## 3 Results and Discussion  
The C/TiO\({}_{2}\) hybrid dots (Figure 1) were prepared by carbonizing organic precursor molecules on the surface of existing TiO\({}_{2}\) nanoparticles, with the remaining or residual organic molecular segments that survived the carbonization processing conditions serving the surface passivation function [18]. For the preparation, the commercially acquired colloidal TiO\({}_{2}\) sample (Degussa P25) was fractionated to harvest the more aqueous dispersible nanoparticles of sizes around 25-30 nm in diameter. The resulting TiO\({}_{2}\) nanoparticles in aqueous suspension were mixed well with the selected organic molecules, followed by the solvent removal to obtain a solid-state mixture for the microwave-assisted thermal carbonization processing, as reported previously [18]. The selected precursor organic molecules were oligomeric polyethylene glycol (PEG, average molecular weight ~1500) and its mixture with oligomeric polyethyleneimine (PEI, average molecular weight ~600). Their corresponding hybrid dots are denoted as PEG-C/TiO\({}_{2}\)-Dots and PEI&PEG-C/TiO\({}_{2}\)-Dots, respectively [18]. In the preparation of the hybrid dots, the thermal processing conditions are unlikely to cause any meaningful changes to the TiO\({}_{2}\) nanoparticles. According to X-ray powder diffraction results (Figure 2), the hybrid dot sample contains largely amorphous carbon in addition to the TiO\({}_{2}\) nanoparticles. One might argue that the sample could be a simple mixture of the TiO\({}_{2}\) nanoparticles with CDot-like entities produced in the thermal processing, but countering such an argument is that the sample was cleaned via prolonged dialysis in the membrane tubing of pore-size 25,000 MWCO. For the control sample prepared without the TiO\({}_{2}\) nanoparticles, the same cleaning procedure with the dialysis eliminated essentially the entire sample. Figure 2: Powder X-ray diffraction patterns of C/TiO\({}_{2}\)-Dots (upper) and the precursor TiO\({}_{2}\) nanoparticles (lower) from the commercially acquired Degussa sample. Colloidal TiO\({}_{2}\) is crystalline, with high microwave cross-sections, thus expected to absorb the microwave energy preferably in the microwave-assisted thermal processing to create very hot TiO\({}_{2}\) nanoparticles for the carbonization of the organic species in the vicinity. Such an experimental configuration for the thermal carbonization of organic species mostly on the very hot TiO\({}_{2}\) nanoparticle surface should be favorable to the formation of the targeted C/TiO\({}_{2}\) hybrid dot structure (Figure 1), namely individual TiO\({}_{2}\) nanoparticles each surface-attached/decorated with nanoscale carbon domains and residual organic species. The latter are structurally equivalent to carbon nanoparticles with surface organic functionalization, or CDot-like, making the hybrid dot structurally analogous to a TiO\({}_{2}\) nanoparticle bound with many CDots. Thus, the use of microwave irradiation to deliver the energy required for thermal carbonization is ideally suited for the targeted hybrid dot structure (Figure 1). C/TiO\({}_{2}\)-Dots due to the hydrophilic organic species on the surface are readily soluble in aqueous or highly polar organic media. In these dots, the TiO\({}_{2}\) nanoparticles are known to absorb only in the UV (cut-off shorter than 400 nm for aqueous suspended TiO\({}_{2}\) nanoparticles of 25-30 nm in diameter), so that the observed optical absorptions of C/TiO\({}_{2}\)-Dots over the visible spectral region must be due entirely to the CDot-like organic functionalized nanoscale carbon domains (Figure 1), comparable with the optical absorptions of the corresponding neat CDots without any TiO\({}_{2}\) and also those of aqueous suspended small carbon nanoparticles (Figure 3). The fluorescence spectra of the C/TiO\({}_{2}\)-Dots are also similar to those of their neat counterparts containing no TiO\({}_{2}\) (Figure 3).