Introduction to Nanotheranostics

This Brief will give an introduction to the current status of inorganic nanoparticles (NPs) and other nanomaterials that have potential applications in nanomedicine. Inorganic NPs are generally classified into six different types: (A) Noble metal NPs such as gold (Au), silver (Ag), platinum (Pt), palladium (Pd); (B) Semiconducting NPs or quantum dots (QDs) such as cadmium selenide (CdSe), cadmium sulphide (CdS), cadmium telluride (CdTe), zinc sulphide (ZnS), zinc selenide (ZnSe), zinc telluride (ZnTe), zinc oxide (ZnO); (C) Doped NPs such as manganese (Mn)—doped ZnS or ZnSe; (D) Magnetic NPs such as iron oxide (Fe₂O₃/Fe₃O₄), iron-platinum (FePt), cobalt (Co); (E) Upconversion NPs (e.g. NaYF₄—doped Er, Yb), and (F) Multifunctional NPs (combination of two or three NPs).

Metallic NPs such as Au, Ag possess excellent surface plasmon resonance (SPR) optical properties that can be tuned from visible to near-infrared (500–1300 nm) which make them ideal candidate systems for theranostics applications.

Semiconductor colloidal nanocrystals are called “Quantum Dots” (QDs). QDs can be obtained when the semiconductor crystals are brought to a smaller diameter which is smaller than the Bohr exciton radius of the bulk material. QDs have a characteristic luminescence with nanoparticle size ranging from 3 to 10 nm. Compared to the conventional organic dyes, QDs have unique properties such as optical, electronic, absorption coefficients, superior signal brightness, resistance to photo bleaching and simultaneous multi-colour imaging with single excitation source.

Magnetic NPs (MNPs) are the most extensively studied group of NPs. MNPs consist of materials derived from cobalt (Co), iron (Fe) and Nickel (Ni).

Multifunctional nanoparticles have been designed for targeted drug delivery (using the folate modification), fluorescence and MR imaging of cancer using mesoporous silica labelled with fluorescent dye molecules and superparamagnetic iron oxide nanocrystals.