*2.3. Preparation of the Carbon Dots*

The various carbon dots (CD-1 to CD-4) were generated through a bottom-up approach, using pyrolysis of citric acid (CA) as the carbon source, in the presence of various additives as passivation reagent: pentaethylenehexamine (PEHA), *N*,*N*-dimethylethylenediamine (DMEDA), branched poly(ethyleneimine) 600 Da (bPEI600), poly(ethylene glycol) monomethyl ether 550 Da (mPEG550), or 2 kDa (mPEG2000) [35,38] (Figure 1 and Table 1). Pyrolysis was conducted under conventional heating or microwave irradiation, and the resulting nanoparticles were purified using extensive dialysis against HCl 0.1 N and ultrapure H2O (MWCO 1000 Da) [35,38]. The CDs were freeze-dried, and 5.0 mg/mL stock solutions were prepared and stored at 4 ◦C until use [35,38]. The size and charge (zeta potential, ζ) of the nanoparticles were determined using dynamic light scattering (DLS) (NanoSizer NanoZS, Malvern UK) and transmission electron microscopy (TEM) operating at 5 kV (LVEM5, Delong Instruments, Brno, Czech Republic) [35,38] (Table 1).

**Figure 1.** Structural features of the various carbon dots employed in the study. The nanoparticles CD-1 to CD-4 were generated through pyrolysis of citric acid (CA) in the presence of various passivation reagents presented in Materials and Methods and in Table 1.


**Table 1.** Characteristics of the various carbon dots (CD-1 to CD-4) employed in the study.

<sup>a</sup> Measured at 1.0 mg/mL in 1.5 mM NaCl, pH 7.4. <sup>b</sup> Reactions were conducted under conventional heating. <sup>c</sup> Reactions were conducted in a domestic microwave oven.
