Effects of surface-modifying ligands on the colloidal stability of ZnO nanoparticle dispersions in in vitro cytotoxicity test media

Figures & data

Table 1 Coating materials used in this study

	Structure	Charge
Cit		Negative
Tris		Positive
PAA		Negative
PAH		Positive
PLL		Positive

Abbreviations: Cit, sodium citrate; Tris, tris(2-aminoethyl)amine; PAA, poly(acrylic acid); PAH, poly(allylamine hydrochloride); PLL, poly-L-lysine hydrochloride.

Figure 1 Physicochemical characteristics of four commercial ZnO NPs in deionized water: (A) ZnO^AA20, (B) ZnO^SM20, (C) ZnO^AE20, and (D) ZnO^AE100.

Notes: The top row shows TEM images; the middle row shows core diameter distribution from TEM images; the bottom row shows hydrodynamic diameter from DLS. Abbreviations: DLS, dynamic light scattering; TEM, transmission electron microscopy; NP, nanoparticle; ZnO^AA20, 20 nm ZnO; ZnO^AE20, 10–30 nm ZnO; ZnO^AE100, <100 nm ZnO; ZnO^SM20, 10–35 nm ZnO.

Table 2 Hydrodynamic diameters and zeta potentials of different surface-coated ZnO^AA20 NPs in deionized water

	ZnO^AA20(Cit)	ZnO^AA20(Tris)	ZnO^AA20(PAA)	ZnO^AA20(PAH)	ZnO^AA20(PLL)
Hydrodynamic diameter (nm)	317±10	421±47	198±37	208±10	237±31
Zeta potential (mV)	-35.2±1.6	22.6±2.1	−32.1±2.0	52.0±2.8	39.8±3.5

Note: The hydrodynamic diameter and zeta potential show results of average and standard deviation by three repetition in deionized water (about pH 7.0).

Abbreviations: NP, nanoparticle; ZnO^AA20, 20 nm ZnO; ZnO^AA20(Cit), sodium citrate–coated ZnO^AA20; ZnO^AA20(PAA), poly(acrylic acid)-coated ZnO^AA20; ZnO^AA20(PAH), poly(allyamine hydrochloride)–coated ZnO^AA20; ZnO^AA20(PLL), poly-L-lysine hydrochloride–coated ZnO^AA20; ZnO^AA20(Tris), tris(2-aminoethyl)amine-coated ZnO^AA20.

Figure 2 Temporal variations in the optical density of ZnO dispersions in RPMI cell culture media: (A) ZnO^AA20, (B) ZnO^SM20, and (C) ZnO^AE100.

Notes: Filled circles show uncoated ZnO without FBS; hollow circles show uncoated ZnO with FBS; filled triangles show PAA-coated ZnO without FBS; hollow triangles show PAA-coated ZnO with FBS; filled squares show PLL-coated ZnO without FBS; and hollow squares show PLL-coated ZnO with FBS.

Abbreviations: FBS, fetal bovine serum; PAA, poly(acrylic acid); PLL, poly-L-lysine hydrochloride; RPMI, Roswell Park Memorial Institute; ZnO^AA20, 20 nm ZnO; ZnO^AE100, <100 nm ZnO; ZnO^SM20, 10–35 nm ZnO.

Figure 3 Temporal variations in the optical density of ZnO dispersions in DMEM cell culture media: (A) ZnO^AA20, (B) ZnO^SM20, and (C) ZnO^AE100.

Notes: Filled circles show uncoated ZnO without FBS; hollow circles show uncoated ZnO with FBS; filled triangles show PAA-coated ZnO without FBS; hollow triangles show PAA-coated ZnO with FBS; filled squares show PLL-coated ZnO without FBS; and hollow squares show PLL-coated ZnO with FBS.

Abbreviations: DMEM, Dulbecco’s Modified Eagle’s Medium; FBS, fetal bovine serum; PAA, poly(acrylic acid); PLL, poly-L-lysine hydrochloride; ZnO^AA20, 20 nm ZnO; ZnO^AE100, <100 nm ZnO; ZnO^SM20, 10–35 nm ZnO.

Figure 4 Hydrodynamic diameter distributions of (A) ZnO^AA20(PAA), (B) ZnO^SM20(PAA), and (C) ZnO^AE100(PAA), after 0- and 30-hour exposures to RPMI media containing FBS.

Abbreviations: FBS, fetal bovine serum; h, hours; PAA, poly(acrylic acid); RPMI, Roswell Park Memorial Institute; ZnO^AA20(PAA), PAA-coated, 20 nm ZnO; ZnO^AE100(PAA), PAA-coated, <100 nm ZnO; ZnO^SM20(PAA), PAA-coated, 10–35 nm ZnO.

Figure 5 Hydrodynamic diameter distributions of (A) ZnO^AA20(PAA) and ZnO^AA20(PLL), (B) ZnO^SM20(PAA) and ZnO^SM20(PLL), and (C) ZnO^AE100(PAA) and ZnO^AE100(PLL), after 30-hour exposures to DMEM media containing FBS.

Abbreviations: FBS, fetal bovine serum, DMEM, Dulbecco’s Modified Eagle’s Medium; PAA, poly(acrylic acid); PLL, poly-L-lysine hydrochloride; ZnO^AA20(PAA), PAA-coated, 20 nm ZnO; ZnO^AA20(PLL), PLL-coated, 20 nm ZnO; ZnO^AE100(PAA), PAA-coated, <100 nm ZnO; ZnO^AE100(PLL), PLL-coated, <100 nm ZnO; ZnO^SM20(PAA), PAA-coated, 10–35 nm ZnO; ZnO^SM20(PLL), PLL-coated, 10–35 nm ZnO.

Figure 6 Optical images of HeLa cells exposed to (A) ZnO^AA20, (B) ZnO^AA20(PAA), and (C) ZnO^AA20(PLL), in DMEM without FBS; and (D) ZnO^AA20, (E) ZnO^AA20(PAA), and (F) ZnO^AA20(PLL), in DMEM with FBS.

Notes: Exposed concentration of ZnO; 20 mg/L.

Abbreviations: FBS, fetal bovine serum; DMEM, Dulbecco’s Modified Eagle’s Medium; ZnO^AA20, 20 nm ZnO; ZnO^AA20(PAA), poly(acrylic acid)-coated, 20 nm ZnO; ZnO^AA20(PLL), poly-L-lysine hydrochloride–coated, 20 nm ZnO.