Summary of the effects of different types of metal oxide nanoparticles (MONPs) and non-metal oxide nanoparticles (only SiO₂NPs) used as elicitors of specialized metabolites in different plant species.

NPs	Size of NPs (nm)	Effective conc. of NPs	Plant species	Culture type	Growth media/conditions	Effects on specialized metabolites	Phytotoxicity	References
CuO	—	1 ppm	Withania somnifera	Shoot and root	MS media	Total phenolic (27.31 mg g−1 DW), flavonoid (91.11 mg g−1 DW), and tannin (32.02 mg g−1 DW), contents were increased	—	70
CuO	25–55	3 mg L−1	Gymnema sylvestre	Cell suspension	MS media	2-Fold increase in production of phenolic and flavonoids whereas 2.3 fold increase in gymnemic acid	—	64
CuO	—	—	Brassica rapa	Hairy root culture	—	14% increase in production of glucosinolates (gluconasturtiin, glucobrassicin, 4-methoxyglucobrassicin, neoglucobrassicin, 4-hydroxyglucobrassicin, glucoallysin, glucobrassicanapin, sinigrin, progoitrin, and gluconapin) and phenolic compounds (flavonols, hydroxybenzoic and hydroxycinnamic acids)	—	71
CuO	—	1 ppm	Cichorium intybus	Shoot and root	MS media	Total phenolic (28.171 mg g−1 DW), flavonoid (9.450 mg g−1 DW) contents were increased	—	72
CuO	47	5 mg L−1	Trigonella foenum-graecum	Seed germination	MS media	Total phenolic (3.2 μg QE per mg DW) and flavonoid (3.7 μg QE per mg DW) contents were enhanced	Shoot and root growth was inhibited at higher concentration (400 mg L−1)	69
CuO	25–55	—	Brassica rapa	Seedlings	—	Increased level of reactive oxygen species (ROS), hydrogen peroxide, malondialdehyde (MDA), glucosinolate, proline, anthocyanin (1.3 fold) and phenolic (1.1-fold) compounds	Concentration of chlorophyll, sugar and carotenoid decreased	63
ZnO	—	300, 500 ppm	Solanum tuberosum	Plants	Potting soil	Total phenolic (99.1 mg g−1 FW) and anthocyanin (3.28 mg g−1 FW) contents were increased	—	77
ZnO	—	25–100 mg L−1	Lilium ledebourii	Shoot	MS media	Enhanced production of total flavonoid (25 mg L−1) phenolics (75 mg L−1) and anthocyanin (100 mg L−1)	—	73
ZnO		75 mg L−1	Echinacea purpurea	Callus	MS media	Increase in total flavonoid (23.25 mg g−1 DW) content	—	76
ZnO	34	1.0 mg L−1	Stevia rebaudiana	Shoot	MS media	Increased production of total phenolic, flavonoids and steviol glycosides (88.21 mg g−1 DW)	—	78
ZnO	—	100 mg L−1	Hyoscyamus reticulatus	Hairy root	MS media	Production of tropane alkaloids (1.2 fold) and total phenolic contents (3.2 fold) were increased	—	18
ZnO	—	1 μM	Glycyrrhiza glabra	Seedling growth	Hoagland's solution	Both ZnO and CuO resulted in increased content of glycyrrhizin, phenolic, flavonoids, anthocyanins and tannins	—	75
CuO		1 μM
ZnO	—	100 mg L−1	Stevia rebaudiana	Callus	MS media	Both ZnO and CuO treatments resulted in increase of total phenolic (5.06 lg mg−1 of DW), and flavonoid (2.23 lg mg−1 of DW) contents	—	79
CuO		10 mg L−1
ZnO	18–20	100–1000 mg L−1	Solanum melongena	Seed germination	Filter paper	Total phenolic, flavonoid and anthocyanin contents were increased in a dose-dependent manner in response to all three types of NPs	Seedling growth was suppressed	80
NiO	10–20
CuO	25–55
Fe3O4	—	450, 900 mg L−1	Hyoscyamus reticulatus	Hairy root	MS media	5-Fold increase in production of hyoscyamine and scopolamine	—	20
Fe3O4	20	30 ppb	Lepidum sativum	Plants	Field conditions	Increase in total essential oil (133%), phenolic (13027 mg GAE per g), and flavonoid (453 mg QE per g) contents	—	81
Fe3O4	—	100 ppb	Hypericum perforatum	Cell suspension	MS media	Both ZnO and Fe2O3 nanoparticles resulted in enhanced production of hypericin (3-fold) and hyperforin (13-fold)	—	83
ZnO
Fe3O4	—	50 mg L−1	Cichorium intybus	Hairy root	MS media	Total phenolic (4.65 mg g−1 DW) and flavonoid (77.34 μg g−1 DW) contents were increased in response to Fe3O4NPs while ZnONPs have no significant effect on specialized metabolites production	—	82
ZnO		50 mg L−1
TiO2	10–15	100, 200 mg L−1	Salvia officinalis	Seedlings growth	Potting mix	Monoterpenes (camphene, p-cymene, 1,8-cineol, cis-thujene, camphor) and total phenolic (35.2 mg GAE per g DW) and flavonoid (21.9 mg CE per g DW) contents were enhanced in response to 200 mg L−1 and 100 mg L−1 concentration respectively	—	90
TiO2	10–15	20, 80 mg L−1	Hyoscyamus niger	Plantlets	Potting mix	Enhanced production of tropane alkaloids (hyoscyamine; 0.286 g kg−1 and in response to 20 mg L−1 and scopolamine; 0.126 g kg−1) in response to 80 mg L−1 conc.	—	91
TiO2	—	6.0 mg L−1	Cicer arietinum	Embryonic callus	MS media	Increased production of phenolic compounds such as gallic acid, chlorogenic acid, o-coumaric acid, tannic acid and cinnamic acid	—	89
TiO2	—	120 mg L−1	Aleo vera	Cell suspension	MS media	Aloin contents (118%) were increased	—	35
TiO2	25	50, 100 ppm	Dracocephalum moldavica	Field cultivation	—	Luteolin 7-O-glucoside (2.1 mg g−1 FW), rosmarinic acid (0.32 mg g−1 FW), p-cumaric acid (8.9 mg g−1 FW), ellagitannin (4.3 mg g−1 FW), gentisic (10.21 mg g−1 FW), chlorogenic acid (32.12 mg g−1 FW), and caffeic acid (8.23 mg g−1 FW) concentration were increased	Gentisic acid contents were reduced	92
CeO2	8	250 mg kg−1	Raphanus sativus	Seed germination	Potting soil	32% increase in antioxidant compounds but no effect on total phenolic and flavonoid contents		95
CeO2	33.05	0.1 mM	Solanum lycopersicum	Hydroponic culture	Hoagland solution	37% increase in total chlorophyll and 26% in carotenoid content was observed	—	96
CeO2	—	1000 mg L−1	Arabidopsis thaliana	Plantlets	Potting mix	Antioxidant enzymes (superoxide dismutase, catalase, ascorbate peroxidase, and peroxidase) concentrations were elevated along with phenolic (27%) compounds	—	97
In2O3
Al2O3	50	40 μg mL−1	Nicotiana tabacum	Cell suspension	MS media	Increase in total phenolic contents (62%)	Decreased cell density and viability	98
CdO	7–60	2.03 × 105 particles cm−3	Hordeum vulgare	Plantlets	Soil, water	Ferulic acid (30%) and isovitexin (183%) were increased	—	99
Mn2O3	—	25 mg L−1	Atropa belladonna	Shoot-tip	MS media	Increase in production of alkaloids (23%), total phenolic (12%) and flavonoid (32%) contents	—	100
SiO2	100		Dracocephalum kotschyi	Hairy root	MS media	Almost 2-fold increase in rosmarinic acid, xanthomicrol, isokaempferide and cirsimaritin increased	—	101
SiO2	—	100 mg L−1	Nigella sativa	Plants at flowering stage	Foliar spray	Elicitation of thymoquinone (2.9 mg g−1 DW) production by up-regulating the expression of geranyl diphosphate synthase gene	—	102
TiO2		100 mg L−1