field of temperature sensors, the presence of two (or more) emission bands and the ability to establish a defined relationship between their emission properties, over the investigated temperature range, advantageously result in a more sensitive, concentration-independent, temperature detection. Furthermore, dual emission-systems do not suffer from environmental interference, overcoming limitations arising from inaccurate detection due to the effect on the photoluminescence of refractive index, surrounding environment, presence of quenching agent [9]. [PERSON] et al. [9; 26; 27; 28] have reported the fabrication of \"giant\" PbS@CdS@CdS QDs (GQDs) where the PbS core produces an emission band in the near infrared (NIR) region and the CdS shell in the visible portion of the electromagnetic spectrum. Due to the \"giant\" CdS shell (from 1.5 nm up to several tens nm), these optically active GQDs exhibit very high photostability towards photobleaching, even under continuous laser excitation, and have been demonstrated to be efficient temperature ratiometric and multiparametric probes [9]. However, being only dispersible in organic solvents, due to the hydrophobic nature of their surface, an appropriate surface functionalization must be developed as a valuable route to improve the GQDs dispersibility in aqueous environment and, at the same time, to make them biocompatible, hence suited for further application as thermal sensors in biological media. This approach may also potentially reduce the release of the heavy metals components forming the GQDs outside, decreasing the nanostructure's toxicity. Among the different functionalization strategies developed to ensure that QDs and NPs are water dispersible and covered by biocompatible matrix, we recall encapsulation in molecular micelles or lipid-based structures [29; 30], polymeric [31] or inorganic shell coating [32; 33; 34; 35]. Here we chose the growth of a hydrophilic silica shell, as it represents a versatile and low cost approach [32; 33; 34]. The silica shell has been reported to be chemically stable in water, although solubility depends on the silica structure and solution pH, it has a low cytotoxicity and can be easily chemically modified [35; 36; 37]. A silica coating can limit diffusion of toxic elements outside and, meanwhile, reduce oxygen permeation inwards, ultimately protecting the core from oxidation reaction, and thus preventing the degradation of its optical properties [38]. In addition, the silica shell, being optically transparent in the visible range, brings a limited contribution to the absorption, which is a critical requirement for being integrated in a fluorescence based temperature sensor [39]. However, a silica shell growth process presents several issues concerning the structure and the properties of the final NP [32; 33; 34]. In general, while single core nanostructures preserve the optical properties of the core, the formation of multiple cores entrapped within a single silica particle, in close proximity with each other, may result in detrimental absorption broadening, fluorescent shift and quenching. Besides core multiplicity, also the formation of an inhomogeneous silica coating and the occurrence of aggregated structures needs to be prevented to preserve the optical properties of the emitting core and convey them to the obtained water dispersible heterostructures, able to limit any release of metal ion in the surrounding environment.