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Magnetic nanobeads

Magnetic nanobeads (also known as magnetic nanoparticle clusters, NPCs) are nanocomposite materials exhibiting magnetic properties. They are composed of a number of individual magnetic nanoparticles and have a diameter of 50–200 nanometers. Nanoparticles can be either fused by sillica or embedded in a polymer matrix.

Ferrite magnetic nanobeads
Magnetic nanobeads with narrow size distribution consisting of superparamagnetic oxide nanoparticles (~ 80 maghemite superparamagnetic nanoparticles per bead) coated with a silica shell have several advantages over metallic nanoparticles:
 * Higher chemical stability (crucial for biomedical applications)
 * Narrow size distribution (crucial for biomedical applications)
 * Higher colloidal stability since they do not magnetically agglomerate
 * Magnetic moment can be tuned with the nanoparticle cluster size
 * Retained superparamagnetic properties (independent of the nanoparticle cluster size)
 * Silica surface enables straightforward covalent functionalization

Magnetic polymer nanobeads
For preparation of magnetic nanobeads several polymers can be used, such as PLGA, PLA, dextran , chitosan , polyethyleneimine and polystyrene. Nanobeads can be prepared by nano-emulsion method, suspension polymerization, precipitation, etc.

Magnetic nanobeads scaffolded by DNA-binding zinc finger proteins
Biotinylated zinc finger proteins (ZnF) were conjugated to DNA templates, followed by incubation with neutravidin-conjugated nanoparticles. The sequence specificity of ZnF and programmable DNA templates enabled a size-controlled construction of nanoparticle clusters.

Nanophotonics
Superparamagnetic ferrite nanobeads with the size 80 – 150 nanometers form ordered structures along the direction of the external magnetic field with a regular interparticle spacing on the order of hundreds of nanometers resulting in strong diffraction of visible light in suspension. When an external magnetic field is applied to colloidally dispersed nanobeads the particles form one-dimensional chain-like structures that exhibit structural color. If a photocurable medium is used for the suspension of nanobeads the photonic chain structures can also be fixed in a specific area by selective UV exposure.