Table 1.

Experimental cell viability results of UCNPs under different conditions

NPs types	Coating layer	NPs size/nm	Concentration	Cell types	Exp. time	Toxicity assay	Results [Ref.]
β-NaYF4:TmYb/NaYF4	Mesoporous silica, PEG and folic acid coating	92	300 μg/mL	HeLa cells	24 h	CellTiter-Glo luminescent cell viability assay	No significant decrease in cell viability.131
NaYbF4:Er	Mesoporous silica	76	21.2 µM	HeLa cells	12 h	CCK-8	Viability =~90% cell.132
NaYF4:Yb,Er	PEG-oleate bilayer	25	75 μg/mL	HAEC	24 h	MTT	Viability =~50% cell.133
NaYF4: Yb,Er and NaYF4: Yb,Tm	Thin amine-terminated silica layer	54, 30, 20	750 μg/mL	FAR-positive KB carcinoma cells	1 h	Light controlled cytotoxicity	No significant decrease in viability of cells in the presence or absence of any exposure to light excitation.134
NaYF4:Yb,Er	Different coating	Different sizes	62.5–125 μg/mL	Dermal fibroblasts and human epidermal linear keratinocytes (HaCaT)	24 h	MTT test and optical microscopy	The fibroblast viability was not compromised by UCNPs and the viability of HaCaT cells varied from 52% to 100% based on the surface coating.136
NaGdF4:Yb,Er	PEG SiO2 and SiO2–NH2	Different sizes: 225–379	2–50 μg/mL	NIH3T3 and RAW264.7 cells	24–48 h	Cell culture viability (MTS), proliferation and apoptosis	No significant toxicity by modified NPs.137
NaGdF4:Yb,Er,Fe	SiO2	20 nm	1000 μg/mL	Human cervical carcinoma cell line HeLa	24 h	MTT	Low cellular toxicity. Cellular viability was estimated to be greater than 89% after 24 h.138
BaGdF5:Yb,Er	Glycerol	93 nm (7%) and 178 nm (92%).	10, 50 and 100 mg/L	1321N1 cells	1–3 h	The MTT Cell, the MTS cell viability assay, Neutral Red assay	No significant toxicity to human brain cells.139