ONPs Types and Applications

Many criteria can be considered when trying to classify ONPs, but in this discussion we consider a few major types of ONPs for biomedical purposes. Physically, viruses comply with all the requirements to be considered as nanoparticles (solid state and nano metric size), but they will not be discussed here. Fischlechner and Donath [73], and Singh, Gonzalez and Manchester [74] have written comprehensive reviews on the subject 

Interaction with light is one of the most interesting properties in ONP research. 

A significant number of the research papers are related to molecules absorbing light, or emitting either fluorescence or photoluminescence. Light interactions with ONPs is an interesting research field for biological applications, as ONPs can be used as tracers or markers of different compounds and, therefore, of processes. 

In this approach, we discuss next issues of biocompatibility and toxicity for in vivo use. 

As with MNPs, the optical properties of ONPs are size dependent. In this sense, it is interesting to mention the work of Fu and Yao s [83], who have studied ONPs made of a fluorescent compound, l-phenyl-3-[(dimethylamino)styryl]-5-[(dimethylamino)phenyl]-2-pyrazoline (PDDP). They found that the optical properties depended strongly on particle size, showing a remarkable bathochromic displacement in the absorbance maxima of nanoparticles, the displacement increasing with size from 50 to 310 nm. Fluorescence emission and decay were also studied, showing changes similar to those in the absorbance spectra. The shift in absorbance and fluorescence maxima must be taken into account for tracing purposes. 

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