Table 3.

Magnetic ferrofluids (FF) applications, descriptions, and challenges in optics and nanophotonics.

Application	Description	Challenges
Photonic materials	Superparamagnetic magnetite nanocrystals or nanoclusters with tunable sizes from 30 to 200 nm in water	NPs with controlled diameters and stoichiometric structures
Organic light-emitting diodes (OLEDs)	Gold-doped magnetite nanoparticles	Size of magnetite nanoparticles and aggregation of nanoparticles
Magnetic field sensors	Combination of different shape of optical fibers and optical grating with magnetic FFs	Long-term colloidal stability of FFs
“Smart” windows	Nanoscale magnetite nanoparticles from 50 to 100 nm used for shading and the optical properties of the window controlled through remote switching of magnetic field	Long-term colloidal stability of FFs
Magnetic resonance imaging	Exceedingly small superparamagnetic iron oxide NPs (up to ~10 nm) with various surface modifications	Reproducibility, scalability of synthesis, and functionalization of the surface for specifically targeting to different tissues and cells
Solar energy harvesting	Sensitized solar cells based on MNPs	Nanoparticle sedimentation and aggregation, cost of nanomaterials, and toxicity