Application of Nanoparticles to the Analysis of Biomarkers

As already explained above, optical and electrochemical techniques can be used to identify and quantify an analyte, by evaluating its interaction with radiation or the current flow during a redox reaction involving it. They can be applied in a variety of analytical systems as final detection device, such as the detection of an unknown antigen in immunoassays.
These systems can be modified and supplemented with the addition of NPs acting as carriers for molecules, tracers to be detected, electron transfer mediators or catalysts of electrochemical reactions. The special optical and electrochemical properties of NPs and the considerable number of labelled molecules they can carry, ensure not only an advantageous detection alternative to conventional procedures, but also a strategy to improve their sensitivity; if a NP acts as a carrier, in fact, the detection signal results amplified by the number of labelled molecules carried. This is particularly useful because biomarkers and biological agents are often present at ultra-low levels, and so require ultrasensitive methods for their detection.
Anyway, before being conjugated to biological molecules and thus used, NPs must be functionalized. Functionalization consists in covering a NP with a biological or molecular coating, which will act as bioactive and selective interface; adsorption, linkage via thiol groups, electrostatic interaction, covalent linkage are some reported strategies.
Afterwards the conjugation is realized using common bifunctional linkers coupled to terminal groups on the functionalized nanocrystal. The binding event occurring onto NPs surface may have a significant effect on its optical (change of the light absorp tion/emission) or electrochemical properties (oxidation/reduction current onto a transducing platform), offering further alternatives for bioanalysis.